Align bore new case?

[JLaw]

Hi Guys,

I'm currently building a 2332 motor with a DPR type 4 centre main crank and a new CB race case. Number 4 main bearing bore in the case is 4 tenths undersized. Its pinching the crank when torqueing up the case. I've made sure its not a bent crank, measured all the other bearings bores and also tried the crank with the other three bearings in the case and it spins over perfectly. Out of interest I tried a couple of other no.4 bearings in the case and they all pinch when torqued down.

So I was hoping for some feedback as to the best option going on from here. Should I have the case align bored, seems a shame as I assume they will have to open all 4 bearing bores up to the next size. Is it possible to polish the no.4 bearing outer to take off the 4 tenths.. Anyone else had this issue?

Cheers,

John.   

[brian e]

Make sure your crank is pushed back to the flywheel side when trying to turn it just to make sure the bearing isn't hitting the radius on the crank.  Also make sure your dowel pin isn't too long. 

I dont see any reason you couldn't chuck the bearing lightly in a 4 jaw and cut or polish the OD to reduce its diameter.  Have you measured the crush between the case and the bearing to make sure its not the ID of the bearing that is too small?   

Brian

[Jim Ratto]

Hi Guys,

I'm currently building a 2332 motor with a DPR type 4 centre main crank and a new CB race case. Number 4 main bearing bore in the case is 4 tenths undersized. Its pinching the crank when torqueing up the case. I've made sure its not a bent crank, measured all the other bearings bores and also tried the crank with the other three bearings in the case and it spins over perfectly. Out of interest I tried a couple of other no.4 bearings in the case and they all pinch when torqued down.

So I was hoping for some feedback as to the best option going on from here. Should I have the case align bored, seems a shame as I assume they will have to open all 4 bearing bores up to the next size. Is it possible to polish the no.4 bearing outer to take off the 4 tenths.. Anyone else had this issue?

Cheers,

John.   

5-6 years ago, brand new Brazil case, main saddle # 2 wasn't straight, axially, it was tight along 1/2 side at rear, and on 3/4 half at front edge. My friend Ray was able to go through it and straighten it and it's still STD. Same deal, once you'd torque 12mm, the crank would tighten up and leave weird witness marks on opposite edges of ID of bearing.

[JLaw]

Hey thanks for the tips.

Brian, Yep checked it with crank all the way back. Measured all the depths of the dowels as well, all good there. Fine until you torque down no.4.

Jim, Sounds very much like this. There is a witness mark on one half edge of the no.4 bearings I've tried after spinning the crank. If it isn't straight axially then polishing the bearing to fit wouldn't be a good solution. Do you recall how your friend Ray machined the case? I was hoping these cases were going to be reasonably good quality as I have three motors to build using them. Hopefully this is not a common occurrence. Are the TF-1 cases a lot better quality?

Cheers,

John. 

[Clatter]

FWIW, I had this a few years ago on a Brazilian mag case.

It got cleaned up just fine with a line-bore to STD..

[Tufty65]

If it's new can you not send the case back as it's not technically fit for purpose?

[JLaw]

I bought the case a few years ago so doubt it would be possible to return it.

Can anyone recommend a very good machine shop in the uk that can align bore this case to standard?

Cheers,

John.

[Tufty65]

I was recommended a guy called Robert parry to do boring he's been doing it for years and sounds like he knows his stuff so might be worth explaining to him to see if he can help?
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