procedure for changing YS91 rear bearing

[claysmith]

I'm getting ready to put a set of Boca bearings in my YS91, but I'm not sure how to do it. Could somebody tell me what the procedure is for changing it?

[DavidH]

First you want to take the cylinder head off the engine.
Then take the backplate off the engine.
Now pull the cylinder liner out of the crankcase.
Now you can take the connecting rod and piston off of the crankshaft pin and remove it out the cylinder of the crankcase.

Now you can take a mallet and strike the end of the crankshaft. The crankshaft should come out the back of the crankcase.
If the main bearing did not come with the crankshaft you are going to have to heat the engine.

Take the carb and regulator off the engine. Insert the engine crankcase into an oven that is about 350 degs. Leave it in the over for approx 20-30 mins. Use a gloved hand and take the crankcase out of the oven. Strike the crankcase against a block of wood. Most of the time the rear bearing will fall out. Then put the new bearing back into the engine while the crankcase is still warm.
Re-assemble in reverse order and engine is ready to go. Be careful installing the cylinder back into the crank case over the piston. Make sure the ring on the piston is in the proper position and the gap positioned over the retaining pin in the groove.

David

[claysmith]

Thanks for the info David.

[rob_jones]

Can you use a torch on a YS? Is there a particular reason for putting it in the oven instead?

[00boto]

Torch or oven...either one will work. If you have any issues sliding the sleve out or in, apply some heat to the cooling fin area and the sleve will slide in/out nice and easy.

Matt

[DavidH]

Rob,
Yeah you can use a torch. I just didn't mention because some people get the wrong impression and think they are suppose to melt the case when heating it up <G>. I use a small micro torch to heat the cooling fin area to slide the sleeve out as Matt mentioned. I then also take the small micro torch and heat the crankcase area where the bearing is seated. You still need to remove the regulator and carb from the engine when doing this to prevent damaging parts of them.

David

[claysmith]

One more question, could a bad bearing make the engine run poorly? Mine isn't making any bearing noise, but it does have some rust on the bearing. I can't get the motor to run right, it keeps sounding lean regardless of how rich i set the needles and doesn't make as much power as it normally does. Check valve is good and i've cleaned the carb 3 times, changed all my fuel line, and everything else I know to do. Runs like a Cspec PS now, not consistent and always wanting to lean out. Any idea what may be wrong?

[DavidH]

What your describing is usually one of the signs of a bad bearing. Usually you start chasing the mixture and have tracked down other things that would cause that.

Do you know if it is actually rust on the bearing, or a residue that is left over from the fuel that coats the bearing?

David

[claysmith]

i'm pretty sure this is rust, I'll be changing both bearings as soon as I can get this damn fan off.

[DavidH]

i'm pretty sure this is rust, I'll be changing both bearings as soon as I can get this damn fan off.

It is hard to tell if it is actually rust or a coating from the fuel till you get the bearings where you can inspect them throughly.

If that is a fan from a Predator kit your trying to remove. I wish you the best of luck getting it off from some of the threads I have read about it.
If your close to John Benario, he might can help you get it off. I think he has the special tools required to do the job.

David