Top-end analysis

I'm putting a new top end in my 03 CR 250 and thought some analysis of the existing piston/head/cylinder would be good. This is a duplicate of the thread in Mods/Performance/Repair that is now MIA.

Here's the link: http://smg.photobucket.com/albums/v474/MattFisher/

Background:
The last ride was a year ago in the dunes, it was making some minor knocking/rattling noises when I shut her down due to injuring my knee (and the noises). I bought the bike used, and was told it had a new Wiseco piston in there (doesn't look like one to me). At the dunes I was running 2 sizes larger than normal main jet, dropped the clip 2 places, and 1 size larger pilot, flowing 91 octane pump piss mixed with Castor 927 oil.

No outerware, though I didn't find any sand in the intake boot or carb. I'll have to check the inside foam of the filter tomorrow. It's a DT-1 (aka: Moose). Just donned on me that the OEM filter box arrangement isn't known for it's stellar sealing around the metal ring, I'll check that too.

I idle it until the expansion chamber has enough heat in it to be felt through my glove, then ride casually for a few minutes before dipping into the throttle.

I didn't find any evidence of coolant in the cylinder.

Maybe the fuel I ran was too old, I don't remember? I could have caused the detonation, or it may very well have been from the prior owner. Prior to the last ride I'd been riding it only on MX tracks (slowly), and the only odd noise was the off-throttle clank often attributed to the RC valve slamming shut.

I am wondering why there is zero carbon build-up on the head or piston? I don't recall taking apart a motor before and not finding even a little bit in there. The tiny black specks on top of the piston are hard like rocks, not soft/flaky like carbon build-up.

The new piston will certainly get the skirt holes drilled. Anything in particular that I should to to prep the cylinder for the new piston?



Thanks for the replies, this is fun. Next I'll post some pic of my son's RM65 top-end for analysis. :cool:

Maxima Castor 927 mixed at 40:1. I'm positive I ran pre-mix; I won't associate with those mouth-breathing 4 stroke guys.... Just kidding ;)

If the motor did injest a bit of ocean front property, could that have cleaned off any carbon, or would the detonation have just knocked it loose?

My son's RM65 runs the same fuel as mine, and his piston has a tiny carbon "W" in the center of it. However, I did buy his used too, it could have been there from the prior owner.

So many options, so few definitive answers.

Well, I am fairly confident that the damage was from detonation, not sand. I pulled the filter (No-Toil, not a DT-1 like I thought) and looked for evidence of sand that had gotten around or through the filter. Nothing that I could find. Really not that much sand in the filter either, though that's not a surprise considering I was riding at the end of December so the sand was a bit damp.

What I don't know is if the damage was there before I bought the bike, or if I caused it. I'm going to place my bets on running gas that was a month or so old (?), because I'd been riding it for the last 6 months with no issues.

Yes, I was revving the snot out of it. My riding buddy really likes to do sand drag stuff on his quad, so I'd probably done 50 or so runs, not to mention several 4-5th gear wind-out sessions.

When the Wiseco arrives, I'll check the squish, drill the piston skirt, check the ring gap, and scotchbrite the cylinder. Riding time is not far away, woo-hoo!