Starting my build

[Rob92XJ]

Ok today I took a 4.0L piston and pressed it onto a 4.2L rod and put it on my crank when at TDC the piston to deck clearance was about .008" I've been reading that most people and one of my co workers had alot more clearance and had to deck the block. The block I'm using is a 96 NVH block the crank and rods are from a 89 4.2 out of a YJ. Has anyone else ran into this? I'm dropping everything off at the machine shop tomorrow since my XJ's engine blew lastnight.

[rradford9]

Was this a stock piston that you pressed on or a new one? Sounds to me (and I'm pretty much a newb) like you used the 4.0 rod instead of the 4.2. Is there a casting # on it somewhere?

[John]

He's right. what is the casting number on the rods, and what information on the pistons do you have. That will let us answer your question a lot better.
John

[oletshot]

I can't figure out what could have happened. 4.0 rod doesn't explain it either. With 4.0 rod being a 1/4" longer than the 4.2 rod, if he accidentally put the 4.0 piston (no matter what make it is stock or aftermarket) onto a 4.0 rod instead of the 4.2 rod, when he connects it to the 4.2 crank it's going to come out the top. Otherwise we would all be doing this and we would much better quench with the poorman's stroker.

Even if you use all 4.0 parts (piston, rod and crank), you don't end up with .008" deck clearance. Best guess I have is reading the measurement incorrectly. Is it possible that it's .080" deck clearance? Bigger mistakes have been made.

If it is .008", and you didn't use any custom parts, there will be a lot of people interested in your combination of parts.

[dwg86]

Did you use bearings?

[Rob92XJ]

OK I left one 4.0L rod and piston together, installed the 4.2 crank and the piston came out of the block .250", removed piston from rod and installed it on a 4.2L rob had .008". Yes I did use bearings the ones from the 4.0 rod since the ones from the 4.2 were wiped. My co workers stroker had about .250 to the top of the block the only difference is his crank and rods were from a early 80's 4.2 and his block is the original from his 93 YJ. My block is a 96 NVH block and my crank and rods are from a 89 YJ. I had a stock 01 XJ in 2 weeks ago for a misfire due to a burned valve and the pistons were not close to the deck at TDC.

[oletshot]

OK I left one 4.0L rod and piston together, installed the 4.2 crank and the piston came out of the block .250",.

I thought when you posted again we would have a logical explanation to this. Unfortunately, above is the only part of your post that adds up. Is it possible your block was decked previously?

[Mgardiner1]

Yes I did use bearings the ones from the 4.0 rod since the ones from the 4.2 were wiped.

Definitly not trying to be a smart ass, but do you have main bearings in too? And, what are you using to measure it?

[Rob92XJ]

OK I left one 4.0L rod and piston together, installed the 4.2 crank and the piston came out of the block .250",.

I thought when you posted again we would have a logical explanation to this. Unfortunately, above is the only part of your post that adds up. Is it possible your block was decked previously?

As far as I know the block was never decked the engine came out of a friends XJ and the person who owned it before him was a really good customer at the dealership I work for. It is weird from what I had seen on others strokers and from when I worked at a machine shop. I was thinking it may have to do with the NVH block.
Everything is at the machine shop now, so I don't have the casting numbers handy.

[oletshot]

From what I remember the new block has a taller deck and would need more material taken off to achieve the deck clearance your finding. Right now, I'm stumped.

[Rob92XJ]

Yes I did use bearings the ones from the 4.0 rod since the ones from the 4.2 were wiped.

Definitly not trying to be a smart ass, but do you have main bearings in too? And, what are you using to measure it?

Yes the main bearings were in too the ones from the 4.0L block, not the 4.2L
What I'm checking it with is this
http://www.handsontools.com/zoomify.asp ... 781123.jpg

My friend and co worker even said his pistons were alot further down the bore then mine are.

[Rob92XJ]

From what I remember the new block has a taller deck and would need more material taken off to achieve the deck clearance your finding. Right now, I'm stumped.

Same here I posted this to see if anyone else ran into this. But I'm not complaining about it, just weird.

[SilverXJ]

Maybe I missed it, but what pistons are you using? Possible different compression height than usual?

[Rob92XJ]

Maybe I missed it, but what pistons are you using? Possible different compression height than usual?

The piston I had pressed onto the 4.2L rod was a bone stock 4.0L piston out of the block. I don't have my new pistons in hand the machine shop is ordering them for me.

[IH 392]

The piston I had pressed onto the 4.2L rod was a bone stock 4.0L piston out of the block. I don't have my new pistons in hand the machine shop is ordering them for me.

Don't the OE pistons have the tallest pin height of all the 4.0 pistons?