5.0 Stroker

[Plechtan]

Well after reading Lee Hurleys comments about the cam/Crank harmonic, I thought it would be a good idea to use a 12 counterweight crank in the Bonneville truck. The stroke would have to be between 3.5 and 3.6" to complete in the 4.3L class , so you could offset grind a 4.0 or 232 crank to get the correct stroke. The problem is, they never made a 12 counterweight crank for either the 4.0 or the 232, only 8 counterweight units are available. that leaves me with a 258 crank which has a stroke of about 3.9". You cannot offset grind it enough to get the stroke down to 3.5". So next stop custom crank? No, That would definitely break the budget. So although i would like to run in the 4.3L class, at the moment it does not seem to be within the budget. The next option would be to run in the 5.0L class. The record there is lower ( 158 mph) and the engine would be cheaper to build.

So the new plan is to bore the block to 4" , use chevy pistons (cheaper) a 258 crank stroked to 4" ( a square motor!) custom connecting rods. The 4" bore should let the valves breathe a little better. I did think about boring a 258 a little bit to stay in the 4.3L class, but i thought the valves would end up too schroded in the smaller bore. everything else on the 5.0L would be almost the same as I would have done on the 4.3.

We will be able to prove out the truck and the modifications to the motor in 2009. If everything goes OK, we plan to return in 2010 with a 4.3 Probably it will be the same motor with a different Crank and rods. If the only thing i have to buy in 2010 is a custom crank and rods, i think i will be ok.

This does raise a question, it seems to be harder to find the 12 counterweight 258 cranks, I think it has been about 25 years since they went out of production. Will the supply dry up? will the demand increase as more people build strokers? Maybe they will be happy with the 4 counterweight cranks from Wranglers. With the aluminum block coming along ( i hope), will there be more of a demand for a performance crank? Hopefully somebody will address this need with at least a cast steel crank that could easily stroke to 4"

[Comanche91]

Peter, where are Lee's comments located? Thanks

EDIT: Nevermind, found them.

[dwg86]

258 12w cranks can be bought from most auto part stores, but they do seam to be ground quite a bit(.030-.060). Check local junk yards. I got 1 standard crank, and 1 .010 crank from the local pull a part. Reground they should clean up at .010 and .020.

It would be nice to see an after market crank being made, but I wouldn't get my hopes up. I have made several phone calls and emails about having forged connecting rods made. The last was to Scat just a few weeks ago. They make an "I" beam forged connecting rod for the amc 304-360. The only differance between the 304 and the 258 rod is the big end is wider on the 258 rod. I thought maybe they could take the raw 304 forgings and just not grind so much off the big end...to keep it at 1.060. They wouldn't have any more cost in making them, they already have the forgings. Just keep the big end wider and put a different part number on it. There reply, and I quote "sorry we can't help you".

I had also sent an email to Eagle about a forged connecting rod they used to make for the 258, P/N EAG SIR6125JB. It was an I beam rod 6.125 length and came in 2 different styles(bushed for full floating pins and press pin). I told them how popular the Jeep stroker was becoming and that Kieth Black was making an "off the shelf forged piston" for the stroker. I thought maybe the old molds might still be around or at least the drawings, or maybe they might see a demand for them. I told them about jeepstrokers.com and how many members are there. There one line reply was "Sorry we don't make them anymore".

The biggest problem with the aftermarket crowd is...if its not for a small block chevy, forget it!

[John]

Peter it seems that most econo built, daily driven Cherokee's is where these strokers are ending up and a awful lot are wanting the 4 cw cranks, Yes they will eventually dry up but it will take a while. They are still fairly easy to find around here. By the way, did you have any luck with contacting the fellow we were discussing?
John

[TurboTom]

I would be more concerned with cylinder distortion at a 4" bore than a 4 CW crank.
I would guess the cylinder shrouding (your going to move the edge of the valve .0625" from the cylinder at best) flow difference for any of these combos would be less than 7cfm at 28"
What head are you using and what are the flow numbers? I can plug these numbers into Desktop dyno and get you some virtual numbers.

[SilverXJ]

258 12w cranks can be bought from most auto part stores, but they do seam to be ground quite a bit(.030-.060). Check local junk yards. I got 1 standard crank, and 1 .010 crank from the local pull a part. Reground they should clean up at .010 and .020.

