Valve clearance, camshaft, camshaft tensioner – a problem or a serious fault?
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Bike Model = : Hyosung GT125 Naked Comet 2007
Hello gentlemen!
Since I don’t want to be bored…. My friend and I decided to eliminate the valve clearance, because metallic knocking sounds started to appear (that was my reasoning regarding these sounds).
After stripping the motorcycle down to its bare bones to expose the camshafts, we measured (hopefully correctly) the valve clearance. The engine was not completely at ambient temperature, it was ± 10 degrees higher, at least according to the thermal imaging camera. You may ask what prompted us to do this? Very limited time to order the shims with fast delivery, get to the place by motorcycle and assemble the motorcycle before the weekend so that we could go on our dream trip. All this happened last Thursday.
It turned out that the shims did not arrive on time, but only yesterday…
Getting to the point, below is a summary of the valve clearance measurements taken on Thursday:Front cylinder
(0.24) EX (0.16)
1.73 1.80 – shims
(0.27) IN (0.22)
1.83 1.83 – shims
Rear cylinder:
(0.19) IN (0.19)
1.85 1.85 – shims
(0.24) EX (0.28)
1.80 1.72 – shimsDespite all the complications, such as a broken thread in the camshaft bridge (it had been tightened so tightly by a previous owner that the thread broke when unscrewing it), incorrectly aligned camshaft positions, and incorrectly measured distances between the timing chain and the marks. On the rear cylinder, we encountered a problem after releasing the tensioner, as the chain started to click, but we took everything apart and reassembled it, and it was fine. Finally, we put everything back together and measured the valve clearances as follows:
Front cylinder
(0.23) EX (0.17)
1.73 – old shim 1.72 – old shim from rear exhaust
(0.07) IN (0.15)
1.95 – new shim 1.90 – new shim
Rear cylinder:
(0.10) IN (0.14)
1.90 – new shim 1.90 – new shim
(0.24) EX (0.20)
1.80 – old shim 1.75 – new shimAll steps regarding measurements, tightening screws, etc., were performed using the service manual (10 crankshaft revolutions before measuring). The shafts were not mixed up and were placed in the correct sockets (matching marks and pins).
I noticed the following symptoms as soon as the motorcycle was started:
1. The sound of the engine is completely different than before the valve clearance adjustment, it is more bassy and deep, you can clearly hear the front cylinder ‘working hard’.
2. The metallic knocking/ticking has not stopped, I am afraid that it is the timing chain or a broken tensioner? This sound can be heard on the rear cylinder on the right side (when sitting on the motorcycle), the tensioner is a long one that is twisted with a key. I will upload pictures of them later on.
3. During the test ride, there was a noticeable drop in power, the motorcycle was not as lively as before, and in addition, after warming it up on the road, I accelerated while overtaking and reached the red zone on the tachometer, more precisely 10.5-11k rpm, and there was a noticeable sluggishness.After two long days of struggle, first with taking it apart, then putting it back together, making corrections after someone who simply screwed it up.
My hands are tired and I personally feel like crying…Today, I intend to take it apart again with a calm mind and humility towards its mechanics and check it, but this time on my own.
I am asking you, quantum mechanics enthusiasts, for your support and help in this process, because I no longer know what to do.
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I’ve made a video how it’s working right now.
#Edited I’ve linked it in this post but it’s not appearing so I’m forwarding the link.
If I will find I will uploads also how it was working earlier.
#Edited2 I’m forwarding the pictures of cam shaft tenaioners
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This may sound stupid, but i trust you already did that but can you tell us what compression is on each cylinder?
As you follow the service manual , i won’t need to explain how to do it but if you get stuck , just reply here again.
Also, when the noise comes from engine –> Get a screw driver and poke the tensioner –> put your ear on the other end of the screwdriver — > ask someone to rev the bike a little bit, so see if you hear any abnormal/weird tensioner noises and cam chain slapping hard ?
Did also check each camshaft is correct ? and checked cam-shaft bearings are OK? – Sometimes previous owner puts a “Rear EX” camshaft in to Front Cylinder and problems start
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Thanks Marcel for your reply.
