Yet anot her low compression thread

[Guest]

Hi all, I have an '83 gs1100E that I'm working on. I have rs34 carbs on it and it'll idle quite well. I read the compression and the readings were (110-80-80-80). The valves may be just a pinch too tight. The bike has 30k miles, am I looking at having to put a big bore kit on this or could there be something else causing the issue?

[Steve]

Yes, valves should be adjusted first to ensure that they are closing properly and at the right time.

More questions:
1. Was the engine warm when you did your compression check?
2. Was the throttle held open while cranking the engine?
3. Were all the spark plugs out while cranking the engine?

.

[gordinho80]

I'm afraid I'm in the same boat as you, newb.

Measured on a cold engine with all plugs but the test in place, throttle held open: 110 - 120 - 100 - 100 from left to right when sitting on bike.

Not as low as your 80s, but I did test it prior without throttle and with all plugs removed, numbers were MUCH lower, 70 - 90 - 90 - 50

[Gs1100newb]

I'm a dumbass. I didn't have the throttle wide open. I adjusted the valves on cylinder 4 just for grins, and got a cold compression reading of 180. Seems awfully high. All plugs removed and throttle wide open.

[Gs1100newb]

Well my success was short lived. The bike is definitely burning oil. After I idled the bike for ~10 minutes I checked the compression of cylinder 1 and it read nearly 200psi. I double checked with a second and even a third gauge.

Looks like I'll have to fire up the compressor today and do a leak down test to figure out if the leak is from the valves or the rings. Urgh

[TxGSrider]

Well my success was short lived. The bike is definitely burning oil. After I idled the bike for ~10 minutes I checked the compression of cylinder 1 and it read nearly 200psi. I double checked with a second and even a third gauge.

Looks like I'll have to fire up the compressor today and do a leak down test to figure out if the leak is from the valves or the rings. Urgh

200psi is allot.

[Gs1100newb]

Well the pistons and rings look okay, seems to be just burnt oil on the tops but I'm not totally sure.

The valvetrain however is rust city. Can't imagine what the seals look like. Anybody have suggestions for rebuilding this top end? 1488519588066219403745.jpg

[cbxchris]

Leak down only way to go. Anything over 6-8% and its to much. My drag engines checked at 0-2 and street not much worse. Just see where the air is going. Only three places it can. crankcase, intake or exhaust.........

With the head off the old way of checking was fill each port with the cleaner of your choice over a vat....see what leaked.. We set up a air table to check heads before ever putting them on the bike. Of course we were drag racing in a rather big way for a a good bit as well. We knew the leak down of the head before it ever went on the bike.