I saw a picture (online) of an upside-down slant six block with the pan off. It was an assembled engine, but the main bearing caps looked like they had been milled flat and had 1" thick pieces of what apeared to be billet backups on top of the bearing caps, running all the way across, and being held in place by the original (or, longer.) main cap studs/bolts.

This seemed like a good idea to me. Would somebody who knows something about it fill me in as to whether it works to strengthen the bottom end, please?

Thanks in advance...


Bill, in Conway Arkansas

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1964 Valiant 4-door sedan, 225 turbo/904

They are called "main straps", and very common in round track racing when using stock main caps. It supports the caps better as they will break in half once you exceed a certain HP level and extended RPM range. For the Slant there is a billet cap option which is used successfully, so straps aren't as good of an upgrade as the billet caps are, and the billet caps are cheaper to install.

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There's no such thing as too much cam....only not enough engine!

Is there anywhere these billet caps are sold, currently, and I am sure they need to be align-bored, right?

Thanks for the information!

Bill, in Conway, Arkansas

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1964 Valiant 4-door sedan, 225 turbo/904

As you might imagine Bill, nothing like this is application specific of the Slants unfortunately. But you can adapt a set of billet caps from a 440 fairly easily because they have the same housing bore size. Also, the thrust bearing cap is narrower on the 440 engines, so you will have to have one made for that location, but its no problem for even a novice machinist. Yes, the block will have to be line bored as well. Ebay has plenty of them available.

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There's no such thing as too much cam....only not enough engine!

After reading your posts and thinking about it, I have decided to take the coward's way out, even though the results won't gain me the degree of stability I really want, and go with the easier-to-accomplish, backup bolsters instead of the more-desirable, 440 caps you recommended.

I realize that this won't afford me the same degree of longivity/stability that the billet caps will, but I am never going to test the limits of strength in the bottom end of this motor. If I ever run, even, 25 pounds of boost, it willl be only for six or seven seconds (eighth-mile drag strip,) which is nowhere near the stress encountered by a Bonneville run that could last a whole lot longer. This is strictly a drag strip car...

So, having said all that, I am now wondering what material I need to buy for the backup bars, and whether the hold-down bolts/studs need to be anything beyond some Grade 8 material. Does ARP have studs and nuts for the studs, in the correct length (since I will need longer fasteners?)

I hope this will be worth doing. The daunting, added work of pulling the crank out for the align-boring operation just isn't something I want to tackle at my age/condition (born 12/20/'38.) I hope this decision doesn't prove to be the wrong one... I don't have another 20-years to get it right.

Thanks for all the good information!!!

Bill, in Conway, Arkansas

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1964 Valiant 4-door sedan, 225 turbo/904

You unfortunately will have to pull the crank because installing the ARP studs and cutting the caps for the straps and adding them will require an align hone at the least. Sorry, but nothing is free it seems. The material is just a mild steel such as 1018. Nothing special!

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There's no such thing as too much cam....only not enough engine!

You unfortunately will have to pull the crank because installing the ARP studs and cutting the caps for the straps and adding them will require an align hone at the least. Sorry, but nothing is free it seems. The material is just a mild steel such as 1018. Nothing special![/quote]

Well, if, no matter what I do, removing the crank is going to be necessary, I will make that a POSSIBLE winter 2016 project... for now, I will just keep the boost at civilized levels and watch my mixture and spark-advance, carefully. Who knows, I may, in a spurt of energetic derring-do, decide that a girdle would be the ultimate main support, and opt for that.... who knows!

Thanks to all, for the good advice and education!

Bill, in Conway, Arkansas

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1964 Valiant 4-door sedan, 225 turbo/904

CNC Dude,

After reading and, re-reading your post, several times, I am (in my ignorance,) having trouble understanding just exactly how disassembling the main caps from my engine, milling the "tops", flat (for the "straps,") and re-installing them, would require align-boring them... My contention is, since the sides of the block, down in the place where the main bearings are a tight (but, not an "interefence fit,") I would think that the caps could not move sideways at all, and longitdinally, the studs/bolts would index them in a fore-and aft position, (and, that would not change with an align-bore,) what has changed to the extent that align-boring is necessary?

