rings and valve lapping, still low compression???

[Bob Shaw]

HI AGAIN,
I have an 82 GS850G. I had low compression in #3, 90 PSI, so I took cylinder head off and while I was at it I might as well do the rings. I bought Genuine Suzuki Parts standard rings. The cylinders were all within specs, maybe a thousands off. Rings measured inside cylinder and had at least a .004 thousandths gap. Ring slots placed properly. I put on all new Vesrah gaskets. Lapped in the valve and after a gasoline test, no leaks. Now I never had great compression, never over 140 PSI and I have owned this bike for almost 8 years. My compression, hot, was 132. 132.128.139 respectively. Any suggestions why my compression is so low or did I leave any steps out? Book says 129-171 PSI is compression range.

 

[Guest]

Valves adjusted properly? Valve timing off?

 

[Nessism]

What type of hone and what grit was used to deglaze the cylinders? What processes did you use to break in the rings? Baby the engine or run it hard, or medium?

 

[Bob Shaw]

I used a friends honing triple stone , I don't know the grit. I'll check with I'm. As far as valve adjustment I have adjusted the valves three different times. I have them opened to .004 on the intake and about .003 on the exhaust to let more air in and that is the present reading. Timing is right on. The bike runs really good, I was just concerned about the low compression. I haven't broken in the rings or valves, all I have done is ride the bike around the neighborhood a couple of times. Should I give it a couple hundred miles and do a compression check then?

 

[hampshirehog]

Sounds like you're still running in. Those numbers are ok - and they're pretty even.

Plus are you sure your compression tester reads accurately. Mine reads low consistently.

 

[jsandidge]

Plus are you sure your compression tester reads accurately. Mine reads low consistently.

Good thing to check. Mine always reads exactly 90 psi on all four cylinders of a perfectly good running bike.

 

[JTGS850GL]

Sounds like you're still running in. Those numbers are ok - and they're pretty even.

Plus are you sure your compression tester reads accurately. Mine reads low consistently.

Agreed with the numbers being OK. Takes a while for the compression to come up after a re-hone and those look in decent condition. Ride the hell out of it and do a good amount of open throttle runs through the gears. Don't cruise at constant speeds.

 

[Nessism]

Those three blade hones aren't the best for deglazing. The dingo ball type is better, in 240 grit.

I'd give that bike of yours the ol Italian tune up (ride the crap out of it). Last thing you want to do is baby it.

 

[Bob Shaw]

Thanks to all of you. I'll ride it and test it again after everything gets seated in. Thanks again....

 

[jdvorchak]

I'd give that bike of yours the ol Italian tune up (ride the crap out of it). Last thing you want to do is baby it.

Never heard of an Italian tune up before but he is right. Ride the crap out of it for break in. Usually they say about 300 miles before everything is seated. The extra hard acceleration actually forces the rings up against the cylinder walls causing them to "seat" more quickly and more uniformly.