Bellhousing runout and correction

[PackardV8]

I do have a question about line boring/honing to Jack Vines (or other qualified individuals). Is a small portion taken off the block and cap and in an exagerated discription resemble a football (smaller than the original circle) then the block/caps are line bored/honed back to size. OR..., are the block caps left as they are and the circle is enlarged having the extra size made up with a bearing that is externally oversized and internally undersized (assuming a turned crank). Is this what a, .020/.020 bearings is? Externally .020 oversized and internally .020 undersized?

Line boring is usually only necessary if the main caps have been changed and no longer align side-to-side. Line honing is the usual method of precision rebuilding.

The main bearing cap mating surfaces are nipped .001" -.003" as required on a Sunnen cap grinder.



The main caps are then installed on the block and torqued to spec. As you suggested, removing material from the mating surface of the caps results in an oval bore, wider at the sides. The line hone mandrel is long enough to go through all five main bores and driven by a large drill motor. About five strokes, remove, measure all five bores with the Sunnen dial bore gauge. When finished all five bores will be round and original ID to within .0005".



When the crankshaft is turned .010" - .040" undersize, the bearings then used are appropriately thicker to maintain the required clearance.

You did ask this question, and while not germaine to Studebaker discussions, 21st century design blocks and connecting rods are manufactured in one piece and the main caps and rod caps are separated by cracking them off. This results in a slightly jagged mating surface which fits together perfectly. Obviously these can't be nipped flat to resize them, so the bores are honed to a specified oversize and thicker shell bearings are available make up the material removed.

jack vines

[TWChamp]

I've always wondered how the factory gets that nice jagged break without any distortion, such a twisting it to break it would cause. Back in the 60's I had a Power Products 2 cycle engine that had roller bearings on the big end of the rod, and it had the same jagged split.

[PackardV8]

I've always wondered how the factory gets that nice jagged break without any distortion, such a twisting it to break it would cause. Back in the 60's I had a Power Products 2 cycle engine that had roller bearings on the big end of the rod, and it had the same jagged split.

https://www.youtube.com/watch?v=wu0DqhI-wGo

jack vines

[Frank DuVal]

Not a Studebaker, but back in the early 80s a friend’s ‘64 Nova 194 cu in six was tired. So, I pulled it down and did a rebuild. I knew to punch mark the main caps, but didn’t.

Upon reassembly, it finally got too hard to turn the crankshaft after the head went back on. Hmm, all those six main caps ( the seventh was thrust bearing, so obvious) weren’t the same, were they.

What to do? I plastigaged the six caps, took note of which of the three measurements on on each were tight and loose, made a plan, shuffled them and measured again. Success! All within .002.

That was over 35 years ago. It was his daily driver and I have re-ringed it once since. Over 250 K miles. He is driving it now as a collector car.

I felt very lucky that night. Never forgot to mark a main or rod cap again.....

[RadioRoy]

I felt very lucky that night. Never forgot to mark a main or rod cap again.....

Great story.

It's amazing how an experience like that will stick in your memory and really teach a lesson. I hate realizing that I've made a fatal mistake just after making it. Much better if I can see it coming before it happens.

[Dwain G.]

On the old air cooled VW engines, when the main line showed wear it was easy to bore oversize with a portable boring bar. Then if the thrust surface was worn it was trued up with another attachment. And if the crankshaft had been turned undersize too.....well it got interesting when ordering new main bearings.

[PackardV8]

FWIW, we made a jig to check rear block face perpendicularity. The current build is off .008", with the right side being that much higher than the left.



I'd guess the transmission and clutch would function satisfactorily with the block being only .008" out of square, but less is more.

Now, the next area of examination is the bell housings. Is the bell housing transmission face parallel to its block mounting face? To use the machine time at $125 an hour to make the block square and then install a wonky bell housing is not gaining anything for the effort.

jack vines

[jpepper]

FWIW, we made a jig to check rear block face perpendicularity. The current build is off .008", with the right side being that much higher than the left.



I'd guess the transmission and clutch would function satisfactorily with the block being only .008" out of square, but less is more.

Now, the next area of examination is the bell housings. Is the bell housing transmission face parallel to its block mounting face? To use the machine time at $125 an hour to make the block square and then install a wonky bell housing is not gaining anything for the effort.

jack vines

I think I would just measure the assembly and shim it if needed. It is interesting that in the shop manual it states something to the effect that if the face is out of perpendicular, replace the bellhousing. I have never checked but I wonder if they were machining error in the bellhousing to accommodate out of square blocks. I guess I'll have to get out my granite surface plate and start checking bellhousing parallelism.

[PackardV8]

We're going to make up a fixture and machine this one block square, but just to prove we can do it.

Agree, in the future, we'll most likely dial indicate the bell housing surface while we're doing the bore and shim the surface square as part of the centering process.

jack vines