I will reply to you under yours questions.
This may sound stupid, but i trust you already did that but can you tell us what compression is on each cylinder?
To be honest I did not do that, is’t not so easy to borrow such an equipment. I will oreder it and I will check it. But form the other hand, there is a relation with low compression on pistons after valve clearance? Forgive me for asking, but I’m a total greenhorn on the subject….
As you follow the service manual , i won’t need to explain how to do it but if you get stuck , just reply here again.
Thanks mate!
Also, when the noise comes from engine –> Get a screw driver and poke the tensioner –> put your ear on the other end of the screwdriver — > ask someone to rev the bike a little bit, so see if you hear any abnormal/weird tensioner noises and cam chain slapping hard ?
Noise comes from rear cylinder (that’s what I’m hearing). I poke the tensioner few times on neutral RPMs, also I puted my ear on a screwdriver and didn’t hear any different noises. Also I was setting tensioners in the same place as they were. Maybe I’m stupid, but I’ve got and idea with yours proposal and I take a small screwdriver and inserted ito the tensioner hole and a little bit released the tension of it, and I’ve heard the camshaft chain clearly, but when I realesed it back I didn’t hear the chain, but it’s still metal knocking.
Did also check each camshaft is correct ? and checked cam-shaft bearings are OK? – Sometimes previous owner puts a “Rear EX” camshaft in to Front Cylinder and problems start
I inserted the camshafts according to the markings and pins in them. The bearings have been checked and are fine, the bridges are not slipped, the camshafts are in very good condition with no pitting or scratches.
For me, currently if I have put it together correctly then it should be all right or, if there were shafts swapped by the previous owner, would there be a problem?Don’t get me wrong, but before the valve clearance, riding was smooth and without any issues, only this metal knocking appears, but it was not so loud. After valve clearance it’s worse. I’m guessing, that something was not properly setted back as it was…
Does the screw force have a big impact on that?
Will the strength, order of tightening of the timing bridge bolts affect camshaft deflection/flexion? Or that it will not tighten the camshaft bearings correctly?
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I can’t edit the previous post, so I’m writing another one.
I have done my homework properly and know that valve lash affects piston compression.
I have checked them and they are:
FRONT – 6,73kg/cm2
REAR – 7,65kg/cm2
It should be 8kg cm2 minimum, so i suspect you have gone over the “safe limit” , as per service manual but the bike is still operational.
Next time you do this ===> Pour a tiny bit of oil inside the RUBBER intake pipes , so that oil will go inside the cylinders
Then see if the compression improves?this will help determine if we have to look at piston rings or a possibly scratched cylinder (A cylinder is easier to replace)#
Keep in mind also, if you or previous owner ever removed the cylinders or changed cylinders (they did, i can see you have mixed size cam tensioners) , then it is possible some compression loss is due to bad gaskets ? It is just a thought . Very common on cars , but you are lucky that if a gasket has problem, your engine is not burning blue smoke (water radiator coolant has mixed with oil!) – Your GT125 only uses oil, so the worst is burning oil (plugs will be oily and very sooty) and loosing compression overtime. It is advised to check ebay for a cheap piston and cheap cylinder as emergency back up. Korea is not making any more cylinders for carby 125cc bikes , so they only make parts for Fuel Injected GV125 now (it wont fit GT)
Also it will be advised 100% to buy spare cam tensioners , it looks like we cannot trust the ones you have. So buy a backup on ebay that’s cheap.
Also don’t forget to get tensioner gaskets! (I have loads), if you re-use tensioner gasket, you will burst oil there, the chains spin a lot of oil!
Also, if you ever get time, remove clutch cover ===> look at the rear cam chain crank, hopefully the right side of the crank does not have damaged teeth causing chains to dance and skip around and knock#
The left side is tricky as you will need to remove the flywheel and magneto, then look at the crank teeth there too
If you go this far, you might aswell replace the cam chains
Another chance with the gap on valve;
Front
0,03 (IN) 0,12
0,24 (EX) 0,26
Rear
0,11 (IN) 0,11
0,25 (EX) 0,16
I’m crying right now…
Front intake is too tight. Try to aim for 0.13-0.15 as perfect mark.
