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Cam Chain & Cams alignment - cam chain rotations vs motor rotation

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Alright here's a real doozy.  I did a valve check today on my 08 YZ250F, all was well except one exhaust valve was .01mm below tolerance, so i removed the cam and shimmed it and re-installed the cam. my way of making sure the cam would properly re-align was taking nail polish and making a mark across the cam and chain to line them up.  It worked... at first.  I figured this would be much easier than trying to line up the TDC mark on the crankcase and the dots on the cams, which it was, if you're EXTREMELY careful.  Stupid me tried to move the kicker while the cam chain tensioner was still out. I learned, never doing that again.  the chain slipped over the teeth of the exhaust cam, and now its misaligned.  It slipped past BOTH cams.

I'll give you a minute to take it in, i apologize, its real hard to explain...

I know im going to have to take out the cam again.  My bike has an aftermarket crankcase side (oil fill side) which has the bolt you open to check for the TDC mark.  Well, the bolt you need to remove is an allen key and is completely stripped out to basically a round hole.  So thats really not an option unless i take the whole side off, which will be MORE of a PITA and I dont want do do that.  

So heres my question:  Does the cam chain rotate a number of rotations in some ratio with cycles of the piston, so that I can bring my nail polish marks back up, line it up, and all will be well?  Or does the rotation of the cam chain not have any even relation to that of the piston?

If the cam chain rotates some random amount, I will not be able to bring my TDC nail polish marks back up, align them with those on the cams, and move on, since the piston wouldn't be at TDC at the same location on the cam chain it was before.  I think i'll experiment tomorrow and feel in the spark plug hole with a screwdriver and see if i can feel the piston align at TDC at the same time as the chain, then I'll know it works.

Thanks for the reading my novel lol I'm real sorry its hard to explain 

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You must find TDC. To assume the chain did not skip a tooth or more on the crank is foolish.

A pencil/screwdriver in the spark plug opening will only get you close to TDC.  Even a dial indicator will not get you at the correct point.

 

If you guess, realize being wrong will cost you new valves, possibly a barrel, piston and crank.

 

 

A crank has to rotate twice for everytime the cams rotate once. There is no uniqye 'TDC' for cam timing. With the cams out then reintaslled, TDC is TDC, Once the chain is on and tensioned, then every other TDC is cam timing TDC

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the piston has a little dwell time at tdc that can make just a pencil or straw check off a little. But if you did it  AND checked the marks on the crank or flywheel to verify it would be good,  also note there may be 1 or 2 firing marks (F) that are not TDC marks (T), in the direction of motor rotation they will be the 1st marks you come to.

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Buy a new inspection port plug. Remove the old one with a chisel. A few raps in the direction of removal will pop it loose. Next time, do not over tighten it. just snug. The oring seals it.

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Are the plugs pretty common at powersports stores or will i need to order one? I'll try the chisel method you said, if that doesnt work I'll JB Weld an allen key to it and knock it off.   Btw, i didnt do it lol the guy i bought it from did, and the screw was already half stripped, so for all i know it may not even be that tight.  thanks guys, withouty you i might've screwed up big!!!

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I chiseled off the timing incpection screw, worked great! theres several marks on the stator and its my understanding that the " I " mark is TDC.  It was a struggle aligning the cams on the chain while not letting the stator move by myself lol but i did it.   all i have to do is put the ACCT back on, the head and spark plug on, and the plastics.  Hopefully i got it, I'm pretty sure  I do.

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So I put it back together, I aligned TDC on the Stator with the " I " mark (is this the proper one? theres one before and one slightly after it with different symbols... looks kinda like an I in the manual to me...) and aligned the punch marks on the cams with the flat of the cylinder head... seems like its running a little funny. it runs, but its real hard to start. think ill be taking it apart again.  Is it possible that when i aligned it at TDC it wasnt on the compression TDC? would it run if this was true? I didnt change any shims or anything.  its real hard to start, seems a little louder, backfires once in a while, sometimes the kicker blows back real hard, and when i kick it over it just feels different... when its not on the compression usually it moves pretty easily, now its sort of resisting all the time...  Maybe i was a tooth off on the alignment, maybe i didnt align TDC on the compression, maybe I used the wrong TDC mark.  is there any way to tell without looking at the way the cam lobes are pointing (since that could be the problem in the first place) which stroke is the compression stroke as opposed to the exhaust stroke? 

