Question About Cam Timing Marks

[crazy steve]

Ok, I've got a head-scratcher on my hands; I finished up my valve adjustment, reinstalled the cam, etc, and can't quite get the intake cam mark to line up with the mark on the cam cap....

[IMG][/IMG]

If you look closely, you'll see the exhaust cam mark lines up perfectly with the cap, but the intake is 'leading' the mark by about the diameter of the 'dot' on the cam. At first I thought I'd missed the cam sprocket by one tooth... but when I changed it, the dot moved to the other side of the mark, off by the same amount. Hmm....

I know the cam chain is properly engaged on the crank, as this will repeat when turning the motor by hand. I verified that the cam sprocket is installed correctly. I thought about a stretched cam chain, but the exhaust is spot-on when the timing pointer is at 'T'; it's only the intake cam that's off. So my thought is the mark on the cam or cam cap is slightly off or the cam/cam sprocket machining is a bit off; looks like 1/2 a tooth. If I have to choose, I'd rather run the intake advanced a bit as shown as that will help with high-rpm power.

Anybody run into this? And more important, did you find a fix?

[bikerphil]

I just did a valve adjustment to a motor with 60K on the cam chain. The exhaust cam dot was slightly tardy when the intake cam was spot on. I left it alone and my engine runs fine this way. I would say your predicament is the combination of a slightly stretched chain and possibly normal wear to the cam sprockets.

[Lonerider62]

My first inclination would be that you were one tooth off on that side but if you move the chain by a tooth and then it's the same amount off on the other side then you may very well have a stretched chain. My chain was stretched to the max and my tensioner was all the way out but my marks did line up perfectly. It took me a couple tries when I put the new chain on to get both marks to line up but they did. The motor will proably run OK with that little bit off but I'd make sure the cam chain isn't beyond it's wear limit and the best way to determine that is where the chain tensioner is as far as the amount left after it has moved to the tensioned position. If it's out of movement (at it's limit) you need a chain.

[crazy steve]

See, that's what makes this strange; if the chain were stretched, it should be the exhaust cam that would be off, or more off than the intake. But it's right on the money....

I'll admit I don't know the miles on this motor; there was 30K showing on the speedo but the bike hadn't been running for a number of years and the seller didn't know much history. But it checked with great compression (190+ in every hole), and it still has almost 1/2" of travel available in the OEM cam tensioner; hardly the mark of a worn chain.

I do have a couple of spare cam sprockets, I think I'll tear it down and see how they compare....

[BA80]

Don't sweat it Steve. That's no more than maybe 1/2º and won't make enough difference to notice. You may even be able to loosen the cam gear bolts and move the gear enough to line them up.

I run into that a lot on automotive engines, especially those with belts instead of chains.

[JasonRedbeard]

I'll second BA. I replace timing belts and chains on automotive engines all the time, and it's not uncommon to see a little variation in how the marks line up. Production tolerances alone can cause that much of a shift, and you'll never notice it in the performance.

[skids]

I replaced 3 camchains on 3 xs11's. Two of them were adjusted as yours was and I found that the other was closest when the intake dot was just to the left of the center of the pointer. That one would have been worse to put the chain on the next sprocket tooth, making it way too far to the right. Sprocket wear? Don't know. The bikes all run fine.

[bikerphil]

Steve, I know you, your probably slotting the cam gears right now.

[TopCatGr58]

Hey Steve,

Before tearing it down, try loosening the cam sprocket bolt at the dot, then rotate to the 180 bolt and loosen it, then rotate back to the dot with the exhaust dot lined up. Then put a wrench on the intake cam and see if you can rotate/turn it a smidge to line up the dot without the chain moving very much, retighten the dot side cam sprocket bolt, rotate 180, tighten the opposing bolt, then rotate a few more times and see if the dot ends up closer to it's alignment? You might find a few thousandths of slack around the cam sprocket bolt holes to allow you to adjust it??

If it still doesn't line up...as stated by others, just button it up and ride it, you don't have much spare time to be "Playing" with that motor right now...
too many tech tips need editting!!!

T.C.

[crazy steve]

Well, after spending a couple of hours screwing with this and getting nowhere, I remembered I took a pic of the alignment marks when I was tearing it down for the valve adjustment....duh. Sure enough, the marks are in the same place as where they started from... Digital cameras are a wonderful thing, as long as you remember you took the pic...

I've never been lucky, so I've learned to be thorough. It's all good... Thanks!

[bikerphil]

If you really want to know....

http://www.xs11.com/forum/showthread...t=degree+wheel

[ddragon63]

Steve just an FYI... Retarded cam will help with top end power advanced will help lower end. If you take cam timing away from an engine (retarded) you are changing the cam center line up in degrees. IE if center line is suppose to be 108 deg and it goes in 2 degrees retarded its center line will now be 110 deg. and so in retrospect if it goes in 2 deg advanced it will be in @ 106 deg. the close the number is to 0 the more lower to mid range torque a motor will make the further away from 0 it is the more top end hp it will make.

you can have a a difference of 2 to 4 degrees and really not notice in most applications. for example if a fella installed a performance street cam in a small block chevy and just lined up the timing marks it could be up to 4 degrees off as most aftermarket cams come with 4 degrees advance already ground in to the cam. they do this because you can have up to 2 degree's difference in either direction due to chain slop. Thats why when degreeing a cam you have to measure the timing in both directions of the nose of the cam and split the difference for the happy medium to get your true center line.
these other good reasons but it gets even more complicated. we'd have to start talking about intake draw vs intake contamination due to a highly retarded cam @ idle. but these points are irrelevant for the situation @ hand as your intake and exhaust are on 2 seperate sticks.
I would always err on the side of advance... you feel torque more than total top end power.

just the 2 cents of a ex race car engine builder.... just don't ask me to wire it for you

[TADracer]

Before I moved to slotted sprockets my marks were always off a bit like yours. No biggie.

You have to remember there are alot of parts between the crank and head that are coming together right up there so a bit of slop should be expected. Another bit of slop to consider is that in the stock timing wheel (not very accurate). First time I installed a degree wheel I checked before removing the fixed sprockets and there was no more than 1/2 degree off of the 101 degree lobe centerline.

I would not worry about it at all.

[James England]

Mine were exactly like that when I did my shims.

[DGXSER]

I'd suggest drilling the hole in the cam a little bigger so it looks like it is lined up.

Really though, your giving the machinist way to much credit. If the chain is on the gears and your THAT close, its all good.