Rear = It will need re-doing as both EX & IN are on the tight side , if the engine gets hot, you will get problems and possibly cylinder head damage as hot heat reduces the clearances even more, so it is like we are “chocking” the bike’s neck and it can’t breath like it used to.
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Camshaft tensioners – I’ve checked them, they are moving smoothly, and the spring it’s pushing these pistons quite hard.
Plugs – they are looking good? They are afer my first valve clearance and done on it approx 20km, 10km test drive, and next 10km to my garage. I’m thinking they are not oily, but I’m guessing they will need replaceing… They are NGK IRIDIUM CR8EIX, replace them with LASER IRIDIUM?I will redo clearance, but if I’m in such a position with the bare bones of my bike I’m thinking to replace the camshaft chain right away.
Marcel I will write to you an email for a quotation.
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Hi Maciek. Your REAR CamChain TENSIONER is not the right part. Your Front tensioner is the correct part. It’s 27.1 mm in diameter, from memory. Try a wrecker or new aftermarket part to see if that eases the noise.
The manual says to TURN THE MOTOR 10 times, at least, before measuring VALVE CLEARANCES. Pop the right shims in both cylinders and it will sound & run better. I didn’t read all your post – is your rear cam chain ruined for sure? It may not be idk.
When you lay your cams on the head, place the cam that’s furthest away from the tensioner, on first. After i lay the 2nd cam down, under the chain, i press my finder in the TENSIONER HOLE to apply the pressure to the cam chain, so i can see how it will look when the tensioner is installed). Then i release the pressure & rotate this cam until its in the right spot. Bike will run with the cams out a bit but it sounds bad & the bike doesn’t like it. I use NGK CR8E spark plugs & testing CR7E from memory.
-----LaserBeam---->
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Camshaft tensioners – I’ve checked them, they are moving smoothly, and the spring it’s pushing these pistons quite hard. Plugs – they are looking good? They are afer my first valve clearance and done on it approx 20km, 10km test drive, and next 10km to my garage. I’m thinking they are not oily, but I’m guessing they will need replaceing… They are NGK IRIDIUM CR8EIX, replace them with LASER IRIDIUM? I will redo clearance, but if I’m in such a position with the bare bones of my bike I’m thinking to replace the camshaft chain right away. Marcel I will write to you an email for a quotation.
If you’re sure the tensioners are good, then no problem. Usually if i hear them making noises , i replace them immediately.
Laser or normal CR8E is better. I don’t think Hyosung bikes like “iX Iridium” plugs very much , despite them being overhyped. If my bike is good and well taken care off, i can survive 2-3 years with the same Laser Plugs. This is far cheaper than replacing plugs every few months / few thousand miles, it gets expensive
It is like getting a K&N Filter , you don’t need to replace stock filter all the time anymore , expensive is K&N to buy now but it makes long term financial sense.
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Hello, since I decided to replace the timing chains right away and, while I was at it, the already dismantled cylinders, I stopped at the stage of removing the magneto…
Do I need a special puller for it?
I have a puller in my workshop, but it is too small to fit the magneto.
Are there any other ways to remove it?
I checked the serial number of the tools from the service manual, but I don’t need them for that amount of money, as I will only use them once. (hopefully 😉 )
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Hello, since I decided to replace the timing chains right away and, while I was at it, the already dismantled cylinders, I stopped at the stage of removing the magneto… Do I need a special puller for it? I have a puller in my workshop, but it is too small to fit the magneto. Are there any other ways to remove it?
I checked the serial number of the tools from the service manual, but I don’t need them for that amount of money, as I will only use them once. (hopefully 😉 )Try M30 x 1.5 puller from Amazon, it pulls rotors of different 125 motocross bikes.
