Is 110 PSI compression ok?

[B-rent]

I have a 78 gs750 with 31K miles on it. I checked the compression in all cylinders the other day and they were all 110 PSI +/- a few pounds. I put some oil in the cylinder for the second reading and found that the pressure went well over 150 PSI in all cylinders. It seems the valves are ok, but should I be worried about the compression? The service limit is 100 PSI. How much longer can I expect to ride this bike? I guess you should know that I'm not afraid to red-line it once in a while. I just ordered 3 Ohm Dyna coils and Dyna-S electronic ignition and I'm wondering if I should return them and use the money to rebuild the cylinder instead.
Thanks for your input.

 

[Spyderman]

that compression is fine for some time yet put the coils and ignition on and enjoy the bike no need to worry yet

 

[Guest]

I know blokes that have raced them with 70 psi so you should be ok for a while yet. Cheers , Simon.

 

[mighty13d]

so it's the rings that aren't keeping the compression up... have you been running it this way for a while? if not, then the rings might loosen up and actually raise your compression after a while.

 

[B-rent]

so it's the rings that aren't keeping the compression up... have you been running it this way for a while? if not, then the rings might loosen up and actually raise your compression after a while.

This is the first time I have checked them. I have had the bike for about 2 years now and it seems to perform the same as when i first bought it. I will have to check them again after a while and see if it improves or gets worse.

 

[Nessism]

How long since your last valve adjustment?

 

[tkent02]

Jeeze, This thing again, adjust the valves, tune it up and run the hell out of it.
Probably it's weak because some wimp actually followed what they read in the owner's manual about taking it easy during break in thirty years ago.
It will be fine until it blows.
Rocket science.

 

[B-rent]

How long since your last valve adjustment?

I adjusted them early this season. The intake valves on 1 and 4 seem to need adjusted more than the others. I'm thinking of replacing the springs on 1 and 4 and the seals on all the valves.

 

[Nessism]

I adjusted them early this season. The intake valves on 1 and 4 seem to need adjusted more than the others. I'm thinking of replacing the springs on 1 and 4 and the seals on all the valves.

Why would changing the springs help? New springs if anything will have more seat pressure which will increase wear.

 

[tkent02]

Why would changing the springs help? New springs if anything will have more seat pressure which will increase wear.

And why bother with the seals, is it smoking or burning a lot of oil?
It sounds like you really want to tear it apart to see what's inside, go for it.

 

[B-rent]

Why would changing the springs help? New springs if anything will have more seat pressure which will increase wear.

I never thought about that. I could see how that would increase wear, and more headache trying to adjust the valves.

 

[hampshirehog]

Just take it in to the red zone a few times - it'll be fine.

 

[B-rent]

And why bother with the seals, is it smoking or burning a lot of oil?
It sounds like you really want to tear it apart to see what's inside, go for it.

It doesn't burn any oil that I can see, and I never have to add oil between oil changes. I really want to tear into it, but I want to make sure I have a good reason to before I screw something up. I probably won't be doing this for a while. I've been looking for a parts bike to screw around with but they are hard to find around here in Idaho (I check craigslist at least a couple time per week) and it seems people want money for them too, crazy. When I bought this bike I knew nothing about it and thought I would be lucky to get one season out of it before it died. I was very wrong about that.

 

[Pete Logan]

Just thrash it. If it's not using any oil then it's gonna go at least twice that mileage before it starts to. And then the same again before it needs any attention beyond regular servicing.

 

[tkent02]

Just thrash it. If it's not using any oil then it's gonna go at least twice that mileage before it starts to. And then the same again before it needs any attention beyond regular servicing.

Agreed, run the crap out of it, it is all good. Buy a dead Honda or a lawnmower or something to take apart. It's just as much fun.

 

[B-rent]

Well I feel better now about the coils and ignition that i bought for it. I had a guy back into my bike and tip it over about 2 weeks ago. He payed me cash and I felt that before I dump the money back into it I should check the compression to see how things are. I feel better after hearing all your comments.

 

[Pete Logan]

Well I feel better now about the coils and ignition that i bought for it. I had a guy back into my bike and tip it over about 2 weeks ago. He payed me cash and I felt that before I dump the money back into it I should check the compression to see how things are. I feel better after hearing all your comments.

Oh crap, that really wasn't what we meant.

What we really meant was the thing is a pile of junk, but no worries, I'll take it off your hands for $50 plus shipping

 

[Guest]

If it aint broke fix it till it is.

Sorry, old harley motto.

 

[Pete Logan]

If it aint broke fix it till it is.

Sorry, old harley motto.

Plus ten characters

 

[mike_of_bbg]

I put some oil in the cylinder for the second reading and found that the pressure went well over 150 PSI in all cylinders

Define "some" oil. Should be about one tsp, just enough to help seal the rings. If you put too much in you're shrinking your combustion chamber and that will make your readings go up artificially (i.e., past what you'd get with a ring replacement). Service limit on the 70s 550s was 90 psi IIRC, and 100 after 79.