Offset Grinding 428 crank

[ERA713]

Motor heads.Can the 428 crank be offset ground to a 4.125 stroke?my builder has mentioned this but I have never heard of anybody doing it.I have the 6.7 chevy rods and had planed on using the cast scat crank.he says stroking the 428 cj crank would be better?thanks

[LMH]

I can't comment specifically about 428 cranks but the practice of grinding a crank to increase the stroke used to be common in the VW world. The problems arose because the "inside" had the hardness ground off and added material on the "outside" wasn't hard enough either. I've seen a number of ground cranks fail in VW's in the past because of such grinding.
Of course, once manufactured stroker cranks started showing up, no body ground them anymore.
That was my experience with them but maybe the 428 crank is a totally different beast.
Larry

[ERA713]

Thanks LMH for the info. It makes sence to me. I think i'll stick to the original plan and get a new crank from scat.

[Barry_R]

I was gonna say - - the Scat cranks go for under $800, your existing 428 one would sell for $400-500. You'd be hard pressed to get a decent offset done for the three hunny difference...

[DavidNJ]

What would make a 35 year old forging worth using? Was it 5130 or 4340? Was it a non-twist forging?

[ERA713]

I don't know dave.I'm starting to wonder about this guy.I don't want to mention any names.I've not heard of any problems with the scat crank as long as its balanced properly.he thinks if its made in china its no good.

[Keithc8]

It would cost more than it would be worth to stroke the 428 crankshaft. Sell the 428 crankshaft and use the Scat cast steel crankshaft. I have used these in engines over 700 HP for three years now with zero broke. The way that the engine is used in most Cobra Replica cars you will never hurt one. I can get you a new Scat stroker crankshaft for 695.00. This would be in either a 4.125 or 4.250 stroke. These use a 2.200 BBC rod journal and most people use a 6.700 to 6.800 long rod. We can also get you a nice complete kit together as well for about 1895.00 Thanks and good luck, Keith Craft

[Carnut427]

Originally Posted by DavidNJ

What would make a 35 year old forging worth using? Was it 5130 or 4340? Was it a non-twist forging?

The 428 cranks were cast, not forged.

[Excaliber]

I don't get this 'age of parts' thing I seen every so often. Things like, why would you use 35 year old Le Mans rods?

Well, why WOULDN'T you? Does age mean 'metal fatigue' sets in? Do rods get alzhiemers or something? Are old blocks just naturally weaker because their 'old'?

...I don't get it, I think it's a bunch of hog wash myself. If you want modern stuff, OK, go for it! If your building a 1500 horse power monster that going to run 8000 rpm, you might consider 'new' (as in MODERN) rods! If your building a street\race Cobra motor and you check out your crank, rods, etc and there 'good to go' I believe there MORE than 'stong enough'! Last year I was running my 'alzhiemers' Le Mans rods to 7000 rpm, with my poor old 'arthritis' ridden 428 crank being thrashed about in that tired old 427 iron block, poor thing, I showed it NO mercy! Had the rods, crank and block checked out when I did my rebuild, "good to go", I'm using 'em again!

All modern parts in an all modern engine, like a Dove or Shelby all alloy configuration are just as subject to failure as an all '65 engine depending on how you RUN it! Don't think you can't 'ventilate' a modern block with a modern rod!

[Power Surge]

Originally Posted by Excaliber

I don't get this 'age of parts' thing I seen every so often. Things like, why would you use 35 year old Le Mans rods?

Well, why WOULDN'T you? Does age mean 'metal fatigue' sets in? Do rods get alzhiemers or something? Are old blocks just naturally weaker because their 'old'?

...I don't get it, I think it's a bunch of hog wash myself. If you want modern stuff, OK, go for it! If your building a 1500 horse power monster that going to run 8000 rpm, you might consider 'new' (as in MODERN) rods! If your building a street\race Cobra motor and you check out your crank, rods, etc and there 'good to go' I believe there MORE than 'stong enough'! Last year I was running my 'alzhiemers' Le Mans rods to 7000 rpm, with my poor old 'arthritis' ridden 428 crank being thrashed about in that tired old 427 iron block, poor thing, I showed it NO mercy! Had the rods, crank and block checked out when I did my rebuild, "good to go", I'm using 'em again!

All modern parts in an all modern engine, like a Dove or Shelby all alloy configuration are just as subject to failure as an all '65 engine depending on how you RUN it! Don't think you can't 'ventilate' a modern block with a modern rod!

My guess would be simply because you can buy BETTER parts, cheaper, nowadays. A 35 year old LeMans rod may be fine for use, but it still doesn't compare to a modern H-beam rod. Plus, the fact that it's a used part, leaves a bit of an uncertainty to using it. How do you know it wasn't abused? How do you know the guy didn't run these rods in a motor that was sprayed with a 300 shot of juice? You just don't know. So why bother spending the money to buy a set of Lemans rods, have them reconditioned, and then chance how long they'll last, when you can buy a set of stronger, more precision made H-beams, with superior rod bolts, for $500 and have no worries. Same goes for ANY used parts, not just FE stuff.

My 390 has reconditioned stock rods and stock crank in it. But, I also paid only $3200 for the entire long block, with intake manifold and covers. It's a 400hp motor that will serve it's purpose for a few years until I build a 427. But when I do, it will have all aftermarket parts inside. And if I can come up with the dough, it will have a Pond block, not a vintage S/O block.

