Low cylinder compression on GS1000 = rebuild?

[GSnovice]

Just got a 1980 GS1000G the other day and did a cylinder compression check. Not sure what the proper cylinder numbers are, but from sitting on the bike, the left two cylinders had a low compression, one at 60 and the other at 80. The right side cylinders were at 120-130 psi. compression check was done cold with oil squirted into the cylinders, but forgot to put it at full throttle. No adjustments to the valves, manifold, carbs were made and have not been checked.

I am being told by an acquaintance with a lot of mechanical and motorcycle experience that the engine will need to be rebuilt. He says the compression is too low to be recovered simply by adjusting the valves.

I am looking for info from the experienced GS owners here to get some input into this issue and whether or not there is a solution other than a rebuild.

 

[Big T]

You can't do a proper compression test without adjusting the valves

It is often the case that the valve adjustment is overlooked, the bike runs more and more poorly, so the owner gives up on the bike and parks it. Then, the rings stick to the pistons, further lowering the compression.

Quite a few members have adjusted the valves, dribbled some Marvel Mystery Oil into the cylinders and ran the bike hard for a few hundred miles to find compression restored.

Was this bike sitting for a few years before you bought it?

 

[GSnovice]

Yes, bike had been sitting. Owner had never ridden or started the bike, as a family member died in a motorcycle accident and he lost interest in riding. I don't know much more about it. Bike has 65,000 miles though.

 

[fastbysuzuki]

Get the manual first you can find it here http://members.dslextreme.com/users/bikecliff/ Do he valves clearances first, even if the clearances are wrong the important thing is you should be able to push the keepers and rotate them by hand if not then you are likely to have burned valves a lot of us push the clearances to .004" if everything is ok then put some miles on it after warming it up give it some hardshish burst of acceleration this should free off any sticking piston rings then whilst warm do your compression test not forgetting to hold the throttle wide open take note of the numbers and post them on here.
use the shim club on here for valve shims.
but do the valves first or you could cause damage.

 

[Guest]

I wouldn't trust that acquaintance..... as said, do the valves, get it running, give it the ol' italian tune-up, then take a proper compression reading.

 

[GSnovice]

Thanks for the feedback. It might be a while before we get it sorted but I'll post an update after doing the valves and running the bike.

 

[Johno]

Totally agree with the advice above. My bike was layer up for 14 years. I took it to a Suzuki dealership to get the carbs cleaned. They told me they did a compression test and found low compression. This was apparently done cold not starting the engine. Said I probably needed an engine rebuild.

Took it to an Old school mechanic who cleaned the carbs and adjusted the valves. 50,00 kms later all is good and compression great.