Jump to content
Sign in to follow this  

91 CR250 engine rebuild?

Recommended Posts

I am in the process of completly rebuilding a 1991 CR250 engine for my senior project. The previous owner told me that he has never split the cases to replace anything. It is getting new crank bearings, rebuilding the stock crank, and then all trans bearings and such..

Any hints or tips would be greatly appreciated.

Thanks

Share this post


Link to post
Share on other sites

Go to youtube and look up RockyMountainatv--they've got some good videos showing you how it's done and the tools that you'll need to do it right.

You'll definitely want to replace the main bearings and all the seals. I think that you can get away with keeping some of the other bearings that the shift drum and primary and output shafts ride on if they inspect well (they need to spin easily without any hang ups. You'll also want to replace the crankshaft, or else get someone experienced to check your old crank out and tell you if it is still usuable.

The most important advice I can give you (besides checking out the videos mentioned above), is to work slow, and keep your parts together in an orderly way. Take pictures even. You don't want to get thrust washers and bearings out of place when you put it back together, or it will be a short life engine (maybe only seconds). You can also reference the exploded view of the engine that is available in your service manual (you've got one, don't you?) for help.

Good luck!

Share this post


Link to post
Share on other sites

Yes I have a service manual... I have already ordered the rod rebuild kit, so i'm gonna have a local machine shop check the crank... I want to port everything to match, but it depends on how my deadline is looking; i'm doing this for my senior project at school and it has to be completed by a certain date... But i did want to clean up some of the cylinder porting alittle and then match the cases..

Thanks guys, any other ideas...

BTW. while inspecting my piston i noticed a few scratches on it that caught my finger nail.. I have all the stuff(rings,pin,circlips, top-end bearing) to replace the piston but the piston is no good(according to my judgment). I would like to replace it with another wiseco, but all i can find are the piston kits and they are like $150... What is a cheaper alternative? but i would still like to use all my wiseco piston parts i mentioned above..

Thanks

Share this post


Link to post
Share on other sites

The service manual should give you a spec for the piston diameter that will tell you whether it is still a running piece. I am told by a professional builder that alot of people replace their pistons more often than necessary because they don't know how to measure them.

As for alternatives to a forged Wiseco, there are several cast options that are as good as OEM and are quite a bit cheaper. Vertex and ProX are two options that are cheaper than Wiseco.

You're going to learn alot through this!

Share this post


Link to post
Share on other sites

I do not believe anyone sells a complete crank. You are correct to rebuild the stock one if there are not big grooves from the seals rubbing. Have someone do the work that has dealt with the Honda shrouded crankshafts before (light metal covering over the actual steel crank webs). Have the cylinder measured for size and out of round. The plated cylinder can wear out for a bike this old. All seals and the 4 main trans bearings should go also. The first thing to do is pull the small outer cover off of the water pump so you can look at the condition of the case. I think 91 is the last year Honda used these magnesium cases that corrode. A lot of the parts from 1988-91 are the same.

Share this post


Link to post
Share on other sites

Thanks guys, I should be splitting the cases first of next week... I'll keep yall posted on it...

Another question about my other bike: I just put a new chain and sprockets on my 06' CR250. I went up 1 tooth on the rear sprocket and front is stock and i also put a parts unlimited "Z-ring" chain on it(I know it is thicker than stock chain), but my question is it normal for the thicker chain to rub just alittle on my case where the front sprocket is? it is not rubbing bad, it is just enough to where you can tell it has took alittle metal off the case.

Thanks

Share this post


Link to post
Share on other sites

I would probably be careful about using chains that are too wide. I'm not really sure what the danger aspects of using a wider chain are, but anything that is taking bits off your case can't be good. You may be able to go up a few teeth in the front to help get the chain get way from the case, but then you'd have to go up at least 4 teeth on the rear.

Share this post


Link to post
Share on other sites

Yeah true... Thanks man, i'm just gonna keep a real close ey on it and see how it goes... As for the 91' engine... I've got inside the engine and noticed that the cam follower(little piece that is attached to the cam spindle which runs the power valves) has alittle "wing" on it kinda like a cam lobe.. Well the "wing" has been broke off so my powervalves have not been working probly since i got the bike from the previous owner... My problem is that the part is discontinued from honda and i haveno clue where to look a specialty part like this anywhere else...

All help is appreciated, Thanks guys

Share this post


Link to post
Share on other sites

You may be able to get that part from later year bikes maybe, but I think that only the 1988-1991 cr250's are compatible with each other. You can try out E-bay or even check out the classifieds section her on TT to see if anyone is parting out an engine.

Share this post


Link to post
Share on other sites

Hey guys, this is my first post so please feel free to mock if i have posted in the wrong place lol....

I have just bought a 1991 cr250 and on closer inspection its a project crapper more than i thought . Imslowly having to rebuild everything i have noticed that the gear foot pedal is catching on the ignition cover quite badly and seems to have a lot of lateral movement in it, any ideas of what that could be? Many thanks for any ideas.

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  

×
×
  • Create New...