[dynoroom]

Try the word "cycle time". Everything has a life cycle. You may not have reached it with you "old" rods but your closer than I am with my new one's.

[Excaliber]

Actually I was thinking more along the lines of NOS (new old stock) where 'age' should not be a deciding factor.

But the point is not lost:
NEW parts because you can't be sure what abuse has been handed down to 'old' parts. Now I feel comfortable with my 'old' parts because I had them checked out for size, straightness, balance, etc. Short of having them 'x-rayed' I think it is reasonable to assume there 'good to go'. Even a NEW part can be 'defective', and in that regard there is always a 'risk factor'.

I'm not NASCAR where you throw away 'old' parts after one race, x-ray new parts, and money is no object. I would guess few of us are! I think it's reasonable to look for a balance between 'cost\benefit', I wouldn't turn up my nose at a 428 1U crank at a yard sale for a good price, for instance.

[DavidNJ]

The older parts weren't designed with current computer or manufacturing technology and generally are weaker. If it wasn't NOS it could also be subject to corrosion, high cycle fatigue, and cracks or stress risers from mishandling or misuse. NOS could still be subject to corrosion (at least parts from the 30's are).

If Keith and Barry agree exactly, it would be very hard to argue any other result. This is a very important quote: "I have used these in engines over 700 HP for three years now with zero broke."

The prices Keith listed are very reasonable, especially from a shop of KCR's caliber.

BTW, did that include balancing, rings, and bearings?

[blykins]

Manufacturing processes and tolerances are a million times better now. Parts are cast in molds that are more efficient....higher pressure....less porosity....or they're forged.

The guys above are right. There is such thing as fatigue stress. I couldn't tell you as much about it today as I could 4 years ago when I graduated engineering school, but in our mechanical design courses, we had to design parts for a certain life cycle. Fatigue stresses along with stress concentrations will slowly beat a part down.

With the price of new parts, I don't see any advantage whatsoever in buying 35-40 year old pieces. I bought a new set of Scat H-beam rods for under $400 with shipping. Forged pieces with ARP rod bolts.

I wouldn't even consider using an old part unless it had been magged, x-rayed, resized, rebushed, fitted with quality fasteners, and shot peened.

By the time you put all that money into that old part, you could have bought brand new stuff.....

Not to say that new parts will never break, but I'd much rather trust a new one than an old one.

[Excaliber]

Of course the balance included all the rotating assembly parts. Even clutch cover!

[blykins]

I think he was asking about the rotating assembly that KC was selling up above.

[ERA713]

Thanks alot for all the advice,this forum is great.I called the engine builder today & told him I wanted the scat crank.he has port matched edelbrock 427 heads to bluethunder med rise manifold,it will have roller cam,hyd roller lifters,comp cams hd roller rockers,ross 10to1 pistons,scat 6.7 rods & chevy size pistons.I will ask him tomorrow what the cam specs will be.I found a 427 center oiler block with stock bore that was in fresh water boat in very good condition with no measurable core shift for 1500.00.hope I can get this engine back to my shop in a few weeks and get this thing licenced before winter.thanks jim

[Keithc8]

The kits include the crankshaft, H-beam rods, Diamond pistons, Mahle rings, Federal Mogul bearings, piston pins and locks. The balancing runs extra because it depends on the crank stroke and bobweight. Some of the balance jobs require more heavy metal than others. Most of the balance jobs will run 175.00 for no metal to about 350 for the 4.240 stroke with 3 pieces of heavy metal. We can balance the pressure plate if it is sent in and would need to flywheel that it will balance to. We then stamp them so they go back on the way that they were balanced. Hope this helps a little.
The cycle time is the most important thing about the used parts to consider and we do not have that answer. We have used the 390 steel truck crankshaft a lot in our 428 NHRA Super Stock engines. We off-set ground them to 3.997 because the rules allowed us a plus .015 stroke to the crankshaft. These cranks worked fine for a few years untill we started to make 720 to 740HP and turn these engine 8000 to 8400rpms. We had a main bearing problem and had not had this problem before. We wet magged the crankshaft and it had a crack in the radius. Then when we were freshening one of the other engines we found a small crack as well. The customer ask me what was going on and I told him that I did not know how the guy that drove the dump truck that the crank came out of had driven 35 years ago. We wet magged all of these crankshafts as well hear treated them and even cryoed some of them. They just reached a point where they could not take it. I do agree that most of the regular FE parts will work fine in most cases if checked right as long as you do not make much more than550 to 600HP. This use to be a lot for a FE engine but not any more so this is the reason for using mostly new parts. I also like the BBC 2.200 wide rod journal for bearing life. I use the original FE parts all the time in the restoration engines we do.
I for one wish it was all cheaper and easier. Thanks, Keith

[Excaliber]

Oops, thanks for that up-date Blykins!

But it's still a valid point, I chose to do the whole shooting match on my balance. Because I had new (modern ) pistons I really had no choice. It cost me about $300, so it sounds like KC's prices are right in the ball park. I've heard some guys bring in TWO pressure plates (cluch covers) so they have a balanced 'spare' for the future.

[DavidNJ]

I'm confused again. Isn't the rotating assembly internally balanced and the pressure plate, flywheel, and damper zero-balanced?