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Hi Maciek. Your REAR CamChain TENSIONER is not the right part. Your Front tensioner is the correct part. It’s 27.1 mm in diameter, from memory. Try a wrecker or new aftermarket part to see if that eases the noise. The manual says to TURN THE MOTOR 10 times, at least, before measuring VALVE CLEARANCES. Pop the right shims in both cylinders and it will sound & run better. I didn’t read all your post – is your rear cam chain ruined for sure? It may not be idk. When you lay your cams on the head, place the cam that’s furthest away from the tensioner, on first. After i lay the 2nd cam down, under the chain, i press my finder in the TENSIONER HOLE to apply the pressure to the cam chain, so i can see how it will look when the tensioner is installed). Then i release the pressure & rotate this cam until its in the right spot. Bike will run with the cams out a bit but it sounds bad & the bike doesn’t like it. I use NGK CR8E spark plugs & testing CR7E from memory.
I noticed that too, but it happens in UK too. Owners mix cylinders (eg. Front engine use 2016 cylinder with updated tensioner and rear cylinder use 2003 cylinder that uses Generation 1 tensioner)
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I noticed that too, but it happens in UK too. Owners mix cylinders (eg. Front engine use 2016 cylinder with updated tensioner and rear cylinder use 2003 cylinder that uses Generation 1 tensioner)
Oh i see. So your Front Cylinder is from an EFI (Electronic Fuel Injection) bike. Which means theres a HOLE in the FRONT CYLINDER that runs down from the HEAD & out the lower/rear of the Cylinder. It is for measuring GASSES but your carby bike won’t measure them. Have you plugged this hole? It will leak exhaust gasses if you don’t & you will lose some power – reduces the backpressure i think. I’ve been told i can plug that hole on the outside of cylinder, next to the tensioner. There’s 3 holes, the 2 on the outside are for screws, the inside hole is exhaust gas. Luckily i found an old cylinder for my carby bike so i didn’t need to buy an EFI cylinder & different cam chain tensioner & different tensioner gasket.
If your bike was running better before the valve clearance and NEW shims were put in, i’d put the old shims back in.
I’d also check the manual for the TORQUE of the camshaft retainers, just to see if that helps reduce chain noise. Apparently most of the noise comes from the chain hitting the GREY metal piece, i think it’s called a cam chain GUIDE. Check that that baby is not too tight or too loose also. I get ticking noise a bit, mostly when the bike is cold. Usually the front cylinder. I don’t like the noise but mines not that bad.
If your SHIMS were TOO BIG, the cams could be pushing the valves onto the pistons. That will make some noise. Bad noise. Could be terminal if left unattended. Won’t do much for the compression either. I’d check the shims again before doing the cam chain, unless you are sure the chain is buggered as i don’t have a puller to remove that flywheel & i kind of like it where it is. 🙂
-----LaserBeam---->
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Hi, I haven’t been here for a while because I was struggling with the availability of parts, and whenever I took something apart, new unwanted parts came out that were simply worn out. I removed the magnet wheel and replaced the timing chains. I compared the timing chains to new ones and it seemed as if they had stretched by as much as 2 pins. Is it possible for these chains to stretch that much? I don’t know if I measured them correctly, placing one against the other, against a flat metal element as a starting point (one full chain link, two pins) and stretching them lengthwise and comparing them visually (I didn’t measure them with a tape measure).
I replaced practically all the seals I encountered along the way, except for one that is in the cylinder cover and seals the spark plug.
Not to mention the repairs of broken threads (two in the cylinder in the camshaft bearing mountings and two from the cylinder cover mounting…).
Everything I did, I did according to best practice and the service manual. Everything I removed from the motorcycle that was described in the service manual, I measured, checked for compatibility, and if it was incompatible, I replaced it, and if it was compatible, I put it back in. I recorded every step of my work with a GoPro, so I tried to put everything back together in the same order and sequence as I took it apart (of course, confirming everything with the service manual to make sure it was correct). I tightened each screw with a torque wrench and applied threadlocker where indicated in the service manual.
The valve clearances are currently as follows:
Front0.15 (IN) 0.13
0.24 (EX) 0.26
Rear
0.13 (IN) 0.14
0.26 (EX) 0.24
I performed the cylinder compression test again, which now looks like this:
Front – 10.2 kg/cm2
Rear – 10.6 kg/cm2
The compression test was performed with a drop of oil poured onto the piston.I read your answers regarding the tensioners, and I installed specially ordered 0.5 mm thick gaskets under each one (the same as the ones that were installed previously). Both the front and rear cylinders had only two holes for screws, none of them had a third hole. Unless we are talking about a milled groove inside the tensioner hole?
