Critique these oil clearances

[boxer74]

I'm building an 1835 for a friend. Oil clearances on a few of the main bearings are a little outside Bentley spec. Here are some details.

- Standard size stock VW crank, polished by machine shop, mic'd to be within Bently spec by me.
- AS41 case freshly line bored and checked with a dial bore gauge by me to be good.


I measured main oil clearances by mic'ing the crank journal and then zeroing my dial bore gauge and then checking the bearings which were installed in the case and torqued to 25 ft lbs. Here's what I measured:

#1 0.0016" (thrust)
#2 0.0043" (split)
#3 0.0014"
#4 0.0024" (nose)

From Bentley, tolerances are: 1 and 3 (.0016-.004), 2 (.001-.0035), 4 (.002-.004)

So the #2 split bearing has too loose a clearance by 0.0007" but still not near the wear limit of 0.007".

And the #3 bearing is 0.0002" too tight.

These are quite close to the spec. The only thing I can think of that's causing this is poor quality control in the manufacturing of the bearings. They are Silverline mains. I've seen some previous posts about this. Should I be concerned and try another set? In Canada, bearing availability is pretty much limited to Silverline from the major online suppliers. I may waste $60-80 trying to solve a problem that may not really exist.

What do you guys suggest?

Thanks.
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74 Super
84 Westy

[Bonesberg55]

What did your old #3 bearing measure & what was it's condition?

[boxer74]

[ZEKE65]

When I built my engine in 2021 I found the same problem. I went through three sets of Silverline bearings trying to get the clearances within specs. I ended up buying Mahle bearings, and they were much closer to the correct clearances. But I still had to buy two sets of Mahles to get what I was after. I am sure it will run with the larger clearances, but I was concerned that it may drop oil pressure, or not last as long.
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1965 VW Sedan, 1968 C10 Step BB, 99 C5

[Bonesberg55]

I assume the case fasteners that were torqued to 25 ft. lbs. were the 6 large ones. Were your case halves dry? If so, I would expect that those clearances would open up ever so slightly when sealer was used so #3 might very well fall within spec. I'd be more concerned about the looser #2.

[boxer74]

[modok]

Not quite good enough, but maybe they could be fixed if you have some way to do it.

[mark tucker]

steel or aluminum center main? the bearing may be too "tall" that is the only clearance issue I see the rest are fine for my builds. I do not like the steel center bearings.

[boxer74]

[Brian_e]

[boxer74]

[nsracing]

Every engine builder should own a fine bearing scraper.

With Silverlines, it is hit or miss. Better the clearances too tight than too loose. I do not need to explain what the bearing scraper is for.

Enjoy -

[Clatter]

Have you checked to see if the center main is holding the case halves apart?
Perhaps it needs sanded where the halves meet.

Check using a feeler blade above/below the bearing with case torqued.
You’ll be able to see a gap with a flashlight positioned perfectly.

[boxer74]

[boxer74]

[Clatter]

Check my Bergmann bomb thread for some more fun with this.

Some say a center gap is a Silverline feature.
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Bus Motor Build

What’s That Noise?!?

[boxer74]

[boxer74]

Tried a new silver line centre main. Clearances are now in spec:

#1 0.0016"
#2 0.0022"
#3 0.0016"
#4 0.0020"
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74 Super
84 Westy

[SGKent]

good work. .004" was too much for an around the town engine.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raymon covey]

Slowly sand down center main to.002 would be my and check to see that case halves come together with some crush on the bearing. If its not coming together the clearance will change as it comes together.