The thing is that the part houses list one crank that is either the 12 wt or the 4wt. You usually have to wait until it comes in to check it. I tried Autozone... they don't sell them 258 cranks anymore, and I tried Advanced. Advanced ordered it and it came in. Not only was it a 4wt crank but it was turned like .040. They also said that they usually send teh best cranks first. I declined that and just got the 4wt crank that my machine shop could get that was turned .010.

The biggest problem with the aftermarket crowd is...if its not for a small block chevy, forget it!

Meh.. I really dislike the chevy any block. SBC FTL

[Plechtan]

I would be more concerned with cylinder distortion at a 4" bore than a 4 CW crank.
I would guess the cylinder shrouding (your going to move the edge of the valve .0625" from the cylinder at best) flow difference for any of these combos would be less than 7cfm at 28"
What head are you using and what are the flow numbers? I can plug these numbers into Desktop dyno and get you some virtual numbers.

According to Lee Hurley, the later 4.0 blocks were designed to go to 4" I checked a later model casting i have and the walls on the left and right side of the cylinders ranged for about .250 -.310 the front to back numbers were thinner , more in the .150-.200 range. I do have one cylinder that has a thin spot on the back, and we are trying to figure out if we should sleeve it or look for another block.

We intend to use the Hesco Aluminum head, I should be interesting to see what kind of flow numbers we get. Hesco will not install larger valves in this head, So you are stuck with the stock sizes. They did offer to sell me a unamchined head, but that is a little more than i want to tackle right now.

[seanyb505]

Dont know the condition, but Oreilleys carries 12wt cranks :
http://www.oreillyauto.com/EW3/DisplayT ... Count=1313

I got my 4wt from there, but it was ground .040 over on the mains Cheap though

[Plechtan]

If you look at the listing, it specifies 2 casting numbers. the one ending in 723 is the 12 CW I believe the other one is only a 4 CW.

[seanyb505]

Its not a dead end yet though.

[Plechtan]

I did find the 723 casting at Rock Auto. I used a 75 CJ as the vehicle. I placed the order on Thursday, They called yesterday and said that the part number i wanted was not available, however they would be happy to "upgrade" me to a more modern design that was more lightweight. I told them to cancel my order.

Guess I am still looking.

[dwg86]

check www.standardcrankshaft.com or www.atlantacrankshaft.com If I remember correctlyI think they both had one. It's been a while since I talked to them. (casting number 3214723 for the 12wt.)

[Alex22]

You could also call RPM Machine and talk with someone there and ask specifically for a 12 counterweight crank. Last time I was looking for one they had one that was .010 under but since I was looking for a standard crank I didn't buy it. I think Liberty engine parts or New England might be able to find one as well.
Have you asked your crankshaft grinder if he could check with his core suppliers?

Custom pistons aren't as expensive as they used to be so maybe a set of SCAT Chevy I6 rods and custom pistons (Diamond & JE usually have them made in a few weeks) might be within your budget. I have seen the rods for $500 and custom pistons are typically in the ballpark of $100 each.

~Alex

[Plechtan]

I called around and found a couple of 70's era CJ5/7s that are ready for the bone yard. I will probably just get a crank from one of those motors. Hopefully they won't be too bad. I think somebody should be looking at making at least a Cast steel crank with a 4" stroke that would accecpt Chevy rods. Although the crank would be expensive, you would probably be able to save money buy using stock rods.

I can buy a 232 of 4.0 crank kit for about $100.00 the 258 is at least double that or more. So $200- $300 isn't the end of the world. if you hant to make a custom stroker, then you have to add in the cost of offset grinding the crank and custom rods. So maybe an aftermarket crank wouldn't be a bad idea.

[dwg86]

An aftermarket crank would be nice. Forged would be great, but even a nodular iron cast crank would be nice(I did some reading on it. Seams to be almost as strong as forged be a lot easier on the pocket book). Maybe if there were enough interest it could happen...if the price wasn't to high.
After reading some other post about turning a stock 258 crank to 8000rpm, it would seem the stock 258 crank is pretty strong. As long as we can still get the 12w 258 cranks, how many would put up the extra money for a new crank. Unless we could get them for what the small block chevy and ford cranks cost...around $200.00.
I got 2 258 12w cranks from the local pull a part for $35.00 each. One is standard and one is .010 under(mains and rods). To have them turned will cost $130.00. So Now I am looking at $165.00 for a used crank, and that doesn't include any other extas like nitriding or shot peening. Since my stroker will be a DD, I see no need for the extras. But, I would pay some extra $$ for a new crank.