Generally speaking, before the entire replacement procedure, after opening the rear cylinder, you could see the chain jumping on the sprocket – as if the tensioner was not tightened. But it was not possible to tighten this chain. After replacement, this effect is not present when turning the magneto by hand.
I am currently in the process of putting everything back together, I still have to install the airbox on the carburettors, install the tank, connect everything and fill it up to start it. If the bike heats up and continues to make noise, the rear tensioner will be the first to go.
My question is, what if the tensioner is replaced and it still makes noise? Where should I look for the cause? Could it be that one of the valve springs has reached the end of its life?
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The clearances look good! , the compression should be good when it warms if it is showing 10kg cm2 cold.
The tensioner, if it makes a noise then yes replace it because it seems like you replaced almost all other components inside the motor.
Do you think the cam shaft bearings & crank bearings are OK during your inspections ?
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Late yesterday evening, or rather at night, I started my motorcycle.
The noise is still audible. Following your recommendations, I would replace the timing chain tensioner, but with the engine running, I gently pulled back the tensioner and had to pull it back quite a bit to hear the chain noise, so I’m guessing that’s not it…
But I tried to locate the noise more precisely and it seems to be coming from the exhaust pipe of the rear cylinder, at least that’s what I hear.
This raises the question, could it be something to do with the piston? Could it be something to do with the valve springs?
The noise is cyclical, I have the impression that the valve spring is broken or worn out and does not retract the valve and hits the cylinder. I don’t know, maybe I’m fooling myself with the easiest version of this problem, but I prefer to eliminate all unwanted faults rather than remove the entire cylinders and replace the pistons with rings…
The bearings and their mountings were fine, I didn’t hear any noise from the bearings when I had the camshafts removed.
During disassembly, I did not remove the crankshaft bearings, so I have no idea what condition they are in.Overall, the motorcycle was difficult to start without choking.
After starting it and letting it idle for a while so as not to seize anything and to allow the oil to spread everywhere, I tried to gently accelerate, but it did not respond and even stalled.
After running for a while, gently operating the throttle, it couldn’t rev up, as if it were sluggish when opening the throttle (despite smooth movements, no jerking of the throttle).Overall, it was smoking heavily, and it was hard for me to tell if it was because it had been standing for so long, because the engine was cold, or because I had poured oil on the pistons for the compression tests. The exhaust fumes did not smell strictly of burnt oil, it was a bit like burning a 2-stroke mixture, I don’t know how to describe it.
In the evening it was cooler, but not enough for the steam from the engine to be visible. -
Put a screwdriver pointy part on to the engine where the noise is , then the handle side on your ear , can you hear the sounds changing as you rev ?
If pistons where hit = it would likely be thudding hard and you will feel it when your hand is on the engine.
If you leave the bike on full choke, does it ride even a little bit ?
And does the smoke stay constant on the exhaut, or does it only puff smoke when you rev fast and let go (throttle blips) ?
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Marcel, I will check your steps as soon as I have the opportunity to go to my garage.
Overall, the motorbike was totally struggling to fire up after being serviced and standing dry for so long. Despite the fact that it could be heard that the carburettors were filling up, only after adding choke did it start but I didn’t keep it on choke only after it fired up did I turn off choke so as not to seize it just to give it a moment to start lubricating with oil.
There was smoke from the exhaust pipe the whole time the engine was running.
Worst of all (that I’m afraid of) I’ve got this timing set wrong…. I have read on the internet problems with adding gas, that it could be a misaligned timing….
How exactly do I determine the top dead center of the piston on the front cylinder as I have a stripped timing? Maybe I have actually misaligned it? Because if I couldn’t get the magneto off then I’m sure my engine was spinned and not set correctly.
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The TDC would be specified in the service manual , but you know by now if the timings were bad, the valves will 100% hit the piston and engine won’t even do 1 single full revulotion at this point, you would see dents in the pistons caused by a valve
If you took the valve heads off , did you notice the valves ? Are they fully sitting inside the head ? If not could we assume maybe “valve seals” need changing or double check the piston rings
They have notches , but Hyosung wants rings to be staggered ie.
