[66coupe]

I am working on a sand rail with a friend. The problem is that it wants to backfire at idle real loud just on the right side. The engine is a 78 231 V6 w/HEI. owner claims he did a compression check. I think it is a valve issue. What is your take on this problem.

[timothale]

some of the GM v 6's have odd crank and cam, fire not 120* apart...The spark plug wires and distributor have to be in the right position per the shop manual or you can have 3 cylinders right on and 3 mistimed.

[66coupe]

All my shop manuals don't even show HEI and this engine has #1 on the right side unlike anything I ever seen and Distributor in the front. Do you have a pic?
Thanks for your response.

[timothale]

I tried an on line search and didn't find anything. I have a T bucket project, donor was a V6 Vega that I had repaired a couple of times and was still owed for some of the work. after the 3rd crash the kid had it towed to my place and handed me the title. He only owed me $ 300 but had recently spent $ 2k on the engine-5 speed. bored, hotter cam, holly 4 bbl aluminum manifold. headers. When they first put it together, the kid looked at the rotor and stuck in the plug wires. It ran poorly. He took it to a shop and the mechanic Knew about correct dist position and wires, a simple fix. We arae still up north, won't go south this year until after christmas. I have a shelf in the south shop with about 6 ft of shop manuals. there should be one for that engine. I have gone to bigger public libraries that have an automotive reference section and coppied the pages I needed. The V6 engines were factory installed in Jeeps and a popular swap to early ones You might get some info from one of the jeep forums

[cobalt327]

Originally Posted by 66coupe

I am working on a sand rail with a friend. The problem is that it wants to backfire at idle real loud just on the right side. The engine is a 78 231 V6 w/HEI. owner claims he did a compression check. I think it is a valve issue. What is your take on this problem.

Be sure the firing order is correct at the cap and at the plugs. The firing order was different between odd and even firing engines, IIRC (odd fire is 1-6-5-4-3-2, the even fire is 1-4-5-6-3-2). Be sure #1 is really on the side you think it's on. I'm not a Buick V6 expert, but I had thought it was on the driver side. Both positions (driver and passenger side) are shown on various websites.

Often if the problem is distributor (not firing order) related it's due to a "odd" or "even" fire distributor mismatch.

The first 231V6 Buick engine was an "odd fire" (firing at 90º-150º-90º-etc.). Mid-'77- up engines- like yours- were changed to an "even fire" (firing every 120º) configuration by splitting the rod journals to allow those rods to be offset from one another. This required a different crankshaft, camshaft, distributor and flexplate/flywheel. So be sure the engine matches the distributor, whether it's odd or even fire. I'd double check the block casting number and date code to be sure it's the year and type you think it is. .

HERE is an article explaining how to convert an even fire distributor to odd fire. Obviously the opposite can be done by using the right pick up coil assembly.

Other things to check:

Also see that there is no crossfiring between the plug wires going on. Check the distributor cap for any signs of carbon tracking or cracks.

If you have a net lash valve train and the block and/or heads were milled an/or the head gasket thickness is different than stock, this can cause problems w/the valves being too tight. Or if the valve train is adjustable, if they're too tight they can be the cause of the backfiring.

[cobalt327]

The firing order was different between odd and even firing engines, IIRC (odd fire is 1-6-5-4-3-2, the even fire is 1-4-5-6-3-2).

Be sure to check the firing order info above. I have reason to believe this is incorrect and should read:

(even fire is 1-6-5-4-3-2, the odd fire is 1-4-5-6-3-2). Again- be sure to verify what you have and to use the applicable firing order.

As for you thinking the passender front cylinder being #1, there are various diagrams that may be confusing, like:



The small diagram to the front left of the bigger diagram looks something like a firing order diagram, but it is how the coil packs are configured- not how the cylinders are located on the engine itself.

[cobalt327]

What I'm seeing is ALL the Buick V6 321/3.8L/3800 engines share the same 1-6-5-4-3-2 firing order, regardless if odd or even. It is amazing the amount of BS that is out there.

[wade braaten]

The Buick 231 odd-fire has a firing order 1-6-5-4-3-2. As the crankshaft is rotated through the 720° required for all cylinders to fire, the following events occur on 30° boundaries:
Angle 0° 90° 180° 270° 360° 450° 540° 630°
Odd firing 1 6 5 4 3 2
Even firing 1 4 5 6 3 2

More modern 90° V6 engines avoid this problem by using split crank pins, with adjacent crank pins offset by 15° in opposite directions to achieve an even 120° ignition pattern. Such a 'split' crank pin is weaker than a straight one, but modern metallurgical techniques can produce a crankshaft that is adequately strong.

In 1977, Buick introduced the new "split-pin crankshaft" in the 231. Using a crank pin that is 'split' and offset by 30° of rotation resulted in smooth, even firing every 120°.

[cobalt327]

Originally Posted by wade braaten

odd ver even firing order on buick 231

With due respect, posting an excerpt from a Wikipedia article- errors and all- is not really too helpful here.