Edited by YZmikeydubs1997

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OK.  took it all apart again.  Looks to me like the cam punch marks are aligned properly, to the outside and flat with the cylinder head, as the TDC Mark is lined up on the side cover.  My question remains - The TDC mark on the Stator comes around 2 times per fire of the engine.  Is it possible, then, that I aligned the cams on the wrong stroke when the piston was in the up position? in other words, The cams are on the TDC compression stroke while the Stator and motor are actually on the exhaust TDC stroke?  I would think that it wouldnt have run at all if this was the case, but it did run.  

 

After a hard start and a couple minutes of running, when i took the thing apart again, I noticed the plug was wet and black just on the tip, and its never done this before.  When I started the bike, I also noticed a little smoke and smell of burning oil.  And behold, when I cracked the head cover off, theres a puddle of oil almost halfway up the camshaft (see attachment). is this normal? It sure doesnt seem like it, and i dont remember it being that way when i first took it off. This is likely the problem of the hard start and funny running if this isnt normal, the oil will just keep fouling plugs.  Why would this happen? did the gasket not align right and cover an oiling port or what? this isnt making sense.

 

0914131800-01.jpg

 

 

For reference, in the attachments is how my cam lobes are aligned at the TDC Mark.  in this position, they are on the compression stroke, but again is there any chance i aligned it 180 degrees off and the motors on the other TDC stroke?

 

0914131833-00.jpg

0914131833-01.jpg

 

Also, in the attachments, is how the punchmarks on my cams are aligned.  Please help guys. I'm beyond baffled.

 

0914131831-00.jpg

0914131832-00.jpg

 

*Edit: noticed the lifters sitting a little higher... checked my valve clearances, the Throttle side of the bike's intake valve clearance went down .02mm to where I have to Jam a .10mm (bottom of tolerance range) feeler in there to fit it; same story same side with the exhaust valve but at .17mm

 

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The spark plug fires every rotation, the cams are what determine the whether it is an intake stroke or a power stroke. This is called "wasted spark ignition" since the spark at TDC after the exhaust stroke does nothing. This way it is much easier to assemble the engine since you don't have to worry about being on the right stroke when you put the cams in.

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The spark plug fires every rotation, the cams are what determine the whether it is an intake stroke or a power stroke. This is called "wasted spark ignition" since the spark at TDC after the exhaust stroke does nothing. This way it is much easier to assemble the engine since you don't have to worry about being on the right stroke when you put the cams in.

I was wondering to myself about this.  Thanks for confirming.  That rules out one possibility.

 

So is that much oil normal in the head, or is that causing my problem and fouling the plug? If so could it result from an improperly seated gasket? should i use sealant on the gasket? I dont quite understand.  To my cam lobes at TDC look lined up right in the pics i posted (is it normal for one to be a tad off like that)?  Or am I a tooth off?  I really need suggestions.  I would adjust and test but its time consuming and risky to do so.

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On my hotcams, the exhaust cam has machined, well defined punch marks.  On the intake they look like someone just took a screwdriver and a hammer and pounded a scratch onto them.  Not sure what thats all about but it makes me doubt that theyre reliable to line up?  I really dont want to take this thing to the dealer.  It seems like a cop out and a total waste of money, considering the whole reason i did this was a valve check and the valves are in spec anyway.

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So heres my question:  Does the cam chain rotate a number of rotations in some ratio with cycles of the piston, so that I can bring my nail polish marks back up, line it up, and all will be well?  Or does the rotation of the cam chain not have any even relation to that of the piston?

If the cam chain rotates some random amount, I will not be able to bring my TDC nail polish marks back up, align them with those on the cams, and move on, since the piston wouldn't be at TDC at the same location on the cam chain it was before.  I think i'll experiment tomorrow and feel in the spark plug hole with a screwdriver and see if i can feel the piston align at TDC at the same time as the chain, then I'll know it works.