====____=====__====
__===Each row is a ring , but the bottom _ dash is a gap, they must be some distance away from each other ,
If you get 10 kg cm2 compression, that’s GOOD! – now test compression again after running on choke for 5 minutes , so we know the compression values when it was hot vs cold to see if it went up or down.
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My frustration is reaching its zenith…. Today after firing up the motorbike with the suction on, it ran reasonably cool and even. The sound of this regular metallic knocking continued, I was ausculting the engine with a screwdriver and gently gassing it and looking for any anomalies and this metallic sound was coming exactly from the rear cylinder, exactly this sound could be heard on the cylinder cover in the lower left year as you look at it from the top. As I was fitting a new drivetrain I decided to go for a round of literally one kilometre to see how it was performing and how the bike was going.
Overall it ran very well, it’s been a while since I’ve ridden it but it didn’t feel like it had a mule or anything. The only drawback I found was a mega vibration at high revs and a horrible noise from the front of the bike, as if something started to shake that wasn’t tightened and started to bang against something….
So I didn’t gas it up any higher and went back to the garage to check the pressure on the pistons and found I had 6kg/cm2 on both of them on a warmed up engine o.O
After checking and breaking down completely came the icing on the cake and while tightening the spark plug the threads came off and stayed in the cylinder (I was unscrewing them with a torque spanner)…. And these were new spark plugs bought….
Also, I still have a long way to go as I will probably have to strip the rear cylinder down to the smallest detail anyway to see if anything has fallen into the piston….
front cylinder
rear cylinder
New spark plug…Also no fumes today, but I’m a little bit concern about this oil on this plug…
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I feel like i have to send you some spare engine parts at this time, do you think you have a local source to grab cylinder heads (doesn’t matter condition of valves) because you can re-use your old ones and maybe spare used pistons & spare cylinders , at least this time, you can make a build for one last time that should cross the 125 psi mark (not ideal but it is survivable for a good while , just don’t go racing!)
I am sorry about the stripped spark plugs but i have a SUSPICION that you may have been sold fake NGK’s , oh yes , the most faked plug on the planet , so unless you got it from a direct distributor that NGK Japan knows, then that’s strange! – That has never ever happened on my side, i have probably touched maybe 500+ spark plugs from my bikes and fixing customer bikes and even old cars i owned in the past , that just never happens. I can excuse the plug breaking if it was covered in rust and vehicle was dumped in the river etc.
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The availability of engine parts (used) is not that bad, but the price is often staggering… Both cylinders with pistons and rings approx. 162 pounds.
I will be able to unscrew the remaining spark plug thread, I have special ‘screw extractors’, but I am more concerned that any filings have gotten onto the piston and that will be a problem…
And now my question arises, what to invest in?
If the compression is so poor on a warm engine, should I buy used pistons, rings and cylinders (they are available separately) blindly?
Or maybe it would be more profitable to recondition the current cylinders (sleeving)?
There is also the issue of this cyclical metallic knocking. Can someone tell me what the potential cause might be? Even in bullet points, so that I can check everything is OK one by one?
Personally, I’m starting to suspect that the spring on the valve tappet has lost its effectiveness or broken, and the valve is knocking against the glass or the piston?
Should I take everything apart first and then look for the causes?
I don’t know whether to hire someone to do the job or continue doing it myself…Regarding the spark plug I just bought it online, so I do not know exactly from were it is…
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I have the opportunity to purchase the entire engine for parts, but the question arises: since the seller insists that the bearing is damaged, is it worth buying?
The cost of the entire engine is approximately £244.
At that price , if he can be sure other parts are not damaged and the compression was good, then you can rebuild that engine using new bearings in this case or use it to salvage parts to your main one.
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He can’t even tell me what the compression level is in this engine, which has been removed from the motorcycle since May and has been sitting untouched.
