New Bike - Need some help - CR250 -

[Igofaster13]

Here is my new bike, Its a 93 Honda CR 250. I got it complete for $150. I am planning on rebuilding the engine soon, It was seized up when I got it. I am currently working on it, I got the piston turning but it stops when it gets to the bottom (or its lower stroke. Is this thing hard to rebuild? I have years of knowledge from Marine and Automotive work. I would like to know what exactly what could be wrong with it? Rings?

Thanks

 

[Igofaster13]

How can I post pics here? I cant link them, & and I dont see a place to upload them.

 

[Okiewan]

You need to make a certain number of posts before linking will work.

 

[Igofaster13]

How many?

 

[2strokerfun]

Don't know about links, but it is usually the piston, rings and cylinder that cause this. Sometimes it is the crank. The former is easier and cheaper than the latter. If you're mechanical and it's the top end, you shouldn't have (m)any problems.

 

[ignatius2071]

sticky crank

What you are going to find ; the piston that was in the bike that you have cracked and small chips of the piston are down inside the case, the clearance between the crank and the case at the bottom of the stroke is very small so when you rotate your crank to the bottom it sticks. You have to get all of the small pieces out of the case. If you pour some really thick oil onto crank with the head removed of course, and rotate your crank back and forth by hand the small pieces will stick to the oil and you will be able to pick them off the crank be sure to check for pieces wedged between the crank and the piston rod. Your engine will then turn freely. Next do a couple of oil changes and install a new piston and ring s and off you go.

 

[TimberPig]

If it's bad enough that you've got pieces of piston wedged in between the crank and case, or crank bearings that were seized, then that engine needs to be torn down and completely flushed out. If you are lucky, the crank is ok, and can be reused once it has been flushed to remove every last bit of piston that is stuck in it. If you don't get it completely cleaned out, the crank will not live long after the rebuild. It may still not last long depending upon how many chips went through the bearings.

Sorry to say, but your safest bet is to tear the engine right down, flush it out and go through everything. If you want to gamble, you could try flushing the crank without splitting the cases, but you may not get it all, which could toast your new top end in short order. For the slight added expense to tear it down completely, I wouldn't risk it by trying to avoid a complete disassembly and going over.

 

[KX250Dad]

Decisions... older bikes can start to get tricky when splitting cases. Depending on the previous owner(s) and how often the bike has been taken down and up and whether torque spec's were followed, etc., sometimes splitting a case to flush can very well create more issues. While I don't care to take short cuts, flushing the crank can work and I've used my 32:1 as the flush agent. Actually filling the crank and slowly tilting the forward will get most particles to exit. It's a gamble, and nothing I would do on a race bike doing 70' triples. Obviously, I'd get the crank free rotating first and check both axial and thrust runout. look hard at the nylon thrust washers...
Good luck...

 

[actual mechanic]

Seriously if you are a mechanic you know what to do , stop being a butcher and fix it properly. Dont listen to that useless dribble about thick oil on the crank, if i have to explain you shouldn't be touching a motor! :bang: You really dont want to destroy that pretty new top end..

 

[pryor]

I kinda liked the sticky oil idea, dont know if I would use it on a nice bike but wouldnt qualify it as "useless dribble"either. :|

 

[actual mechanic]

As I do this for a living, I have to do things the right way - cutting corners ends up in expensive blow ups that I have to fix under warranty - at my expense. That's how I know its useless dribble. But, you make your own mind up after you've fixed as many as I have.....

 

[mrimike]

keep in mind that if you want to split the cases you need to buy the special tool.. cant just use any auto puller..
around 125 bux