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J.C.you · 03-15-2012, 10:23 PM

[QUOTE=Singleton;4579024]I have a SD421 "990" crank that has the fully grooved mains. This was apparently done on 11/19/62, the date scribed on the first counterweight. It was also stroked to 4.5" at this time, which I assume was not common for the time period. Inscribed next to the date is "Lees Custom Motors". I haven't been able to find any info on this machine shop.

Tony

Have you weighed the 421 crank Tony? Curious, guessing 80+ lbs.

Formulas · 03-15-2012, 10:24 PM

Didnt we have engines leave the factory with full groove main bearings .. Same same as a groove in the crank. They seemed to do well..

At this build level its all a moot point... either full groove 3/4 groove or half groove main bearings will work great..

Singleton · 03-15-2012, 10:53 PM

Quote:

Originally Posted by J.C.you

Have you weighed the 421 crank Tony? Curious, guessing 80+ lbs.

I believe it's 78lbs, but that was on a bathroom scale, so not very accurate. It has obviously been extensively welded/balanced due to the added 1/2 stroke and the 4.180 M/T pistons that came with all the parts.
I would have never thought a SD 494 cid pontiac could have been built back in 1962, but obviously someone did it.

How much weight was removed from your crank?

tom s · 03-15-2012, 10:56 PM

my cheater-matchrace 421 engine had a 1/2 in stroker crank in it.That was in late 63 early 64.Tom

Singleton · 03-15-2012, 11:03 PM

Quote:

Originally Posted by tom s

my cheater-matchrace 421 engine had a 1/2 in stroker crank in it.That was in late 63 early 64.Tom

Really? Bet that was badass.
Did you know of anyone else running a 4.5 Sd motor back then?

J.C.you · 03-15-2012, 11:39 PM

Quote:

Originally Posted by Singleton

I believe it's 78lbs, but that was on a bathroom scale, so not very accurate. It has obviously been extensively welded/balanced due to the added 1/2 stroke and the 4.180 M/T pistons that came with all the parts.
I would have never thought a SD 494 cid pontiac could have been built back in 1962, but obviously someone did it.

How much weight was removed from your crank?

Doesn't surprise me a bit. M/T must have had a batch of stroker pistons made. M/T had the fastest poncho powered car in the world and the record still stands! Anyone want to step up and try to best M/Ts poncho record?

My unit weighs 64 lbs now.

tom s · 03-15-2012, 11:46 PM

we did not run it much,CR was stupid high for back then.Tom

Singleton · 03-16-2012, 12:03 AM

Quote:

Originally Posted by tom s

we did not run it much,CR was stupid high for back then.Tom

Guess that explains why my 127 heads had the 68cc chambers opened up to 76cc's; to keep the compression around 12.5 or so...

BruceWilkie · 03-16-2012, 07:52 PM

Well I measured the crank groove. Not as deep as I thought or quite as wide. It's .080" wide by .015" deep. The crank is already .010 under another .010 off the journal reduces the groove depth to .010" and will reduce the width some.

I'm not going to worry much about it. Just going to use a regular upper groove only set and chamfer the bearing oil hole toward the sides a bit.

Took some pics then put it on my scale. Nice... 65 lbs. Think more could come off it.

Half-Inch Stud · 03-16-2012, 09:23 PM

That's good.

Or your could have an 80 mil grove cut deep into the LOWERs, just for "theoretically positive" oil pressure at all crank positions..

BruceWilkie · 03-16-2012, 09:50 PM

Quote:

Originally Posted by Half-Inch Stud

That's good.

Or your could have an 80 mil grove cut deep into the LOWERs, just for "theoretically positive" oil pressure at all crank positions..

Not me! The little bit thats there now might add just a touch more oil to the rods. At most mod the bearing a bit to get oil halfway between groove and outer edge and I should be fine.

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