[steve25]

I just for the second time watched the video titled “ 455 casting and machining in production of 1970” and I was very impressed by a fact that I missed the first time watching it,
Pontiac during production did a ruff balance of the crank and then once the short block was assembled they spun it up to do the final balance.
This was done to a tolerance of 1/2” ounce which is to me amazing since the average balance job done by a machine shop is 3” once ,

Does anyone know what the other GM divisions did and used in there balancing jobs?

[61-63]

Great video

https://www.youtube.com/watch?v=9LuXf6gJ-jg

[PunchT37]

I have built a `70 Buick 455, a `71 Ford Cleveland, `71 Mopar 340, `78 Mopar 440, and a few sbc`s. Pontiac factory machining and tolerances are pretty damned good for factory "crap".

[cdnroundport]

Look at the Pontiac employee at 9:56

Sure looks like the guy from Article in 1981 Car Exchange

[TedRamAirII]

Originally Posted by cdnroundport

Look at the Pontiac employee at 9:56

Sure looks like the guy from Article in 1981 Car Exchange

I think you are right!

[Mike Davis]

Guy probably took pride in what he did everyday.
Kids now have no work ethic.

[hurryinhoosier62]

Too bad that precision didn’t carry over into their grinding of crankshafts. The “best” one I have seen was only .005 under stroke. The worst was .020 under stroke.

[Dragncar]

The 1970 455 with 71 HO heads that has a bazillion runs on it has the factory line bore and deck job. Mains studs too, never align honed. ( 4 bolt)

[steve25]

Your judging that difference in stroke ground into the Crank without having the original Rods and Pistons and there tolerance's that where related to it all during production I bet, so you can't judge what the actual final deck height was on any given cylinder just by looking at the Crank!

[hurryinhoosier62]

Originally Posted by steve25

Your judging that difference in stroke ground into the Crank without having the original Rods and Pistons and there tolerance's that where related to it all during production I bet, so you can't judge what the actual final deck height was on any given cylinder just by looking at the Crank!

Steve, I have ground thousands of cranks. Some of the worst were GM cranks in regards to being out of stroke. All OEs have a machining tolerance to allow for variations in piston deck height, rod center-to-center length and variations in stroke, but .020 or more( I’ve seen virgin BBC OE forged cranks be as much as .030 out of stroke) is beyond any reasonable tolerance considering most machining tolerance are +/- .001-.003. By comparison, 6.9/7.3 IDI cranks averaged a .003-.005 over stroke verses an under stroke. 6B Cummins were even closer to their advertised strokes. Even 4.6 Romeo/Windsor cranks were far closer to their advertised strokes then GM cranks.

[Formulajones]

I'm with Hoosier. Don't know why anyone would be googly eye'd over any factory machined mass produced engine. I've never had a virgin engine rebuilt in any brand that had nice tolerances. Cranks with shorter than advertised strokes, uneven deck heights all over the place, and don't even get others here started on Pontiac cam tunnels.

[mgarblik]

Originally Posted by Formulajones

I'm with Hoosier. Don't know why anyone would be googly eye'd over any factory machined mass produced engine. I've never had a virgin engine rebuilt in any brand that had nice tolerances. Cranks with shorter than advertised strokes, uneven deck heights all over the place, and don't even get others here started on Pontiac cam tunnels.

I tend to disagree with this when compared to the competition in the time frame we are talking about. Late 1950's to 1980. IMO, Pontiac block and head machining was as good as the other GM divisions, better than Chevrolet, and better than Chrysler. Less personal experience with Ford, but the cam tunnels on Ford FE blocks were the worst I have ever dealt with. Never had a cam install properly without massaging the housing bores or bearings. Usually #4. Pontiac's had fully machined combustion chambers that were pretty nice. Blocks fairly square, decent finishes. Want to see a complete pile of junk in a GM block? Take a look at a SBC made in Mexico. Horrible surface finishes, blocks off square .015-.025 side to side, line bores and cam tunnels in a zig-zag configuration. Can't believe they don't break more shafts. Much as I hate to admit this, Honda produces some of the most dimensionally accurate blocks I have ever measured. They are blueprint quality right from the factory. If they would install better piston rings and an oil ring with a little radial tension, they would last even longer.

[steve25]

I am sorry about starting this thread talking about factory balancing, when you guys want to talk about other tolerance's , lol!

[racegto65]

Originally Posted by steve25

I just for the second time watched the video titled “ 455 casting and machining in production of 1970” and I was very impressed by a fact that I missed the first time watching it,
Pontiac during production did a ruff balance of the crank and then once the short block was assembled they spun it up to do the final balance.
This was done to a tolerance of 1/2” ounce which is to me amazing since the average balance job done by a machine shop is 3” once ,

Does anyone know what the other GM divisions did and used in there balancing jobs?

I think you may be a little off on your figures. 3" ounce off will cause the crank to almost bounce off of my machine. I don't know what other shops balance tolerances are but I balance all street motors to .5"(1/2") ounce or less and race motors to .3"(1/3') ounce or less.

