Low compression cylinders 3 and 4

[gplouff]

My 81 1100 sat for way too long - 14 years as far as I can tell. There's rust everywhere outside, so I guess that means I could have some on the inside, like on the rings. I've had the engine running a couple of times, but the plugs show rich on 3 and 4. Only then was I smart enough to check compression, and I found in cylinders 1 - 4: 145, 150, 90, 115. Obviously this is not good. Adding oil brought them all up by about 5 lbs. Gee wiz. I should note that this was on a cold engine without opening the throttle. I'll check it hot and with wide open throttle next time. My brother in law, who is one of America's absolute best mechanics (seriously), said soak those cylinders with "something good, like CRC". I wish I'd done that before I got it hot a couple times, but I'll do it now and see what happens. The question is, am I eventually looking at a phase 2 of this project, that being an engine refresh? I'm thinking it will need rings, possibly pistons, and a clean up of the head, and then she'll be good for the next umpteen miles. I figure I could do that work myself , but I never planned on getting in that deep. I'm not exactly a motorcycle mechanic, but I did stay at a Holiday Inn Express Friday night. I don't own a bore gauge, or a hone, or a valve spring compressor, but I do have everything else. What would I need for tools and parts, and what should I expect for problems? My plan for now is to run it, once it's streetable, and see what happens. Bike currently has 20,000 miles.

Thanks,
Gary
81 GS1100e, needs everything.

[posplayr]

Soak it and fun it; why test without opening the throttle ? Like drama?

[tkent02]

Then adjust the valve clearances and run it hard for a month and check the compression again. It will come up. In fact just adjusting the valve clearances may fix the compression if it hasn't been done in a long time.

If your brother in law didn't tell you that he's not as good as he says.

[JayWB]

If the compression numbers came up only 5 psi with the wet test your problem almost surely isn't rings, it's valves.

Check your valve clearances.

[ukjules]

Any other issues with the engine , smoking ,won't iidle, lack of power, blown gaskets ?
Do what the guys say, tune it in every way, valves, carbs, timing, and ride it.

If it still ain't right you'll be a step nearer where the issue is.
Can you do it yourself - of course you can ! Just done my head using a eBay £10 valve compressor.
Ride it during the summer , sort engine in the winter .

[Phred]

My bike (81-850)sat for 20 years and when I started working on it I filled the crankcase with oil, poured oil down the plug holes, put the plugs back in and let it sit til I was ready to crank it over. It will take a while to get all the bugs out, but with valve adjustments and once it has been running for a summer the numbers will come up. These engines were built to be bulletproof. Shouldn't have to open up the engine for a long time yet.

[JTGS850GL]

You MUST test compression with the throttle wide open or the numbers have no meaning. 90 psi is typical if you test it without the throttle open. Fully charged battery, all plugs removed and throttle wide open is how to test compression.

[DimitriT]

If the compression numbers came up only 5 psi with the wet test your problem almost surely isn't rings, it's valves.

Check your valve clearances.

+1

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[gplouff]

Thanks for chiming in guys. I plan to "run it and fun it". Since I know it runs, I've turned my focus to getting the rest of the bike roadworthy, which is going to take awhile. I'll post some new numbers in about a month.