Carl's new 427 build thread.

4SPEED427 · A Poncho Legend!

RE: Carl's new 427 build thread.

seventy2plus2 · Canadian Poncho Superstar!

A quick side note: I always thought that 1960's vintage 396's and 427's shared a common crankshaft. While the stroke and flywheel flanges are the same, the counterweights are slightly different.

4SPEED427 · A Poncho Legend!

Yes cranks on 396 and 427 are interesting. Except for the solid lifter engines they all use the same harmonic balancer.

There's three different crank numbers listed for 427s from 66 to 69 in the GM parts book. The 385 and 390 horse use the same crank all the way through, 335 horse I believe is cast and has a different number and the 425 horse has a unique crank. I've never bothered to investigate why the solid lifter crank is different because the 385 and 390 horse crank is already a forged piece. Maybe there's some different balancing because of the different pistons, I don't know.

4SPEED427 · A Poncho Legend!

So it looks like I will be using a 366 crank and getting it all balanced. (Ouch....) No other way to do it since I don't even know where to begin looking for an original 427 passenger car crank.

Can someone confirm that Alvin Colvin's book tells how to tell the big block cranks apart even though they have the "6223" casting number (which mine does)?

Just ordered the last few pieces needed from Rock Auto using the Canadian Poncho discount code. Hoping to start this project maybe next week.

Mike Ward MB · Addicted!

4SPEED427 wrote:
No double roller for me, I don't like the noise they make. Just plain old steel cam gear and regular style chain. Or are the new double rollers quieter? Years back you could hear a double roller chain long before the car pulled up to you.

My 454 has a double roller chain and I have never noticed that it makes too much noise. I thought gear drives were the noise makers.

68 Grande · Guru

4SPEED427 wrote:
So it looks like I will be using a 366 crank and getting it all balanced. (Ouch....) No other way to do it since I don't even know where to begin looking for an original 427 passenger car crank.

Can someone confirm that Alvin Colvin's book tells how to tell the big block cranks apart even though they have the "6223" casting number (which mine does)?

Just ordered the last few pieces needed from Rock Auto using the Canadian Poncho discount code. Hoping to start this project maybe next week.

Carl, from what I read online, the counter weights are different in the 366, 396 and 427 cranks. I found this quote from a 2006 thread on another site referencing Alvin Colvins books.

"I have heard that on the 366 crank the 3rd counterweight is 3/4" thick, on the 396 the 3rd counterweight is 7/16", and on the 427 the 3rd counterweight is 7/8" due to the difference in weight of the pistons & rods. A previous post has the 396 counterweight at 3/4". Can anyone verify the information regarding the with of the 3rd counterweight?

Thanks, I got the 7/16th's from an earlier Colvin books, now after looking at the changes for the 2nd edition I see the change on page 81 to 3/4" for the 3rd counterweight."

So, I am thinking the 2nd edition of Colvins book on page 81 contains this information? Jake

-- Edited by 68 Grande on Friday 15th of January 2021 08:42:16 AM

4SPEED427 · A Poncho Legend!

My one question about that is it still doesn't address the difference on the 427 truck vs. the 427 car crankshaft. I'm sure there must be a change because the truck piston with 4 rings has to weigh more than the car piston with 3 rings.

68 Grande · Guru

4SPEED427 wrote:
My one question about that is it still doesn't address the difference on the 427 truck vs. the 427 car crankshaft. I'm sure there must be a change because the truck piston with 4 rings has to weigh more than the car piston with 3 rings.

I haven't ran across a posting where the difference in counter weights and subsequent total weight of the cranks between truck and car cranks are specifically outlined. However, from the reading that I have done suggests the tall block cranks are heavier to accomodate the heavier piston with 4 rings, which is why you need to drill the 366 counter weight in balancing when you use a 3 ring 427 piston.

So, I agree with you that there "has" to be a difference somehwere in literature that describes the 6223 crank differences (and other tall block cranks) between car and tall block engines.

It would be nice to actually see those differences outlined somehwere in GM literature.

4SPEED427 · A Poncho Legend!

Exactly. I just haven't been able to find actual fact, it's all just "I did this and it worked". And I'm one of those guys, I know of a couple of cases where someone installed a 6223 crank in a different displacement engine, or a truck vs. a car engine and it was fine. I am SO torn on just installing this 366 crank without sending it for a balance just to see if it works!

ARCADIAN · Poncho Master!

Carl I have the 2nd printing of Colvin's book and no mention of the info you are looking for. Just a suggestion as you are using a 366 block why not look in the Large Truck GM Book you may find the info there.

4SPEED427 · A Poncho Legend!

