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Cam Timing Help

  • Thread starter Thread starter justanother54321
  • Start date Start date
J

justanother54321

Guest
My bike: 1979 GS850. Lots of work done since it was last in on piece and ran. Rebuilt original Vm26 carbs as per the rebuild tutorial, valves were just redone. Valve clearances are all within spec. New petcock , new plugs wires, dyna coils, dyna s ign.

I just finished putting my bike back together and it won't start. The starter turns the engine but it doesn't sound like anything is happening.

I've checked for fuel and spark, both are present. I've doubled checked the ign timing.

I did compression test and was getting 100 psi in the cyl # 1 and about 70-75 in the other three. I called the motorcycle machinist that did my valves and said I should be getting about 150lbs. So timing must be off?

Here's some pics:

http://s89.photobucket.com/albums/k207/dopictureslie/Motorcycle/

Should I just shift the intake cam one more pin, even though the count seems right?

As always any help is much appreciated.
 
The cams are timmed properly relative to each other. I assume you have the 1-4 T mark aligned on the crank?

IMG_1378.jpg


IMG_1382.jpg
 
This is similar to my probs on the GS425 twin. So in the pics, is that correct if the 1-4T mark is lined up? I know that the intake camshaft will pull down when the tensioner is put on,lining up the marks parallel to the head and opposite each other.
 
Looks like you've got it right (I just did this yesterday on my 850). On the 850, there's an idler sprocket (what the Brits call a "jockey wheel") between the cams. It'll push the chain down a little further and the intake camshaft will be pulled into the correct relationship.

When you install the idler and the cam chain tensioner, everything will fall into place.


On the twins, I don't think there's an idler, so I think the number of chain pins is different. LOOK IN YOUR MANUAL!!! GS ENGINES ARE NOT ALL THE SAME!!!!

However on all GS engines that I know of, at the 1-4 timing mark (on every other crank revolution), the notches in the ends of the camshafts will be parallel to the head and facing one another. But the number of chain pins to count may be different. If you are too cheap to buy a manual, you could get the timing right by pure trial and error.
 
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I'll double check my T 1-4 mark today. Just wanna make absolutely sure that the cam timing is not the reason why my bike won't start.

Thanks for the input
 
justanother54321 said:
I'll double check my T 1-4 mark today. Just wanna make absolutely sure that the cam timing is not the reason why my bike won't start.

Thanks for the input
Click to expand...

Post a pic while you are at it so we can see too. I just checked my cams and they looked right and they are the same as yours.
 
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