82 GS850GL Compression

[Harry P.]

Did a compression test #1=80, #2=105, #3=105 #4=109...#1 is below the service limit of 100 according to the manual.

How bad is it to run it like this?

What is involved getting #1's numbers up? If I do 1 I guess I'll do them all.

Please advise...thanks guys.

[Steve]

A couple of things to check before the wrenches fly:

1. Did you hold the throttle open for all the readings?

2. Were the readings taken cold or warm?

3. Were the readings taken dry or wet?

4. Have you adjusted the valves?



1. If you don't hold the throttle open, the cylinder will have a hard time inhaling air to compress.

2. Readings are usually better when warm because all the parts are expanded to proper clearances.

3. If the readings were 'dry', add a teaspoon or so of oil to each cylinder and try it again. If the readings go up dramatically, you have bad seals on the rings, and the oil just helped seal them. If the readings did not go up very much, you likely have problems with the valves.

4. If the valves are too tight, pressure might be leaking out past the tight valve, giving you a low reading. Make sure the valve adjustment is proper and try again.

.

[spyug]

Need more input please.
How many miles on the bike? Has it been sitting any length of time or been used continuously? Does it use oil? Any leaks?

Low compression could be as a result of bad valves or piston rings or both but in order to determine which you would need to use a leak-down tester to be sure(available from auto parts stores or Harbour Freight but you need a compressor to attach it to) . If you pour in a little oil and re check does the compression go up? If so its rings.

Low compression in one cylinder is not going to cause a lot of grief so i wouldn't get too worried unless its accompanied by banging and clanging. Ride the snot out of it and if you feel up to it in the down season rip into it.

Good luck.
Cheers,
Spyug

[tkent02]

How bad is it to run it like this?
Won't make it any worse, maybe just run like crap, maybe a rough idle.

What is involved getting #1's numbers up?
Has the bike sat a long time?
Most likely, adjust the valves, and go ride it for a while.

Please advise...thanks guys.

Post a little more info, history, maintenance, etc.

[Harry P.]

Looks like I jumped the gun on the test...

Have not adjusted the valves, carbs and airbox are off, engine is cold, have changed the oil and turned it over a dozen or so times thinking this was sufficient to get oil where it needed to be.

Bike is new to me with 70,000 miles, not sure of PO maintenance, wasn't running when I got her..cleaned the carbs, replaced O rings, adjusted the floats, she fired up and sounded strong...but bogs down when she gets hot.

I'll do the valve clearance check tomorrow night, get it in spec, replace the carbs & airbox...run her for a bit off a temp tank to warm her up and see where I am then. If this isn't right let me know.

I am a noob...please be gentle. Thanks.

[tkent02]

If this isn't right let me know.

Probably will help a lot, probably get your test numbers in spec, but several hours of running may be needed to get the compression test numbers up to where they should really be, especially if it has sat unused a long time.
70,000 miles is nothing for an 850 given proper maintenance, and if it has not been overheated, run too lean, run with valves too tight, or with any of a number of other problems having been neglected...

[bwringer]

Please, please, PLEASE check the valve clearances.

[Nessism]

Please, please, PLEASE check the valve clearances.

Amazing how many people don't check the valves.