#1 main bearing case width spec

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Neil M. Fennessey
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#1 main bearing case width spec

#1 Post by Neil M. Fennessey »

Listers,

I'm looking for considered opinions regarding the acceptable width of the #1 main bearing saddle in a 912/C/SC block. Such a spec would guide one as to whether a thrust cut is necessary or whether the case needs to be welded up and remachined to accept a standard in-between-flange-width #1 main bearing. I don't find any such spec in the factory's "Little Handbook."

Thanks!
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 - Neil
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Martin Benade
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Re: #1 main bearing case width spec

#2 Post by Martin Benade »

Good morning, I’ve missed you here.
I assume the case needs a line bore already for you to consider whether the thrust surface needs attention too.
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Neil M. Fennessey
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Re: #1 main bearing case width spec

#3 Post by Neil M. Fennessey »

Hi Martin,

The relentless clash of Big Egos led me to abandon the Registry chat. Mike Horton does a rather commendable job of 'riding herd' on the 912 BBS and so I hang out in that sandbox.

As to the align bore, it's too soon to make that judgement. I've had one local shop measure the bores but their use of a bore gauge without using a bore standard leaves me with doubt.

Looks like the last engine builder "recycled" his/her #1 main. It moves back and forth in the case very nicely. The backlash on that bearing is 0.011" whereas the backlash of a used bearnig from my stash is 0.002". Thusly, the flange inner-width of the engine #1 main bearing was widened and not the case bearing saddle. That is, unless The Force (or something else) narrowed the flange-inner-width on the #1 main from my Stash. Prelim. #1 main bearing OD measurements suggest the the "wide-flanged" bearing is super crushed from new OD. Hence, my request for a case saddle width.
Last edited by Neil M. Fennessey on Wed Sep 28, 2022 10:03 am, edited 1 time in total.
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Martin Benade
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Re: #1 main bearing case width spec

#4 Post by Martin Benade »

If you can slide either of these shells sideways by hand when seated it sounds like you have no crush.
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Neil M. Fennessey
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Re: #1 main bearing case width spec

#5 Post by Neil M. Fennessey »

There will most certainly be no crush if the measurement is made with the bearing mounted in a case half.
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Jacques Lefriant
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Re: #1 main bearing case width spec

#6 Post by Jacques Lefriant »

Hi Neil
try a new bearing or have someone measure a case. if the case has the proper crush you will not have end play due to the bearing moving. you may be able to just line bore the case and use a new bearing. you can size the oversize thrust bearing to match the case thereby eliminate the welding.
j
 

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Neil M. Fennessey
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Re: #1 main bearing case width spec

#7 Post by Neil M. Fennessey »

Jacques Lefriant wrote: Wed Sep 28, 2022 11:28 am Hi Neil
try a new bearing or have someone measure a case. if the case has the proper crush you will not have end play due to the bearing moving. you may be able to just line bore the case and use a new bearing. you can size the oversize thrust bearing to match the case thereby eliminate the welding.
j
Hi Jacques,

I plan to try a new bearing in a case half and measure that backlash. I also plan to find someone who can do a proper job of measure the bores. There's a guy near the Cape who knows what he's doing.

But, back to my original programming. How do you decide whether a case needs a thrust cut or not, i.e. what is the minimum acceptable width of the #1 bearing saddle? Fitting a bearing is good, but having a measurement spec is even better. Do you employ some top secret spec to make that determination? If it's not top secret please share.
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Martin Benade
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Re: #1 main bearing case width spec

#8 Post by Martin Benade »

Its true that using only one case half there’s no crush but the width of the hole at the case parting line is less than the diameter of the shell. It should press in with hand pressure and be somewhat tight. If yours slides sideways I’d say it is not somewhat tight. Also if you know the previous bearing was moving around, it almost had to wear the bore diameter.
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Neil M. Fennessey
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Re: #1 main bearing case width spec

#9 Post by Neil M. Fennessey »

Martin Benade wrote: Wed Sep 28, 2022 12:30 pm Its true that using only one case half there’s no crush but the width of the hole at the case parting line is less than the diameter of the shell. It should press in with hand pressure and be somewhat tight. If yours slides sideways I’d say it is not somewhat tight. Also if you know the previous bearing was moving around, it almost had to wear the bore diameter.
Hi Martin,

Per my original posting above and again in my reply to Jacques, I'm looking for an actual width spec. Do you know what that spec is? But, that's not to say that feelings are unimportant...

https://www.youtube.com/watch?v=RrkVyXFsx6Y
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Re: #1 main bearing case width spec

#10 Post by Martin Benade »

I am sorry I don’t have the answer to your question.
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Neil M. Fennessey
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Re: #1 main bearing case width spec

#11 Post by Neil M. Fennessey »

Martin Benade wrote: Wed Sep 28, 2022 1:24 pm I am sorry I don’t have the answer to your question.
Thanks for chiming in. Those who haven't considered the issue will certainly benefit from your comments.
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Re: #1 main bearing case width spec

#12 Post by Jacques Lefriant »

Hi Neil
i am sure there is a spec for the width of the case on the factory dwgs. bearing manufactures have specs for the bearings. replacement bearings with thicker flanges are designed to be machined to suit existing worn or resurfaced cases it is the machinist responsibility to determine. restoring the case to it's original dimensions is pointless. that is my feeling.
j
 

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Re: #1 main bearing case width spec

#13 Post by Olivier AUVRAY »

Few years ago, I had the same problem....

I machined a notch in the engine case and I put piston ring from a moped. The ring that I found had the exact size of the bearing flange. The tolerance was adjusted by grinding the thickess of piston ring.
By this way, I used a regular number one bearing.

The engine is still alive......

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Re: #1 main bearing case width spec

#14 Post by Jacques Lefriant »

Salut Olivier
Chapeau
Neil
oversize #1 bearings are available now. back in the day when VW cases were line bored it was customary to address the case flange at the same time. Olivier's solution is superior to the welding option.
j
 

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Neil M. Fennessey
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Re: #1 main bearing case width spec

#15 Post by Neil M. Fennessey »

Jacques Lefriant wrote: Wed Sep 28, 2022 2:43 pm Salut Olivier
Chapeau
Neil
oversize #1 bearings are available now. back in the day when VW cases were line bored it was customary to address the case flange at the same time. Olivier's solution is superior to the welding option.
j
Hi Jacques,

I remember how back in the day that most VW engines needed to be align bored and thrust cut. The "machinist" that I knew who cut the cases just sort of did them without much thought. The customers didn't care. AA lists a wide flange bearing. Stoddard doesn't but then I have not yet called to inquire. Does Scott's Porsche stock #1 mains with various oversize flanges?

I think that you said in your earlier post that you leave the decision to perform the thrust cut or not up to your machinist. Could I have their contact info? I would enjoy chatting with them about this particular block dimension.

Thanks in advance!
Back to the Ivory Tower I go!
 - Neil
'67 912/356D (Ol' Blue)
'82 HP 34C

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