https://www.streetmusclemag.com/fea...block-mopar-b-rb-main-caps-from-milodon/

In case this helps some of you.

those look like very nice caps.
however, i have always wondered if the big block had enough wall material in the skirt for cross bolt caps.
how much would the minimum wall thickness have to be after the spot face for the bolts ?

Yeah the 512 low deck in my Duster is done that way. It is a bunch of work and not really worth it in the end.

I question the value of this mod too. Seems to me if you're making the power that needs four-bolt mains its time to step up to an aftermarket block - probably for not a whole lot more money than the machining and mains will cost.

When Mopar designed the B and RB motors there was no intent to make the main webbing thick enough to support 2 bolt crossing through that webbing to help strengthen the bottom end, DON'T do that Drilling through the main webbing is asking for a disaster to happen later when the main webbing fails and you run over the crankshaft
I have replace the stock main caps with both Ductile iron and aluminum along with ARP main studs because at that time that was the only option in trying to improve the strength of the stock RB and B blocks, not so any more
I'm buying new better blocks so I can really twist the tail of the Tiger to make the new motors wail like a banshee
Save your money on buying them and invest it into a good block

The article states that the new design doesn't interfere with the oil pan bolts. When did you do this Andy? J.Rob

Not sure, maybe 20 years ago.

I have a set of Pro Gram 4 bolt caps for sale in the for sale section. Ad #2828673 about 1/3rd of the way down the page. They were installed on my 400 block, but they could be line bored for a RB. Align boring would need to be done anyway. 200.00 plus shipping.
Pro Gram Main Caps

Dave

The Milodon caps go further down the main web than the Program caps do. Really depends on the block wall thickness in the main web area after machine work is done wether it adds strength or not. I personally don't like cutting the main web gusset out.. Whats needed is a true (vertical) 4 bolt main. Creates more clamping force. Side bolts tie the block together but create zero clamping force.

I installed a similar set of caps on a 440. I taught at a tech school, and the machine shop did the work so cost was not an issue. But after three seasons of running pulled it apart to freshen, and it had cracks between the cam journal and the no. 2 main bearing web. Over the years, I did all the normal stuff, block filling, different main caps, girdles, etc. As many have said, if you are building anything much over 600hp, get an after market block, at least they are making them again.

Always thought it was a shame that Ma Mopar didn't decide to offer B&RB blocks with the Hemi bottom end in them. Not sure if it would have been a financial success or not, but it would have made it a lot easier for the guys like us today.

If the Mopar engineers had been thinking they would have cast the bosses in the side for the cross bolts and just left them unmachined on the production blocks. It would not have cost any more money but it would've made the blocks capable of being properly cross bolted down the road. They could sold cross bolted wedge blocks over the counter thru Direct Connection. They just weren't thinking that far ahead.

They did produce some cross bolted wedge blocks for NASCAR so they knew how to do it. They just never convinced the production guys to add the material for the bosses.

The bean counters saved 4 cents a block NOT doing that.

I have a 426 marine block that has the bosses cast in to the sides like a Hemi block. They are not machined, but the bosses are there.

That block casting looks a lot like the later (1965 and later)H.D. truck 413 blocks
I built a 1972 413 Truck H.D. block for my 1963 Fury street car, I'm going to pull the oil pan off and take a look inside to see if it has those bosses

750,000 440's X 4 cents is $30,000 bucks over about 12 years!! That guy got a raise!!

I saw a block like that a few years back but I didn't have a camera with me at the time. Is there a casting number on the back of the block by the oil pressure port? What does the ID pad say? I don't remember what the ID pad said on the block I saw but I remember that it was a 426 wedge block. The guy who owned it said it came out of a NASCAR shop.

No casting number on the block that I could find, but it looks like the industrial block. I apparently didn't take a photo of the pad, but as I recall it had 426 MAR on it. I don't know if these were the ones they used in NASCAR or not. I seem to remember reading that the Petty's used the Hemi block and drilled and tapped the top row of head bolt holes. Chrysler probably dropped off truck loads of parts to them back in the 1960s and 1970s.

My personal opinion is that anything that helps tie the bottom end together will be beneficial. When the piston fires it’s not a straight down push but at a 45 degree angle to the main cap-bottom of the block where the side bolt would be.

This. Wouldn't it have been nice to go to the boneyard and pick a 400" "B" block from a 77 Newport and throw on a crossbolt upgrade kit and have a 1300-1500 H.P, tolerant package?What could have been....