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?
Unfortunately, if it's suddenly lost half the clearance since the last time you serviced it, I suspect you need more than some thinner shims.
How many miles ago were the clearance checked previously and seen to be OK?
I wouldn't expect thin valve gaps to affect starting, particularly cold starting?
How many miles ago were the clearance checked previously and seen to be OK?
I wouldn't expect thin valve gaps to affect starting, particularly cold starting?
littleredrooster said:
We call it a thou, some Americans apparently call it a mil. Confusing.
It can be.You'd think it was obvious, a 'one mil thick' washer can only mean one mm and a '20 mil shim' is going to be 20 thou thick?
But when you're arguing about tolerances you can have some comedy international conference calls!
A 'mil' is also two slightly different units of angle.
Back to the topic, people have also made mistakes with feeler gauges when two blades get stuck together, some synthetic oils are apparently good at this.
The last time I checked them they were in spec but since then it had a new piston done by the dealer and I did not check the valves since then (until now).
I did make sure I didn't have two feeler gauges stuck together - several times just in case!!
A shim kit will be arriving this week.
However I'd like to know what the OEM standard shim size is from the factory, when I try searching all I get is how to check or change them.
If the shims in there are thicker than factory then that is good, I can put in the correct size and assume that when the dealer did the piston they put incorrect ones in. If however the ones in the bike are OEM or thinner then there is a problem coming up at some point as the valves are moving up into the head.
In the meantime I can get the tolerances correct though!
I did make sure I didn't have two feeler gauges stuck together - several times just in case!!
A shim kit will be arriving this week.
However I'd like to know what the OEM standard shim size is from the factory, when I try searching all I get is how to check or change them.
If the shims in there are thicker than factory then that is good, I can put in the correct size and assume that when the dealer did the piston they put incorrect ones in. If however the ones in the bike are OEM or thinner then there is a problem coming up at some point as the valves are moving up into the head.
In the meantime I can get the tolerances correct though!
Gnits said:
However I'd like to know what the OEM standard shim size is from the factory, when I try searching all I get is how to check or change them.
If the shims in there are thicker than factory then that is good, I can put in the correct size and assume that when the dealer did the piston they put incorrect ones in. If however the ones in the bike are OEM or thinner then there is a problem coming up at some point as the valves are moving up into the head.
In the meantime I can get the tolerances correct though!
You won't find a 'standard' shim size because there won't be one. If the shims in there are thicker than factory then that is good, I can put in the correct size and assume that when the dealer did the piston they put incorrect ones in. If however the ones in the bike are OEM or thinner then there is a problem coming up at some point as the valves are moving up into the head.
In the meantime I can get the tolerances correct though!
Due to manufacturing tolerances every head will be a little different and so be shimmed accordingly - that's why they make different size shims in the first place.
I have a fair bit of experience with valve shims on Ducatis and have a large range of shims to suit all eventualities, that's just the way it is.
You'll see how much valve recession or otherwise when you have to change them during successive servicing.
Gnits said:
The last time I checked them they were in spec but since then it had a new piston done by the dealer and I did not check the valves since then (until now).
I did make sure I didn't have two feeler gauges stuck together - several times just in case!!
A shim kit will be arriving this week.
However I'd like to know what the OEM standard shim size is from the factory, when I try searching all I get is how to check or change them.
If the shims in there are thicker than factory then that is good, I can put in the correct size and assume that when the dealer did the piston they put incorrect ones in. If however the ones in the bike are OEM or thinner then there is a problem coming up at some point as the valves are moving up into the head.
In the meantime I can get the tolerances correct though!
I don't see why anyone tasked with changing a piston would touch the valve shims?I did make sure I didn't have two feeler gauges stuck together - several times just in case!!
A shim kit will be arriving this week.
However I'd like to know what the OEM standard shim size is from the factory, when I try searching all I get is how to check or change them.
If the shims in there are thicker than factory then that is good, I can put in the correct size and assume that when the dealer did the piston they put incorrect ones in. If however the ones in the bike are OEM or thinner then there is a problem coming up at some point as the valves are moving up into the head.
In the meantime I can get the tolerances correct though!
Would you not just take the head off, complete with valves and camshafts, then deal with the barrel and piston, then replace the head as a unit?
Unless the head or valves or seats were seen to need attention when the head was off, maybe the valves/seats were lapped or cleaned up to remove traces of the old piston? What actually happened to require a new piston?
Thanks catso, I kind of expected them all to be made with a standard size and then to wear differently as they age.
Piston replacement was a 'standard maintenance item' on KTM's schedule so I thought I would go along with it. It would have been the only time someone else has done anything on the bike so I was hoping that was why the gaps were smaller. You are right though, the head will come off without messing with the valve clearances.
Shim kit arrives later this week so will try that. Looks easy enough on Youtube, how hard can it be?!
Piston replacement was a 'standard maintenance item' on KTM's schedule so I thought I would go along with it. It would have been the only time someone else has done anything on the bike so I was hoping that was why the gaps were smaller. You are right though, the head will come off without messing with the valve clearances.
Shim kit arrives later this week so will try that. Looks easy enough on Youtube, how hard can it be?!
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