Fixing boogered up cases

I bought a '97 CR250R in May from someone who had just rebuilt the engine. The bike has both burnt and leaked crankcase oil like a pig ever since I got it. I just got around to splitting the cases to find out what the problem was, and it became obvious that the previous owner had pried the cases apart with screwdrivers and a hammer (notice in the pictures I used a Tusk crankcase splitter). Some of the screwdriver gouges in the sealing surfaces are pretty severe.

I'm looking for advice on how to repair this. The previous owner apparently tried to help the Honda gasket out with lots of silicone sealant, but that didn't work. What about JB Weld? Machine work and an extra gasket? Welding?

I enjoy riding the bike, and appreciate any information from someone who has fixed this before!






Maybe someone can tell me how to post pictures.

Suffice it to say the mating surfaces of the cases have deep screwdriver gouges. They aren't going to seal without some repairs.



There are people that can weld magnesium (I think those are mag), then just machine the surfaces; probably someone local to you. No biggie. Belzona Molecular makes an epoxy product that will work too, but it's rather expensive (but probably less than replacing a case if it ever came to that).

Fwiw, link pics from

If I was you I would do it right and buy 2 new cases.

If I was you I would do it right and buy 2 new cases.

Isn't that like $600... ? :ride:

I'd think it would be cheaper to fix them or get an engine off of ebay and pray the cases aren't equally buggered.

Yeah, I don't think new cases are going to be my first option because of the cost. And I really think this should be fixable--I just haven't done it before. Also, are you sure the cases are magnesium? I'm thinking they are aluminum.



There's a test for it; the shop that you take it to should do it before welding. If they use an aluminum stick on a mag case or vice-versa, the weld will corrode (turn to dust) and fail. (one test: aluminum is attacked by caustic soda, magnesium is not - you can do this at home if you have the chemical and a small scraping from the case; here's a link: ) In either case, whether they're mag or aluminum, a local shop with a TIG and a skilled welder should be able to fix those up for you at a reasonable price.

I like JB-Weld for lots of things, not so much where it's in contact with petroleum products for a long time. Surface prep is key if you're going to give it a go.

I've had cast aluminum tig welded before, works fine. If your handy with a file you could most likely get it 90% there, then flat sand it a ground plate or granite slab.

Devcon (I think that's right) is an industrial type metal epoxy similar to JB Weld that would be reasonable to use, should be able to finish the same way as weld. I don't think pre-mix won't penetrate the epoxy, and provided its applied to a clean surface, it shouldn't get between the case and epoxy. Keep in mind porters have used expoxy inside cylinders & cyclinder heads for years with great success.

Devcon =

Do a google search for: cyclinder head epoxy

My rod failed and fragged my cases out pretty good, I brought them to a local genius fabricator/machinist, he filled them in and ground them down.

They look great and it was $100, and I had some big chunks gone. I think the key is not much heat, these things warp like crazy if they get hot.

Good luck.

Clean them up real well and use jb weld. Let it set up 24 hours the see if you need to add more. File it down with a large flat file then use a large sheet of sandpaper to finish. The trick is to go easy with the file. When you are ready to put it together with a new gasket, use Yamabond or Hondabond sealer on the whole thing and you should be good to go. If you have to take it apart in the future, use some heat from a propane torch to loosen up the sealer. I have used this around the crank area of 2 strokes and never have had a problem. Don't you love HACK mechanics!

I've fixed more things on this bike than I care to mention:smirk:. The powervalve wasn't functional when I got the bike. Also, I took the head off and found it had been pulverized from the previous blowup, and there were still pieces of bearing embedded in the combustion chamber!

I don't hold a grudge though--it was my fault for not being more careful with the purchase. Besides, it's been fun to fix the thing and get up to speed on 2-stroke repair.

For that kind of gouge, JB weld is the ticket.

A piece of glass with emory cloth is a great way to do the final sanding. Put the glass on a table, tape the cloth down to it, and slide the case across it

Well, here's my apology to 97 Polaris. After cleaning up the cases this afternoon, I've found that the right side has a crack running from the bottom of the main bearing journal all the way to the bottom of the case. That must be why when I pressed out the crank, the bearing stayed on the crank instead of inside the case.

Looks like I will be buying a new (or good used) right side case at the least. Fortunately, the right side is the one that has been chewed up the most. Dang hillbilly mechanics!

Anyone got a good right side case for a '97 cr250r?

Expoxy the low spots and file them to match the gasket surface. The gasket will take up some small imperfections so don't worry if it's not perfect.

Honda has a good right side case, it will cost you $150-180, though.

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