EarlyCJ5.com Technical Library

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Buick 225 and 231 Parts Interchange Guide*

Distributors

The most commonly swapped item I would guess. 231 Odd-Fire HEI distributors are a good replacement for the points system that was stock in the 225. Available at your local autoparts store get a distributor for a 1975 Buick Apollo with a 231 or 3.8L engine.

See these pages for good information on what's involved. Making GM HEI Run Right on a 225 V6 by Rich Motts and R. Bucholz's Even-Fire/Odd-Fire HEI Spotters Guide.

Other 231 HEIs can be made to work if they're even fire units with some effort. See Convert an Even Fire to an Odd Fire HEI by Bill Marsh

Brackets

Question for those who have done Buick V6 swaps: Do the pulleys and peripherial brackets (alternator, power steering pump) interchange between the 225 and 231? I have the opportunity to pick up a cheap 225 but it doesn't have the pulleys; can I just find a Buick in the junk yard for a donor?

Can't say for all applications and all years, but yes, sorta - the 231 has a longer shafted water pump so it sticks out farther, it also has a triple pulley on the crankshaft end - 231 has a different alternator mount bracket, plus lots of stuff the Jeep version of the 225 did not normally see, such as power steering and air conditioning - but, all in all, you can use the 231 stuff and get everything to work fine - note that the longer pump puts the fan closer to the radiator on a 231, so if you have to change pumps to get something to align or have a space for everything, check clearances

Exhaust manifolds

You can interchange exhaust manifolds for all years. The drivers side 231 exits directly to the rear though, whereas the 225 exits forward (it is simply another passenger side exhaust manifold) and the exhaust needs to wrap around the motor mount.

For this reason the 231 manifolds seem to be generally preferred because it frees up room for a Saginaw steering box and shaft.

Heads

The head design between the 225 OF and the 231 EF was changed, the ports do not line up on the intake manifold. The heads will swap with a little work to the coolant ports.

This is from the Forum: There is a book entitled "V6 Performance" that states the 231 heads/intake will bolt up to a 225 but you have to do some work to the water passages on the heads in order to make it work. You have to weld up the outer passages and then drill out to match the head gaskets/block. The heads do flow better.

Intake Manifolds

The intake manifolds only swap until '79 231s after that, the high port heads are introduced.

Flywheels/harmonic balancer

The flywheel and harmonic balancer of a 225 and Odd Fire 231 will interchange. A heavier 225 flywheel can be used on an Even Fire 231 if it is balanced with the crank.

*This guide is in no way complete, if you have more to add or a correction to make please E-mail me