Hi Chris. Which GM truck book are you referring to? The parts book?

ARCADIAN · Poncho Master!

No isn't there a service manual available?

4SPEED427 · A Poncho Legend!

Yes for sure but I don't know that there's any information like that in there. I'll have to look. Thanks.

seventy2plus2 · Canadian Poncho Superstar!

Are you taking the 366 crank out of that assembled 366 engine you have?

A guy here in Calgary can supply you with a 396 cast crank for $200, or $450 for a steel one.

-- Edited by seventy2plus2 on Friday 15th of January 2021 05:19:44 PM

4SPEED427 · A Poncho Legend!

No, I just can't bring myself to strip that engine. I have a pair of steel 366 cranks here to choose from. A friend closed down his auto/truck wrecking a few years ago, just fixes and resells write-offs now but he still has scads of medium duty truck parts stashed in old buses and semi trailers. I picked up 2 the other day and he told me to keep the best one, return the other. His price for a crank is not cheap but it's here and I don't have to buy sight unseen plus deal with freight which is a plus. And it seems no matter what I buy I'll have to balance it unless I can find an original 427 car crank (what are the odds......) I sure am temped to try it though without balancing it!

seventy2plus2 · Canadian Poncho Superstar!

Why the fear of having it balanced? Are you getting outrageous quotes?

4SPEED427 · A Poncho Legend!

I only called one shop so far, $450.

seventy2plus2 · Canadian Poncho Superstar!

I wouldn't even think about running an unbalanced engine.

4SPEED427 · A Poncho Legend!

I know guys who've done it with no issues but so far I've always used the matching components on big blocks I've rebuilt. I know guys who've used 366 cranks to build 427's but for some reason I'm nervous to try it without balancing.

I'm going to make more calls though to check pricing.

4SPEED427 · A Poncho Legend!

So today I had an opportunity to have a set of complete 366 piston/rings/rod assemblies here. They were here to have the pins pressed out so the rods can be salvaged for a big block build project (not mine). I wanted to do some weight observations on the components. Here are the results and also the weights of stock 427 car engine components.

366

Piston/rings/pin assembly 1065 grams

Piston/rings assembly 916 grams

Piston only 831 grams

Connecting rod only 835 grams

TOTAL WEIGHT OF THE PISTON ASSEMBLY WITH THE ROD IS EXACTLY 1900 GRAMS

427 CAR

Piston/rings/pin assembly 930 grams

Piston/rings assembly 776 grams

Piston only 711 grams

Connecting rod only 835 grams

TOTAL WEIGHT OF THE PISTON ASSEMBLY WITH THE ROD IS 1765 GRAMS

This is all just for curiosity but I've never learned the how's and why's of engine balancing and now I want to! Input welcome from anyone who has experience with it.

68 Grande · Guru

So, its 135 grams (1900-1765) per cylinder or 1080 grams for the whole assembly. At 540 grams / 1.19 lb, the whole 366 assembly would be 2.38 pounds heavier than the 427? Yes?

-- Edited by 68 Grande on Friday 22nd of January 2021 06:13:14 PM

seventy2plus2 · Canadian Poncho Superstar!

The piston, rings, pin & small end of rod is considered the reciprocating assembly.

The big end of the rod and the rod bearings are considered part of the rotating assembly.

The mass of the reciprocating assembly of each cylinder must match. Then the rotating assembly is done.

I saw a good video on balancing an engine on one of the TV shows likely 15 years ago, maybe on Dream Car Garage.

4SPEED427 · A Poncho Legend!

68 Grande wrote:
So, its 135 grams (1900-1765) per cylinder or 1080 grams for the whole assembly. At 540 grams / 1.19 lb, the whole 366 assembly would be 2.38 pounds heavier than the 427? Yes?

Yes, I would say that is the correct math.

cdnpont · Canadian Poncho Superstar!

I spent good money and had my Scat crank and rods balanced and matched at a shop in California. The pistons and pins came all matched weight. The only differences that could throw it off would be the rings and perhaps the rod bearings.

I don't know if it was money well spent, but the engine certainly feels smooth as it pulls up into the higher revs.

4SPEED427 · A Poncho Legend!

Suddenly tonight I had a crazy thought. I wonder if the pilot bushing hole in the 366 crank is the right size, because on a 366 the pilot bearing is in the flywheel, not the back of the crank. Sure enough, compared it with a small block crank and the hole size is wrong in the 366. It appears the hole in the 366 crank is 1.06" vs 1.09". 1.09" is the standard Chevy pilot bushing.

Looks like I will need to find a conversion bushing for one of the earlier engines where the crank was originally in front of an automatic. Those ones have the hole that measures 1.06"