Hi again Guys.

Can it be true that the 260 crank, and the 403 is one and same counterweight?

Have a issue with a crank from Mabbco is 1900 grams to light on the counterweights, so i am looking on casting # 556607 and 418882 is both listed as 260 1975-76 and 403 1977-79

Seems strange to me that rotating assembly should be the same, and even if so why this big weightloss, on a crank that not have been cut down on counterweight radius (just barely clears the pistons by 1/8th) or drilled like crazy?

 

All gasoline SBO cranks (260, 307, 330, 350, 403) have the same stroke and bearing dimensions, but the later 77-up cranks are lighter weight than the earlier ones. This coincides with the windowed main web blocks that appeared in 1977 for the overall goal of making the engines lighter.

 

Thanks for reply.

Are you serious?

They did not consider the weight difference on rods and pistons, just made one cast for all SBO engines?

1900 grams is a lot of mallory, and since it is sold as "stock replacment" i doubt the engine would had run a summer, without my kidneys gave up ;-)

Just wondering why they bothered drilling balance-holes, only made it worse on the 403

 

Yes, since the stroke and rods are the same (except for the 403 rods), only the piston weight is different. The balance pads on the existing counterweights and on the rods have sufficient material to balance the rotating assembly for any SBO.

FYI, the 455 and G-block 400 use the same crank. The 425 and short-stroke 400s also use the same crank.

 

Thanks Joe

Since i could not figure it out based on these statements, i contacted the shop, they sent me a casting # 393654 this would fit 68-76 Heavy castings only?

http://www.cleggengine.com/68-76-old...shaft-kit.html

If that is right, mabbco just sent me the wrong one.....

Too bad it would cost more to ship it back to US than i paid, so i guess this would end its days in a dumpster.

 

 

Maybe i am confused

but as i read it, i should never put a old style crank in a windowed block, because it is heavier, and even though it is heavier "as is" we still need to add 1900 grams, to get it balanced to zero.

I cant say whats right or wrong here, just gave up an hour ago and ordered a bone stock crank, pulled from a Trans Am 403 block, then we start there, anyway the casting # would be correct for the engine.

 

The crank and the block are unrelated. Olds used lots of different techiques to lighten their motors starting with the 1977 model year. The lightened crank used in the newer motors just means that 1) it is not as strong as the earlier cranks, and 2) you just need to have the entire reciprocating assembly balanced as a unit. Which crank you start with is irrelevant so long as you have your selected parts balanced as an assembly.

 

Out of interest, is there any fact how much Olds managed to cut off weight from long block approx. , from first 350's to last?

 

I was just afraid that more weight on a windowed block that is weak from factory, would make anything even worse with a heavier crank, we added even more weight to.

The KB should push harder on it (i hope) so was just concerned if it would end up in a blown bottom end, with all this "weight" on the mains.

 

The difference in the weight of the bare blocks is on the order of 20-30 lbs. I've got one data point. Using the finest Chinesium bathroom scale sold by WalMart, I weighted a bare windowed 403 and a bare 455 block. The 403 was 170 lbs, the 455 was 200 lbs. Given the difference in deck height, I'd estimate that a non-windowed SBO would be about 190 lbs.

 

Thanks. As i quessed, not much ( but surprisingly lot for just differences made on existing casting). Wonder was it never worth the effort? For example, windowing the block dont effect friction at all, nor the weight of circulating masses.

Just to think of it, you could have shaved that 20lbs from anywhere else also.
Thats just when looking the top of iceberg, dunno was there some else corporate policy back of it all. Atleast they managed to keep their V8 on production for long.

 

The point is that they WERE shaving weight everywhere. Keep in mind that this was started right after the first oil crisis in 1973-74. The gov't was just starting to enact CAFE mileage rules. Cars were being "downsized", starting with the B/C-body cars in 1977 and the A-body cars in 1978. 20 lbs from the block, more from the heads and crank, lighter TH200 transmissions instead of the TH400, lighter 7.5" axles (even in the B-body cars!), smaller lighter frames and bodies. Of course, this lets you get by with lighter suspension parts, smaller brakes, smaller tires, smaller radiator, less coolant, etc. It's a cumulative effect.

 

i think you are confused. You won't have to ADD 1900 grams to anything, even if you were going from an external balance to an internal. Not sure where you got that idea.
Your balance "bobweight" should be in the 2200 gram range. Your stock 403 crank shouldn't be that far off, normally adding or subtracting less than 30 grams on the counterweights for a stock setup.

 

Okay, then. Thanks for clarification. Seems like they went to extremes if they made even the coolant system contain less coolant. Sure would have hoped that 8.5 rear weighted less when lifting it from table to floor.

Funny to think all of that now, when even the smallest cars start to weight awful lot thanks to all safety and electronical equipment, even when body panels are made of tin-paper and plastic.

 

Just to clear up here.

I bought what i thought was a reground stock 403 crank. (today the casting showed early type 350 crank, did not check that prior)

I am using a new flexplate, and a new balancer, but both external balance models as stock.

KB hyper pistons, refurbished original conrods.

Sent it out to the shop, and they called me with the "we need to add weight to the counterweight" statment, not something i made up for fun.

I told them that they had to check again, the total weight of each pistonset, was 90 grams lighter than stock, so adding weight seems the wrong way to go.

They called back, they where sure on their bobweight calculation, somebody want more or less "reciprocating factor" but they use 50% if not told other factor from customer, and they did 2 other V8s this week, with no issues, small amounts to adjust.

