4.0 cheap stroker

[Jesse J]

 

So I went down a youtube rabbit hole last night and came across this vid 

 

 

Pretty much what they did was take the 4.2 liter crankshaft and connecting rods and they just drop in for some extra ponys. I really would love to do this except I fear I will lose reliability. thoughts? opinions? 

[derf]

If you do it right it will be plenty reliable.  A lot of people try to run too much camshaft on stock springs and have valvetrain issues as a result.  Mostly it's having more than 0.500" lift.

 

There's a forum that doesn't get much traffic any more.  https://www.jeepstrokers.com/forum/ They have some good info though.

[Eagle]

A properly done stroker will not be less reliable than a stock, rebuilt 4.0L. The problem is that "properly done" doesn't mean just swapping the crank and connecting rods.

 

The 4.2L engine did not have the same deck height as the 4.0L. This means if you just swap the crank and rods, using stock 4.0L pistons, you get higher compression. That's great for performance, IF you can control detonation ("ping"). But controlling detonation isn't a simple problem. You get into things like enlarging the combustion chambers, controlling quench, and other things that I used to know but forgot years ago. Most of the stroker engines being sold today, I believe, use custom pistons that produce a correct piston height and compression ratio.

 

Look up Dino Savva's web site.

 

[Jesse J]

huh ok that seems doable. is it something I could do at home fairly easily?

[ghetdjc320]

The short 4.2 rods have kind of a borderline rod angle. The most economical stroker is a mini stroker. Use a 232 crank and the 4.0 rods. Ideally use the 4.2 or scat crank and longer 4.0 rods but you’ll need specific pin height pistons. Keep quench real tight 

[derf]

2 hours ago, Jesse J said:

huh ok that seems doable. is it something I could do at home fairly easily?

There's a few specialty tools you'll need and it's precision work that requires some effort.

 

It's not rocket surgery but you probably want a coach your first time through it.

[Jesse J]

18 minutes ago, derf said:

There's a few specialty tools you'll need and it's precision work that requires some effort.

 

It's not rocket surgery but you probably want a coach your first time through it.

what tools exactly?

[Jesse J]

26 minutes ago, ghetdjc320 said:

The short 4.2 rods have kind of a borderline rod angle. The most economical stroker is a mini stroker. Use a 232 crank and the 4.0 rods. Ideally use the 4.2 or scat crank and longer 4.0 rods but you’ll need specific pin height pistons. Keep quench real tight 

So wait what? that doesnt make sense to me

[Eagle]

21 minutes ago, Jesse J said:

So wait what? that doesnt make sense to me

 

Which part? He sort of mixed two topics into that one paragraph.

 

"The short 4.2 rods have kind of a borderline rod angle. The most economical stroker is a mini stroker. Use a 232 crank and the 4.0 rods."

 

All the old AMC engines, from 1966 on, shared the same block. They were offered, depending on year, as a 199 cubic inch (3.3 liter), 232 cubic inch (3.8L) and 258 cubic inch (4.2L). IIRC, they also all shared the same bore, so the displacement was controlled by the crankshaft throw. The 232 crank with the 4.0L bore would result in an engine with a 3.88 inch bore and a stroke of 3.50", compared to the 4.0L crank throw of 3.41". This would displace 248 cubic inches, or 4.1L compared to the 4.0L, which is actually 3.9L. The displacement wouldn't be much different from the stock 4.0L, but the longer crank throw would mean an improvement in low-end torque.

 

"Ideally use the 4.2 or scat crank and longer 4.0 rods but you’ll need specific pin height pistons. Keep quench real tight "

 

There are two ways to do a stroker using the 4.2L crank. You can use the stock 4.2L rods, which are shorter and not as strong as the 4.0L rods, or you can use the 4.0L rods. The 4.0L rods are longer and stronger, but with stock pistons they push the top of the piston higher than the top of the block. So with 4.0L rods you need special pistons that have the holes for the pins located higher in the pistons.

 

The actual wrenching on building a stroker engine isn't difficult -- it's the same as rebuilding a stock engine. The "gotchas" are in all the little details that crop up because you're mixing and matching components from different engines. If it was easy, I would have done it years ago. I've built several V8s, including race engines, so the wrenching doesn't bother me. Once I began investigating all the details involved in getting a stroker to run right, I decided that it was more than I wanted to take on. YMMV, but don't just start throwing parts at a block and think it's going to purr like a kitten when you fire it up.

