Problem with #4 Bearing

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Alan Winer
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Problem with #4 Bearing

#1 Post by Alan Winer » Tue Apr 06, 2010 5:36 pm

When replacing the #4 bearing in a rebuild I am doing, the new bearing fell right through the bearing bore in the third piece. The bearing I removed (photos attached) is not a standard Porsche bearing and the OD measures 1.988 which is .017 larger than the replacement bearing (1.971). The bearing bore in the third piece measured 1.985 which is .020 over nominal from other unaltered third pieces. So I am perplexed: what type of bearing did I remove from the case and why would the bore in the third piece have been bored +.020. The case has not been lined bored and even so I do not believe that the 3rd piece is ever line bored. The engine is a normal #606421 and otherwise appears unaltered. Any information regarding the type of bearing I removed or suggestions would be appreciated.
Thanks

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Jack Staggs
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#2 Post by Jack Staggs » Tue Apr 06, 2010 5:40 pm

That is a modified VW bearing.

Jack Staggs
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#3 Post by Jack Staggs » Tue Apr 06, 2010 8:05 pm

36 hp, that is.

matt demaria
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#4 Post by matt demaria » Tue Apr 06, 2010 8:10 pm

That is a VW 36 horse nose bearing. A standard OD 36 nose bearing is 50mm. When VW cases wore out on the saddle diameters it was customary to linebore all 4 saddles. The standard ID for the 3 main VW case bores was 60.00mm. Porsche standard ID bore was 60.25mm.
In the late 70's and 80's when linebored bearings were (and still are) scarce for the AB cranks the customary practice was to use linebored sets for VW. Since the first oversize for Porsche was 60.50mm, you then ordered the second oversize for the 36 HP engine case. However the nose bearing for the 36 HP was .5mm oversize. You normally lathed it down to 50.00 instead of 50.50 to fit the third piece.
In your situation I would bet that someone used the first oversize VW main bearings and instead of lathing the nose bearing back to 50.00 they bored the case .25 mm to fit the VW nose bearing.

Guest

Problem with #4 Bearing

#5 Post by Guest » Tue Apr 06, 2010 10:48 pm

Alan,
What has happened is that the main bearings have been line
bored and they also did the #4. This bearing is not usually
done but yours has been. I will look at my stash of bearings
to see if I have one and there might be people out there
that might also have one. I usually don't do this bearing
since most kits came with standard and this one was not
damaged. First are all your other bearings line bored?

Alan

Alan Winer wrote:
When replacing the #4 bearing in a rebuild I am doing, the new bearing fell right through the bearing bore in the third piece. The bearing I removed (photos attached) is not a standard Porsche bearing and the OD measures 1.988 which is .017 larger than the replacement bearing (1.971). The bearing bore in the third piece measured 1.985 which is .020 over nominal from other unaltered third pieces. So I am perplexed: what type of bearing did I remove from the case and why would the bore in the third piece have been bored +.020. The case has not been lined bored and even so I do not believe that the 3rd piece is ever line bored. The engine is a normal #606421 and otherwise appears unaltered. Any information regarding the type of bearing I removed or suggestions would be appreciated.
Thanks

[Image: http://s1.postimage.org/faRNJ.jpg ] (http://www.postimage.org/image.php?v=gxfaRNJ)

[Image: http://s1.postimage.org/fb0Mi.jpg ] (http://www.postimage.org/image.php?v=gxfb0Mi)

------------------------
Alan Winer





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Alan Winer
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34 bBearing Problem

#6 Post by Alan Winer » Wed Apr 07, 2010 8:49 am

The case was not linebored. I used std./case-1st under/crank bearings. #1-3 mains fit well, only #4 presented a problem. It appears from Matt's post that I can substitute a 1st over VW nose bearing without any additional machining.
Alan

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Mike Klapac
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#7 Post by Mike Klapac » Wed Apr 07, 2010 9:23 am

Other than the machining of the nose bearing, do the 36hp bearings fit and work fine? Are the bearing widths the same?

matt demaria
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#8 Post by matt demaria » Wed Apr 07, 2010 9:59 am

The bearing widths for the vw shells for 2 and 3 are 5mm skinnier.

Jack Staggs
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#9 Post by Jack Staggs » Wed Apr 07, 2010 10:35 am

Oil holes are smaller.

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Mike Klapac
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#10 Post by Mike Klapac » Wed Apr 07, 2010 10:58 am

Oil holes would be easy enough to fix. Any experts think the narrower bearings would make much difference on a mild, A Normal motor?

Just looking for an excuse to build the OG motor that came with my 58. 4-500 Bearings are a deterrent!

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Ron LaDow
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Problem with #4 Bearing

#11 Post by Ron LaDow » Wed Apr 07, 2010 11:43 am

Mike,
You've already got a marginal oil pump; and then removing ~20% of the bearing area sounds like you're testing how far you can go.

Thanks,
Ron LaDow



Oil holes would be easy enough to fix. Any experts think the narrower bearings
would make much difference on a mild, A Normal motor?

Just looking for an excuse to build the OG motor that came with my 58. 4-500
Bearings are a deterrent!
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Ron LaDow
www.precisionmatters.biz

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Mike Klapac
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#12 Post by Mike Klapac » Wed Apr 07, 2010 2:34 pm

Good point.

Guest

Problem with #4 Bearing

#13 Post by Guest » Thu Apr 08, 2010 10:26 pm

Mike,
The 36 hp VW did not use a #4 bearing so you need to be
careful about what you use.

Alan

Mike Klapac wrote:
Other than the machining of the nose bearing, do the 36hp bearings fit and work fine? Are the bearing widths the same?





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Guest

Problem with #4 Bearing

#14 Post by Guest » Thu Apr 08, 2010 10:28 pm

Mike,
Get a real set of 356 bearings, they are available. You
also need to get the oil pump size right.

Alan

Mike Klapac wrote:
Oil holes would be easy enough to fix. Any experts think the narrower bearings would make much difference on a mild, A Normal motor?

Just looking for an excuse to build the OG motor that came with my 58. 4-500 Bearings are a deterrent!





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Albert Tiedemann
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Re: Problem with #4 Bearing

#15 Post by Albert Tiedemann » Thu Apr 08, 2010 11:40 pm

Alan Klingen wrote:Mike,
The 36 hp VW did not use a #4 bearing
Alan

Is this true? If true, then what was used?




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