Jump to content
Sign in to follow this  

does my cr250 need a bottom end? need help..

Recommended Posts

Ok so I rebuilt the top end on my cr250 and the rod had no up and down movement but did have some side to side.. I have not seen any metal in the oil. But the reason im wondering if I need a bottom end rebuild is that when the bike gets real hot it has a clanking noise off the idle. Doesn't always make the noise but somtimes does. Also my crankcase oil keeps turning grey. When I put it in its red. Even only 30 seconds after an oil change it changes to a grey color. Any ideas? Let me know, thanks.. also just wondering is the bottom end lubercated by the premix? Im mixing at 40:1 and its still running rich.

Share this post


Link to post
Share on other sites

some side to side play of the rod on the crank is normal.

grey oil is either a result of water or a clutch issue. ive personally never seen oil turn grey from a slipping clutch but i have heard about it. are you sure it is grey and not milky from water contamination?

Share this post


Link to post
Share on other sites

Yes bottom end gets it's lube from your fuel oil mix. You should have residual oil there at all times. If you are not loosing coolant your grey gear oil is from clutch plate contaminates. You prob have the stock stack with if I recall correctly 5 aluminum and two steel plus 8 fiber plates. When you pour new gear oil in, it flows over the plates bringing contaminates. It's normal, but you'll want to inspect for excessive wear at some point anyway, so it wouldnt hurt to take a look.

Clanking off idle could be detonation, or something as simple as worn exhaust flange o ring.

Share this post


Link to post
Share on other sites

So you believe the crank and bearings are still in good condition or should I pry replaace them anyways. The bike has 90 hours on it

Share this post


Link to post
Share on other sites

And I have powerwashed the bike. Im wondering if the power washer was getting water in there.

Share this post


Link to post
Share on other sites

1st: Premix lubricates the bottom end of the CRANK / ROD. The crank / rod are completely separate from the transmission. The two compartments do not interact. Running 32:1 or 40:1 has no impact on transmission oil.

2nd: The grey coloring is aluminum contaminants as stated above. You can eliminate it by replacing the 5 aluminum discs (see above) with 5 steel discs. After a few oil changes, the contaminants will be flushed out. This is NOT a sign of a worn crank / main bearings, as the two compartments are, again, completely separate.

3rd: The knocking noise you are describing sounds like the powervalve (PV) assembly rattling inside the cylinder. This is actually very common on the 02+ CR250s. The servo motor and cables that turn the PV sometimes don't keep the PV under tension, and it will move a bit. If it was a crank / rod issue, it would make noise at all RPM. In general, don't sweat it.

  • Like 1

Share this post


Link to post
Share on other sites

Alright thanks for all your help. I am getting my cylinder recoated by eric gorr, should I replace the bottom end to be safe while I am at it or should I be ok

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×