Looking for original big block specifications/dimensions for '67

[Anthony S.]

Looking for known data or seeking good references for this data?
Looking for: cylinder bore diamter size, piston type/size, for the 435 hp block, as well as the the 390 / 400 hp versions????.
Any pictures of original pistons for the big block '67s would also be useful....
Thanks Tony

[Mike T.]

Re: Looking for original big block specifications/dimensions for '67

Anthony - Would the detailed info you're searching for be found in the 67 Service Manual? Back in the early '80s I ran across a '67 435 horse 'JA' shortblock but never did take pics, unfortunately. I sorta detuned it for my '69 Bigblock roadster and used the replacement Speed Pro 2300(going off memory only) forged pistons with the smaller dome which, with the factory thin gasket, would have yielded somewhere in the low 10 to 1 compression ratio found in the hydraulic cammed engines. Care to fill us in on the project you're working on?

[Joe L.]

Re: Looking for original big block specifications/dimensions for '67

Looking for known data or seeking good references for this data?
Looking for: cylinder bore diamter size, piston type/size, for the 435 hp block, as well as the the 390 / 400 hp versions????.
Any pictures of original pistons for the big block '67s would also be useful....
Thanks Tony

Tony------


Cylinder bore size for all 427 and 454 was the same-----4.2495 to 4.2525.

L-71 pistons were impact extruded aluminum alloy (forged). Pistons were domed. Piston-to-cylinder wall clearance was 0.0040" to 0.0050". Piston pins were interference fit in rods.

L-36/L-68 pistons were conventional cast aluminum alloy. Pistons were domed (but less dome height than above). Piston-to-cylinder wall clearance was 0.0024" to 0.0034". Piston pins were interference fit in rods. Piston pins were very slightly offset to thrust side making pistons specific to right or left cylinder bank.

[Richard M.]

Re: Looking for original big block specifications/dimensions for '67

Be careful with the CSM's as they contain errors. I got burned a few years ago on a '60 engine rebuild when reading the specs from the ST-12 CSM. The AMA Specs are the ONLY references I use. Duke Williams put me/us on to them years ago, and I've downloaded most of them for future reference.

Every year Corvette AMA Spec can be found at the GM Heritage Center website. Go to ....Archive.....Vehicle Information Kits.....etc

The 1967 AMA spec pdf is here.....

https://gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Corvette/1967-Chevrolet-Corvette.pdf

The engine data you're looking for starts on Page 28 of the PDF. Probably more info than you need.

Rich

[Joe L.]

Re: Looking for original big block specifications/dimensions for '67

Be careful with the CSM's as they contain errors. I got burned a few years ago on a '60 engine rebuild when reading the specs from the ST-12 CSM. The AMA Specs are the ONLY references I use. Duke Williams put me/us on to them years ago, and I've downloaded most of them for future reference.

Every year Corvette AMA Spec can be found at the GM Heritage Center website. Go to ....Archive.....Vehicle Information Kits.....etc

The 1967 AMA spec pdf is here.....

https://gmheritagecenter.com/docs/gm-heritage-archive/vehicle-information-kits/Corvette/1967-Chevrolet-Corvette.pdf

The engine data you're looking for starts on Page 28 of the PDF. Probably more info than you need.

Rich

Rich-------


There are errors in the AMA specs, too. In fact, I've found more errors there than in the factory service manuals.

[Richard M.]

Re: Looking for original big block specifications/dimensions for '67

Rich-------


There are errors in the AMA specs, too. In fact, I've found more errors there than in the factory service manuals.

I guess there's always a possibility of that when things get translated. That ST-12 got me confused once regarding piston specs and the AMA spec had it right. It makes one a little gun-shy researching sometimes.

Rich

[Duke W.]

Re: Looking for original big block specifications/dimensions for '67

The AMA specs were essentially an engineering document and got updated through the year if specs changed and was also updated to correct errors, although some probably still remain in some years.

The service manuals were written and published and that was it - no revisons, so errors never got corrected and are in the manuals that are sold, today, so it's always a good to check the AMA specs if there is any doubt, and there is information/specs in the AMA specs document that is not in any service publications.

Duke

[Domenic T.]

Re: Looking for original big block specifications/dimensions for '67

Joe,
Regarding the offset piston pins, you made me think. The notch was to be forward, so that would tell me that it would be possible (with notches forward), to get the offset on the wrong side of the rod when installing the piston to rods. Keeping the odd left bank rods and even right bank numbers in place, and piston notches forward then i would think that the pistons ( notch forward) could be installed with offset backwards? If so then wouldn't part #s be different for right & left bank pistons? Now I've got to go to the shop and open piston set boxes and check!

