Converting a 2-bolt 427 to a 4-bolt

[Steve Antonucci]

I have a question regarding the conversion of a 427 2-bolt main block to
a 4-bolt main block. As most of you probably know, the availability of
427 4-bolt blocks is quite scarce. When one does appear ( ebay usually )
it commands big bucks! However, most 4-bolt main blocks have been used
hard and as such usually have larger overbores. I don't like that.

Over the last year, I have run across a few 427 2-bolt main blocks with
standard bores. I like that! The challenge now is to determine if a 2-bolt
main block can be converted into 4-bolt main block. Now, I'm not asking
about the mains. That is an easy modification. I'm referring to the oil
plumbing fittings on the left side of the engine ( over the oil filter boss ).
One member of this forum was very kind to assist me while determining the
viability of particular blocks for this purpose.

So the question stands in regards to this oil plumbing. Have any members
gone through the pain & expense to have the oil plumbing modified ( drilled )
to reflect a factory 4-bolt main block? I didn't think it would be that
difficult, but after purchasing a 2-bolt main block, I now find that the
machine shops interested in the project are now concerned about ruining the
block. I would assume that these holes need to be gun-drilled. Can anyone
recommend a machine shop that can handle this modification? I'm in North
Carolina, but that isn't as big a deal as getting the machining done properly.

I would greatly appreciate any and all recommendations.

Steve

[mikemccagh]

Re: Converting a 2-bolt 427 to a 4-bolt

Steve: you're about to do something that's been done before. when you drill and tap for the plug that's common to 4 bolt main block, just drill SUPERFICIALLY enough to run a bottom tap and then modify the plug so that only a couple threads catch yet appear to be threaded into the block as far as a 4 bolt block plug inserts. I'd guess the machine shop is hesitatant in that they think you want the holes drilled thru so that you could use a remote filter. just tell the machine shop the plug is for cosmesis, not functionality. good luck, mike

[John M.]

Re: Converting a 2-bolt 427 to a 4-bolt

If I remember right the HIGH PERF is larger on the 4 bolt #351 block

[Werner R.]

Re: Converting a 2-bolt 427 to a 4-bolt

this raises an interesting point. i bought my 64 with a BB already installed. in checking the numbers, i found that the block came off of a 67 chevelle 427 and is a 4 bolt block. when i first asked about this on another forum, i was told that those blocks are a dime a dozen. however, i have also been told that the block has value. i have no idea about whether or not it has been overbored because i have never removed the heads. if it is standard bore or even .030 over, do i have a dime a dozen block?? as far as i know there are no cracks or defects etc. any thoughts would be appreciated.

[mikemccagh]

Re: Converting a 2-bolt 427 to a 4-bolt

any "351" cast # block, with late 66 to mid 67 casting date is not without value. bare cases, std to o30 bore will typically fetch 1 - 2 k at carlisle. don't throw it on the scrap pile---if you're gonna, i have a mobile scrap pile and can pick it up for ya. regards, mike

[Werner R.]

Re: Converting a 2-bolt 427 to a 4-bolt

thanks mike. i think mine is a 351, but i will check my records again after i get home tonite. it runs quite well so [hopefully] it won't see the scrap heap for a while.
werner

[Clem Z.]

there were no 67 427 chevelles except yenkos.

the largest BB chevelle from the factory was 396 in 1967

[Mark #28455]

Re: Converting a 2-bolt 427 to a 4-bolt

Updating your block to 4 bolt main appearance isn't difficult - drill and tap the holes over the filter mount. If you measure any old 4 bolt block, you can determine the correct depth to drill for the oil cooler valve also, but I would only drill deep enough to re-tap the correct plug size. Also, real 4 bolt blocks (427 size) had the bores notched for valve unshrouding - you don't have to do this, but it's an easy way to check for a converted 2 bolt block. All big blocks used the EXACT same castings so externally they are the same except machine work. After you line bore the block, don't forget to use the Cloyes timing chain specifically for the line bored block or you'll have a lot of slop in the chain.
Good luck,
Mark

[Werner R.]

Re: there were no 67 427 chevelles except yenkos.

clem
the engine pad is gone due to decking. the block casting # is either 3094351 or 3904351. i am at the office and am not comletely sure, but it is one or the other. the prior owner said it is from a chevelle. i am completely confused here. can you tell me anything about the block from the casting #??
thanks werner
i thought i had a 427, not a 396. i have never had the heads off.

[Clem Z.]

Re: there were no 67 427 chevelles except yenkos.

the 351 block would be a 427 but it could be either a 2 bolt or 4 bolt mains because that block was used in 67 for engines from 385 to 435 HP. the oil cooler holes in the block sometimes will tell you if it is a 4 bolt but do not count on that.

[Werner R.]

Re: there were no 67 427 chevelles except yenkos.

thank you clem