Maciek
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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?
Hi, on the first two pictures is Rear spark plug and the two last one is the front spark pług.
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.
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.Okay, I found a more precise diagram of the carburettors in the GV125 service manual.
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.
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.
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.
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…
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…
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.
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.Gave it to someone (bike could start, drive, acted like it didn’t get enough fuel and leaked) and now bike will start but even slight throttle move will stall it Problem is most of mechanics will just tell me “sorry, not touching V Hyosung bikes” or tell me they won’t touch the carbs without OEM rebuild kit which is literally impossible to get in Poland That’s why I even tried to look which other bikes use bds26 or “bds-like” carbs that would fit my bike so that I can get it to work and then rebuild my old carbs on my own
Mate, can you tell me exactly who you gave your carburettors to for repair? Because it would be funny if we’re talking about the same person 😀
I sent mine (by post) last winter for reconditioning, and the guy took care of everything + adjustments based on the modifications made to them (he got the adjustment right in 90% of cases).
For complete reconditioning + cleaning, replacement of fuel strainers, needle springs, gaskets and nozzles, I paid 550 PLN, I think.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?
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 😉 )
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.
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…
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
Did you check the valve clearance?
Lack of compression is one of the symptoms of valve leakage.