I have NO automotive machine shop experience and am pretty much, operating "in the dark," here...

Please help me to understand what I am missing; I am obviously missing SOMETHING....


Bill, scratching his head, in Conway, Arkansas

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1964 Valiant 4-door sedan, 225 turbo/904

No problem Bill. Once a part such as the connecting rods or main saddles are originally machined or even reconditioned, re-machining the main caps for instance by milling the tops off in this manner, releases stresses internally within the main caps that distorts it and will no longer let it return to its originally machined condition when installed back on the block. It may still fit snugly within the saddles in the block, but the housing bores will be out of round and not on size any longer. Also, once a part such as the connecting rods or main caps are machined with bolts, and then replaced with studs, or even a better grade of bolt that requires a higher torque value, it again will have to be re-machined because a stud generates a much higher clamping effect even if torqued to the same value as the bolt it was originally machined with, thus closing the housing bores more and distorting the housing bores differently than with a bolt.

I'll also mention a little more about connecting rods. Just the act of removing the rod bolts and re-installing them no matter how delicately you try to do it, tweaks and distorts the housing bores and requires them to be reconditioned. So you need to do this in the correct order when your engine goes thru the machine shop or you may be having to pay for them to re-machine your rods or block again if they have to change the fasteners after the fact. The same holds true for grinding on the rods to balance them after they have been reconditioned. Again, stresses are released and the housing bores distort and change. So do any grinding, polishing and install bolts before they are reconditioned as well.

Also, line boring and align honing are 2 different operations, while being similar. When installing aftermarket caps or even mismatched factory main caps, line boring is required because the aftermarket caps are only semi-machined inside the housing bores and requires a boring bar to remove the excess material to a size closer to the finished housing bore so a hone(align honing) can then be inserted to bring it to its final size. Align honing can almost always be all that is required to install main straps to restore the housing bores where they need to be, and its cheaper than line boring.

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There's no such thing as too much cam....only not enough engine!

Wow... Thanks!!! I never knew how MUCH I didn't know~~~~ lol!

I am going to have to read that about three or four more times, to try to assimilate all the good imformation presented, therein.

I do appreciate the depth and scope of the info presented; I was really, really, ignorant about the fine-points of this area of proper machinework practice, but am learning... slowly.

With the .003"inch main bearing clearance (.025" on the rod bearings,) I am wondering if that would be a factor in making the operation "do-able" (the out-of-round dimension would be somewhat less than the .003" clearance,) so as to npt be perfect, but workable? I guess, what I'm asking is, "How much 'out-of-round' might that main(s) cap be, once the top portion is milled flat enough to attach a block of billet to the flattened area? It may not be a question that is answerable without mic-ing the three caps, after machining, I dunno...

I would like to make this strap idea work without removing the crank from the block, but realize it may, simply, not be possible... and, is not desirable, at best... I understand that. This is just a hobby car; not an NHRA Competition Eliminator racer... and, as, such, will never see Bonneville, nor the Texas Mile, just 1/8th mile drag racing, but I have been racing since 1955 and have seen a LOT of engine-failures... and, really don't need another one....

Your machine-shop-knowledge is, indeed, impressive!

Thanks again!!!

Bill in Conway, Arkansas

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1964 Valiant 4-door sedan, 225 turbo/904

Thanks a lot Bill. I do come by it honestly though by being fortunate to have worked in a very top shelf and highly respected race engine shop for over 15 years. The amount of distortion varies from part to part and engine to engine, with no rhyme or reason or consistency, that makes it unpredictable unfortunately. I don't think it would be a tragedy to wait until you could do a full teardown to eliminate and avoid the unknown for now. I'm sure other engines of this HP level have never done this modification, so it isn't likely its an immediate rush to do this.

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There's no such thing as too much cam....only not enough engine!