Rookie Yamaha R5 engine rebuild

VonYinzer said:
There's a specific measurement for all of the bearing surfaces in the crank case. If the motor siezed up or was damaged (we don't know the extent of he engine wear) it could have damaged those surfaces. I was trying to save him a real headache down the road. Sorry for that. Won't happen again.
Click to expand...

I don't know what that spec would be, other than comparing to the bearing o.d., or how one would measure it with a micrometer, short of bolting the cases together and measuring the bearing surface bore with an inside mic but I've never seen the need to do this. I've seen bearings spin in the cases and the damage would have been clearly visible in the pics had that happened. The bearing is held from turning, as was pointed out, with pins as stock or sometime with o-rings in aftermarket and given that it is not a true interference fit I don't know what an acceptable bearing to case clearance would be if measured.. Thought maybe the OP and myself could learn something. If your reaction is to withdraw future help that seems a bit extreme but only you can decide if that is appropriate.
Sorry to the OP if my innocent question created some kind of drama.
 
Re: Re: Rookie Yamaha R5 engine rebuild

dcracing said:
I don't know what that spec would be, other than comparing to the bearing o.d., or how one would measure it with a micrometer, short of bolting the cases together and measuring the bearing surface bore with an inside mic but I've never seen the need to do this. I've seen bearings spin in the cases and the damage would have been clearly visible in the pics had that happened. The bearing is held from turning, as was pointed out, with pins as stock or sometime with o-rings in aftermarket and given that it is not a true interference fit I don't know what an acceptable bearing to case clearance would be if measured.. Thought maybe the OP and myself could learn something. If your reaction is to withdraw future help that seems a bit extreme but only you can decide if that is appropriate.
Sorry to the OP if my innocent question created some kind of drama.
Click to expand...

It's done with plastigauge for the bearing shells, and yeah you basically assemble it, spin the crank, take it back apart and then measure the wear. Usually the fsm has the tolerable wear limits in it. Cb400f's are really susceptible to crank bearing wear, but i don't know about the RDs.
 
No drama. You know the bearing sizes. Go from there.

Maybe using an inside mic is overkill. I'd rather spend 5 min doing that than find an issue later. Again, I only suggest this because there's a lot of visible wear muck. Don't want to see him rebuild something that will fail.

My only point is that when dealing with a motor that you do not know the history of, but that you know has some issues a complete and thorough inspection is a good idea. You obviously work on motorcycles often and I'm assuming from you screen name, race engines are a part of that. Do you not go over every part of your motor before bolting everything back together?
 
To the OP. I'm not trying to scare ya into thinking something is wrong with this motor. That said, go over everything. No point in wasting time with bad components.
 
Re: Re: Rookie Yamaha R5 engine rebuild

Kanticoy said:
It's done with plastigauge for the bearing shells, and yeah you basically assemble it, spin the crank, take it back apart and then measure the wear. Usually the fsm has the tolerable wear limits in it. Cb400f's are really susceptible to crank bearing wear, but i don't know about the RDs.
Click to expand...


RDs use a roller not a plain bearing
 
Re: Re: Re: Rookie Yamaha R5 engine rebuild

dcracing said:
RDs use a roller not a plain bearing
Click to expand...

Gotcha, then it's a free play measurement. Hell, you're in it this far, might as well replace them.

See I did learn something! ;)
 
I have a few questions. The transmission looks quite good and the bearings are nice, do you guys think I should do anything to it? (I am going to take it out and replace seals and also so I can have it bead or sand blasted.) Also how hard is it to find the top half for these motors cause mine is missing a fin on each side and one side had a piston brake or something cause the top of the cylinder is all scratched up or is there a way to fix it?
 

Attachments

  • download-2.jpg
    download-2.jpg
    212 KB · Views: 166
Heads are pretty easy to find. Cylinders are a little harder (and pricey).

Find a cheap set of replacement heads.
 
That head could probobly be reworked. What's the cylinder look like? That's the tricky part. As far as the fins being broken, if its just one on either cylinder I wouldn't worry about it. They were probobly stuck and someone tried to pry them up.
 
Re: Re: Re: Rookie Yamaha R5 engine rebuild

Kanticoy said:
Gotcha, then it's a free play measurement. Hell, you're in it this far, might as well replace them.

See I did learn something! ;)
Click to expand...

I almost always replace outer bearings, regardless of how good the crank looks once, I have it out. It's easy. The only exception is if I know they're already pretty fresh. TBH I don't worry much about the case bearing surface unless it looks really bad. Unless it's worn out of bore alignment there's not much proper bearings with pins won't fix.
 
Lowered13 said:
I have a few questions. The transmission looks quite good and the bearings are nice, do you guys think I should do anything to it? (I am going to take it out and replace seals and also so I can have it bead or sand blasted.) Also how hard is it to find the top half for these motors cause mine is missing a fin on each side and one side had a piston brake or something cause the top of the cylinder is all scratched up or is there a way to fix it?
Click to expand...

If you have access to a competent machinist familiar with 2 strokes the heads can be repaired and improved. Some changes to the squish band / combustion chamber transition would be worth doing IMHO while achieving prooper squish clearance and combustion chamber volume.
R5 cylinders are around but not as common as RD stuff (hint hint). The transmission could be improved with the addition of a 6th gear (see earlier hint)
 
The cylinders look good. They are a little rusty from sitting for a while put that doesn't matter cause I am going to bore them some. And what exactly would be the change I would make to the head so that they are better? And do you think putting in a 6th gear, for a person that has done nothing of the sort, be do able?
 
Putting in a six speed is easy, basically swap the whole tranny, drum and all, from an RD. One thing I'd do with an R5 head if I were having it machined is eliminate the radius at the edge of the squish band, make it a sharp corner.
 
So I was wondering if there is something I need to replace on the points thing? Or are they so much of a pain that I should replace them with something and if so what is that something I should replace them with?
 

Attachments

  • download.jpg
    download.jpg
    194 KB · Views: 179
You got the points cam?

As for replaceables. there is brushes and points & condencer in that mess i would check all that stuff and replace what needs it. Clean the contacts on the rotor and check the resistance on it. electronic ing for these bikes are pricey but ill tell you for a fact that points will suport a big power rd. so its a matter of what you want to spend. Ive seen people use chevy distributer magnetic pick up and build there own but never tried it.
 
You must log in or register to reply here.

DTT Light or Dark

  • DTT Light
    • www.jadusmotorcycleparts.com
    www.lostapostle.ca/
    www.sparckmoto.com

    Spread the Love

    Back
    Top Bottom