What Crank???

[classical glass]

Hi everyone, I'm looking at a Factory 5 cobra and the owner states that it's a 427 side oiler with a 428 crank. Well it's decently a 427 side oiler w/2 4s and well built with many goodies. The only grey area is that he states it has a 428 crank installed when the motor was built about 10 months ago. He has all bills and receipts and all looks legitimate and well done. My question is the crank shaft and pulley. The only numbers on the pulley are L 138 664 and the puzzling thing is the harmonic balancer and the pulley are one piece. Any body have any sound input? The engine runs strong with on issues. One other thing he has March aluminum pulleys on the water pump and alternator but not the crank. I asked about it and he stated all that was up to the builder and he honestly didn't know. I tried to contact the builder which since then has major medical issues with no luck.
Thanks

[MOTORHEAD]

I have a 428 crank in my Shelby alum block, and the damper and pulley are separate, although in searching for a new damper, I saw both configurations of pulley / damper.
If you go to a fluid damper, you will have to go with separate pulley.
I am running the steel factory crank pulley, as it is a bit larger than the ones in the aluminum sets. and the factory larger dia. will turn the alternator and water pump a bit faster, which is helpful in hot weather stop & go traffic.

Ted

[FWB]

early FE dampers had an integral pulley, no issues there, before after market cranks
that was the method of stroking a 427, installing a 428 crank into a 427.
427 stroke =3.78
428 stroke =3.98
several manufacturers had and still has off the shelf pistons to do this combo

[classical glass]

I,m still in the dark over what this crank is out of. It does not have a counter weight on the rear of the harmonic balancer and pulley and balancer are one piece. I do know the engine has chev pistons in (don,t know why) and runs very strong. Also can this assembly be replaced with a aluminum one? One last question if this is a 428 crank with chev pistons (wisco) stock bore, what will the cubic inch be for this engine? Sorry I don't have more info on this topic but either does the owner, who is 81 years old. But very sharp...

[FWB]

so the counter weight isn't needed after you zero balance the 428 crank with the new reciprocating assembly, that was a factory setup. the chevy piston, is kind of a mislabeling, the pistons are probably for a 4.250 bore(chevy stock size)
so your motor if it is 4.250 x 3.98 stroke, i think it will end up being around 440 cu/in.
your bore could also be a overbore of the chevy size also, +.010, +.020....etc

[olddog]

Originally Posted by fwb

s if it is 4.250 x 3.98 stroke, i think it will end up being around 440 cu/in.
Your bore could also be a overbore of the chevy size also, +.010, +.020....etc

pi* (4.25/2)^2 * 3.98 * 8 = ~452

[olddog]

Originally Posted by classical glass

I,m still in the dark over what this crank is out of. It does not have a counter weight on the rear of the harmonic balancer and pulley and balancer are one piece. I do know the engine has chev pistons in (don,t know why) and runs very strong. Also can this assembly be replaced with a aluminum one? One last question if this is a 428 crank with chev pistons (wisco) stock bore, what will the cubic inch be for this engine? Sorry I don't have more info on this topic but either does the owner, who is 81 years old. But very sharp...

A 428 is the same engine family as the 427. The are both FE engines. Nearly the same cubic inch displacement, the 427 has a larger bore shorter stroke, and the 428 has a smaller bore with longer stroke, relative to each other.

By using the 428 stroke in a 427 bore block, you get around 450 CID depending on the final bore diameter after you clean up the block.

The 427 crank shaft was internally balanced from the factory, as most other FE engines. FE engines that shared the 428 crank shaft were externally balanced. I believe only the flywheel was weighted, with the exception of the Le Mans. The Le Mans version had a counter weight behind the harmonic balancer that is often called the hatchet. That engine had heavier rods. This all said, I could be wrong, and the harmonic damper may be weighted, but I do not think so.

Now days it is commonly practiced to drill holes in the counter weights of a crank shaft and weld in slugs of malory (SP?) metal. The malory metal is much more dense and allows them to balance out the rotating assembly all internally. Then a zero balance flywheel and harmonic balancer can be used.

So, this engine could be either internal or external balanced. The builder could have chose to do either. What you need to know is that if it is externally balanced, you cannot change the harmonic balancer or flywheel without matching the offset weight. Personally, I wouldn't change either unless there was a strong need. The rotating assembly may have been balanced with those attached, which is a more exact result. If it ain't broke don't fix it, cause the cure may make it worse.

It's a bit cheaper to leave it external balanced. Most people tend to assume internal balance is better, but either works, if done properly. When you get to the extremes of racing at the edge of maximum rpm, there are all types of little things that start to matter on balance, but that's for other people to worry about.