akadeutsch wrote:The 4.2 rods will run long and hard for you. The 258 was known to be a long lasting engine. It ran in jeeps from around 1975 to around 1987 and it is said by some (Novac Conversations) that "The AMC 258 is probably the most recognizable and longest-running Jeep powerplant in the brand's history."
The 258 used the shorter rods and it created the same geometry we see today in our short rod strokers. I just can't find any FACTS that support the claim that the long rods will last longer.
You're forgetting one important point.
The cylinders in the 4.0L block are shorter in length than those in the 4.2L block (designed for the shorter stroke of the 4.0L crank) so when you use the 258 crank & rods, the lowest part of the piston skirt is visible from the bottom of the cylinder at BDC. It's not enough to be an issue in normal day-to-day driving but there might be an increased risk of breaking piston skirts if you run the engine hard for extended periods.
If you use the 4.0L rods with IC944 (or custom forged pistons), the lowest part of the piston skirt is a 1/4" further up the cylinder at BDC so there's no potential breakage issue. You can also run a tighter quench and thereby improve your chances of being able to use lower octane gas without detonation.
jsawduste wrote:Try looking at the long vs. short rod with an advanced eye. Considering things such as dwell angles, rod angularity, bore to engagement, compression and quench, effects of volumetric efficiency for starters. There are more but this is a start.
There are basic fundamentals that "should" be adhered to if you want to "optimize" your investment in time and money.
Unfortunately someone reads it on the internet or perhaps even builds there own engine and they become experts without fully understanding the dynamics.
For kicks, do research on detonation. You will find that EGT and combustion temps actually go DOWN. Imagine that !!
Im not trying to argue but I'm board so here goes.
I did consider these things, WITH an "advanced" eye. My diploma in auto mechanics says that my eye is advanced enough.
Riddle me this. How does rod length effect volumetric efficiency if the deck clearances are equal? The FACT is that the 258, with its higher "dwell angle" and greater "rod angularity" was/is still a very long lasting durable engine.
I am not for or against the different rods. If I would have had the extra ~300 dollars laying around then I would have went that way as well, and then I would also have thrown a blower on it too.
P.S. I have an extra set of short rods in Denver if you want them.
Thanks dude, that's awesome. I've decided to go with the 944s because of that deal, and doing my numbers again, I found that I can get them. If I couldn't do the 944s, I would have stuck with the 4.2 rod build. I have my used 4.0 rods that I'm planning on using, thanks.
When you recondition the rods make sure the overall length is checked and set to be equal from one to the next. Don`t be surprised if you see a little twist in those rods also. Those roughly .25 longer rods will help keep your pistons happy at BDC where the piston has tendency to rock for lack of engagement.
Encourage you to spend a few moments searching the web for a better understanding of a long vs. a short rod and how that plays in the building of a typical stroker engine. Grasp the meanings of quench and compression and how they relate. You may come back surprised at the knowledge you gain. This knowledge can be useful in better understanding a number of factors surrounding the building of a typical stroker engine. It will also help in choosing the dynamics of cam selection for your use. Keeping in mind there are significant differences between a 4.0 and a 4.2 block while you study.
Don`t take my word for it. Study on your own and make conclusions based on how they fit your needs. There is a wealth of information available and much of it from very reputable sources.
When your done not only will you understand how your engine is put together the way it is but why.
Where I was proven to be wrong not only in that thread but after researching it on my own it was a fundamental I was wrong about universally. That was 5 years ago. That was a lesson that really stuck and no longer do I take info as gospel without being able to back it up.
jsawduste wrote:When you recondition the rods make sure the overall length is checked and set to be equal from one to the next. Don`t be surprised if you see a little twist in those rods also.
My 2001 rods had a slight bend to them. I believe it's referred to as 'parallelism' . The result is the deck clearance varied a bit from one side of the piston to the other. I freaked when I found this. Went back to the machine shop that reconditioned them, and they showed me the fixture they used to check them.... it doesn't measure, but just gives a good/bad indication. Further research showed they were within factory specs, so they were used as is.
If you do get the reds reconditioned, new rod bolts from ARP are another extra-cost upgrade. Bought mine from Falcon-global.
If you have a scale handy, weigh each of the rods to see if they're close.
Walt K
Eastern Pa
2001 Cherokee 4.6 stroker 90 day build
Buick GS's and Saab turbos for other days...
Retlaw01XJ wrote:If you do get the reds reconditioned, new rod bolts from ARP are another extra-cost upgrade. Bought mine from Falcon-global.
Make sure you use ARP's torque spec as well as their assembly lube on the rod bolts. Also, the bolts should be changed prior to resizing the rods, and when you change bolts you need to have the rod resized.
