Made a 231 into a 225 ??!!??!!??

The other day I made a comment in error, overstating the similarities between a 225 and a 231. I really did appreciate some of you catching me on that because it got be thinking. Wow, I really messed up! Here's what I did, please feel free to comment.

When I got my '67 CJ5 I was assured it had the original 225. The first thing I did for the rebuild was to tear down the engine and take the block and crank to a rebuilder. I didn't bother checking any specs and just told the rebuilder to bore it and grind the crank. The rebuilder called me and said the bore was too far out of tolerance and he would have to sleeve the engine. I told him to go ahead.

Neither he nor I realized I the engine was a 231 and not 225 and that was why the bore was out of tolerance for a 225. I got new 225 pistons and bearings, put it all together and it looks fine.

The stroke for both engines is the same and the pistons come right up to the top of the cylinders like they should. Can anyone think of a reason why this setup should not work?

Yes, I do deserve the "Bonehead" award.

 

Compression is gonna be affected, don't know by how much. Balance on the engine will be affected due to lighter pistons. As far as the pistons coming all the way to the top, that might or might not be correct.
Next time always check the pistons for a size marked on them they are stamped or marked if they are oversize. If you had seen a 225 torn apart you would have instantly known the difference between a 231 and a 225 when you seen the rockers, rods or pushrods.

Heres a piece of advice: (Please don't take this wrong) When in doubt or you really don't know, ask, the only stupid question is the one you didn't ask!
My father told me that years ago and it stuck!!!

 

I was thinking the same thing. That McRuff is a smart boy.

 

Well Mike, I agree, McRuff probably hit the nail on the head. The one thing I didn't consider was the weight of the pistons affecting the balance. I may have a 6 cylinder pogo stick!

 

would a good engine rebuilder not know the difference?

 

Bill,

I could blame the engine rebuilder for not checking the casting numbers, but then, I should have checked it also. The guy never saw an odd-fire before. The work he did do was very good.

I'll just have to chalk it up to experience. Read the motto in my signature.

 

i see so can you find out if it will run before putting it all the way back together

 

Bill,

It will be some time from now. I don't have a suitable stand for test running and I am still at the frame-off stage of the rebuild. In fact I just painted the frame with Rust-Bullet.

You can bet when I do start it, I'll have a remote starter switch with a long cord.

 

maybe it will lope like the 383mag i had in my roadrunner.

 

I think you will be ok. I am not fimiler with how the 225 or the 231 are ballance internal or external. my advice would be turn the motor over by hand to check internal clerance and the have external ballanced.
They are both odd fires? arnt they.

 

Sparky,

I went the other way. I told the rebuilder the block was from a 225 by mistake, it actually was a 231. He checked the bores and said they were too far out of spec for a 225 so he sleeved then down to the standard size for a 225. That's how I ended up making a 231 into a 225. All I can do now is put it in the Jeep and see what it does.

 

When I read the title to this thread I thought - aha ... sleeves! 8)

Couple of points - my Dick Datson Jeep engines book says you can use a std 231 piston in a 225, and that it's the same as a 50-over piston. At the time the book was printed, 231 parts were way cheaper than 225 parts, or so it says.

Also, pardon my ignorance, but why would the compression be any different from a stock 225? I'd think the combustion chamber could be the only difference: same bore, same stroke, same deck height.

 

A multitude of reasons, I put that there as a generic reason not knowing what he actually has. 225 heads are different from 231 heads, may have a different volume. Pistons can be sunk farther down the bore or raised in the bore. As for the psitons he shrunk the bore by .05" from orignal design. The pistons can also be a different shape (tops) between the 225 and 231 depending on the year, all factors that could effectivley change the compression. Without actually seeing what he has and measuring it, it would be nearly impossible to know so I listed it as possible change/problem. i do know that the modern .030" over pisrons I put in my 225 when I rebuilt it were 85 grams lighter per piston then the original factory units, and the dish in the top was cut shallower.