Arghh! Cylinder/PV Trashed - Ideas???

Picked up this 2000 RM250 a month ago. Of course I was told the top end was done recently. Without knowing where the top end was at I automatically ordered a piston & rings & a manual. The manual finally arrived so I tore it down today. I was shocked to see the condition of the top end. The piston has a lot of debris imbedded in the top of it. :yikes: The top of the head is pretty beat up as well. There's a couple of deep scores in the piston and the cylinder at the same spot. There appears to be a lot of slop in the main bearings so possibly one of the cages let loose which dumped all this metal. I haven't pulled the engine yet to find out. The really odd damage is to the top of the exhaust port and power valve. I've included some naked cylinder pictures so I won't have to type a thousand words.



Another look from the bottom up:


Here's the score in the cylinder:


And finally the piston:


First off, any ideas on what might have caused the damage to the exhaust port and valve? As you can see it's very deep on one side and tapers out towards the other. I don't see any damage to the piston in that area.!? I'll send the cylinder to US Chrome and get it repaired and plated, but what are my options for the power valve? Bandit lists a replacement at over $160 and I've already dumped way too much cash into this thing.

Finally, with this much metal floating around, I'm going to have to deal with the bottom end. What's the best route on the crank - rebuild or replace? Who does good crank work or has decent pricing on complete units?

Any help would be greatly appreciated!

Marc -

GMC, thanks for the flea-bah thought. I sniffed around there for bearings, but didn't think to look for the cylinder. As far as the crank goes, I checked BikeBandit and they're listing $434.48 for the crank assy. less mains and seals. :yikes: Do you know of a cheaper source? I know the mains are bad because there's play in the crank wheels when I apply a lateral force to the rod. I think the rod bearing is toast because I'm able to get quite a few degrees of sideways tilt on the rod. Once I get the crank out I'll do a proper inspection but it don't look good. :yell:

The movement on the crank is radial, in the neighborhood of .010 so I planned on pulling the engine and crank. The only question is going to be what the condition of the rod bearing is. After discovering all this damage I just got depressed and left. When I get out to the shop tomorrow I'll check the side clearance between the rod and crank wheel to get a better idea of condition. Looking around there doesn't appear to be too many alternatives for the RM. Wiesco makes cranks for a lot of other bikes, but not mine. There's a brand new crank assy on the bay but it's already over $200 with 5 days left so I'm sure it's going to go a lot higher. I now have to figure out how the case splitters work so I can make one.

Update on this mess. When I got out to the shop, I started to pull the rest of the motor apart. I didn't have a puller for the flywheel so I stopped to make one. I didn't have any metric threading data so I took a WAG at 28x1.0 which, of course, was wrong. Turned out to be 27x1.0 so took a mm off and recut the threads. Great! Except for the fact that it's a left hand thread - Doh! Third times a charm! Between all that time wasted and getting some more mowing done, I didn't get around to making a case splitter to crack it open. I did however check the rod slop which actually wasn't as bad as I thought it was yesterday. Both the lateral play at the top of the rod and the clearance between the bottom and the crank were less than half of the limit so it's looking like I might get away with mains & seals :). Still have no idea what the source of the debris that wiped this out was. Tomorrow's another day. Thanks to all for your help..

Marc -

I talked to Eric about the rod. He sold the one he had, but suggested I send it to a buddy of his who would do it for $125 with parts. At this point I think the rod is OK, just crank bearings. I just picked up a set of All Balls with seals. When I get the crank out I'll inspect the center of the needles that I can see and check the clearance to be sure it's OK. If there is a problem, I'll send it out to Eric's buddy.

GMC, looking at the Clymer manual, the case splitter is just a 3 armed puller. I'll just adapt one of my pullers to split it. Installing the crank back in the cases looks like another special tool I'll have to make. No big deal other than time - that's why I have a machine shop.

The big issue now is the power valve. How critical is it? I'm just riding for fun, no intentions of racing. Can I get away with repairing the cylinder and leaving the PV the way it is?

I appreciate everybody's input!

Marc -

Yeah that's the direction I'm leaning. I'd rather get my cylinder straightened out and fresh so I know what I have than take a chance on something used. The last time I played on dirt bikes I had a '79 RM400 so a lot has changed in the past 20 years. Since the PV clearance to the piston is relatively tight, I'm sure the wear on mine will have some impact on performance, I would assume only in the low to mid band. I just wanted to get some ideas from some of you guys who are more familiar with the newer technology.

Marc -

I just made simple adapters to match a few of the case bolt holes for one of my pullers. This made splitting the cases easy. The rod and bearing are good. Unfortunately, so were the main bearings. The play on the L/S of the crank is due to a bad journal. It's about .001" undersize one way, then turn it 90 deg. and it jumps up to close to .003" (inline with the rod). The corresponding main bearing is nice and tight and spins smoothly. The ID of the bearing looks good. There are some strange patterns and slight discoloration on the crank journal, but it doesn't look like it spun. Not sure but I think it may have been manufactured undersize and over time worn at the bottom of the stroke. In any event, it's trashed and has to be replaced.

No, I didn't talk to Eric about the cylinder. He's really busy with moving so I didn't want to pester him unless I was going to send it his way. Now with the discovery of the bad crank, I'm even less sure of what to do. There's a complete motor on fleabay off a supposedly low hour bike for $500. The clutch cover doesn't look too badly worn and the shots thru the intake and exhaust look OK. But the bike I have now looked OK thru the exhaust, didn't rattle, and had decent compression (195), and it's wasted. This just sucks-