[ghetdjc320]

36 minutes ago, Eagle said:

 

Which part? He sort of mixed two topics into that one paragraph.

 

"The short 4.2 rods have kind of a borderline rod angle. The most economical stroker is a mini stroker. Use a 232 crank and the 4.0 rods."

 

All the old AMC engines, from 1966 on, shared the same block. They were offered, depending on year, as a 199 cubic inch (3.3 liter), 232 cubic inch (3.8L) and 258 cubic inch (4.2L). IIRC, they also all shared the same bore, so the displacement was controlled by the crankshaft throw. The 232 crank with the 4.0L bore would result in an engine with a 3.88 inch bore and a stroke of 3.50", compared to the 4.0L crank throw of 3.41". This would displace 248 cubic inches, or 4.1L compared to the 4.0L, which is actually 3.9L. The displacement wouldn't be much different from the stock 4.0L, but the longer crank throw would mean an improvement in low-end torque.

 

"Ideally use the 4.2 or scat crank and longer 4.0 rods but you’ll need specific pin height pistons. Keep quench real tight "

 

There are two ways to do a stroker using the 4.2L crank. You can use the stock 4.2L rods, which are shorter and not as strong as the 4.0L rods, or you can use the 4.0L rods. The 4.0L rods are longer and stronger, but with stock pistons they push the top of the piston higher than the top of the block. So with 4.0L rods you need special pistons that have the holes for the pins located higher in the pistons.

 

The actual wrenching on building a stroker engine isn't difficult -- it's the same as rebuilding a stock engine. The "gotchas" are in all the little details that crop up because you're mixing and matching components from different engines. If it was easy, I would have done it years ago. I've built several V8s, including race engines, so the wrenching doesn't bother me. Once I began investigating all the details involved in getting a stroker to run right, I decided that it was more than I wanted to take on. YMMV, but don't just start throwing parts at a block and think it's going to purr like a kitten when you fire it up.

 Yeah I should have clarified I just didn’t have much time to reply lol. Eagle is correct. There are a many different stroker “recipes” I’ve build 3 of them along with several “high performance” naturally aspirated 4.0’s. The basic stroker recipe is to use the 4.2 crank and rods. To keep things relatively economical and plug and play you ideally you would want a donor 87-90 YJ 4.2 (258). As was mentioned, the rods front the 4.0 are longer and stronger so they don’t operate at such steep angles like the shorter 4.2 rods do. The 4.0 makes its power up higher which is typical of an over-square engine design (larger bore than stroke). The 4.2 crank with its longer stroke combined with the larger bore of the 4.0 gives a fairly “square” setup which is nice for all around power. Using the longer 4.0 rods though give a better rod angle which generally translates to durability at higher rpms. 
Another neat option is to get a crank from an amc 232 engine found in several 70’s amc cars. It’s has a 3.500” stroke vs the 3.411 of the 4.0. You can use a couple varieties of of the shelf pistons along with a .060 bore and get a pretty nice combo with the stock 4.0 rods. Not as torquey down low as the 4.2 based stroker but a nice hybrid. 
 

Here is a ton of good information I researched before building my strokers: http://jeep4.0performance.4mg.com/stroker.html

[Jesse J]

wow thanks very very helpful. I  need to spend a lot of time researching engines and what not. What basic tools would I need to get. I 'd also like to make a stab at regearing myself so probably one of those compass lookin things that measures ( I forget the name)

[ghetdjc320]

1 hour ago, Jesse J said:

wow thanks very very helpful. I  need to spend a lot of time researching engines and what not. What basic tools would I need to get. I 'd also like to make a stab at regearing myself so probably one of those compass lookin things that measures ( I forget the name)

 

For regearing it depends on the axle but in general you would need: a press, dial indicator, micrometer (not digital calipers), beam style torque wrench in inlbs (for pinion preload), pinion yoke holder, and a gear bearing puller set (this one is insanely helpful for setting up gears but not 100% necessary. I use a unit from revolution axle and gear. You could also use setup bearings or make your own setup bearings with a die grinder and some old bearings.) A variety of large sockets is also a must along with a good impact wrench, vice and possibly a case spreader. Setting up gears requires a sizeable tool investment but the actual install isnt too hard. You just need to always be thinking in 3D (X, Y & Z axis) when making adjustments. 

