flathead line bore

[john mullen]

I have a 52 8RT block that is in very good condition except it has no main bearing caps. I have purchased a used set and hope to line bore the block with the new caps... Any comment's or suggestions on the subject ????

[bobH]

It's done often. Install them and measure, up-down, east-west. Feel for 'step' at the parting line - if no step, or minimal step, should be good to go (for line bore).
Hopefully, the experts will chime in.
I've only dealt with this situation once, and it was on a 59A block. With help from my machine shop and engine builder, we tried caps that he had, and found a set that had NO step felt at the parting line, and he gave the block (with caps) just a light 'touch'. I think it was a hone, but I'm not sure of that.

[old46]

Also do a line hone for the last few .100'ths much more accurate.

[JWL]

I have found caps from other engines to perfectly align with the block in my hands. Maybe you will be lucky and no machining will be necessary?

If the new caps require align bore and hone you will need to find someone with the knowledge and experience to cut the clamping face of the caps. I have a special fixture for the lathe which I think I pictured in my book for everyone to see. But, it could also be done in a milling machine with very careful attention to detail. The amount to be machined from the face is usually only about .005 but some shops are accustomed to removing much more and that should be avoided. In some shops they think it is best to machine the pan surface of the block rather than the caps. If it is a matter of only a few thousands to allow for align honing I might not raise objection to that method. However, it has been my experience the normal situation is to lay the block on the table of the machine and begin cutting. Often it requires .020 or more just to get the pan deck parallel with the intake manifold deck. In other words there should be an aligning and shimming operation performed with a dial indicator before any cutting is done. Again, best to deal with a Flathead experienced shop and/or be certain it is even necessary.

[Ol' Ron]

Jwl x 2, great teacher.

[Cecil/WV]

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I had an 8BA a couple of years ago that had no caps and I found caps in my stash that fit pretty good(no offset in mating surface) and had it align bored. Shop said they had very little to do.

[GOSFAST]

Having a limited amount of "spare" caps to work with lessens the chances of a "perfect" fit. They may be close however.

I would add this tip here, if possible try to avoid milling the pan-rails, this is a "down & dirty" option to "shrink" the holes. We recommend milling the caps, more work involved but usually a better outcome. This can be accomplished on a Bridgeport in conjunction with decent rotary table.

After having the procedure finished I would record the center-to-center distance just as a precaution. It's nice info have on the build.

(Add) Hi Ron, Happy Birthday (belated), just saw that post. Stay healthy up there!

Thanks, Gary in N.Y.

P.S. Try to find a shop that can "align-bore", using this method you can actually "hold/maintain" the center-to-center from the mains to the cam tunnel. This cannot be done with "align-honing" equipment! This subject was up here recently about "fixing" connecting rod lengths!

[Ol' Ron]

Yes, this is all good info. The fixture I made for the lathe makes it easy to remove .005 off the mating surface. I don't have a rotary table.

[Bored&Stroked]

All good information from the crew. Couple comments:

- Normally you do not use a honing operation - unless you've done an align bore. You cannot accurately use a hone to move or re-size a bore. So you align bore first, and then 'finish hone' a minute amount for surface finish.

- As noted, you can mill the pan rails or the cap bottoms. On the recent 41/42 Merc engine I'm doing, I added a new Doug King billet center main cap, so I had an align bore/hone operation done. Fowler Engines used the pan-rail method (is just fine) - with the block being setup in a big Bridgeport mill.

- Only the minimal amount of material is removed on either method to 'shrink the hole' as you don't want timing gear to crank gear issues from the mesh being too tight (as the cam/crank centerline locations will be closer together). There are some 'undersize' cam gears available to account for this . . .

- Due to the above, remove the LEAST amount possible from the block side of the bore.

- Make dang sure the shop understands flatheads, has great machine operators and has really good equipment - being able to accurately do these operations is very important.

- Bearing Clearances: Even with perfect align bore/hone operations, I still find it necessary to sometimes try multiple sets of bearings to 'tune' my final main clearances (but I'm really picky on race motors). This is not due to the bores themselves, or the crank work (as my guy holds 2 tenths), but the fact that bearing shells frequently have slight variations in thickness. On a modern OHV engine (say a race BBC), I can order bearings with +/- .001 undersizes . . . and half-shell or full-shell a particular main journal to get exact clearances - we don't have these bearing options on flatheads (I sure wish we did!). I recently used two sets of main bearings from the same manufacturer to mix/match shells to get things the way I wanted them to be.

[tubman]

Not to take away from what these gentlemen have to say, as I have the greatest respect fr all of them. I just would like to add that I too, was able to find a matching cap that worked well for a rebuild of a stock engine. I had a bunch at my disposal, and the first one fit perfectly.

[Ol' Ron]

I have a large box of them, and have found several that worked just fine. This is an attribute to a fine design and manufacture.

[john mullen]

Thanks to everyone for your comments... This info is encouraging and has helped me in the dissension to go forward with saving this block.. Thank you all... John

[BILL WZOREK]

Originally Posted by Ol' Ron

Yes, this is all good info. The fixture I made for the lathe makes it easy to remove .005 off the mating surface. I don't have a rotary table.

Ron:

Can you show a picture of that fixture

THANKS

[Bored&Stroked]

Originally Posted by Ol' Ron

I have a large box of them, and have found several that worked just fine. This is an attribute to a fine design and manufacture.

I agree - and I also believe a large part of this is due to the cap 'indexing' methods that were used. Those large circular 'tongue and groove' slots may be a pain to deal with (making new caps or to machine for align boring), but they do lock the caps down in very specific positions.

[Ol' Ron]

If I can remember to take the camera out to the shop, prett simple to make.
I like making fixtures, have always done this. Always trying to make something easier to do, lazy I guess.

[russcc]

Fixture, hallmark of a good machinist. One guy we knew made fixtures for multiple parts. Other guys in the shop, made the 1st & 2nd parts quicker, and then fixture man, blew right by everyone, and every piece was on the money.

[john mullen]

I purchased a main cap set off the e/net and they fit so close that I can't believe my eye's. I'm thinking I want to have them very lightly honed just to be sure they are ok.