If you have a scale handy, weigh each of the rods to see if they're close.
The machine shop should do this and match the small end and large end to the lowest weight rod. Same for the pistons. It is part of the balancing.
If you have a scale handy, weigh each of the rods to see if they're close.
The machine shop should do this and match the small end and large end to the lowest weight rod. Same for the pistons. It is part of the balancing.
If he's on a budget and doesn't want to spend the extra $$ for a full professional balance, much of it can be done at home by weighing the pistons (should be real close), and the individual rods. If they are relatively equal, much of the balance job is done.
The crank can be spin balanced by itself if you want to be sure all is good.
On a 'V engine you pretty much have to have it rebalanced when changing to pistons with different weight. On an inline, one cylinder is counter balanced by another, so weights between cylinders just need to be equal to each other. When I rebuilt my first inline 6, I didn't realize they didn't require the same spin balance with bob weights that the 'V' engines do. My machine shop was honest enough to tell me it isn't a 'must do' on my 4.6.
Walt K
Eastern Pa
2001 Cherokee 4.6 stroker 90 day build
Buick GS's and Saab turbos for other days...
Retlaw01XJ wrote:
If he's on a budget and doesn't want to spend the extra $$ for a full professional balance, much of it can be done at home by weighing the pistons (should be real close), and the individual rods. If they are relatively equal, much of the balance job is done.
He would need a pretty good scale as well as a fixture to weight each end of the rods. Simply weighing the whole rod won't cut it. He could make the fixture for the rods himself though.
Man, RPM machines sure takes their time to process orders. Placed my order last week and they haven't shipped it yet, they say it takes about 5-9 business days to process online orders so I can't complain yet haha.
So my order has been on Awaiting Shipment since the 8th of December, and I've been trying to contact RPM Machines to find out what that means, but no one has gotten back to me. Kind of bummed cause I would of had some time to work on my engine if only I had what I needed. Does anyone know what that Awaiting Shipment status means?
It could mean the pistons are not in stock and they're waiting for them to arrive from the manufacturer.
Or, they are being shipped directly from the manufacturer to you.
Summit Racing and Jegs show ship dates of 1/7 or 12/29.
Walt K
Eastern Pa
2001 Cherokee 4.6 stroker 90 day build
Buick GS's and Saab turbos for other days...
Retlaw01XJ wrote:The later stock cam works well. If you go to a cam with much more lift, you'll need to use different valve springs, retainers and might need to have the head machined to fit the different springs.... that all adds to the cost. I went with a Crower 44243 which is a bit bigger than stock but still works with the stock valvetrain.
You can upgrade some of the components for a slightly higher cost.... I went with moly rings, Clevite bearings instead of Kings, and brass freeze plugs. Also got ARP rod bolts for my 4.0 rods. Best to call them and discuss options. Good folks to deal with.
4.0 rods will require the KB forged pistons. They're pricey right now.
Can I use the standard size bearings from this kit for my stroker, if no resizing is needed for the bearings? Looks like my pistons are being shipped, awesome.
SilverXJ wrote:You have to use the bearings that fit the crank. If your crank has been turned .010" you need .010" bearings. Standard sized bearings won't work.
Thanks. I talked to the machinist today and he just got done taking measurements and was going to turn it .010, but then I asked if he took measurements for a 4.0 cranks or 4.2. He accidentally took the measurements for a 4.0 cranks, but he was confident that the measurements between the two should be the same since I was going to use 4.0 bearings and he was going to double check to make sure. Is that true though? Are the measurements between the two cranks the same? I guess what I was trying to make sure earlier also is if I can use 4.0 bearings with the stroker build.
Also, lets say the crank ends up needing to be turned .020? Is that safe? He wanted to try .010 first and see if it'll need to go to .020 from there. I finally got my pistons!
optmaxx wrote:He accidentally took the measurements for a 4.0 cranks, but he was confident that the measurements between the two should be the same since I was going to use 4.0 bearings and he was going to double check to make sure. Is that true though?
Yes
Are the measurements between the two cranks the same? I guess what I was trying to make sure earlier also is if I can use 4.0 bearings with the stroker build.
Yes. The rod bearings are the same for 4.0 & 4.2 cranks of all years ('72-'06). However, the main bearings for the 4.0 HO blocks ('91-'06) have the locating tangs in the center whereas the main bearings for AMC 4.2/Renix 4.0 blocks ('72-'90) have the locating tangs offset to one side. The journal sizes are the same though.
Also, lets say the crank ends up needing to be turned .020? Is that safe? He wanted to try .010 first and see if it'll need to go to .020 from there.
Not a problem. The rod & main journals can be turned up to 0.030" undersize.
