Crank mods

Jyrki

Jyrki

Team Member
Moderator
I'd like to learn from other people's experience on lightening the stock crankshaft. What works and what doesn't? At some point Allleycat was in the process of modifying his 263 crank, but I haven't heard back. I was able to get a spare 320 short block that I'm going to build for serious power.
 
Jyrki,
I'm interested in doing that as well.

How has your EFI and dampner/crank trigger ignition worked out?
 
Efi

No progress on the EFI system - have been busy with other things over the summer. It's soon time to close the garage door and get back to it.
 
Jyrki said:
I'd like to learn from other people's experience on lightening the stock crankshaft. What works and what doesn't? At some point Allleycat was in the process of modifying his 263 crank, but I haven't heard back. I was able to get a spare 320 short block that I'm going to build for serious power.
Click to expand...

First thing that can be done is stress relief the crank by removing all the forging marks and making a smooth surface like you would a connecting rod beam.
In order to remove material from the counter weights the weight of the piston and rods need to be reduced so the crank can still be balanced. Good aluminum rods will work fine for street use and if you are wealthy use titanium. If you are changing the rods then both the 263 and 320 can be stroked 1/8th of an inch by going to smaller rod journals (2.0 for the 263 and 2.1 for the 320). If you can afford it you can stroke further by welding the journals and regrinding. If the journal moves out enough to expose the oil passage then the passage will need to be relocated.
The 263 block will accommodate a 4.5 inch stroke with 2 inch rod journals.
It will be difficult to make an after market rod big end small enough to pass through the stock bore diameter on the 263 (3.187) for engine assembly even with 2.0 journals and 5/16 inch bolts. Also the bottom of the bore would need to be notched to clear the rod beam for a large stroke. A larger bore solves both problems.
The bore spacing on a 263 is as follows:

3.725 Between 1 and 2, 3and 4, 5 and 6, 7and 8
3.750 Between 2and 3, 6 and 7
4.185 Between 4 and 5

The block can be sleeved for a .200 overbore using a .125 thick sleeve and still have deck material and water jacket left between. With a bore and stroke of 3.387 x 4.5 your 263 becomes a 324.
Doing the same for the 320 (3.637 x 4.5) and you have a 374.
No one has forged rod blanks long enough so only billet rods are available.
For our project Oliver was the cheapest at $1800 for a steel set. Aluminum should be around the same price but I'm not really sure.
 
I'm still out here! However, I've not been able to do much work on any of my car type projects. House projects MUST be done befor winter sets in, my shop must be upgraded in order to do some of these "out there" projects I've thought up, and there has been a coupla deaths in the family and I was executor on one and it takes a lot more time than I thought to get past all this!

So, I'm still working on the 248 crank, and this is where I am. Nobody here or in California will touch the crank other than for minor refurbing. So I have to do it all myself. I have to make all the tooling and all the fixturing, this is just as big a job as lightning the crank itself. This is what I have determined about the crank in reguard to making it a LOT lighter. V8 cranks and str8 cranks are totaly different animals. A str8 crank has "perfect" balance. I don't like the word "perfect" because it can be very subjective, but in this case it works. Every throw arm, every rod journal, every everything is counterbalanced 180* away, so the only out of balance that will occure, is in the ammount of metal, more or less, that is in the rod journals. So, if it's all equal, it's in balance. It dos'ent matter how much or how little it is. The flyweights, the "pork choppy" chunks hanging off the opposite sides of the rod throws, are strictly there for the balance of the rod and piston, nothing more. So, keep the piston/rod assembly light, light is good, removing metal from the flyweight balances the piston/rod.

