Cam timing never perfect

[DimitriT]

So this is on the 82 gs550L

I'm putting on cams and the procedure is fairly simple. Line up the T 1-4 mark. Take slack out of the chain. Arrow 2 on exhaust cam points up. Arrow 1 points parallel to head surface. 20 pins over to intake arrow 3. She's lined up.

The problem is that after everything is put back and the tensioner is activated and the crank is turned, the arrows now point about half a tooth late (meaning to the left when looking at the exhaust cam).

I've tried advancing the exhaust cam one tooth but once everything is put back, now the arrows point about a tooth to the right.

Why can't I get this to look just like the nice picture in the service manual?

In the end I went with the "half-tooth late" since this appears to be closer to the T 1-4 mark.

Cold compression test says everything is good (115, 120, 125+, 120).

 

[sharpy]

So new cam chain or one from maybe 1982?

 

[fastbysuzuki]

Funny you should bring this up as I have just had my tentioner off to renew the seal and oring when I put it back and checked the valve timing I had the same result, I did not try to adjust, as the pin in effect was sitting in between the teeth where the arrow is but looked slightly out. I had checked the cam chain 3k ago and it was well within spec.
The only thing I could think off is the chain was sitting a little high on the sprocket which would make it look slightly out and when the engine runs under power the tentioner will tighten the chain which would pull the pin down closer to the arrow.
well that's all I could think of as I could not see the chain stretching to out of spec in 3k personaly even if the chain was stretched the roller that the pin is in the centre still has to sit between the teeth which is where the arrow is.
i have not run the engine yet but have tested the compression 1= 165 2= 168 3= 165. 4=164 no carbs fitted.
i checked the tentioner by turning the engine anti-clockwise whilst turning the tentioner knob anti-clockwise then turning the engine clockwise after releasing the tentioner knob and it rotated and moved freely as the chain tension was taken up.

Be interested in other opinions though.

 

[DimitriT]

So new cam chain or one from maybe 1982?

Old chain but well within spec.

 

[Tom R]

Sounds like either stretched cam chain or the tdc mark is a bit off...

 

[Guest]

If the head has ever been resurfaced you will get the same result also

 

[gs550]

Did you find something about this issue , same thing for me

 

[Rijko]

If the head has ever been resurfaced you will get the same result also

Please elaborate on that ....

 

[Steve]

WOW!!! There is nothing like bringing back a thread that has been dormant for three years. :-\\\

Please elaborate on that ....

When you surface the head and/or block, you remove material from them. The cams and the crank now sit a little closer to each other, but the chain did not change length, so the cams rotate a bit to maintain that same distance.

.

 

[Nessism]

As the cam chain wears it will get longer so the hash mark on the exhaust cam should point above the gasket surface. If it's angled down you're off a tooth.

 

[Rijko]

WOW!!! There is nothing like bringing back a thread that has been dormant for three years. :-\\\


When you surface the head and/or block, you remove material from them. The cams and the crank now sit a little closer to each other, but the chain did not change length, so the cams rotate a bit to maintain that same distance.

.

What surfacing is, is taking off the protruding parts of scratches.
We're talking thousands of inches, not tenths.
A resurfaced head should show a lot of the original surface, with just
parts touched to correct.

But even if they take off tenths when hightening compression, that does not
change things up top.

There always is slack in the chain, which is taken up by the tensioner.

The distance between the marks on the cams, with the tensioner mounted as mentioned, is determined by the chain and how worn it is.

 

[Rijko]

Maybe the cam wheels are slotted ?

Or the tensioner does not take up the slack properly.
The chain should be tight.

 

[Rijko]

i checked the tentioner by turning the engine anti-clockwise whilst turning the tentioner knob anti-clockwise then turning the engine clockwise after releasing the tentioner knob and it rotated and moved freely as the chain tension was taken up.

Releasing the tensioner and rotating back could allow the chain to jump a tooth ...

With the tensioner mounted and the crank rotated a few times so all slack is taken up,
rotate the crank back and forth slowly a few millimeters.
The cams should rotate exactly at the same time. If one cam moves and the other one starts moving a bit later, something is wrong.