Odd Fire 231 - 1977

Finally got the engines out and cleaning and decided to once and for all figure out what type of engine was really in the Jeep. I need to verify my thought processes on the odd / even fire. Here are the questions.

Even Fire
1. On an even fire motor will Cyl 1-4 be at full extend at the same time (1 on fire stroke & 4 on exhaust)?
1a. Two Cylinders always at top - 1-4, 2-5 and 3-6?

Odd Fire
1. On an odd fire motor will Cylinder 1 be at TDC 30 degrees before Cylinder 4 gets to top on exhaust?
1a. Two cylinders always 30 degrees from the other 1 leads 4 to top, 3 leads 6 and 5 leads 2 by 30 degrees.

Basics
1. Are the changes in the engines basically Crank and Cam and are they interchangeable (as long as you change both)?

If the above staements are true then I have an Odd fire motor that someone put an Even fire distributor. The more I get into this the less I am surprised by this. I also have to verify that they did not change the cam and put a Even fire one in. When I took my 225-V6 block apart the timing of the cam was one tooth off (retarded). Figure they had to do that to try and get the motor run .... it had an even fire distributor cap.

Oh well back to work.

 

If you have the engine apart it is real easy to tell if it is an odd fire engine. An odd fires crank shaft rod journals are one. In other words 1&2 are on the same journal. 3&4 are on the same journal. 5&6 are on the same journal. In the even fire engine Buick spilt the journals by a few degrees so that for example 1&2 have a small section of casting between them. They also because of the split journals required that that the rod centers be moved apart. But because the centers of the cylinders did not move the rods on the even fire are cranked to one side. if you look at them from the side they are not symmetrical
Remember the odd fire engine was created out of 90 degree engine technology. With 90 degree crank shaft throws 6 does not divide evenly. So that when they made it into an even fire engine the crank shaft journals had to be split. That is why modern V6 engines are 60 degree engines.
There is a book on V6 engine building called V6 performance by Pat Ganhal you can by it on amazon.com for about 13 bucks that tells you everything you would ever want to know about Buick V6 engines. It is one of my favorites.

 

I would say that if you know for sure that the motor is a 1977, I would guess the odd's being it is a odd fire. Late 1977 Buick switched from odd to even fire. 1978 on the motor is a even fire. There are alot of site's out there that you should be able to figure out odd/even off of the block casting number.