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Wiseco big bore compression numbers?

  • Thread starter Thread starter 80GS1000
  • Start date Start date
psyguy said:
sorry to say but i think the compression numbers should be higher after a re-bore and new pistons/rings and new valves, and after that break-in mileage
Click to expand...

well, i guess i forgot to ask about the camshafts and any other relevant changes and was jumping to conclusions :o
 
OK, got to do some more testing tonight.

Plugs out, engine stone cold because the bike is now inside the house for the winter months.

First test, 1 through 4, 120-120-120-120 across the board.

Second test with a teaspoon of motor oil in each cylinder. 145-145-145-150, holes 1-4.

So it sounds like the rings are not sealing quite right yet...?

Rings still need time to seat you think? Or is re-ringing in the future? The guy who did the top end is a 25+ year GS dragbike mechanic and machinist so hopefully he did a good hone job, bore job, and installed the rings correctly.
 
Last edited:
If it leaks less than 6%, then the low numbers would be the cam timing.

Jay
 
A compression increase with oil in the cylinders is normal, although I'm not sure to what extent. Sounds like a Leak Down test is in order to remove some doubt about the cam timing and such.
 
i say those are GREAT numbers for a bone cold engine.

What are you worried about?

ring end gap is unknown
deck height is a large value
piston to cylinder clearance is unknown
cam overlap is more than stock.
test numbers from a cold engine

looks good from here. I hope you are not a hypochondriac .

get a leak down tester for more precise information,
and be sure to test it at the proper temperature.
 
He's right. 120 is great cold numbers. Could rise up to 30# when hot.
If you have determined that the black plug is oil I'd sweat that. Those oil rings need to go in a certain way. If it was the oil ring you would be smoking like crazy though. I'm pretty sure it's got to be fuel unless it's the same plug you broke the motor in with .
 
How are the cylinders numbered, left (shifter side) to right (throttle side) 1-2-3-4? or vise versa?
 
I made a leakdown tester from some plans on the internet and it didn't cost a dime. I used stuff I had laying around...


http://microracing.com/forum/blog.php?b=7

http://www.mytractorforum.com/showthread.php?t=21948&goto=nextoldest

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