GS1000G Compression levels

[LJR47]

Hello All,
I currently have a 1981 gs850g and the engine is very tired, at a guess I would say that I would be up for around $3k Aus Dollars for a complete rebuild, this would be upper and lower works, pistons rings valves etc etc etc. Apart from the substantial cost there is the issues of obtaining all of the parts required for the rebuild, I have a mechanic here in Melbourne that can do the job but he wants me to source the parts.
I have the opportunity to pick up a 1981 GS100G for around the $3K mark, the seller tells me the engine is in good condition, he has just had it serviced, oils and filters etc.
I'm considering purchasing this bike, and using both bikes as donors to build one good condition bike.
I know that both the 850 and 1000g's are a bit like a sewing machine cam chain noise etc, I'm thinking of taking a compression tester with me when I view the 1000g.
Can anyone please tell me what the compression should be in each cyclinder? and whats the best method for testing the compression, engine hot or cold?

Regards,Merry Christmas and Happy New Year.
LJR47

[Guest]

I'd say anything above 120 would be good. I can't quite remember what the difference between the highest and the lowest is allowed to be but I think it's no more than around 15? Just check the manual. If you can check the compression warm that's best but if you do check it cold it just means your numbers will be a bit lower. But remember many an engine has been bought with low compression like 70-90 and a valve clearance job brought them up to 130. Don't forget to have the throttle held open when you check the cylinder compression or your number will be low.

[Datsa Noydb]

How long has it been since the engine in question has run? If it has been a while (months? years?), the rings might be stuck, which will show up as lower compression numbers.

Even if an engine has been run somewhat recently, but has worn rings, numbers will be a bit low, so take along a squirt can with some oil. Get some "dry" compression numbers, then squirt some oil in and do the test again. If the numbers go up, rings are the issue. If they don't go up, the problem is in the valves. As mentioned, valve adjustment has worked wonders, occasionally. Sometimes it's simply a matter of verifying valve clearances then running the snot out of it for about 1000 miles to free up the stuck rings.

Any way you go, you are looking more for consistency across the cylinders, rather than actual numbers. About 10% variance is OK.

[tkent02]

Sometimes it's simply a matter of verifying valve clearances then running the snot out of it for about 1000 miles to free up the stuck rings.

This .

[LJR47]

Thanks for the info, very much appreciated.
Kind Regards

[duaneage]

I've got about 135 cold and 140 hot. Mine is far from tired.