compression

[booyababytaz]

was wonderin if anyone knows when a rebuild is necessarry my 700xc is compression is 105 in both and still running strong but is it due for a rebuild....also workin on a xlt which is 100,125,125. anyone know what they are new or how low they can get before new rings and gaskets are needed

[jredneck73]

I would say rebuild as soon as possible . That XLT needs the most attention . Should run 140 all the way across the board . That 100 would be the lowest I would run . Anything below that your asking for a major problem . I would check all the seals also . My RXL is 140 140 and 135 and still going to do total rebuild this summer due to fact of my output shaft . Just my 2 cents ..

[booyababytaz]

tx plannin on rebuildin xlt immediately due to noticing divot in piston. other i was hopin to wait til summer but sounds like i might want to do sooner.

[jredneck73]

Hey the 700 I would just do the top end . Then again just check your compression after each ride if you don't want to do it right now . You could make it the rest of this season if your easy on the motor .

[DRHSpecialty]

I'm not sure you should run right out and rebuild a motor based on a particular number when it comes to compression unless you see a difference from cylinder to cylinder.

You'll see a bunch of different readings with the variety of gauge manufacturers and styles of gauges out there. I'll take my new Snap-On gauge and show you a perfectly good running XCR piston port 600 motor that has only 65 PSI in each cylinder after a rebuild. And then I'll take my Tiawan junk gauge and show a difference of 30-40 PSI between each of the cylinders on that same machine.

All in all I'm not sure that a compression check is any "tell all" for deciding if you should rebuild.

Start the engine, warm it up, do your compression test on each cylinder, note the reading.

Next squirt about a tablespoon of oil into each cylinder thru the sparkplug hole. Turn the engine over to coat the cylinder with the oil. Then do another compression test and check the readings.

If you see a big difference between the two tests you will know only that the rings are not sealing the way they should and IS NOT an indicator that it will fail.

You should always have more information than a compression test and/or advice from the internet when deciding on a rebuild.

[stewart20]

that was well said

[braindead1684]

Yep as mike said, compression is not everything I wouldn't even touch that 700 right now, unless you have other signs, lack of power etc... Maybe during the summer if you want peace of mind mic the just replace top end gaskets and rings.


The XLT looks worst but its hard to say for the same reasons listed above. If the piston shows damage you have more reason for concern there, you can spray some WD-40 behind the clutch on the seal whle its running and listen for a change to see if that side is leaking.

[booyababytaz]

tx for all the advice. am going to wait til summer and check out top end on 700 for piece of mind before i wreck a cylinder it has lost 10 psi in 2 years on same gauge so i think it is due........the xlt we found a plugged jet on the primary 100psi cylinder and from shining flashlight in spark plug hole can see a circular mark most likely a divot in piston so i think it needs immediate attention......any tricks or things to watch for or hints on doin rebuilds..... my first sled rebuilds have only done quads in past or motor swaps?

[hunterjim]

this could apply here If there still running strong leave it alone