KTM Crank Locking Bolt

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pdee4t

hi there. i came back from a ride and had low coolant just below the fins(after only topping up a day before). so i decided to check if my gasket was blown and do a leak down test but this time decided to use the best method recommended by KTM, using the crank lock bolt to stop the engine from turning over during a leak down test(was my very 1st time using the crank lock bolt)...and worked a lot better.



anyway, i began by using my regular method of putting the bike in top gear the putting a balloon on the end of the leak down spark plug adaptor hose and rocked bike back and forward to find TDC(or near abouts) til the balloon blew up, then took out crank lock bolt, removed copper washer, then screwed in crank lock bolt without copper washer by hand til there was a little bit of resistance, then had a helper slowly/gently rock the bike back and forth til the crank lock bolt screwed in properly/all the way by hand.



did the leak down test and i got 11% leakage(on a cold engine which im ok with)..which is the same percentage i got last time.



however i just have a few questions. i did the test 2 times using the crank lock bolt. the 1st test showed 18% leakage(with crank lock bolt in) and the 2nd test showed the same reading as last time(11% leakage)...which is obviously the correct reading. so im guessing the 1st test i did, the piston wasn't at exactly true TDC and just a bit off even with the crank lock bolt in. The 2nd test i did, the bolt would not screw in anymore at all, so that 2nd test was definitely true TDC and the bolt all the way in by hand.



1st question is: during the 1st test, with piston probably not at correct true TDC even though the crank lock bolt was in(but maybe not exactly ALL the way), how come the bolt still went in relatively smoothly and the engine didn't turn over at all during leak down test??



2nd question is: by me having the bike moved back and forth slowly with the crank lock bolt in 98% of the way, that wouldn't of done much, if any damage would it??(usually your meant to turn the flywheel instead but i didn't want to disconnect any stator wires and thought this would be easier). it was only once and very gently.

Bike is a KTM RFS 2004 model for those wondering.
 
SRAD97750

SRAD97750

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are talking about this locking pin? Never seen a setup like this before.

If you are very close to TDC, the reading should be the same as TDC.
What I think occured is, the initial test seated the rings against their land which gave you a better second reading. The rocking back and forth on the piston would have unseated the rings (slightly) from the bottom of the lands, allowing more leakdown. #Theory

I think 11% is good for a cold engine.
You couldn't have damaged anything in that location unless the engine turned while the lock bolt was installed.

-BIG DAN:thumb:
 
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pdee4t

thanks for the replies guys :)
yeah that's the thing im talking about :) mines similar, not as long but similar and with a tapered edge. most KTM's have them.

as seen in the picture, that is where the tapered edge of the bolt goes into.
so the bolt would even go in without being at 100% TDC? because based on the picture, i just don't understand how that bolt would go in because the recess/groove is horizontal and not vertical OR is there a bit of lee way for the bolt to go into the groove and possible that i was near enough to the hole so the tapered end just went in the hole and still was able to hold the engine?
 

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pdee4t

yeah makes sense. im not 100% sure it was in that slot though on my 1st initial test. I just assume it was because the bike didn't move or turn over when i did the leak down test. that's why im concerned if it did any damage or grazed or damaged my crank or something if it wasn't in the hole.
i just don't understand why it gave me 2 different readings. cos 1 of them had to be true TDC and the other may have been a bit off and i just don't get how come the bolt still went in if it was a bit off TDC.
is there a bit of lee way for the bolt to go into the groove and possible that i was near enough to the hole so the tapered end just went in the hole and still was able to hold the engine?
 
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cleonard

cleonard

I had never seen this type of crank locking bolt until I get my beta. It's very similar to the KTM design and even has the same copper washer system. I've not seen the crank yet, but I imagine that there is a small detent in one part of the crank that you try to get the bolt into after removing the copper washer. If you miss the hole naturally the bolt will scrape along the side of the crank. No worries about damage. It might have put a little scratch into it, but it's not really a problem. That's what oil filters are for.

Leak down tests are not usually super exact or repeatable. If you are not a TDC the chamber volume is larger so a constant leak will seem smaller than at TDC. There are several other variables as well. For example the rings are not at exactly that same spot in the bore and the leak might be different.

As far as the coolant goes, what about the bike puking some coolant due to a little overheating? My bike does it all the time if I'm on technical trails. It's the simplest explanation and often the correct one.
 
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pdee4t

Yeah after I checked and ruled out the gasket, I thought it could be from a little overheating.

As for the crank locking bolt, if you do miss the detent or the groove on the crank, wouldn't the engine still turn over when pressurising the cylinder because the bolt isn't in the groove??(mine didn't turn over at all).

The picture in my previous 2 posts is what the crank and detent/groove looks like.

Also, even if im just a wee bit off TDC, would it still be just enough for that bolt to slightly fit into the groove at all or just fit into the groove enough to hold it?

I did also do an oil change afterwards and drained the oil, there were no metal filings at all anywhere on the magnetic drain bolt which im happy about
 
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