 

For engine rebuilding, it all depends on how much you will do yourself vs how much you'll have done at the machine shop. The list of tools here is quite extensive.

[Eagle]

Just going from dim memory here -- assuming you have the block and head cleaned and machined by a shop but you're going to assemble the engine, you would need:

 

A torque wrench

A ring compressor (you can see that being used in the video, to insert the pistons on the block

The ring pliers to install the new rings without breaking them

Valve spring compressor

Plastigage (for verifying the bearing clearance

 

If you'll be buying new pistons, either you'll need a way to press the cross pins out of the old ones and into the new ones, or (recommended) you'll pay the shop to do that.

 

I'm sure there's more that I'm forgetting, but it's late, I'm tired, and it has been literally decades since my last engine build.

 

 

Also, there's at least one thing in that video with which I disagree. He recommends using the newer, lighter 4.2L crankshaft. That reduces reciprocating weight (rotational mass), so the engine will rev up marginally faster. I'm not interested in that. It's a Jeep, not a dragster. I'm interested in torque, low-RPM efficiency, and pulling power off-road. The heavier, fully-counterweighted crankshaft, because of the greater reciprocating mass, is better for off-roading because that mass has more angular momentum. It's less likely to stall at low RPM when crawling over an obstacle. It also runs and dles smoother.

 

If I were to do a stroker, I would want the heavier crankshaft.

 

[Eagle]

I made a slight error in my post on the engine displacements above. I used 3.1412 for the value of Pi in the formula -- it should be 3.1416. For anyone interested in such esoterica, here's how the purmutations and combinations work out:

 

 

 

The Holy Grail 4.7L stroker is a 258 crank with a .060" overbore. Some engines can be bored to .090 or .120 over but, due to core shift, this is not always possible and most builders just stop at .060 over.

[ghetdjc320]

     Yeah the heavier crankshaft has 12 counterweights and is quite a hefty piece of iron. The trick with it is the snout is a decent amount longer than a 4.0 crank so you’ll need to either have the machine shop grind it down or use a machined spacer for the balancer/pulley. You’ll also need a custom pilot bearing if it’s a manual tranny setup.
     Personally I’ve been quite happy with the newer lighter cranks. If I were going to build something for only low end torque I might consider a diesel. The 12cw crank does have quite a windage issue in the oil pan at higher rpm’s.  I don’t really see the advantage with it but it I have seen both sides argue the issue. To me, you could also have a super heavy flywheel have the same result but we’re talking a very slightly marginal difference in real world application but considerable extra weight. Whichever way you go, I do strongly recommend having the machine shop balance the entire rotating assembly. This makes worlds of difference for a smooth running engine. The 96 and newer 4.0 blocks are also a nice revision since that was the first year of the NVH (noise vibration and harshness) revisions. The 87-90 renix 4.0’s also had a higher nickel content in the block supposedly which could possibly take for a more durable block but it’s just so minimal it’s probably not worth the effort.

     My current 4.0 definitely has more power than my last stroker engine. I took a 96 block, bored 60 over decked for zero clearance, thinner cometic mls head gasket, balanced and lightened 4.0 crank, hypereutectic pistons, mild cam, adjustable billet roller rockers, hylift Johnson lifter, chromo pushrods, melling hv pump, Edelbrock aluminum head, dui ignition, Ford 24# 6 hole injectors, 63mm TB, 99+ ported intake, arp bolts for everything. I don’t have a dyno available here but it’s quick and has loads of torque. 
 

My dream build would be an aluminum block diesel. Basically a light weight lcg diesel build on 37’s. Maybe one day 

[ghetdjc320]

1 minute ago, Eagle said:

I made a slight error in my post on the engine displacements above. I used 3.1412 for the value of Pi in the formula -- it should be 3.1416. For anyone interested in such esoterica, here's how the purmutations and combinations work out:

 

 

[Jesse J]

7 hours ago, Eagle said:

 

Also, there's at least one thing in that video with which I disagree. He recommends using the newer, lighter 4.2L crankshaft. That reduces reciprocating weight (rotational mass), so the engine will rev up marginally faster. I'm not interested in that. It's a Jeep, not a dragster. I'm interested in torque, low-RPM efficiency, and pulling power off-road. The heavier, fully-counterweighted crankshaft, because of the greater reciprocating mass, is better for off-roading because that mass has more angular momentum. It's less likely to stall at low RPM when crawling over an obstacle. It also runs and dles smoother.