Hmmm, i would consider this as a gamble purchase. If you can’t find individual engine parts like cylinder valve head for cheaper, then it is possible you may 50/50 restore this one or just buy to take parts from it and the rest of it is just future spares.
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Hello, after a long absence (holiday), I have returned to the subject of my machine, this time with the help of a mechanic who repairs motorcycles of various calibres (a good old friend). He has already repaired Hyosungs, mostly GV models, but this is his first time with a GT, although it has the same engine.
I need information on whether there are any more detailed carburettor diagrams available than the one in the service manual?
I mean one that describes the individual components of the carburettor and what they are. Unfortunately, the service manual has a diagram but no description…The good news is that my vacuum gauge (even though it is new) was showing me incorrect values, or I used it incorrectly. I have a pressure of 10 kg/cm2 on the cylinders when cold and 12.5 kg/cm2 when the engine is warm.
As for the carburettor, I took it to a service centre in winter (for cleaning, replacement of nozzles, strainers, etc…), and it turned out that the mechanic, who has been working on Hyosungs for 15 years, screwed up the carburettor so badly that he could be called a master of doing everything half-assed…
He didn’t have the screws that come from the float chamber above the needle, so he replaced them with soldered nozzles…But enough complaining, because there is good news: I don’t have to replace the cylinders and pistons, so we’re moving on and looking for the source of those strange metallic clicking noises.
As soon as we find it, I’ll describe everything.
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Okay, I found a more precise diagram of the carburettors in the GV125 service manual.
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Hello,
Rather than incurring further costs for diagnostics and replacing everything that could be causing this cyclical knocking, I’m letting the problem go.
At most, I’ll have to replace the entire engine (oh well), there is a large selection of engines available at affordable prices, and it’s also easy to import motorcycle parts from abroad.
But after all this fuss and putting the motorcycle back together, I encountered a problem.
The bike starts up fine – the carburettors are synchronised and adjusted – I still need to sort out the issue of air leakage at the airbox – maybe you have some information about the rubber parts that connect the airbox to the carburettors? I would be grateful for any suggestions.
Despite revving up, the motorbike does not reach the same speed as before.
The modifications made during servicing are as follows:
replacement of the front drive sprocket with a 14-tooth one – the entire drive set, DID 428 chain on X-rings, front sprocket and rear sprocket
Carburettor regeneration (if you can call it that), unfortunately I did not take an active part in the carburettor regeneration and I do not know exactly what was put inside.With these problems, I have some concerns that my friend went all out and replaced everything in my carburettor (in the sense that he replaced all the components with those from a second carburettor purchased from GV125).
I will check carefully today which parts of the carburettor remained after this repair and describe the issue again.What else could be the reason that the v-max speed is now borderline miraculous to maintain a constant 90 km/h in 5th gear and the motorbike does not have the power to accelerate to 100 km/h?
Previously, despite valve clearances above the norm, the motorbike could easily reach 100 km/h, and could even accelerate to 115 km/h on a straight road. -
Hey,
I would drop down to 13T , 14T is too heavy for it. I almost never use 14T when i do 520 conversions. As you have 428 , i do not know what tooth count of rear sprocket to comment further, this could contribute to speed issues. 67MPH is usually the factory speed but here in UK National speed is 70mph and that is even dangerous for some riders as cars normally drive to 80mph + all day long, hence the need for a longer gear rear sprocket but also quicker small front sprocket , so you have to experiment with ratios that suit you.
Clutch Plates = Some minor HP loss happens if springs are heat fatigued & plates are too worn down ? = Less HP transfered to back wheel, so it is possible that it may contribute to your vmax issue.
Intake System = Connect the carbs to the airbox first ====> then tighten nicely.
Now your carbs and airbox are fully sealed up.
This means you have one big piece (carb+airbox) going down to the intake pipes connecting the engine.
Be VERY cautious as it is getting harder & harder everyday to get good condition rubber parts and they are very delicate things.
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Hi, I received a 13T sprocket, so I will be experimenting with gear ratios to find the optimum one for me. The rear sprocket has 52 teeth, supposedly for the 428 kit.
I sealed the entire system step by step, just as you described. I used new clamps everywhere, which were narrower than the standard ones (they did not push out the carburettors or stick into the intake manifolds).