Thanks for the reading my novel lol I'm real sorry its hard to explain 

I've set mine at TDC and marked the chain and cams with paint.  Then turned over the engine until the all the paint marks lined up again.  It took about 12 revolutions. 

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I've set mine at TDC and marked the chain and cams with paint.  Then turned over the engine until the all the paint marks lined up again.  It took about 12 revolutions. 

hmm,  that'll be my next check.  i nail polish marked mine.  I'll keep turning it over ans see if theres a recurring pattern of where the paint ends up and see if it makes sense to adjust to that point.  If its far off is it possible the chain slipped on the crank when the tension was off it or is it on there real good where it wouldnt slip?  If the prior owner advanced or delayed the ignition it it possible the TDC mark lines up differently on the stator?

theres just so many possibilities and i cant conclude anything. seems like somethings up with the oil though cuz it made the plug wet and theres a deep puddle in the head.  

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hmm,  that'll be my next check.  i nail polish marked mine.  I'll keep turning it over ans see if theres a recurring pattern of where the paint ends up and see if it makes sense to adjust to that point.  If its far off is it possible the chain slipped on the crank when the tension was off it or is it on there real good where it wouldnt slip?  If the prior owner advanced or delayed the ignition it it possible the TDC mark lines up differently on the stator?

theres just so many possibilities and i cant conclude anything. seems like somethings up with the oil though cuz it made the plug wet and theres a deep puddle in the head.  

I've replaced my cam chain but I don't remember if there was room for the chain to jump teeth on the crank if it was loose.  It may be worth pulling the spark plug and dropping a pencil in the whole, turning the engine and see if the TDC mark is accurate.  I've worked on bikes, and cars, with sheared keys.  Some ran if they were not too far off.   No idea what that puddle of oil is caused by. 

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yeah i put a straw in the spark plug hole. TDC is accurate on the stator at least.  Not sure if the cams are exactly in the proper position. I'll do some more work tomorrow

Edited by YZmikeydubs1997

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I ride an 08 YZ250F.  The Exhaust Cam has well defined perfect punch-marks at 9 and 12 o'clock positions making it super easy to line up.  The intake cam, however, doesn't have these well defined punch-marks - there's 3 really faint ones that look like someone took a screwdriver and a hammer and put a little scratch on it.  these three marks also don't align 100% true to 0, 90, and 180 degrees on the cam (although its close); it looks like someone eyeballed it - one's lined up with a tooth and the other two are lined up between two teeth.  so its not perfect, making it hard to line up - I keep second guessing whether i'm one tooth off.  The bike ran a little funny when i put it back together the first time, so i took it apart again and this is a 2nd attempt.  I havent changed anything yet... 

Should the exhaust cam (which i know is correct) lobes be pointing at the same angle as the intake? it seems like my intakes are rotated a little less steep of an angle at TDC.  is this typical or does it mean I'm a tooth off and should rotate it?  Starting to envy the UniCam on the hondas  :rolleyes:

On a side note, on the first assembly, which again, is now taken back apart, it was really hard to start after it stalled a minute in, revved a little rough.  It left a wet oily plug, black on the tip, its never done this before.  Theres also seemingly an excess of oil in the head, like a half inch submerging the cams.  Is it possible i somehow blocked an oil passage or what?  Also three of the valves jumped down .03 to a tad below tolerance and now I have to shim them. Hopefully i didnt damage valves... Heres some pics of my cams, lobes, and the head AT TDC:

 

 

0914131833-01.jpg0914131833-00.jpg0914131831-00.jpg0914131832-00.jpg0914131800-01.jpg0914131800-00.jpg

 

 

thanks a ton in advance  :thumbsup:

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yep.  Just baffled over the oil buildup, and wondering if thats what caused it to run funny or if it ran funny bc the cam is misaligned.  And it scares me that my valve clearances jumped after one minute of running.  Everyones intake cam seems to have the EX and IN markings, its beyond me why mine do not.

Edited by YZmikeydubs1997

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