427 Chevy Block 2 bolt vs 4 bolt

[Rumbleguts396]

Hi Guys, I've been searching for a 1969 427 Chevrolet passenger car block for a future project for several months now. I really would like to find a 4 bolt main. Most of what I have found are already 30 over and needing to still be bored or are 60 over. Not really interested in that. When I find a nice standard bore or nice 30 over 4 bolt main they are way out of my budget. My question is has anyone taken a factory 2 bolt and drilled it for a 4 bolt main with good results? I've found some real nice standard bore 2 bolts in my price range. Is drilling to a 4 bolt as strong as a factory 4 bolt ? Anyone done this with good outcome ? Lucky I'm in no rush, so time is on my side for finding a good block within budget. My plan is to build a nice healthy solid lifter motor for a 1969 Camaro Street car with a few runs a year at the track. Mostly street driven. Many Thanks for thoughts, ROB

[Lynn]

I have a set of Milodon splayed main caps for an SBC to be used in an upcoming project.

Expensive, but some swear it will be stronger than the factory four bolt main cap block

They make them for BBC as well. No personal experience as far as testing.

https://www.jegs.com/i/Milodon/697/1...ontent=Milodon

[luzl78]

Originally Posted by Rumbleguts396

Hi Guys, I've been searching for a 1969 427 Chevrolet passenger car block for a future project for several months now. I really would like to find a 4 bolt main. Most of what I have found are already 30 over and needing to still be bored or are 60 over. Not really interested in that. When I find a nice standard bore or nice 30 over 4 bolt main they are way out of my budget. My question is has anyone taken a factory 2 bolt and drilled it for a 4 bolt main with good results? I've found some real nice standard bore 2 bolts in my price range. Is drilling to a 4 bolt as strong as a factory 4 bolt ? Anyone done this with good outcome ? Lucky I'm in no rush, so time is on my side for finding a good block within budget. My plan is to build a nice healthy solid lifter motor for a 1969 Camaro Street car with a few runs a year at the track. Mostly street driven. Many Thanks for thoughts, ROB

Tony (scuncio) has a 69 427-335hp complete motor

[scuncio]

Sorry, I sold that a couple years ago.

[luzl78]

Originally Posted by scuncio

Sorry, I sold that a couple years ago.

I’m tryin!

[Rumbleguts396]

Originally Posted by rszmjt

I have converted 2 bolt "512" & "351" blocks to 4 bolt caps before for restorations, its not that hard to do just time consuming , it helps to have a good supply of used 4 bolt caps to trial fit on the block to make sure the parting lines are very very close, unless you have someone weld up the cap registers and re machine to center the caps on existing bore. Check with local machine shops to see if they have a supply of used 4 bolt caps to trial fit onto the block. Also the rear cap seal parting line area should be super close to avoid any rear seal alignment issues. Once you find some suitable caps you have to put the block on a mill or bed type drill press and drill & tap the outer bolt holes. I made a thin drill sleeve and used the outer cap holes to drill the block and used the caps as a tapping guide.
Then the block needs to be align honed ( if caps are super close) or possibly line bored. If you want block to look correct from the outside the 1/2" pipe thread 2 bolt oil plug above the oil filter must be tapped to the 4 bolt 3/4" pipe plug. It is a lot of work and can get expensive if you have to get someone to do the mill work and align hone or bore.

Hope that Helps.
Mike.

Thanks Mike much appreciated!!!

[Vortecpro]

Originally Posted by luzl78

Tony (scuncio) has a 69 427-335hp complete motor

I have those as well.

[Vortecpro]

Originally Posted by rszmjt

I have converted 2 bolt "512" & "351" blocks to 4 bolt caps before for restorations, its not that hard to do just time consuming , it helps to have a good supply of used 4 bolt caps to trial fit on the block to make sure the parting lines are very very close, unless you have someone weld up the cap registers and re machine to center the caps on existing bore. Check with local machine shops to see if they have a supply of used 4 bolt caps to trial fit onto the block. Also the rear cap seal parting line area should be super close to avoid any rear seal alignment issues. Once you find some suitable caps you have to put the block on a mill or bed type drill press and drill & tap the outer bolt holes. I made a thin drill sleeve and used the outer cap holes to drill the block and used the caps as a tapping guide.
Then the block needs to be align honed ( if caps are super close) or possibly line bored. If you want block to look correct from the outside the 1/2" pipe thread 2 bolt oil plug above the oil filter must be tapped to the 4 bolt 3/4" pipe plug. It is a lot of work and can get expensive if you have to get someone to do the mill work and align hone or bore.

Hope that Helps.
Mike.

I have run across this conversion a few times, and its always to pass a converted 2 bolt block off as a production 4 bolt block. Heres where they make their mistake, 4.250 bore two bolt blocks do not have the bores notched on the intake side, 4 bolt blocks do, and replicating the factory notches is not something these conversions have successfully been able to do at least when I examine them.

[Xplantdad]

Originally Posted by Vortecpro

I have run across this conversion a few times, and its always to pass a converted 2 bolt block off as a production 4 bolt block. Heres where they make their mistake, 4.250 bore two bolt blocks do not have the bores notched on the intake side, 4 bolt blocks do, and replicating the factory notches is not something these conversions have successfully been able to do at least when I examine them.

Mark is a wealth of information...and builds killer big blocks that make really good horsepower on pump gas.

[big gear head]

It's not worth the effort for a street engine. I have a friend who is running a 396 in a B/S '69 Camaro running high 9s at over 8000 RPMs with a 2 bolt main block. If you can find a good 2 bolt block then it's going to be more than good enough for a very strong street/strip car. Too much machine work involved in installing 4 bolt caps on a 2 bolt block. After you get the caps installed you have to get the block line bored. If the rear cap doesn't fit just right you may have problems with the seal and thrust surfaces.