L36 discoveries

[Douglas L.]

Took the oil pan off my 68 L36 today and found a couple of odd things. First off, to my surprise it has 4 bolt mains and secondly, to my even greater surprise, cast crank!

It definitely has been rebuilt(someone installed forged pistons and spent a lot more time on a balance job than GM would have) so the crank could easily have been replaced but the block has a appropriate casting date for the car and a pad stamp that looks good to me. I had heard that some L36/L68s had 4 bolt mains but thought they all had forged cranks.

Anyhow, I was somewhat surprised and thought I'd share the info.

[Joe L.]

Re: L36 discoveries

Took the oil pan off my 68 L36 today and found a couple of odd things. First off, to my surprise it has 4 bolt mains and secondly, to my even greater surprise, cast crank!

It definitely has been rebuilt(someone installed forged pistons and spent a lot more time on a balance job than GM would have) so the crank could easily have been replaced but the block has a appropriate casting date for the car and a pad stamp that looks good to me. I had heard that some L36/L68s had 4 bolt mains but thought they all had forged cranks.

Anyhow, I was somewhat surprised and thought I'd share the info.

Douglas-------


Some 68-69 L-36 or L-68 did have 4 bolt mains. However, 4 bolt mains could also have been added. This is quite easy as the same block casting was used for either 2 bolt or 4 bolt finished blocks. The tappings above the oil filter will usually tell the tale of whether the block was an original 4 bolt as folks rarely drill and tap the bosses when they install 4 bolt mains.

What is the casting number on the crankshaft?

[Douglas L.]

Re: L36 discoveries

Some 68-69 L-36 or L-68 did have 4 bolt mains. However, 4 bolt mains could also have been added. This is quite easy as the same block casting was used for either 2 bolt or 4 bolt finished blocks. The tappings above the oil filter will usually tell the tale of whether the block was an original 4 bolt as folks rarely drill and tap the bosses when they install 4 bolt mains.

What is the casting number on the crankshaft?

Joe,

It does have the drilled and tapped oil cooler bosses. I remember reading in the GM high performance book that all 4 bolt blocks
had drilled and tapped bosses but always wondered if it was true.

The crank # is 3804815NF. I heard that Chevy started putting cast cranks in the more pedestrian big blocks in 68 and remember from my Oldsmobile days that 68 was the first year for cast cranks for pretty much all engines for them(even W-30) but the consensus seems to be the L36 and L68 retained their steel cranks up until 69.

[Joe L.]

Re: L36 discoveries

Joe,

It does have the drilled and tapped oil cooler bosses. I remember reading in the GM high performance book that all 4 bolt blocks
had drilled and tapped bosses but always wondered if it was true.

The crank # is 3804815NF. I heard that Chevy started putting cast cranks in the more pedestrian big blocks in 68 and remember from my Oldsmobile days that 68 was the first year for cast cranks for pretty much all engines for them(even W-30) but the consensus seems to be the L36 and L68 retained their steel cranks up until 69.

Douglas------

GM casting #3804815 (or, 816) is a cast 3.76" stroke crankshaft. The "NF" (nodular ferris) absolutely confirms that. I believe it's probably original to the engine. I could never figure out where this casting number comes from, though. This number implies a first use for 1962. Of course, no Mark IV big blocks were being produced anywhere near that early.

I seem to vaguely recollect that L-36/L-68 with cast cranks are usually found with 4 bolt mains.

Believe it or not, back in the late 60's big block cast SERVICE cranks actually cost slightly more than the SERVICE forged cranks, including the L-88 crank.

[Larry E.]

Re: L36 discoveries

Douglas------

GM casting #3804815 (or, 816) is a cast 3.76" stroke crankshaft. The "NF" (nodular ferris) absolutely confirms that. I believe it's probably original to the engine. I could never figure out where this casting number comes from, though. This number implies a first use for 1962. Of course, no Mark IV big blocks were being produced anywhere near that early.

Joe: NASCAR mystery engine was about that time--1963 Daytona Pole by Jr. Johnson. IIRC--Larry

[Larry E.]

Re: L36 discoveries

1963-1963-chevrolet-impal-10_800x0w.jpgFWIW: Here is a picture of the "mystery" engine.

[Joe L.]

Re: L36 discoveries

Joe: NASCAR mystery engine was about that time--1963 Daytona Pole by Jr. Johnson. IIRC--Larry

Larry----

The "mystery engine" was a Mark II big block. I believe it used a crankshaft more like the Mark I ( 348 409).

[Duke W.]

Re: L36 discoveries

Nodular cast iron is a very strong, tough, and durable material - almost as good as typical medium carbon forging steels and more than adequate for a road engine that will only see 6000 revs occasionally.

Nodular cast iron is a quantum leap above gray cast iron.

I think Chevrolet began producing nodular iron cranshafts beginning in 1967 or '68. The '67 350 may have been the first and other low to medium performance engines followed. Pontiac and Olds may have started using nodular cast iron a few years prior.

Duke

[Joe L.]

Re: L36 discoveries

Nodular cast iron is a very strong, tough, and durable material - almost as good as typical medium carbon forging steels and more than adequate for a road engine that will only see 6000 revs occasionally.

Nodular cast iron is a quantum leap above gray cast iron.

I think Chevrolet began producing nodular iron cranshafts beginning in 1967 or '68. The '67 350 may have been the first and other low to medium performance engines followed. Pontiac and Olds may have started using nodular cast iron a few years prior.

Duke

Duke------


I agree. Cast iron crankshafts are often maligned but they are more than adequate for virtually all street applications. Between 1970 and 1997, forged steel crankshafts were used only for LT-1, L-82, and LS-6 engine applications.

[Bill L.]

Re: L36 discoveries

Duke------


I agree. Cast iron crankshafts are often maligned but they are more than adequate for virtually all street applications. Between 1970 and 1997, forged steel crankshafts were used only for LT-1, L-82, and LS-6 engine applications.

Pretty sure the 69/70 L46 had the forged steel crank as well.

Bill

[Joe L.]

Re: L36 discoveries

Pretty sure the 69/70 L46 had the forged steel crank as well.

Bill

Bill------


Yes, it did. I should have said between 1971 and 1997.

Actually, the L-82 was an L-46 with 9:1 compression. Strangely, when the LT-1 dropped from 11:1 to 9:1, the LT-1 RPO remained the same. However, the same thing didn't happen with the L-46. Most likely, this was because 2 years elapsed between the death of the L-46 and the birth of the L-82.

[Duke W.]

Re: L36 discoveries

Duke------


I agree. Cast iron crankshafts are often maligned but they are more than adequate for virtually all street applications. Between 1970 and 1997, forged steel crankshafts were used only for LT-1, L-82, and LS-6 engine applications.

I think when most guys hear "cast crank" they think of gray iron even though most cast cranks have been nodular iron for nearly 50 years. I'm surprised that GM continued to use a forged, Tufftrided crank in the low compression single catalyist L-82. IIRC the tach redline was less than 6000 and they didn't make useable power much beyond 5500.

But the tooling was probably fully amortized, so no investment was required to continue with the forged crank for that one low volume application, and I expect they sold relatively well over the counter to guys who were building souped-up 350s.

Duke