Valve gaps too small
Discussion
I have a 4 yr old KTM 500 EXC which has so far been really good. I ride it in the UK and have done a few trips to Europe for the Trans Euro Trails, it has 8k miles (314 hrs) on it. I do servicing on it myself (about every 1,000 miles) and last time I checked the valve gaps they were in spec.
Since then I sent it to a dealership to have the piston replaced and then I did another trip. However, I have just checked the clearances and they are less than the required spec (0.05/0.06 for inlet and exhaust). The bike still runs and seems fine so I will keep riding it and check again next time I service it. I am puzzled by them being tight.
The only explanations I can think of are:
1) Dealer put in larger shims (given it is ALL the valves this seems most likely)
2) Valves are all eating their way into the head
3) All the valve shoulders are wearing
I can't ask the dealership about this as they have gone out of business like a lot of others, any thoughts?
Not too keen to take the head off unless there is actually a problem. Anyone heard of this before?
Also, before anyone starts ...yeah, yeah, I have heard all the stories about unreliability etc. shouldn't have bought one etc.
Since then I sent it to a dealership to have the piston replaced and then I did another trip. However, I have just checked the clearances and they are less than the required spec (0.05/0.06 for inlet and exhaust). The bike still runs and seems fine so I will keep riding it and check again next time I service it. I am puzzled by them being tight.
The only explanations I can think of are:
1) Dealer put in larger shims (given it is ALL the valves this seems most likely)
2) Valves are all eating their way into the head
3) All the valve shoulders are wearing
I can't ask the dealership about this as they have gone out of business like a lot of others, any thoughts?
Not too keen to take the head off unless there is actually a problem. Anyone heard of this before?
Also, before anyone starts ...yeah, yeah, I have heard all the stories about unreliability etc. shouldn't have bought one etc.
This will be caused by the valves receding into the head, and is quite common and the main reason that valve clearances need keeping on top of. If you carry on riding with the valve gaps tightening up, eventually the valves will fail to close properly losing you compression and making it hard to start and potentially burning out a valve.
I am unsure whether the 500EXC has titanium valves like a motocross bike, but if it does it will need new valves as once they start to go through the hard coating they will fail very quickly.
I am not sure what you were expecting maintenance wise from an enduro bike though, as over 300 hours without a top end rebuild already is very good going!
Edit to add:
If the dealer didn't charge you for valve clearances and shims then they definitely didn't do it, and there is no reason they would shim them up to be too tight,
I am unsure whether the 500EXC has titanium valves like a motocross bike, but if it does it will need new valves as once they start to go through the hard coating they will fail very quickly.
I am not sure what you were expecting maintenance wise from an enduro bike though, as over 300 hours without a top end rebuild already is very good going!
Edit to add:
If the dealer didn't charge you for valve clearances and shims then they definitely didn't do it, and there is no reason they would shim them up to be too tight,
The dealer will have had to take the head off anyway to change the piston; they will rhen have had to do the valve clearances anyway as part of the reassembly procedure.
Could be that the mechanic used the wrong figure, could be that he did it wrong, could be that the valve seats are wearing.
Either way, you shouldn't just ignore them if they are too tight as this will only cause more damage.
Could be that the mechanic used the wrong figure, could be that he did it wrong, could be that the valve seats are wearing.
Either way, you shouldn't just ignore them if they are too tight as this will only cause more damage.
Taking the head off many engines would not affect the valve clearances.
Some heads come off without disturbing the cams.
Others, the cams and everything else will go back in the exact same place they came from.
Other engines, like a pushrod motor, you have gaskets etc which will be renewed altering clearances.
How far out are the clearances?
Are you sure they were measured correctly, with the engine properly cold?
Personally I would monitor the situation, but the clearances in the manual probably have a fair safety margin before the engine gets to below zero clearance and burning valves when it's hot.
Very often there are two sets of limits, a small tolerance of what an engine should be built to, and a wider tolerance of what's acceptable before intervention is needed, or even desirable.
Some heads come off without disturbing the cams.
Others, the cams and everything else will go back in the exact same place they came from.
Other engines, like a pushrod motor, you have gaskets etc which will be renewed altering clearances.
How far out are the clearances?
Are you sure they were measured correctly, with the engine properly cold?
Personally I would monitor the situation, but the clearances in the manual probably have a fair safety margin before the engine gets to below zero clearance and burning valves when it's hot.
Very often there are two sets of limits, a small tolerance of what an engine should be built to, and a wider tolerance of what's acceptable before intervention is needed, or even desirable.
Thanks for the input folks.
I am pretty sure that the head can be removed without disturbing the valves.
