Bearing Istallation

[Terry Keeley]

Terry, do you have a dimensioned drawing for a cmb 67 case? I like that fixture it would make the job easier.

I could go buy a new case but to me this kind of stuff makes the hobby more interesting and fun.

Brent

I got 44mm (1.732") between the vertical flats under the lugs, I'd make the case fit tight in the fixture there to help align it lengthwise to the spindle.

The holes are 52mm wide (2.047") x 31mm long (1.220"), check these to be sure, it's from an old drawing I dug up.

You have a bore gage? Gonna make up some plug gages?

 

[Will slagel]

B

 

[Terry Keeley]

Terry, is that a pcd tipped boring bar? PCD cuts aluminum like butter.

It's just a WCOW carbide insert with a TiAIN coating, I got that little boring bar a few years ago and it's been great, C06-24W405 on pg. 53 if interested.

The case bushings actually have to be done from the back so the 4" long solid carbide bar really helps.

I did get a Sumitomo PCD insert (holy crap $!) recommended to me by Neil Lickford, I'll use to make some RSA 431 pistons this off season.

 

[Daniel's Racing]

CMB's bearing to case fit on most sizes is between about 5-7 tenths, the tight side of M5-M6:

https://www.skf.com/ca/en/products/...ring-interfaces/tolerances-and-resultant-fits

If you were somehow able to press in a bearing with a 2.5 thou interference fit it wouldn't even turn as the high end of C3 internal clearance for that size is 1.1 thou.

How are you going to do the job? How are you going to measure the bore?

I was thinking that would be really tight but it actually came from SKF specs on a random 16100 2Z 28mm bearing for interference press fit in a housing. Maybe it was a rubber housing. Lol.

Didn't compare to a chart for that size before posting. Probably done by Artificial Intelligence.

Have you noticed that about everything coming from Artificial Intelligence you read that is technical has so many mistakes and often exact opposite of what should be most times. Completely worthless reading 1/2 the stuff on the internet as of late.

 

[Will slagel]

Ops

 

[Daniel's Racing]

Will,
Thanks man. No worries I understand it was just a mistake. I will edit it now so as to be more clear.

 

[tnrcboatracer]

It's just a WCOW carbide insert with a TiAIN coating, I got that little boring bar a few years ago and it's been great, C06-24W405 on pg. 53 if interested.

Thanks for the info Terry. Very interesting tooling. I like the micro inserts with coolant thru.

IIRC, the 10mm 4 flute PCD reamers we used at work were north of $1k ea. But we could resharpen every 10k holes up to 10x. So 100k parts/reamer. This was a dedicated transfer lime spitting out a completely machined v6 cyl head every 36 sec.

 

[Tom Foley]

Thanks Al, to add to the info here's how I do it but I now also put the case in the oven at 250F. You can use a torch but you havta be careful how much heat you use and the most important thing is to let the case cool naturally.



edit: crank sizes (from CMB at least) have gotten better so no need to loctite the rear bearing anymore.

Question for you , do you think that our bearings inner races were spinning or rather skidding on the cranks causing the loose fit ? I have noticed on my VAC 91 cranks in particular that even after installing new bearings you can turn the crank and not see the bearing turn . If you put a little axial load on it with your finger as it turns then it will turn . I always think of the rotation of the engine under load keeping the bearing turning and not skidding . Just a thought .

 

[Al Hobbs]

Question for you , do you think that our bearings inner races were spinning or rather skidding on the cranks causing the loose fit ? I have noticed on my VAC 91 cranks in particular that even after installing new bearings you can turn the crank and not see the bearing turn . If you put a little axial load on it with your finger as it turns then it will turn . I always think of the rotation of the engine under load keeping the bearing turning and not skidding . Just a thought .

Jim Allen liked the inner race to be a tight fit on the crank.

 

[longballlumber]

Jim Allen liked the inner race to be a tight fit on the crank.

Nice to see you back Al!