[hurryinhoosier62]

Originally Posted by mgarblik

I tend to disagree with this when compared to the competition in the time frame we are talking about. Late 1950's to 1980. IMO, Pontiac block and head machining was as good as the other GM divisions, better than Chevrolet, and better than Chrysler. Less personal experience with Ford, but the cam tunnels on Ford FE blocks were the worst I have ever dealt with. Never had a cam install properly without massaging the housing bores or bearings. Usually #4. Pontiac's had fully machined combustion chambers that were pretty nice. Blocks fairly square, decent finishes. Want to see a complete pile of junk in a GM block? Take a look at a SBC made in Mexico. Horrible surface finishes, blocks off square .015-.025 side to side, line bores and cam tunnels in a zig-zag configuration. Can't believe they don't break more shafts. Much as I hate to admit this, Honda produces some of the most dimensionally accurate blocks I have ever measured. They are blueprint quality right from the factory. If they would install better piston rings and an oil ring with a little radial tension, they would last even longer.

Mike, most of the cores we dealt with while I worked at JET were early eighties to early 2000s. The earlier stuff was far better than the latest “garbage”. I have to agree about Honda. Their machining is “dead on” accurate. We had one late Pontiac 400 block ( gas line got too far behind in production so I got that block) that was absolutely “jacked up” when it came to deck heights( .015 difference between decks if I recall correctly). Our machining foreman( the only other Pontiac guy besides me) took one look at the main cap alignment and the deck height issues and said “Junk it!”. We didn’t “junk” a block unless they were BER (Beyond Economic Repair).

[hurryinhoosier62]

Originally Posted by racegto65

I think you may be a little off on your figures. 3" ounce off will cause the crank to almost bounce off of my machine. I don't know what other shops balance tolerances are but I balance all street motors to .5"(1/2") ounce or less and race motors to .3"(1/3') ounce or less.

Back in my aviation days, we balanced the engines we overhauled to within .5 gram. This is using pistons and pins that weighed POUNDS instead of ounces. The factory tolerance for balance on these engines was 6 grams difference between cylinder(horizontally opposed engines). I saw at least two engines that had balance variations of 20 grams( factory reman’d engines at that)! The owner wondered WHY he couldn’t keep oil coolers or alternator brackets on these engines. When our TCM service rep contacted the engineering dept. at TCM, he was informed by an engineer that dynamic balancing did NOT affect engine performance or longevity. After hearing this, the TCM Rep, our engine shop manager and I just looked at each other in total amazement.

[Dragncar]

Originally Posted by racegto65

I think you may be a little off on your figures. 3" ounce off will cause the crank to almost bounce off of my machine. I don't know what other shops balance tolerances are but I balance all street motors to .5"(1/2") ounce or less and race motors to .3"(1/3') ounce or less.

The final unbalance on my rotating assembly Lewis racing engines did was

left 0.41 grams

right 0.44 grams

This was a re-balance from another shop I thought was questionable.
It started out as initial unbalance
left 28.5 grams
right 22.2 grams

Going to Lewis was a good decision.

[Schurkey]

Originally Posted by steve25

This was done to a tolerance of 1/2” ounce which is to me amazing since the average balance job done by a machine shop is 3” once

I don't know enough about balancing. I know that the balance spec includes both a distance and a weight--inch-ounces, or meter-grams or hectare-fortnights or something.

Makes me wonder about Pontiac spec when they talk about "half-ounce" but no distance measure.

Originally Posted by steve25

Does anyone know what the other GM divisions did and used in there balancing jobs?

The absolute goofiest has got to be Buick. Typical Buick rods don't have balance pads at the big end and small-end; they've got balance pads halfway down the rod beam. Point is, a REAL balance job has all the big ends the same weight, and all the small ends the same weight--but with Buick you just get an overall rod weight.

Then the torsional damper is neutral-balanced but with a series of holes drilled in the outer ring. The factory spins up the engine, and then pounds steel pins into the torsional damper--or punches holes in the flexplate--or both, to suit each individual engine that comes down the assembly line.

If an aftermarket shop hacked-up the flexplate or screwed with the damper, I'd call them butchers. Buick does it as a matter of course. As a result, replacement flexplates have to be match-balanced to the original, and you'd need to have the original steel pins removed from the factory damper, and pounded into the replacement (in the same relative positions).

Originally Posted by hurryinhoosier62

Back in my aviation days, we balanced the engines we overhauled to within .5 gram. .

Damn fine work.

1/2 ounce = 14 grams. I didn't have a good concept of how much a gram was. My wife tells me that 1 gram = 1 raisin (more or less.)

[Formulajones]

Here's a screen shot of the balance job Paul did for me on the last 455 Pontiac and what I've come to know as the normal quality I get from him, and why I don't like to use anyone else. Factory stuff doesn't even come close.