[prostreet64]

Just finished the tear down on the 400 in my son's 69 Bird. I was reminded that the block, which is a 1970, is drilled for 4-bolt mains. Just curious which blocks would have come with 4-bolt mains?

[tom s]

real 4 bolt mains block are considered ones that come with 4 bolt caps.The factory produced a lot of 4 bolt drilled blocks.Tom

[turbo69bird]

I think he was asking which blocks would have come w the caps Vs the ones that came w the holes drilled but 2 bolt caps

[tom s]

In 70;RA III and RA IV and I would assume the HO non RA engines?In 69 Only IVs got the 4 bolt caps.Excluding RA Vs.Tom

[25stevem]

If you want to make the block stronger without going thru the expensive procedure of installing 4 bolt caps
Then order up six 1/2 “course thread Allen cap bolts That are long enough to stop 1/8” or so before the bottom of the bolt hole .

Make sure the bolts and thread holes are totally free of oil and crap and then red Loctite them in .

You only to Torque these 6 bolts to 20 ft lbs with the Loctite so the it should not pull the line bore out of wack, but you should check anyway.
This process also stops the outer walls of this 6 holes from cracking, which is one thing you should check out also.

I have seen 2 1970 blocks used in front of automatic transmissions that had one of the outer walls of the added four bolt cap holes with a pretty good long crack running down it, most likely from the factory taping process.

These cracks where ground out and the Allen head bolts installed and these two motors are still running today some 20 years later and making 300+ hp over stock!

[Gary H]

Gates, in addition to the ram air II, 70' ram air III, and ram air IV blocks being 4 bolt main, I've seen multiple SR 400 blocks with 4 bolt mains over the years. Don't think they all were though.

[prostreet64]

Thanks guys. We don't have a need to go to 4 bolt mains with this rebuild but I was just curious how common these blocks would have been in 1970. Since this tear down and refresh was triggered by water getting into the #4 cylinder, we will be having the block and heads magna fluxed to make sure we don't have any cracks.

[turbo69bird]

I run a 2 bolt 455 in my turbo car , cast crank, too and I been running 9s with it for many many years I haven’t even changed a spark plug. So 2 bolt blocks are plenty stout. It’s detonation that kills Pontiacs typically, but a set of eagle H beams is cheap insurance. Of course if your detonating the thing I dint care what rod you shoes your gonna pound the bearings out of it. Keep the thing fat and lazy itll run forever

I do like the idea of getting bolts in those extra tapped holes though.
I also hard block all my blocks up to the bottom of the freeze plugs except for my ram air IV or RAV blocks.

[25stevem]

Fact, the blocks drilled and taped for 4 bolt caps but not using them are weaker then the blocks that are not, especially the large main blocks!

[prostreet64]

I like the idea of filling the extra bolt holes. Never thought about them being a weak link if not running the 4 bolt caps. Block is filled to the bottom of the freeze plug holes and we already have forged rods and pistons. Crank is nodular. Main bearings look perfect; back in the day we had Ken Keefer send them off to have a coating applied which gave us the clearance we were looking for. Rod bearings look good too for the most part; one or two have a thin sliver of cooper showing at the very edge. Maybe a high spot on the journal? Anyway, after 12 years of beating on this engine pretty hard, we can't complain. Just need to confirm the source of the water in #4 was the head gasket.

[AG]

Originally Posted by prostreet64

Thanks guys. We don't have a need to go to 4 bolt mains with this rebuild but I was just curious how common these blocks would have been in 1970. Since this tear down and refresh was triggered by water getting into the #4 cylinder, we will be having the block and heads magna fluxed to make sure we don't have any cracks.

Every non RAIII and RAIV 400 block cast in 1970 is just like the one you have.

[25stevem]

I agree with the above as I have had two 70s with the 350 hp rating with a auto trans, and both where set up for 4 bolt mains.

[Tom Vaught]

That is why Marty Palbykin and I used a 1967 400 2 bolt main block.
Because the webs were perfect and NO 4-bolt Main hole drillings in the webs.
We installed PROGRAM STEEL SPLAYED Main caps on the block.
1600 hp without issues for 3 years.

Tom V.