 

If I were to do a stroker, I would want the heavier crankshaft.

 

 

ok thats pretty useful. I think I agree it is a jeep not a dragster. I probably will the heavier crankshaft.

[Jesse J]

are there any other parts that would add some decent horspower with out breaking the bank? because right now I'd spend the same amount of money stroking it if I just rebuild with the machine shop time(other than the cost of crankshafts and whatever) 

[89 MJ]

11 minutes ago, Jesse J said:

are there any other parts that would add some decent horspower with out breaking the bank? because right now I'd spend the same amount of money stroking it if I just rebuild with the machine shop time(other than the cost of crankshafts and whatever) 

It really depends on your definition of decent. Adding 4 hole injectors and a bored throttle body will up you power for around $200, but they won’t compare to a stroker. 

[Jesse J]

2 minutes ago, 89 MJ said:

It really depends on your definition of decent. Adding 4 hole injectors and a bored throttle body will up you power for around $200, but they won’t compare to a stroker. 

 

i was more thinking like lifters or springs you know. I'm just thinking here

[75sv1]

37 minutes ago, Jesse J said:

 

i was more thinking like lifters or springs you know. I'm just thinking here

As above to the camshaft and springs.  I am building a stroker. I went with Russ Pottenger.  He did recommend aftermarket valve springs vs stock if going with an upgraded cam. The diameter of the springs are thinner in the aftermarket, so they do not bind. I would say a bore TB, a 99+ intake and some exhaust improvements will net some results. Also, you might check into injectors. Also, search budget stroker. 

[Jesse J]

1 hour ago, 75sv1 said:

As above to the camshaft and springs.  I am building a stroker. I went with Russ Pottenger.  He did recommend aftermarket valve springs vs stock if going with an upgraded cam. The diameter of the springs are thinner in the aftermarket, so they do not bind. I would say a bore TB, a 99+ intake and some exhaust improvements will net some results. Also, you might check into injectors. Also, search budget stroker. 

k will do

[ghetdjc320]

9 hours ago, Jesse J said:

are there any other parts that would add some decent horspower with out breaking the bank? because right now I'd spend the same amount of money stroking it if I just rebuild with the machine shop time(other than the cost of crankshafts and whatever) 

As I mentioned, my current 4.0 definitely feels mor powerful than any of my strokers (except the one that had a 100hp shot of nitrous. The 12 counterweight cranks are very tough to find and will require additional machine work. They’re not tough to find because they’re so valuable either. They we’re just redesigned early on. When Skat, who is probably the biggest stroker crankshaft player in the industry built their stroker crank based on the 4.2, they scrapped the idea of the 12cw crank. Once you get more power, are you really going to keep it at lower rpm all the time? Engines that don’t drop rpm fast after you let off the throttle feel like they lack compression or the turbo wastegate didn’t open. The heavier crank really doesn't keep the engine running any better at lower rpm. 

[Jesse J]

k many things to consider thanks . I was thinking If a crank and what not aren't very valuable then it's a pretty cheap way to get power witch would be nice. I won't make up my mind until it's lifted and has tires and gears. so Idk

[Eagle]

IMHO, doing a stroker is not a cheap way to gain power. Your idea of cheap may be different from mine, but as you've seen a stroker involves a lot more than just "dropping in" a crankshaft. If you farm out the machine shop work and do the assembly yourself, you're still looking at a couple of thousand bucks or more. For something to just drop in, I think a camshaft make more sense. But you will have to decide whether you want a cam that produces high end/high RPM power, or something that's more like an RV cam that increases the low- and mid-range power but doesn't like to rev.

 

Just replacing the lifters and springs won't gain anything.

 

A stroker might make sense if you're going to do a complete rebuild anyway -- otherwise, it doesn't make sense.