[John Eiseman]

Was curious as to whether a set of 389 main caps will work on a 400 block ? The main caps are from a 64 389 block that was cracked and scrapped. These caps have been hot tanked and magged.

[tom s]

It is possible but NOT always EZ to use used caps from another block.I got a block without caps,bought a full set of used caps and only one would work.Bought a set of new billets.The new caps have Xtra material so they virtually dont have to take anything from the block.Tom

[25stevem]

Why, Does the 400 not have caps?

Unless the 389 caps are 4 bolt ( and very rare!) then they are of no better cast iron then the 400 caps.

[hobbygto65]

Don't forget if you do this they have to be line bored which is not cheap.

[b-man]

All good advice here in this thread.

Unfortunately once the caps go missing it’s an expensive proposition to replace them on a block.

Spending the money on machine work to get some used 2-bolt caps to fit on another 2-bolt block would be a waste of funds in my opinion, and may not even be feasible as Tom has stated above.

Adding aftermarket 4-bolt caps is probably the only way to end up with something worth using when it’s all said and done.

[tom s]

If its one of the 3 center caps it not as bad to just put one billet on,the first and last are the expensive ones.Tom

[ANDYA]

I would say that you would have to be very, very, lucky to get a set of caps from one block to fit another on the first attempt. A few years ago I was getting ready to build a 455 for my GTO. I had a standard bore block with 2 bolt caps but drilled for 4 bolt. Nunzi had my block and I told him what I wanted to do. He said the factory caps fit tight on the dowel pins and the alignment of the caps to the block was perfect and to leave it alone. But to satisfy me he brought out two milk crates of used 4 bolt main caps to try. We agreed that if I could find 3 caps that would fit good enough that we didn’t have to remove the dowel pins and that a bore and hone alone would do the job then we would go forward. After more than an hour trying lots of caps I only found two that were good enough to use. We were unable to get a thrust cap that was close enough because it needs to align both side to side and front to rear. I gave up and stuck with the original caps. He also told me to never attempt to take a used rear cap from one motor and put it on another as there is more of a chance the rear main seal will leak. If you have used caps from another block and the alignment is way off the caps can still be used but it requires a lot of work. The dowel pins have to be removed. Then the caps need to be fit to the block for best alignment and bolted to the block. Then you have to drill through the caps into the block to install over sized dowel pins. Finally you can align bore and hone the mains. By the time you do all that it’s cheaper to start with a different block.

[Dragncar]

Originally Posted by tom s

If its one of the 3 center caps it not as bad to just put one billet on,the first and last are the expensive ones.Tom

The first one only cost me 75$ back when I bought it. The rear was the killer.

[Dragncar]

The OP might try the malleable iron 4 bolt Milodon caps. They make them in splayed now as well as straight.
I bet they are easy to machine.

[tom s]

I think the billets are about $90 now.Tom