Jeep Strokers

Greetings from Europe !

Im building 89 Wrangler YJ. (sit 7 years under the tree) It has 4.2 AMC 258. Its running now, but its very tired. So im gona stroke it !

So i have complete 4.2 AMC 258 and 88 4.0 from XJ.

Idea:
4.2 3.895" Crank. - problably needs machining.
4.2 Rods. - have them cheked
sealed power 677 pistons .030 over
New rings,bearings etc.
New injectors.
Stock head (DIY port it? ) , intake , exhaust. Bore TB.

Im aware of the big quench problem but for me to order custom pistons and use 4.0 rods is out of the game because of the cost.(shiping etc.)
I dont see detonation problem an issue because we have high octane fuel.

Machining is cheap- i can deck it down .040 ? shorter pushrods?

So my question is, what cam i should buy for this combination ?
Closest dealer is selling Melling MC809 - so this would be the cheapest option. But im willing to go the right way.

And i know. HO engine would be nicer, but in europe we dont have junkyards full of 4.0HO-s so it is what it is. ( Had do buy full XJ to get this engine)
Im not looking 300HP monster. Just a little HP boost with stuff i already have.

Sorry for my bad english , and thank you for this community !

Few pictures if someone cares:

The Melling MC809 is the same spec as the stock cam but if you want a mild performance increase, Russ can supply you with a lower lift version of the CompCams 68-232-4 that allows you to retain the stock valve springs.

Thank you Cheromaniac.

'What can you suggest from the shop?
Maybe something i can find in europe from parts dealers ?

In overall.
Should i deck the block down ?

Some math:

Stroke: 3.895
Rod: 5.875
677P piston height: 1.585
Jeep 4.0 Deck height: 9.450

Deck clearence : 0.043

Compression calc :

Bore: 3.905 inches
Stroke: 3.895 inches
Combustion Chamber: 60cc dremel it to 60 ?
Deck Clearance: .043 inches
Gasket Thickness: .039 inches
Dome/Dish/Valve Relief: 15 cc

Static Compression Ratio 9.36 : 1
Dynamic Compression Ratio 6.92 : 1


In case of stock chamber size
Static Compression Ratio 9.74

Quench: 0.08199999999999999 ?


Am i correct ? Considering high octane fuel in europe. 98 equivalent to 93 in US. Seems okey and safe ?

The original poor man's stroker in my Jeep was almost exactly that spec except for a 3.895" bore (square engine), 677P pistons with dish increased to 17.7cc, and a 58cc combustion chamber. The static CR was 9.25:1 with a deck clearance of 0.045" and a quench of 0.088" (0.043" head gasket).
I had absolutely no problem running it on 95 RON octane fuel (91 US) and that was using the stock Champion RC12LYC spark plugs (not colder plugs).

Great. Ordered the pistons.
I also managed to find 1720 head.- can i still use stock intake and fuel rail or it will choke the good flowing head ?
If im looking to delete EGR system- should i change timing on cam ?
Problably going with the Melling MC809.

The HO head will require an HO intake manifold and throttle body for best results. As for the cam, install it straight up.

What should the bore clearence be?
On the package it says min 0.0001 inch.

It'll be whatever the piston manufacturer specifies 'cause the type of material used makes quite a difference. Hypereutectic pistons require the smallest clearance from the bore since they have the lowest expansion rate.

Hei guys.

Head, block and crankshaft are at machining.

Meanwhile getting other things ready.
Im considering keeping all the 4.2 acc And V-belt.
Just to keep it simple. Because im building a wrangler i will not going to use AC anyway.
And because the 4.0 is from cherokee the fan sits on the other pulley. ( on wrangler its on waterpump) and it will line up with original rad placement.

Any cons goint that way ?

Just make sure you use the right water pump. 4.0 ones spin opposite direction from 4.2s. The AMC guys have been using 4.2 accessories on 4.0 for a while here

AMC 258 crank machined.
7120 resurfaced and new valves.

Supakas wrote: ↑January 13th, 2024, 10:59 am Greetings from Europe !

Im building 89 Wrangler YJ. (sit 7 years under the tree) It has 4.2 AMC 258. Its running now, but its very tired. So im gona stroke it !

So i have complete 4.2 AMC 258 and 88 4.0 from XJ.

Idea:
4.2 3.895" Crank. - problably needs machining.
4.2 Rods. - have them cheked
sealed power 677 pistons .030 over
New rings,bearings etc.
New injectors.
Stock head (DIY port it? ) , intake , exhaust. Bore TB.

Im aware of the big quench problem but for me to order custom pistons and use 4.0 rods is out of the game because of the cost.(shiping etc.)
I dont see detonation problem an issue because we have high octane fuel.

Machining is cheap- i can deck it down .040 ? shorter pushrods?

So my question is, what cam i should buy for this combination ?
Closest dealer is selling Melling MC809 - so this would be the cheapest option. But im willing to go the right way.

And i know. HO engine would be nicer, but in europe we dont have junkyards full of 4.0HO-s so it is what it is. ( Had do buy full XJ to get this engine)
Im not looking 300HP monster. Just a little HP boost with stuff i already have.

Sorry for my bad english , and thank you for this community !

Few pictures if someone cares:

The Melling MC809 offers the same specifications as the stock cam. However, if you're seeking a slight performance boost, Russ can provide you with a lower lift version of the CompCams 68-232-4. This option allows you to keep the stock valve springs while still enhancing performance.

Things are slowly moving.






Managed to find 99 year intake.
Am i right that i need 91-95 TB Because of the MAP sensor. (i have renix)
And also 91-95 Fuel rail.
Can someone suggest Injectors for this setup:
88 block .30+
258 cranck and rods.
7120 head
99+ Intake.