GM# 3735337...327/350 Pistons?

[Tom R.]

After my stop at Indy a week ago or so, I completed my pilgrimage to Chicago visiting my mother and family. But while up there, I rummaged through the garage rafters and decided to fetch those pistons I had stowed up there since 1967. I believe they were from my 327/350 crate motor...dropped into my 67 Chevy II SS. I replaced the original pistons with, I believe TRW, higher compression pistons and rods. In 1967, base engine was a 327/275 and the 350 from 66 was not an option. It came with the base 327/275 and I need more HP for keeping up with traffic.

So is GM# 3795337 a 327/350 piston? Had to look at a couple because the embossed part number is not complete in those I looked at. Also has the GM letters.

PS: After seeing the other post, I took a third look and realized I had read my writing incorrectly...that third digit is a 9.

[David B.]

Re: GM# 3735337...327/350 Pistons?

3795337 is the casting number. I found a similar set in my stash last winter. I did not take the time to convert it to a part number but knowing how long they have been sitting there I would guess you have a set of 327 FI pistons originally listed as 62-67. Since mine still have the rods installed I will do a quick check of the rod journal diameter to confirm.

[Tom R.]

Re: GM# 3735337...327/350 Pistons?

3795337 is the casting number. I found a similar set in my stash last winter. I did not take the time to convert it to a part number but knowing how long they have been sitting there I would guess you have a set of 327 FI pistons originally listed as 62-67. Since mine still have the rods installed I will do a quick check of the rod journal diameter to confirm.

I noticed in the other C2 piston post, reference to this GM# as a FI piston. They must have also been used for the 327/350 hp hydraulic lifter equipped engines.

[Joe L.]

Re: GM# 3735337...327/350 Pistons?

I noticed in the other C2 piston post, reference to this GM# as a FI piston. They must have also been used for the 327/350 hp hydraulic lifter equipped engines.

Tom------


Yes, the same pistons were used for 62-65 SHP with mechanical lifters as were used for 65-68 with L-79.

[Tom R.]

Re: GM# 3735337...327/350 Pistons?

Most interesting. Are they much sought after today? I take it there are lots of options with new pistons as noted in the other C2 piston post.

[David B.]

Re: GM# 3735337...327/350 Pistons?

Checked diameter of original rods still on the 3795337 cast # on the pistons I have and the rod journal diameter was 2.1. This indicates to me this particular set was installed in a 327 1968-69 or possibly a 350 1967-88. Based on this would agree this particular casting # piston was used on a multitude of engines.

[Duke W.]

Re: GM# 3735337...327/350 Pistons?

No, those are early, small bearing rods. The nominal ID of the big end is near 2.1". The bearing thickness is near .050", so the ID with the bearing installed should be just over 2.000". The crank pin diameter range is 1.999-2.000".

The later big bearing rods that mate to nominal 2.1" diameter journals have a big end ID of about 2.2" without the bearing.

Duke

[Joe L.]

Re: GM# 3735337...327/350 Pistons?

No, those are early, small bearing rods. The nominal ID of the big end is near 2.1". The bearing thickness is near .050", so the ID with the bearing installed should be just over 2.000". The crank pin diameter range is 1.999-2.000".

The later big bearing rods that mate to nominal 2.1" diameter journals have a big end ID of about 2.2" without the bearing.

Duke

Duke-------


Yup. Here is a photo of an NOS GM #3864881, the best of the small journal rods. The big end without bearing measures 2.115"

DSCN3147.jpgDSCN3148.jpg

[David B.]

Re: GM# 3735337...327/350 Pistons?

I would have originally agreed with both of you and was a little surprised at journal dimension. I looked at first page small block 5-1 from Chevrolet's Power catalog book and noticed they listed a Rod Journal dia. of 2.0 for the 327 1962-67 small block. The 2.1 was listed as I described previously. I would not argue their printed word but accept as written. If this is crankshaft dimensions and has nothing to do with the actual small rod dimension we are all on the same page.

[Duke W.]

Re: GM# 3735337...327/350 Pistons?

Duke-------


The big end without bearing measures 2.115"

Joe - I looked through my 1963 Corvette Shop Manual and AMA specs and I could not find a precise big end ID dimension. Did I miss it? Where did you find the spec?

Duke

[Duke W.]

Re: GM# 3735337...327/350 Pistons?

I would have originally agreed with both of you and was a little surprised at journal dimension. I looked at first page small block 5-1 from Chevrolet's Power catalog book and noticed they listed a Rod Journal dia. of 2.0 for the 327 1962-67 small block. The 2.1 was listed as I described previously. I would not argue their printed word but accept as written. If this is crankshaft dimensions and has nothing to do with the actual small rod dimension we are all on the same page.

"Rod journal" refers to the diameter of the crankshaft journals that hold the rods, and "main journal" to the crankshaft journals that are held by the main bearings.

I don't know what version of the CPM you looked at, but my 4th edition has a table on page 2-1 that shows nominal crankshaft journal diameters for all OE small blocks.

Naturally, the rod big end ID needs to be greater than rod journal diameter in order to accomodate the thickness of the bearing inserts.

Duke

[Joe L.]

Re: GM# 3735337...327/350 Pistons?

I would have originally agreed with both of you and was a little surprised at journal dimension. I looked at first page small block 5-1 from Chevrolet's Power catalog book and noticed they listed a Rod Journal dia. of 2.0 for the 327 1962-67 small block. The 2.1 was listed as I described previously. I would not argue their printed word but accept as written. If this is crankshaft dimensions and has nothing to do with the actual small rod dimension we are all on the same page.

David-------


Those are crank journal sizes.

[Joe L.]

Re: GM# 3735337...327/350 Pistons?

Joe - I looked through my 1963 Corvette Shop Manual and AMA specs and I could not find a precise big end ID dimension. Did I miss it? Where did you find the spec?

Duke

Duke------


I didn't get it from any reference manual. I measured it from the NOS GM #3864881 pictured.

[Tom R.]

Re: GM# 3735337...327/350 Pistons?

This discussion thread seems to be in the weeds and while I can find my micrometer...can't find my calipers to measure the ID of the rod journals that would permit me to make a somewhat guess on rod design...pre or post 1966 correction to rod design.

So what rods would have come on an L79 with 3795337 pistons?

[Joe L.]

Re: GM# 3735337...327/350 Pistons?

This discussion thread seems to be in the weeds and while I can find my micrometer...can't find my calipers to measure the ID of the rod journals that would permit me to make a somewhat guess on rod design...pre or post 1966 correction to rod design.

So what rods would have come on an L79 with 3795337 pistons?

Tom------


It all depends upon what model year the rods are from. There were several rods used over the 1963-68 period during which L-79's used the 3795337 pistons. All of the 1963-67 were small journal and the 1968 large journal.

In the photo I posted above, note the circumferential machined surface and the "bumps" adjacent to the rod bolt crown. These are characteristic of the GM #3864881 which came into use in late 1965 and is the only small journal rod worthy of re-use. Rods without the "bumps" are earlier rods of several different part numbers and not worth talking about.