Compression questions

[newvined]

I have a 1982 GS850L with 32000 miles that continues to leak some oil. I have replaced the valve cover seal 3 times since
March. (I thought I did it wrong as it kept leaking). The last time I used a Real Gasket and it seems to be holding better. I still have oil leaking from somewhere.

I have replaced the oil sending unit, and am waiting for new seals to redo the cam chain tensioner.

I did a compression test this weekend, and actually did it 3 different ways. Here are the results:

Test 1 with all 4 plugs removed
cylinder 1 -60 psi,
cylinder 2- 70 psi
cylinders 3 and 4 -80 psi

Test 2 one plug removed at a time
cylinder 1- 70 psi
cylinder 2- 80 psi
cylinder 3- 95 psi
cylinder 4- 90 psi

Test 3 one plug removed at a time with oil added to the cylinder
all 4 cylinders tested to 110 psi. (This test tells me I have bad rings which is causing back pressure and the leaking oil.)

So I faxed these #'s to a dealer. They told me that the #'s aren't bad and rings are probably OK, but I don't have any idea what good compression
should be. Thats why we are looking at the cam chain tensioner next.

If any of you guys know what good compression should be would you mind replying with the numbers. Also if you agree or disagree with what I am thinking about the bike needing new rings.

A friend of mine suggested I put an extra breather where the oil fill cap goes. (Like Harley does with some of their bikes) The idea being to give that pressure a place to release and hopefully stop the oil from leaking.

Any opinions on this idea are welcome as well.

Thanks
David
1982 GS850L
I love the bike but this is getting frustrating.

[Nessism]

Compression needs to be tested with the engine fully warm and the throttle held wide open. Did you do this? If not, you might want to check again.

Compression should be between 128 - 171 psi according to the service manual with a low service limit of 100 psi. I've heard of people running even less which is fine as long as it runs and meets your needs.

Many people neglect valve adjustment which could contribute to low compression and cause burnt valves. I trust you are not one of these people.

BTW, you can download a factory manual for you bike for free from the following link. It will save time - you can look up the information instead of asking here.

http://members.dslextreme.com/users/bikecliff/

[Dave8338]

Can't say any more than that, Ness'i...

"Good answer, Good answer.....Top ten people surveyed...AND THE SURVEY SAY'S"...

[catbed]

Compression needs to be tested with the engine fully warm and the throttle held wide open. Did you do this? If not, you might want to check again.

Compression should be between 128 - 171 psi according to the service manual with a low service limit of 100 psi. I've heard of people running even less which is fine as long as it runs and meets your needs.

Many people neglect valve adjustment which could contribute to low compression and cause burnt valves. I trust you are not one of these people.

BTW, you can download a factory manual for you bike for free from the following link. It will save time - you can look up the information instead of asking here.
http://members.dslextreme.com/users/bikecliff/

i always take the air filter out but i dont think that is necessary.

[Billy Ricks]

i always take the air filter out but i dont think that is necessary.

That's not necessary. The throttle does need to be craked to get the butterflies out of the way though.

[newvined]

The bike was warm, I had just gotten off the road maybe 10-15 minutes before we did the testing. We did not have the throttle open however. Just hooked up the tester and hit the ignition switch until the needle stopped moving up.

Since I've never done this before let me ask a question... Why does having the throttle open matter?

Oh and BTW the valves were shimmed up back in the spring. They should be good.

Thanks again

[Billy Ricks]

The throttle plates in the carbs close down almost completely with the throttle closed thus restricting the intake.

[tkent02]

If your compression is that good with the throttles closed, your rings are fine.
There is already a breather, this is not a Harely.
Ride it.

[newvined]

If your compression is that good with the throttles closed, your rings are fine.
There is already a breather, this is not a Harely.
Ride it.

Yeah, I know it has a breather, but if you take the oil fill cap off you get a lot of air blowing out. A good bit more than whats going through the breather.
I thought the breather might be blocked, but its not. For some reason this pressure isn't getting released through the breather, and so I have oil leaking because that pressure has to go somewhere. (or so I'm told).
The idea for the fill cap breather came as a thought to help release some of this pressure that doesn't seem to be getting to the factory breather.

Out of curiosity tkent02, which numbers are that good with the throttle closed?

I don't know what else to tell you guys. Back when I was asking about the valve cover leaking, I heard alot about the breather being blocked and the back pressure causing the leaks. The last time I replaced the valve cover gasket I checked the breather, and even cut a new gasket for it that opens it up even more. This seems to have helped but not 100%. In fact I just remembered that the valve cover gasket was a little oily on the intake side of cylinders 1 and 2. This was a week or so ago. I am still riding but what happens when I get the cam chain tensioner sealed up. I am afraid the valve cover is gonna blow out again, and I am back to square one.

What else could I be missing? I'm no expert, and my friends are helping but I hate feeling like I'm going around in circles and getting nowhere.

[tkent02]

Out of curiosity tkent02, which numbers are that good with the throttle closed?

Mine usually read about 60 or 80 if I forget the to open the throttle, on good engines...
Depends on the gauge, elevation, cranking RPM, all the usual variables.

[Harry P.]

regarding the oil leak check the cover for hairline cracks...mine had a barley noticeable hairline crack that leaked oil when the engine got warmed up. Can be welded but find a pro to do it as you'll be grinding forever if there is a big weld by a bolt internally.

[lecroy]

I have a 1982 GS850L with 32000 miles that continues to leak some oil.
I did a compression test this weekend, and actually did it 3 different ways. Here are the results:

Test 1 with all 4 plugs removed
....

Test 2 one plug removed at a time
cylinder 1- 70 psi
cylinder 2- 80 psi
cylinder 3- 95 psi
cylinder 4- 90 psi

Test 3 one plug removed at a time with oil added to the cylinder
all 4 cylinders tested to 110 psi. (This test tells me I have bad rings which is causing back pressure and the leaking oil.)

Remove all plugs, don't put oil in cylinders, install gauge one at a time, open throttle all the way, charge battery between cycles. Make sure the tester has the valve right at the end that fits into the plug hole. You don't want a tester that has any extra volume.

Seeing you already put oil in the plug holes, start the motor, clean it out and try again. You first test shows a pretty big difference. If you started at 1 and stopped at 4, it's strange as I would expect the battery to have drained as you cranked on it, dropping the pressure. So, if you ran them in the 1-4 order, a difference of 25 PSI is pretty high. On my motors, I normally see less than 5 PSI difference once they are broke in. 2PSI difference is common for me. I would think if you start seeing numbers below 100PSI and everything else including the gauge is good, I would start taking it apart.

Besides the normal wear and gaskets, the cam timing, battery voltage, voltage drop in the connections, wire and starter solenoid will all make a difference.

Never had an 850 but if its like mine, I have damaged those O-rings that are on the two front head bolts before. Oil drains from the top, down past the head bolts and then goes everywhere. Could also be a head gasket. This could be the cause of the huge difference in pressure.

Good luck with it.