1955 331 Engine Over-boring???

[WC Woodman #355]

I have this 331 engine and it is already bored .060 over.  Is it possible to bore it more?  If so, how much, and where would I get the pistons?  Thanks.

Bill

[Dave Shepherd]

Most engines are at there limit at .060 plus Egge only has them in .060 over. The 365 has a .1875 larger bore.

[SixDucks]

The best way to determine how far a block can be over bored is to have the block sonic checked.
This process involves using sound waves to determine the thickness of the parent metal. The cylinder bores are checked at the 3,6,9, and 12 o'clock positions within the bore, beginning at the top and ending at the bottom. Most machine shops will have this equipment.
Should you not be able to find an off the shelf piston set, a custom set of pistons can be ordered from several manufacturers. Although a set of these pistons can be somewhat  expensive it allows for a superior piston that is designed to meet the customers needs be it a race engine or a daily driver.
I have used pistons from Arias, Ross, Venolia, and CP. I have always been extremely pleased with the quality from any of these manufacturers.
Hope this helps.
-Terry

[Dan LeBlanc]

Since a 390 is essentially a 331 bored out .25", if there's enough metal there, theoretically you could bore out to the same bore as a 390 engine (or 365) and use pistons from either if those engines with the matching bore.

[Dave Shepherd]

Dan, not to be argumentative but the 390 block is a recast block. When  I worked for Cadillac starting in 61, we were still seeing late 50's cars in the service dept., one of our techs blew up his 56 engine, when checking with the field engineering staff, he was told .060 that was it and that was the piston size they offered also. Some engines maybe 1/8 which would have been a gamble. I do not believe you would ever get away with 1/4 in overbore with a 331.

[Jay Friedman]

I agree with those posters who said .060 is the maximum overbore.  Yes, you could probably get pistons made, by Egge for example, that are larger, but unless a machine shop could certify that there is enough metal, you would be taking a chance.  I suggest you get another block as there are lots of 331 (365 in '56) engines around.  Try Joe Cutler 49caddymanemail addresses not permitted

[SixDucks]

 
The only way to be certain is to have the block sonic checked. It should also be noted that a thickness of .125 is usually the minimum thickness required on the major thrust side of the bore. In some cases it may be possible to offset bore a block to aid in maintaining that thickness.
I have every engine block I intend to rebuild checked. I do this because on more than one occasion I had blocks that usually can be bored .125 over but when checked revealed that a .030 over was all that was safe.

-Terry

[arton4wheels]

Dan, not to be argumentative but the 390 block is a recast block. When  I worked for Cadillac starting in 61, we were still seeing late 50's cars in the service dept., one of our techs blew up his 56 engine, when checking with the field engineering staff, he was told .060 that was it and that was the piston size they offered also. Some engines maybe 1/8 which would have been a gamble. I do not believe you would ever get away with 1/4 in overbore with a 331.

What does "recast block" mean exactly Dave.  I am trying to decide my overbore right now.  It hasn't been sonic checked yet but I understand that these blocks can be bored to 4" to become a 365 essentially.  My 331 is a 54 block.

There is a guy on the HAMB that bored his 331 out to 4.030"?   I am being told I need to be concerned about it running hotter if I go to the 4" bore, yet I read the specs and the cooling capacity for the 365 was actually LESS than the 331.  That doesn't make sense to me UNLESS the 365 was a different casting than the 331.  I'm also reading on this thread that .060 is the maximum overbore for the 331.  I just wanted to go with the 4" bore and use 365 pistons.  All this isn't making sense to me

[Dave Shepherd]

That is a .180 over, or 3/16.  The casting numbers are different, but may not equate to maximum bore size limits. That much overbore , I believe is risky.

[savemy67]

Hello Bill,

As Dave S. implies, a good way to determine a safe over-bore is to see what oversize pistons were available from Cadillac for the different engines.  You could also check a master parts catalog to see if the bare block part numbers are different.  As Dave suggests, this could mean a difference in the block.

You may want to consider that a used block has had a half century of corrosion in the water jacket.  Some amount of metal on the outside of the cylinders has been lost as rust.  You can bore to a greater oversize, but I think you increase the risk of potential problems.

Hello V8shadow,

A thinner cylinder wall will not get any hotter than a thicker wall.  Generally speaking, combustion temperature would be the same regardless of cylinder wall thickness.  What is different is the rate at which heat will be carried away by the coolant.  A thinner wall will transfer heat more quickly.  When  one considers the alternating temperature between the relatively hot exhaust stroke and the relatively cool intake stroke, there is a rapid akternating cycle of hot and cold in the cylinder wall.

The heating/cooling burden is on the cooling system.  I am not sure, but there may be differences in the coolant flow, water pump, thermostat, pipe diameter, and radiator, in addition to cooling system capacity that affect how efficiently a cooling system works one year to the next.

Respectfully submitted,
Christopher Winter

[V63]

I have a 1955 331 that needs a new home. It has low miles on it,  but the car was a series 62 sedan and I'm parted it out.

Engine is out and  I removed the heads to inspect. I would just 'run' with it, new gaskets, pumps ect.

$800 its in Arkansas, images available too.

[SixDucks]

Hello all,

The best way to determine how far you can bore any engine is with a sonic check.

@ V8 shadow....
If you find that your block can be bored to 4.00 you may want to consider using 390 Cadillac pistons over the 365. You would need to get the crank and rods for the 390 also. By utilizing these components you will have 390 rotating assembly inside a 331 block.

@ V63....
The 1955 Cadillac engine is a different casting than the 1954 engine. The 1954 Cadillac engine has the bell housing cast as part of the block and the 1955 does not and the transmissions will not be interchangeable between the two.
Hope this helps.

Terry

[55 ledsled]

I put a 54 331 into my 55 with ease. You can use the same transmissions for both but will need the sections of the bellhousing if mounting to a 54 engine because the top of the bell housing is part of the engine on the 54. Otherwise everything else is the exact same. You may have to plug one side of the water pump return because it is not used, but other than that it is simple! The only downer of the 54 engine is that you can't get an adapter plate if you wanted to put a different newer tranny on it. You're stuck with the hydromatic which isn't a bad 4 speed auto tranny.

[V63]

I have a 1955 engine available...long block or short block. The engine turns with nary a ridge. The engine was just fine miles were 60k ...but I parted out the car when a HUGE tree branch fell on the roof. It was a 1955 series 62 sedan with factory AC . Most parts available. Engine is in Arkansas.

[55 ledsled]

Yup, I put a 54 on my 55 transmission and it lines up perfectly. Like he said, you will need to put a brass plug on the drivers side water pump. One thing I am having issues with though is the kick down bar length. I am wondering if that is a different because I may have to add some threads to my shift bar to tighten it up some. Other then that you should be good to go.