1990? cr250 Engine I/D Restore upgrade!

godog wrote:

There wasn't much really wrong with those engines. Good maintenance practices in regards to keeping the hpp valves super clean and sliding smoothly is important. Exhaust...

There wasn't much really wrong with those engines. Good maintenance practices in regards to keeping the hpp valves super clean and sliding smoothly is important. Exhaust pipe sealing in the cylinder is a bit of a pain and needs constant attention. The stock clutch pack used aluminum drive plates that would wear out quickly and contaminate the transmission oil. If the aluminum units were replaced with steel drive plates then that is not much of a concern. Typical motorcycle manual transmission oil will work the best for smoothest shifts but it can be argued that it's not truly necessary. Essentially, regular oil changes do wonders for watching for wearing of trans and clutch parts. Fuel/oil mix ratio can be argued to death but the fact is if you plan on beating the life out of this engine and getting it hot for long periods of time use a good castor blended oil at a ratio close to manufacture suggestions like 32:1 and up to 50:1. If you are looking to "rebuild" it eventually, getting complete OEM assemblies like cranks might be impossible. With most of the "kits" available today you get exactly what you pay for. If it's cheap and it's installed wrong it won't last. If it's expensive and installed wrong it won't last. If someone rebuilds the crank with a decent quality rod kit and doesn't smash the crank with a hammer or wedges to true it up it will last a good while. If the cylinder still has a plated bore then a properly sized cast piston will be your go to. Upgrade s....bolt on bits like a reed block assembly never hurts unless installed wrong. The pipe that is in the pics isn't the worst pipe but for the application in a sprint car who really knows what works best? The silencer (if Im reading it right) is a spark arrestor...if you are racing on a closed course "race track" I don't see that it's necessary to use a spark arrestor so you might want to replace that or build a straight thru core. Upon closer inspection of the pics it looks like someone has carved their logo onto the cylinder so it's probably got a decent port layout for the purpose in a sprint car and it has a current reed block assembly already installed. Inspection of the reeds themselves would be a good idea before it gets run.

godog wrote:

https://maximausa.com/series-282-mtl-trans-clutch-fluid.html?locale=en Is a highly regarded oil for the transmission in that CR engine. 03.1315 ProX Con.Rod Kit CR250 ’78-01 + This rod kit will be acceptable...

https://maximausa.com/series-282-mtl-trans-clutch-fluid.html?locale=en
Is a highly regarded oil for the transmission in that CR engine.

03.1315 ProX Con.Rod Kit CR250 ’78-01 +
This rod kit will be acceptable to use if installed carefully.
23.CBS13084 Pro x main bearings and seals
01.1315.A Pro x piston kit with 4 different slight oversizes A1,A2,A3,A4.
A complete gasket kit might be hard to come by but I think most of the gaskets are still available from Honda.

godog wrote:

[img]https://p.vitalmx.com/photos/forums/2022/01/10/527756/s1200_left_crankcase_cover_mediumhu0277e0600c_827d.jpg[/img] The system is pretty simple. It consists of a stator or source coil ( think alternator) with a magnetic flywheel (#8), an external pick up...

The system is pretty simple. It consists of a stator or source coil ( think alternator) with a magnetic flywheel (#8), an external pick up coil (pulse generator)(#8) a CDI unit ( brain box)(#7) and a two sided high tension coil ( primary and secondary) that's about it.....

godog wrote:

ah..yes....the old "broken intake skirt" dilemma...Its a common issue with top ends that went a bit too far out of tolerance and got pushed hard. Many...

ah..yes....the old "broken intake skirt" dilemma...Its a common issue with top ends that went a bit too far out of tolerance and got pushed hard. Many times the larger bits n pieces of the piston get clobbered by the rod at bottom dead center and conveniently poke a hole in the cases. That sorta thing requires a weld repair and a careful lapping of the center mating surfaces. This kind of repair isnt free either so there is a lot to consider here....My best suggestion would be to contact a local reputable engine builder and get a firm quote on the labour to build a crank and install it. If they are "worth their salt" they will be able to give you a good idea on parts supply as well so you wont be caught out waiting weeks for spares. I believe in the short game this engine (once built) will be a better option than going with a used 450 engine.

godog wrote:

I find it a bit sad that any builder would turn you down for the work on this engine. Very much like you said there isn't...

I find it a bit sad that any builder would turn you down for the work on this engine. Very much like you said there isn't much to these motors. Armed with a couple of decent pullers (flywheel & case splitter) a person can have them apart in well under an hour. There are a few really good tutorials on YouTube for tearing it down and gently putting them back together. With the proper use of chilling and induction heating they go together quickly and easily. My suggestion with the crank would be to send it away to a well known crank shop. A quick Google search will get you in touch with a shop ,with at the very least some reviews to be able to judge their work by. With the winter weather in the eastern states I would probably look at a shop out west..like California or Arizona as to avoid shipping delays due to weather. To get some insights on the condition of the cylinder and what direction to go there post up some clear brightly lit pics of the bore and areas around the exhaust and intake ports.