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Building 4.o help

JMOliver

NAXJA Forum User
Location
North Carolina
I have a 99 xj, I picked up a 95 block that I want to build.
I noticed that pistons split year from 90ish-95 to 96 up. Why is that? I wanna order pistons bored .030 over but don’t want to order wrong ones, anyone here that can help?
 
Call Russ Pottenger at Bishop-Buehl and get some advice from him. He can also sell you very high quality rebuild kits.

Russ
Bishop-Buehl Racing Engines
531 N. Lyall Avenue
West Covina, California 91790
Work (626) 967-1000
Fax (626) 967-7836
Cell (626) 673-2203
Email/PayPal: [email protected]
 
The blocks are the same, only the heads/exhaust/intake is different(if it's a XJ block)
 
The blocks are the same, only the heads/exhaust/intake is different(if it's a XJ block)

Wrong!

The pistons are different because pre-'96 4.0's used a slightly longer stroke (3.4375 inches vs. 3.414 inches.) The connecting rods are the same length, however. And the displacement still rounds out 4 liters. To compensate for this and keep deck clearances and what-not the same, the pin location on the pistons is EVER so slightly different between the pre-'96 and '96+ pistons.

If it was me, I'd figure out a way to put that '95 crank into that '99 block (if you've got it.) using pre-'96 style pistons.The '96 and later blocks (ostensibly) had more webbing in the block plus a main-cap girdle. Guys here will claim that that was only done as a noise, vibration, and harshness (NVH), but I still have a hard time believing that that didn't also mean a stronger block. And the longer stroke of the '95 crank should mean a smidge more engine displacement.
 
You know just enough to be dangerous.

That .023" difference in stroke is irrelevant to the already gaping deck clearances and has nothing to do with the Piston change.

And to get a little more stroke you want a 232 crank. Which bolts in with no other changes, no matter if you use early or late pistons.
 
Last edited:
Yes.

But seriously, Call Russ and talk to him before ordering. There are a lot of things you can do to get a lot more for the same money, and his parts prices are competitive.
 
Plus if you play your cards correctly, Russ can raise your compression ratio thru the size of the dish.
 
JM, you need to make sure you have the pistons your going to use before you have the block bored to get the right cyl wall/piston clearances.
 
This is some good info. I am going to slowly be rebuilding the current engine in my XJ (went to change the rear main seal and found the main bearing on the rear cap totally dry) and was going to be asking some of the same as the OP.

Thanks!
 
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