231 Buick Odd or Even Firing Engine?

[kermitj]

Have a 69 Commando Wagon, 231 & 400 automatic. But unsure if I have a Odd or Even engine. The casting #  1254083  GM  4  shows to be 75-87 from my web searching.  The sites I looked at say it is an Even fire engine. But it does have an Odd fire distributor. It runs, but is it right ?

Would /Could an Even Fire run with an Odd Fire HEI ?  

Did Buick use the same block to build Odd and Even fire engines when they transitioned from one to the other ?

Also: Is the HEI coil on the GM V6's all the same, or is the Buick reversed polarity ? saw this mentioned, but parts guys look at me funny and say they do not find a Buick specific coil.

[Moses Ludel]

kermitj...There were a number of carryover parts related to odd and even fire 231 V6 engines.  We recently went down a rabbit hole with crankshaft interchangeability between 225 and 231 odd-fire engines, and you will find that exchange of interest.  See my replies as this topic unfolded:

Regarding your specific concern around the block, this block number does show up as specifically 1977 odd- and even-firing applications plus 1978 even-fire.  (The odd-fire 231 V6s were built from 1975 to early '77;  late '77-up are even-fire.)  This certainly suggests that you could have an odd-fire 1977 231. 

The spark firing order for a 225 or 231 odd-fire or a 231 even-firing engine is the same (1-6-5-4-3-2), so this in itself is not the deal breaker.  The distinction is the distributor cap's contact pins for each cylinder.  The odd-fire contacts have 135/120 degree spacing while an even-fire distributor has a uniform 120-degree spacing between cylinder firing events.  Odd-fire or offset cap firing is required to account for the shared connecting rod pins on the crankshaft.  Rods are paired as:  1-2, 3-4, 5-6.

Your distributor cap is odd-fire (offset contacts) as you note.  An odd-fire distributor/cap would make your engine an odd-fire.  If you provide your Delco-Remy distributor housing number, I'll run down the specific application for this distributor.  My guess is early 1977 based on the block number and the odd-fire distributor type.  It would also fit 1975-76 odd-fire engines without your block number.  Your block is distinctly 1977-78.

I have a failsafe suggestion.  If you have access to an inexpensive bore scope, pull the oil drain plug, drain the oil and take a look at the crankshaft.  If each connecting rod has its own crank throw, you have an even-fire engine (late-'77 or '78 block).  If the rods are paired with two rods sharing a crankpin (3 rod throws on the crankshaft), you have an odd-fire crankshaft and engine, specifically early 1977 with the 1254083 block casting number.

Let us know what you find...

Moses 

[kermitj]

[kermitj]

HI

I just pulled in Iowa, got a 1800'er with bad transmission line. But will get into the crank ID soon as I am back.