Hi all,

I have a used 2002 DS650 that I am unsure of how many hours are on the engine. Would anyone know what the compression test results would be for a stock motor with a fresh piston and rings. I would like to determine how worn out my engine really is.

 

http://www.mityvac.com/pages/products_ede.asp

They are on ebay new. $60 retail, less on ebay.


http://www.ljsoftware.com/DS/DS650Main.html

specs at top of page 9.7:1

 

I think you missed my point.... I would like to know what readings you would get doing a compression test on a stock motor with a fresh piston and rings, are we talking 140psi, 150psi. That way, when I do a test on my quad, I would have an idea of how worn out it would be. I know all quads will be different, but if a rebuilt motor is in the 140-150psi range and mine shows 120, sounds like it's time for a rebuild. I have read that you should do a compression test on your motor after break in, and then at service intervals, say every 20 hours. If the reading drops by 15%, then it is time for a ring job. As I did not buy this quad new, I have no baseline as to how worn out it is. After looking at different threads on this site, it sounds like the rotax can go hundreds of hours before needing a rebuild, but before I start modifying my quad with a pipe, carb, cam etc, I would like to know if I would be better off doing a rebuild.

 

http://faq.f650.com/FAQs/CompressionTestingFAQ.htm

1 bar equals 14.5 psi

150 - 175 psi good

Below 150 is up to your riding needs

Check the end of the breather tube from the crankcase.
The factory connects it to one of the inlet tubes to the airbox.

If the end of tube appears to be wet with oil, do this test.
Wipe inside of tube(1 1/2 inches of end) with alcohol, you want a dry surface.
Go for a 1/2 hour ride where you on on the throttle alot.
Check the inside of breather tube. If wet again, you are getting excess ring blowby.
Time for new rings.

 

OMR,

Thanks for the answer. I will test your breather tube idea, but I think I already know the answer. The last race I entered the DS in, we were averaging 60mph and I'm pretty sure the breather was fairly soaked with oil. I'll back it up with a compression test, but I'm betting it's time for new rings, possibly a piston.