The previous clamps were wider and I couldn’t fit the carburettors precisely onto the intake manifolds, and ultimately the carburettors popped out of the rubber.
I encountered a problem after the last carburettor adjustment.
Namely, regardless of whether the motorbike is warm or cold, it chokes when starting in first gear and in every other gear if I am at low revs (below 3k rpm).
And now I don’t know what to do, because when I rev it up, I can smell unburned petrol in the exhaust fumes. Could this be a further problem with the carburettor adjustment? It turned out that the jets are set to 90 and 92.5. But I don’t know if they are mixed up? I don’t know if I should take the carburettors apart and check what’s going on inside them? Could it be that the needles are set incorrectly?There are a lot of guesses and I don’t know what to do at the moment.
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Can you show me the spark plugs ? = Get new CR8E , and try to go for a ride, come back, let it cool down, show me the colours of your spark plugs , i can tell you if the mixture is good or not.
Also take picture of the side-ways of the spark plug , so we can see how many threads are dark etc. I have a keen eye on these things.
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Mixture is OK = Center white cone is brown. At full throttle.
Idling rich or burning oil ? = The circle ring at the base of the plug = front engine.
C-shape tip (half moon tip) , coils seem to spark OK. = Nice brown shade.
Threads look black and wet = Burning oil? or signs of engine overheating?
Also get rid of the ix plugs as they don’t really like them but use either basic CR8E or NGK LASER only.
Then show me again ? You want maybe only 4-5 lines of threads dark (normally) but if all the threads towards you finger are all black, either it’s overheating or eating a little bit of oil each time ? unless the fuel is bad ?
Check your oil level and rev it fast in neutral to see if it “puffs out” some smoke ? (VALVE SEALS or VALVES not seating)
or will it smoke if you hold it at 4k revs for a few seconds ? (piston rings , cylinder wall scratched?)
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Hi,
Generally speaking, these are spark plugs that have already travelled 8,000 kilometres with me. I put them back in after the last overhaul, when it turned out that a regular NGK CR8E spark plug had left its thread in the cylinder, which is why I prefer not to use regular ones… I’m afraid that the next one will blow and I’ll be forced to give it to my friend again, who will take everything apart, unscrew it, reseal it, etc…
Perhaps there is another brand worth recommending besides NGK, such as Denso? I have read in various groups that NGK spark plugs are often counterfeited in Poland… I don’t know whether to believe it, but after what happened to me, I really have doubts about the authenticity of this product…
Generally speaking, as for smoking, it smokes slightly when the engine is warming up, then when the engine is warm, there is no smoke, and when accelerating with the throttle at idle, it does not spit out any smoke or ‘splash’ anything from the silencer (I drive without a DB killer).
I use the most expensive fuel available in Poland, which is 98 octane petrol.
As for the spark plug threads, when it comes to the seal on the valve cover, there are no leaks, the chamber where the spark plug is located is dry, and the only residue is oil from the vacuometer tests when we injected oil through it to seal the piston rings. I will clean threads there to be sure.
Should all these tests be carried out on a cold engine or a warm engine? -
Warm engine is good for testing the cylinder health , cold testing is best when checking the “oil pressure” so you can record the “cold value” and “hot value” as the oil gets thinner and circulated.
Yes fake NGKS exist but sadly i’ve tried other brands , and NGK wins every time especially with their own NGK caps. Just that the “IX” in particular is more overhyped and quite an annoying plug.
I’ve got the same LASER plugs in one of my bikes for 2 years and has not missed a beat, LASER is also OEM to some Suzuki bikes. So go to a Suzuki dealer and ask for a CR8E LASER plug. Suzuki using LASER plugs is enough confidence for me to keep using it. It’s usually NGK’s flagship plug for bikes (also most expensive for good reason)
Here is more info on NGK’s official site in regards to spotting fake plugs:
https://www.ngkntk.com/newsroom/blog/emea/fake-or-not/if not , go to a BMW dealer and ask for a BOSCH plug to replace your CR8E , as BOSCH is typically an OEM plug to some BMW bikes & BMW cars
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