Rodding out the details

[neonhomer]

Well, building a stroker (duh!) for my 96ZJ. I have the block, the crank is coming, and the cam and lifters are here. I'm trying to work out a few issues.

I'm doing this low buck. Here is the parts list so far..

96 4.0 block
96 4.0 head (0630)
83 8CW 258 crank
83 258 Rods
Comp 68-232-4 cam


Now, this is the issue I have. I don't want to have to buy new pistons, nor can I really afford them. So i am going to be stuck with the 4.0 pistons. I have read that using the 4.0 pistons puts the CR into the 10's.. which will be unsuitable for 87 oct gas.

So the question is.. which rods? I will have a choice of the 258 or the 242 rods. It seems from a wear standpoint, the 258 rods would be better.

The block has not been decked or anything. It was just at the machine shop to be honed and have new cam bearings pressed in. The deck surface was good, so they did not need to remove any material.

So I am at a holding point while I am waiting for parts. Any help would be appreciated.

[Missourian]

I don't believe you can use the 4.0L rods with stock pistons as the stroke will be too long having a 4.2L (258 c.i.) crank installed in the 4.0L block. You may want to research that for yourself.

Here is a couple great sites to help you.

http://www.jeep4.0performance.4mg.com/stroker.html

http://www.angelfire.com/my/fan/selection.html

[GoMopar440]

If you go with the 4.2 rods you can get new pistons on ebay for about $150. Look up the ebay seller "falconglobal". The various piston part numbers you would need are all in the FAQ section.

The pistons get quite a bit more expensive if you try to use the 4.0 rods. Most common being the Keith Black Icon forged ones (944's) for somewhere between $400 to $450.

[neonhomer]

CRAP CRAP CRAP CRAP!!!

Well, the only pistons I can find are going to require a minimum of a .020 overbore. My block has already been finished. New cam bearings, new freeze plugs, and Sunnen Honed.

The KB Icon pistons show to only be available in 3.895"... whereas stock bore is 3.875"..

So, either I have to send the block BACK to the machine shop, or just say screw it, run the 258 rods w/ the 4.0 pistons, and hope for the best. Or just build this as a 4.0, and sit on the crank/rods, and build my current, 230k mile motor, into a stoker....

I didn't see the mentioned dealer on eBay.....

[604rail_king]

you can buy stock bore 4.0 pistons and a 258 rods set to complete your setup if your cylinders are already finished

[SilverXJ]

The machine shop finished the bores without the pistons on hand?

[GoMopar440]

+1 What machine shop bores cylinders without the pistons? There's absolutely no way to set your cylinder to skirt clearance accurately without them. At best they might get lucky with a random parts match, but the most likely result will be either a tight skirt or a loose piston-slappy engine.

All isn't lost yet, but it probably isn't going to be as cheap as you had originally planned. You can try to get pistons to match your bore and play the odds (I wouldn't) or get the pistons now and have the block matched to them.

You can get Icons in other than the common sizes, but for other than standard sizes you'll have to call around and find them. The other option is to try to get some Bultear pistons made to (hopefully) match your engine specs. They cost a little less than the Icons, and are supposed to be fully customizable, so that might be an option. Worst case get them a few thousandths tight and hone the block to fit. Then you'll have a known skirt clearance and you will just have to clean out the mess from the honing. Probably the cheapest/safest way at this point. (if you went with 4.0 rods)

This isn't an endorsement for them, since I've never dealt with them myself, but here's the link to Bulltear's pistons. In your case, if they do all they say they might be a good solution for you. http://www.bulltear.com/catalog/product ... cts_id=242
EDIT: I found where they advertised their pistons here on the forum back in September '11. Link: http://www.jeepstrokers.com/forum/viewt ... =21&t=2704

I didn't see the mentioned dealer on eBay.....

They're still there... http://myworld.ebay.com/falconglobal/?_ ... 4340.l2559


BTW: Did you get your rods reconditioned yet, and which ones are you using? 4.0 or 4.2 rods? Might have another idea based on your answer.

[neonhomer]

Okay... All that was done was to have to block honed. It wasn't bored. We are re-using the original pistons in this engine, but with new rings.

The plan has changed some. The block we have now we are going to just build back into another 4.0.

I am going to take my original block, and have it bored into the stroker block. That way I can take the time needed to do and have everything done right.

Then I can have the rods redone, crank balanced, etc etc... as I get the money to do so.

The motor I am building now will be to get my Jeep back into dependable service.

To answer - No, I haven't had the rods reconditioned. I will have both set of rods available. Just depends on which ones I want to use.

[GoMopar440]

Hope I didn't come off sounding hostile, as that wasn't my intent. Just trying to figure out the problem so we can help you come up with a workable solution.