Then i scratched my head, and googled for hours with not much luck, wrote here, and decided to buy a stock crank from a olds 403, since the problem could only be with the crank somehow.

I did not ask how much bobweight they had on, since i did not know any number to aim for,nor have any reason to doubt their work, but now i know, and will ask to see if the shop or the crank is "off"

Thank again for all the posts, very educational.

 

Extremes when there really was no oil crisis. What you have now is less refineries. This is how they control prices when a refinery shuts down. Take a look at how many refineries no longer exist verses how many remain. There were better ways to remove weight than main webs and engine valleys. The radiators could have been made of aluminum. The heater cores could have been made out of aluminum. Wheels could have been aluminum all intakes could have been made of aluminum. Ect, Ect. I don't know how this lie got started i just know it is bull S--t. To the op i hope you get this straightened out.

 

Manufacturing capabilities and costs associated with aluminum back then were not what they are now. A car built with the aluminum content we have today would not have been competitive.

 

Unless you know the complete history of the crank, rods, flexplate and balancer, this may be entirely correct. The flexplate or balancer may also have been modified. New balancers are not necessarily made to spec- my machinist had to remove 20% of the counterweight on my brand new Professional Products balancer.

It's normal to add - or subtract - weight from the counterweights when balancing. The old 350 pistons were pretty heavy, and the KB's are lighter construction, but a fair bit larger. If that crank was ever balanced for a lighter assembly, then you would certainly have to add weight.

In any case, adding weight is not unusual. If you really want to know what's going on, then go to the shop and review the balance card and ask them to show you how it's all done. They should know that weight needs to be added because of how it spun on the machine.

The readings off the balancing machine matter much more than any theoretical stock configuration or comparison.

Google and old specs won't help you. Go to the shop and learn how the math works and the machines work.

 

I understand the process of balancing, Bob Weights and all, but was stunned by the fact they told me they needed to add almost 1900 grams to at crank that have never been changed since factory (counterweight height stock, and no heavy drilling done to them).

I also understand it could be done with mallory, but i hate adding weight to the 403 bottom end.

 

Shop told me it needed ADD 1900 grams, but i just called them, they confirmed they need to add this, and the bobweights @2258 grams.

 

LOL ! I am not talking anything except weight savings. They made aluminum wheels back then that are lighter than steel. So i don't see your point. Cost associated ha. Sound like you are grabbing straws with nothing but assumptions. I think the op needs a different machine shop.

 

TBT_DK:
I ran into a similar problem when doing the machining for my engine. I bought a PRW, SFI-rated balancer that was much heavier than the stock balancer. The PRW balancer was 7 lbs heavier and using it straight "out-of-the-box" meant adding mallory to the crank counter-weights, and the nose (front) of the crank was still much heavier than the rear. My rotating assembly (Icon pistons and Chevy rods from Scat, bob weight=1910g) was lighter than stock, so adding weight to the crank seemed to be going the wrong direction.

The solution:
The PRW balancer came with a removable counter-weight so it could be used in externally or internally balanced engines; so the machinist took the material off the counter-weight which evened out the front to back balance then he only had to drill 2 small holes in the crank counter-weights to get everything balanced. Modifying the balancer counter-weight was a little unorthodox and received some criticism from the CO community, but it made perfect sense to me especially since the new balancer was so much heavier than the stock one it replaced.

I'm not saying this is your problem, but certainly worth looking into if you don't want to add weight the crank. Good luck!

Rodney

 

Thanks a lot, makes sense.

I bought a SFI Fluid Damper and suitable flexplate from Oldsrocketparts, just figured they would work "out of the box" for stock engines, they would work without messing to much with the bobweights.

I know the flexplate is heavy, since it is thicker material, but did not think about the fluiddamper would make a difference in "offsetting" the weight just total weight of rotating assembly.

But since the weight on this damper is a part of it, and not removable, i will leave it alone.

 

2258 is a little heavy but close for this combination.
But let me just put this in perspective. If you went from an external to an internal balance, typically you need to add in the area of 200-300grams.
If your crank is "1900" grams out then that means it was originally balanced for a bobweight of approx. 400 grams. Does that make any sense to you? The rods alone weigh 600+. Something is wrong here. If its 1900 out it will literally want to jump off the balancer. You need to watch them do this process and explain what they're seeing to you then go from there.

 

They cant get any kind of rpm on the crank, and even at very slow speed it jumps like crazy in the machine.

I am not changing from external to internal balance, flud damper with balance weight and flexplate with balance weight added, so the only thing different from stock setup, is the 90 grams (times 8) lighter rod / piston setup.

I have confirmation that the new crank is packed with the new engine block, so we have to see what kind of weight that demands, if we are still way off, i will have to check their calculation of bobweights.

 

TBT_DK:
I'm no expert on this (maybe Mark will chime in again with his experience) but I recall reading that Fluidamper recommends balancing the crank using the stock balancer. Has your machinist tried balancing the crank with the OEM stock balancer for a comparison?

 

t,
Are they trying to balance the crank with the Fluiddamper on it ???? If so that is part of the problem. You have to disassemble the damper and just use the hub with the weight on it. If you try to spin the crank on the balancer with the entire Fluidamper on it the moving weight in the damper will drive you crazy.


Something is definitely not right. 1900 grams of weight would mean adding 19 or 20 slugs of heavy metal. I think that either they are doing something wrong or your flywheel and or damper are incorrect.

 

By the way, the actual weight of the damper and flywheel means nothing. The amount of unbalance weight built into each is what matters. You can have a 5 lb damper and a 50 lb damper that both have the same amount of unbalance built into them.