camshaft timing slightly retarded.

[mikebgs]

Hello. I have just replaced the front cam chain guide and reassembled the front cam shaft on my 1978 gs750.
The Clymer manual tells me that the #1 mark on the exhaust cam sprocket must point exactly toward or slightly below (1-2mm) the gasket surface.Mine is slightly above, apparently meaning that the timing is retarded.
I did not disturb the rear camshaft sprocket/chain placement while replacing the guide.
I was wondering if this is a regular type of wear occurrence or would the PO have set the camshaft timing incorrectly? cheers. Mike.

 

[mikebgs]

update

update

I have advanced both camshaft's timing 1 tooth on each sprocket. The #1 mark on the exhaust cam sprocket is now about 3mm lower than the gasket surface. So i think that makes it a little advanced rather than a little retarded. Not sure which is better?
On the photo attached to this update you can see the #1 level with the gasket surface but the arrow mark is below gasket surface.

 

[tom203]

Did you remove and then adjust camchain tensioner for this operation? Is tensioner in now? My poor memory is that my 650's #1 mark was slightly above.

 

[Gorminrider]

The chain tensioner shouldn't matter much per this question If you ALWAYS turn the crankshaft in the correct direction

ie: via the chain, turning crankshaft "pulls" on camchain to turn the exhaust cam which in turn pulls the intake cam ....and slack as the chain "returns" to the crank is dealt with by the tensioner..

Cam chains and cam sprockets will wear eventually and just like the wheel sprockets' chain, the chain wear is be checked by measuring length...but , a good supply of oil up there , means they last many times longer than the wheel sprockets' chain!

See if you can find a Haynes manual or the original shop manual somewhere. These will describe the cam chain setup per marks and "links between" in a different way with different diagrams. This can help a lot.

 

[Nessism]

As the chain elongates the 1 -> mark will move up, above the gasket surface. Your photo shows the mark a little higher up than is usually the case though. You might want to measure the cam chain for wear (specs in the manual) just to be sure it's within the service limits.

 

[mikebgs]

Thanks for the replies.

I would like to check the cam chain length. I've found the diagrams in the Suzuki service manual and am aware of timing mark setup, but I'm unable to find a measurement for the chain service limit (20 pin length).
I have measured my chain and it is 149mm or 5.866" for 20 pin length centre to centre.
If anybody knows the cam chain service limit or new length of the 20 pin length?
I have ordered a Haynes manual and it should be here in a week.

The tensioner has been serviced and it's working well. Many thanks.

 

[Nessism]

6.213" measured between 20 pins is the service limit as shown in the 850 manual. You are good.

Your two photos show the mark either too high or too low. Maybe you should double check the crank position? 1-4 T must be aligned and the pistons at TDC.

 

[Brendan W]

6.213" measured between 20 pins is the service limit as shown in the 850 manual. You are good.

Your two photos show the mark either too high or too low. Maybe you should double check the crank position? 1-4 T must be aligned and the pistons at TDC.

I was looking at the 850 and thought, no way, too different.
Then, is that about .016" per pin ?

 

[Nessism]

Based on the numbers the chain is 5/16" between pins and Suzuki's wear allowance is very generous.

 

[Brendan W]

Based on the numbers the chain is 5/16" between pins and Suzuki's wear allowance is very generous.

Probably the same all over the bike and why these things are still running
Thankfully the bean counters hadn't figured out what was going on back then.

 

[mikebgs]

update

update

Hi. I Found a diagram online for a gs850g that describes the process for measuring the cam chain service limit. I had previously been measuring incorrectly.
The service manual explains that I should be measuring 20 pitch lengths equaling less than 157.8mm. That is the distance from the 1st pin to 21st pin centers (or same edges). I had previously been measuring one pitch short.
My apologies for the false reading.
That puts my chain at approximately 157.5mm which would, I think ,explain the retarded camshaft timing.
My plan is -
purchase a DID 219fts cam chain
Break open the old chain
Pull the new chain through
rivet new chain.

and learn to count.
Thanks. Mike.

 

[Nessism]

Hi. I Found a diagram online for a gs850g that describes the process for measuring the cam chain service limit. I had previously been measuring incorrectly.
The service manual explains that I should be measuring 20 pitch lengths equaling less than 157.8mm. That is the distance from the 1st pin to 21st pin centers (or same edges). I had previously been measuring one pitch short.
My apologies for the false reading.
That puts my chain at approximately 157.5mm which would, I think ,explain the retarded camshaft timing.
My plan is -
purchase a DID 219fts cam chain
Break open the old chain
Pull the new chain through
rivet new chain.

and learn to count.
Thanks. Mike.

Sorry, I mentioned measuring between 20 pins too. Oops. Glad you figured out what to do anyway. How many miles on that motor anyway? The cam chains typically last for a LONG time so just wondering.

 

[mikebgs]

My Gs750 has 84000km on the clock. I know nothing of the bike's history. it may have been around the clock.
The bike was in poor condition when I bought it. I have been working through a few issues along with the 30000km service.
I am really looking forward to getting it back on the road.
Thanks again for the replies. Mike.