225 to 231

Will a 1977 231 odd fire short block replace my 1969 225 short block. I will be swapping over all the 225 heads, intake etc... Just asking the experts!

 

Yay! I can help on this thread!!! I have a 231 block in my '70 CJ5. While the block is certainly a 231, nearly every piece on it belongs to the original 225 that came in the CJ. I know (according to the paint color and other guessing) that the water pump, timing cover, intake manifold, and flywheel came from the 225. I don't want to say any more than that in fear of saying something that isn't entirely correct. I do know it works though, mine is a hybrid and it is a little beast of an engine especially with that oversized flywheel.

 

I read the tech section and I didn't specifically see anything about the short block interchange. I guess I could infer that it would work from the parts interchange, but I wanted to be sure. I have an opportunity to get a short block 231 OF to replace my ailing 225. Ghost's post seems to confirm it, since he's using it. I'm going to try getting a little more info before I do anything.

 

I am running a 1979 231 even fire engine from a Chevy Monza. I had the 225V6 flywheel balance at a shop. I also used the oil filter mount from the Dauntless so that the oil filter would fit right with the lower radiator hose. Other than that it was a direct bolt in.

 

I have a 231 OF short block on the way! I will keep track of things and report back!

 

I just got finished with swapping a 68-69 225 with a 74-75 231. I used the intake, distributor, fuel pump, headers, timing cover (with chain and gears), all gaskets, and motor mounts. I think parts interchange depends a lot on the year of the engine. Hope it helps.

 

77 and older "should" have all the same water passages. 79 and up is a different ball game.

Need a 231 EF shortblock cheeeeeep?

 

This is my first report back. I received the short block. It's an early 1977. There are differences. The easy one to overcome, dipstick, its down low on block, not cast in upper block. There are other minor things but not show stoppers. Now for the more difficult issue, the heads, the oil to the rockers is fed through the block to head and up the rocker tower to the rocker shaft. The 231 block does not have that oil passage to the head. That means I need heads from a 231 with steel pressed rocker, and oil fed up the push rod. The 225v heads fit but without the oil passage it will not work ( if someone has a solution please chime in)!. Soon I 'll get some pictures.

 

OK,
I think I have everything to mix and match all of my Buick V6 parts into one running 231. It seems GM made some sort of change to the 231 OF every year from when they got it back from Kaiser until they made it a even fire. Anyway, the first question I have is the front cover on the 225 only has two bolts on either side of the water pump passages, the 231 has three. I was thinking all I have to do is screw allen set screws with thread sealant into the holes and plug them off, and use the 225 front cover. What do you think?

 

The later 225's do have the bolts like you mentioned on the 231, my factory (71) 225 has those bolts. I personally would find a 225 cover that fits right.

 

That's the way I am leaning, getting a timing cover with three bolts. I was kind of looking at a lower dollar direction, the timing cover from my donor engine has deep gouges in the oil pump so I have to get a new one.
Rockauto seems reasonable http://www.rockauto.com/catalog/x,carcode,1309429,parttype,5737

 

The water passages in the heads/block are different between even and odd fire too.

 

Bump for an update. I'm planning on using an 85 231 EF. I was wondering if I can just swap the intake manifold, exhaust manifolds and valve covers from the the 225?

 

I have put later intakes on early heads, but the 225 intake won't cover the later heads (79and up???) openings. Might have to play around with different years gaskets.

 

The valve covers will not work. Top of the head is slightly different from the 225. I think the exhaust manifolds will work. I used the my headers from my 225 on my 231.

 

I'm not sure the headers will work either. I believe the 231 EF had what Pat Ganahl refers to as a high port head, meaning the exhaust ports are cast higher up on the head versus the low port odd fire heads. Pat Ganahl's book really is invaluable for anyone playing the mix and match game with these engines.