I can JUST get the crank in my mill. It takes several drills progressing to about 2 ft long. The headstock is cranked to the point it will just hang on to the post. It's really close! I'm drilling a 1" hole through the rod journal, dead center. I think moving the hole outboard by about 1/8 or so, would have been better, but it's too late now, and things MUST be kept even. I'm about half way through the crank, then it must be fliped for the other end and some more tooling must be made. It's looking like the crank will weigh about 52 lbs when I'm done. A stock 248 crank is about 80 lbs, a 263 is close to 90 lbs, and I'm not sure what the 320 is. But with larger rod journals, and thus larger drilled holes, a similar weight reduction could be had. And, 30 lbs ain't small change. I'm even thinking that the throw arms could be ''I-beamed" but I'll leave that for later. Then! All the sharp edges must be radiused, oil supply tubes pressed in, grinding, polishing and all that "finishing" stuff, then the rod & mains got to be sized...Going to be a work of art! Unfortunatly, once it's in the engine, nobodys got a clue it's there....alleycat
 
Hello guys and thanks for the input! I've been recently traveling, that's why it took so long to reply. Alleycat, I'd really like to see some pictures - I cannot imagine from where are you going to find such decrease in weight?

Have any one of you tried to contour the counterweights - bullnosing, knife-edging etc?
 
Jyrki said:
Hello guys and thanks for the input! I've been recently traveling, that's why it took so long to reply. Alleycat, I'd really like to see some pictures - I cannot imagine from where are you going to find such decrease in weight?

Have any one of you tried to contour the counterweights - bullnosing, knife-edging etc?
Click to expand...


There is no reason that you could not do this. On an inline engine the crankshaft is balanced by itself with no bobweights representing the rods and pistons. As long as you take equal amounts off the crankshaft counterweights front to rear, you should not throw the balance off so far that it isnt correctable by your engine balancer.
 
Jyrki,
As for boring .200, it's both expensive and risky. With a turbocharged motor. The high cylinder pressures at the top can be disastrous especially if you have any hint of detonation. To put a .125 sleeve in, you have to remove almost .325 of material from the wall and you lose nearly all of the support from behind. Be safe and don't exceed .150 on an extreme application. We did all of the bore and stroke above, and we got two pass' on the block and had to coast through the last mile on the Salt to set a 169 record .[188 first pass, and 161 second pass coasting] Here's a picture of the result. More on the Salt Cat Racing Facebook page.
Doug
 
Doug
In your case would you be willing to switch to alcohol then you could partially or completely fill the block so you can stay with the piston, rod and crank combination you already have?
Never seen a piston and ring modification like that. Incredible!
We run a filled 430 cu. in. V8 iron block, 1600 ft lbs of torque, 2400 HP, twin turbo on methanol.
For street use your advice is best.
The 263 block has much less cyclinder wall than the 320 (The 2 blocks I have measure .165).
Paul
 
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I've taken 10 pounds off of a cast 292 Chevy 6 inline crank for drag racing. If you have access to a Bridgeport mill, you can make a v-block fixture to hold the crank horizontally, and scallop out material at the front and rear of each rod journal cheek. Then you can rotate the crank and turn the head and knife-edge the counteweights. You can also stick it in a lathe and remove material from the OD of the counterweights if you still need more material removal. I have also gun drilled the rods journals and mains journals on some other inline cranks as well as some V8 cranks, you can also do it on the Straight 8 if the oil holes are not in the way. You also will need some long drill bits to do that with, but its another option.
 
CNC-Dude said:
scallop out material at the front and rear of each rod journal cheek.
Click to expand...

When looking at the str-8 crank, it looks like the cheeks are already scalloped to high degree. Then again, I'm not 100% sure if we're talking about the same thing?

I'd really like to gun drill the rod journals, but I quess the holes should dead accurate at the same location within all 8 journals, to avoid imbalance. Could be done in a mill or in a CNC machining center?
:clonk:
 
Overbore

Doug, what's that chunk of metal you're holding? It looks like it came from a meteorite!

As for the overbore, I went thru some older postings and it seems like there's general consensus that a .125 overbore is the maximum without sleeving (and with a perfect block with minimal core shift).

Congaratulations on the new records, Doug! :1st:
 
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