With the block, either boring and honing or just honing by itself, The shop doing the work would need to have the pistons to get to the correct diameter for your application. The different types of pistons, OEM forged, hypereutectic or forged, each have their own different recommended bore clearances due to each pistons individual metalurigical properties. In a nutshell, they all expand at different rates, and to different amounts, when they heat up from running in the engine. Not enough clearance for expansion could bind your pistons in the bore and break the skirts, too much and you'd have a ton of noise and blowby. It's a pretty important measurement in all engine builds and that's why we were so concerned about it.

Even if you are going to put the original pistons back in the block, please make sure to measure the piston clearance to the bore. If it was just a quick hone job you might be fine with just new rings, but you'll still want to know the bore clearance for the reasons stated above. If your bores were at the outside edge of the tolerance limit when you started, a simple hone job could possibly put you out of spec. It's a very possible scenario if you had an engine that left the factory on the high side of the tolerance limit, and then add wear and tear from thousands of miles of use. It's easy to check before hand while everything is apart so there's no reason not to.

I don't blame you for putting the stroker on hold if you need your Jeep running right now. There's a lot to learn up front to get it right, and it's a pretty big investment, even if you go the low buck route. This is the place to find out anything you need to know about doing a stroker right the first time around though. The guys on the forum here pretty much have the answers to any question you may have. Be sure to check out the Stroker Compression Ratio Calculator (upper right side of the forum page) once you start to get some ideas of the particular parts you want to run. It'll save you a lot of headaches figuring out what works with what. If you get stuck, use the Search function on the forum and you'll find a ton of specific info. It's usually quite a bit quicker than posting a question and waiting for a response. Don't be afraid to ask if you still can't find the info you need though, we're here to help.

[GoMopar440]

Here's a vid that explains the clearance issue a lot better than I can. http://www.youtube.com/watch?v=fEpQJY8P ... re=related

[SilverXJ]

The shop doing the work would need to have the pistons to get to the correct diameter for your application. The different types of pistons, OEM forged, hypereutectic or forged, each have their own different recommended bore clearances due to each pistons individual metalurigical properties.

OEM Cast, Hypereutetic cast, forged 4032 or forged 2618.. and even then each manufacturer may specify a different clearance based on the piston cam and other manufacturer's changes... along with your intended use.

Even if you are going to put the original pistons back in the block, please make sure to measure the piston clearance to the bore. If it was just a quick hone job you might be fine with just new rings, but you'll still want to know the bore clearance for the reasons stated above. If your bores were at the outside edge of the tolerance limit when you started, a simple hone job could possibly put you out of spec. It's a very possible scenario if you had an engine that left the factory on the high side of the tolerance limit, and then add wear and tear from thousands of miles of use. It's easy to check before hand while everything is apart so there's no reason not to.

x2. Worn piston worn bore = lose clearance. Add a hone job and you have a noisy engine that has blow by issues and a short life. You will also want to thoroughly check the pistons for cracked skirts and any other damage.

[Dezertxj88]

Just to throw it out there, but theres been many cases of the stock 4.0 pistons breaking off at the side skirts and such after being reused! I'd assume just from wear and then being reused in the rebuild, more wear and they go ca-put!
I would personally wait till you have another 300 bones. Grab a set of pistons, send oletshots a Pm and get em dished to the correct dish for deisred compression ratio! Pistons run about 200-300 pending what you get and oletshots does the dishing for 85 per 6 I believe. Its not worth it to have nagging questions in the back of your mind..."should I have done this, I should have gotten better pistons ect ect."

Wait an extra month, eat top romen and get her done up right! Nothing like spending 1000+ and having the motor break. Its worth it to spend the extra now my man!

[Cheromaniac]

Just to throw it out there, but theres been many cases of the stock 4.0 pistons breaking off at the side skirts

Yeah and in each instance it's been '96+ pistons that have broken at the skirt, probably because they were rocking too much inside the cylinders.

[neonhomer]

I would assume the clearance spec is listed in the FSM. The machine shop honed the block based on the fact that we were going to just put the stock pistons back in the block w/ new rings.

Will have to see when we put the lower end together. If the clearance is too great, then we're going to have to stop, and see where we are. At this point, the block WILL have to go to the machine shop, and new pistons WILL have to be ordered.


What is a safe size to order for pistons? More than likely, I am going to order the Icon IC944's, but not sure if I should get the .020 or the .030... I don't want to take too much material out of the block if I don't have to.

[Retlaw01XJ]

The shop needs to measure the present bore before determining which oversize pistons will work.
If there was no or very little ridge at the top of the bores, 0.020" oversize will most likely work.
Best to let the shop tell you what to order.