Dom

[Joe L.]

Re: Looking for original big block specifications/dimensions for '67

Joe,
Regarding the offset piston pins, you made me think. The notch was to be forward, so that would tell me that it would be possible (with notches forward), to get the offset on the wrong side of the rod when installing the piston to rods. Keeping the odd left bank rods and even right bank numbers in place, and piston notches forward then i would think that the pistons ( notch forward) could be installed with offset backwards? If so then wouldn't part #s be different for right & left bank pistons? Now I've got to go to the shop and open piston set boxes and check!

Dom

Dom------


The part numbers WERE DIFFERENT for the left and right bank pistons. These were original GM pistons, PRODUCTION and SERVICE. However, the aftermarket generally dispensed with the off-set piston pins and made one part number fit all eight.

[Duke W.]

Re: Looking for original big block specifications/dimensions for '67

The reason base small block pistons have four valve notches is so one piston can be used on both sides. IIRC the offset is .060", but aftermarket typically don't have offset. The original forged SHP/FI pistons also have no offset.

The purpose of the offset was supposedly to reduce "piston slap" noise. Piston offset was common back then, but I don't think its used on most modern engines.

Duke

[Domenic T.]

Re: Looking for original big block specifications/dimensions for '67

Joe,
Thanks for the part # answer. Makes me wonder now, when I ordered 8 factory pistons and installed them on the rods, did I get them on the wrong sides? I never read about left and right side offsets when installing pistons. Not to say that the reading isn't there but I would usually review the page when I first started doing the machine work.
I have seen the offset purposely reversed when modifying engines.
If the after market had the offset with the same part # then the pistons would have to be measured for the left & right banks, right? If I remember the numbers are inside and under the top?

Dom

[Joe L.]

Re: Looking for original big block specifications/dimensions for '67

Joe,
Thanks for the part # answer. Makes me wonder now, when I ordered 8 factory pistons and installed them on the rods, did I get them on the wrong sides? I never read about left and right side offsets when installing pistons. Not to say that the reading isn't there but I would usually review the page when I first started doing the machine work.
I have seen the offset purposely reversed when modifying engines.
If the after market had the offset with the same part # then the pistons would have to be measured for the left & right banks, right? If I remember the numbers are inside and under the top?

Dom

Dom------


I don't think the aftermarket ever offered pistons with an off-set, at least for the L-36 applications. It's possible they did, but, if so, I'm unaware of it.

[Domenic T.]

Re: Looking for original big block specifications/dimensions for '67

Joe,
I'm going to check my stock of factory SB pistons and see what I can learn. If my mind serves me right I think TRW made most pistons back then.
One tid bit that I can share is that all the factory pistons for a certain displacement weighed the same. I would check each rod & pistons weight to match the factory crank balance. The flat top, domed & truck rods & pistons were the same weight. Now every group of 8 is different and a balance is necessary. It makes production sence to have all cranks balanced the same and all rods, pins & pistons the same weight rather than doing each engine separately. This may bring a dispute but I proved it in the parts department. A local speed shop thought I was crazy until they put them on a scale.

Dom

[Joe L.]

Re: Looking for original big block specifications/dimensions for '67

Joe,
I'm going to check my stock of factory SB pistons and see what I can learn. If my mind serves me right I think TRW made most pistons back then.
One tid bit that I can share is that all the factory pistons for a certain displacement weighed the same. I would check each rod & pistons weight to match the factory crank balance. The flat top, domed & truck rods & pistons were the same weight. Now every group of 8 is different and a balance is necessary. It makes production sence to have all cranks balanced the same and all rods, pins & pistons the same weight rather than doing each engine separately. This may bring a dispute but I proved it in the parts department. A local speed shop thought I was crazy until they put them on a scale.

Dom

Dom-----


TRW made the piston FORGINGS for engines with forged pistons. These were, by far, the exception for both small block and big block engines. As far as I know, the pistons were machined in-house at the engine plants. Cast pistons which were used on the vast majority of engines were, I believe, cast at the GM foundry in Bedford, IN and machined at the engine plants.

The only pistons I know of that used different part numbers for the left and right cylinder banks were those for 1966-69 L-36/L-68 and 1970 LS-5.

The engine plants machined the pistons to fit each individual cylinder bore and delivered them on conveyor to the engine assembly line in sets with each piston destined for a particular bore.

[Domenic T.]

Re: Looking for original big block specifications/dimensions for '67

Joe,
I remember the #s stamped on the block at the pan gasket surface for each cylinder. A number 12 meant .0012 over bore so a piston .0012 would be fit to that cylinder. A number 6 meant .0006.

DOM