What is boggling is that all the valves are about the same gap, if they were worn I'd expect a) that the gaps would be increasing or b) that there would be more variance. Engine was about room temp (in the garage) and both inlet and exhaust were either 0.05 or 0.06.
Inlet should be between 0.10 and 0.15 and exhaust between 0.12 and 0.17.
I did try rotating the engine a few times to check incase there was some kind of fancy double cycle or other guff. I would not have worried if they were a bit closer to tolerance but this seemed a bit far, although there is still A gap and the bike seems fine.
I am pretty sure that the head can be removed without disturbing the valves.
What is boggling is that all the valves are about the same gap, if they were worn I'd expect a) that the gaps would be increasing or b) that there would be more variance. Engine was about room temp (in the garage) and both inlet and exhaust were either 0.05 or 0.06.
Inlet should be between 0.10 and 0.15 and exhaust between 0.12 and 0.17.
I did try rotating the engine a few times to check incase there was some kind of fancy double cycle or other guff. I would not have worried if they were a bit closer to tolerance but this seemed a bit far, although there is still A gap and the bike seems fine.
Gnits said:
I would not have worried if they were a bit closer to tolerance but this seemed a bit far, although there is still A gap and the bike seems fine.
I'm not familiar with your bike so don't know the specifics but, if the clearances are too tight, there may not be any clearance when hot?
Gnits said:
Thanks for the input folks.
I am pretty sure that the head can be removed without disturbing the valves.
What is boggling is that all the valves are about the same gap, if they were worn I'd expect a) that the gaps would be increasing or b) that there would be more variance. Engine was about room temp (in the garage) and both inlet and exhaust were either 0.05 or 0.06.
Inlet should be between 0.10 and 0.15 and exhaust between 0.12 and 0.17.
I did try rotating the engine a few times to check incase there was some kind of fancy double cycle or other guff. I would not have worried if they were a bit closer to tolerance but this seemed a bit far, although there is still A gap and the bike seems fine.
You wouldn't be the first person to be using an imperial feeler gauge to check a metric gap.I am pretty sure that the head can be removed without disturbing the valves.
What is boggling is that all the valves are about the same gap, if they were worn I'd expect a) that the gaps would be increasing or b) that there would be more variance. Engine was about room temp (in the garage) and both inlet and exhaust were either 0.05 or 0.06.
Inlet should be between 0.10 and 0.15 and exhaust between 0.12 and 0.17.
I did try rotating the engine a few times to check incase there was some kind of fancy double cycle or other guff. I would not have worried if they were a bit closer to tolerance but this seemed a bit far, although there is still A gap and the bike seems fine.
I learned at work never to say 'mil' for millimetres, because it means 'thou', 1/1000 of an inch to Americans and sometimes to random foreign people!
I had a works Ducati manual which was in six languages, everything had been translated into imperial units in the English language sections. Including putting the oil capacity in cubic inches.
I check my feeler gauges with a micrometer.
Apologies, I did not even consider that, so for clarity...I was measuring in mm and checking against the spec in mm.
(I'm happy with miles, and height in feet or hands and weight in stone, the rest of that nonsense can get stuffed, metric all the way!!!!)
Also just did an oil change so will try and put a few more miles on it in the next few weeks and see what happens. At least checking the valve gaps is not difficult or time consuming, takes about 10 mins!
(I'm happy with miles, and height in feet or hands and weight in stone, the rest of that nonsense can get stuffed, metric all the way!!!!)
Also just did an oil change so will try and put a few more miles on it in the next few weeks and see what happens. At least checking the valve gaps is not difficult or time consuming, takes about 10 mins!
OutInTheShed said:
I learned at work never to say 'mil' for millimetres, because it means 'thou', 1/1000 of an inch to Americans and sometimes to random foreign people!
.
Come again?.
Mil is exactly that. 0.1 would be 0.1 of a millimetre or just under 4 thou.
0.1 (imperial) is 100 thou' or 2.54mm
Why would you saying mil be confused with imperial measurements, regardless of nationality?
Or have I misread?
STe_rsv4 said:
Come again?
Mil is exactly that. 0.1 would be 0.1 of a millimetre or just under 4 thou.
0.1 (imperial) is 100 thou' or 2.54mm
Why would you saying mil be confused with imperial measurements, regardless of nationality?
Or have I misread?
We call it a thou, some Americans apparently call it a mil. Confusing.Mil is exactly that. 0.1 would be 0.1 of a millimetre or just under 4 thou.
0.1 (imperial) is 100 thou' or 2.54mm
Why would you saying mil be confused with imperial measurements, regardless of nationality?
Or have I misread?
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