foolish newbie questions

[riversidefort]

So, I’ve decided to take the plunge and stroke out the motor in my 1997 cherokee. I’ve read all the basics and I still have a few questions…

1. what special steps need to be taken when stroking a motor attached to a manual tranmittion(an ax15 in my case)?
2. what’s the difference between the “metric” pistons and the non metric? And are the 1997’s metric?

That being said here’s how my plan goes incase it helps; 258 crank and rods 242 pistons with the dish volume taken out to 22cc and a .043 head gasket an no block or head machining.

Thanks in advance for any input

[John]

So, I’ve decided to take the plunge and stroke out the motor in my 1997 cherokee. I’ve read all the basics and I still have a few questions…

1. what special steps need to be taken when stroking a motor attached to a manual tranmittion(an ax15 in my case)?
My YJ is a 4.6 stroker to a ax15 transmission. The only item specific for this physical application is the pilot bushing for the crankshaft. I doubt the one in your 258 crankshaft will be correct to mate with the ax15 input shaft.

2. what’s the difference between the “metric” pistons and the non metric? And are the 1997’s metric?
Ring width is the difference. Don't know what rings you have in that motor.

Do you plan on doing a valve job and checking the head and block for flatness?
John

[Flash]

So, I’ve decided to take the plunge and stroke out the motor in my 1997 cherokee. I’ve read all the basics and I still have a few questions…

1. what special steps need to be taken when stroking a motor attached to a manual tranmittion(an ax15 in my case)?
2. what’s the difference between the “metric” pistons and the non metric? And are the 1997’s metric?

That being said here’s how my plan goes incase it helps; 258 crank and rods 242 pistons with the dish volume taken out to 22cc and a .043 head gasket an no block or head machining.

Thanks in advance for any input

The AX15 is strong......just bolt it up!

The metric pistons us a different piston Ring

Sounds like you have a good plan started.

Flash

[seanyb505]

Your Compression ratio and quench will go up, so youll probly have to use premium gas.

Make sure you get the right pilot bearing, #53009180AB. You can usually pick them up for less than 20 dollars. The transmission should be fine other than that.

The main difference between metric and standard pistons is the cost of the rings, both pistons are the same diameter and have the same wrist pin height.

Im sure youve heard this before, but if you do it right the first time, you wont be doing it a second time for a while. Im sure there are some guys who are just throwing a crank and rods in and calling it a day, but Im going with all new parts and any machining where necessary just so I know I wont be having to replace anything soon. Hope this helps!

[riversidefort]

thanks for the input . and to address the question of checking the block and doing a valve job... having the head rebuilt is almost a certainty as the engine has 180k on it at the moment and could probably use it. as far as checking the head and block for flatness, and will correct them if need be. i'd just prefer to leave the block unaltered.
good to know about the pistons by the way. i was worried there could be some difference in pin diameter or some other ridiculous change.

[oletshot]

My experience is, you can find the metric pistons cheaper than standard pistons, but as seanyb505 pointed out the cost of the metric rings makes the metric piston/ring combo more expensive than standard.

[seanyb505]

It was one or the other I cant remember but I had the same thoughts when I first started looking at pistons. I talked to summit on the phone about the 802 and the 825 and which ever was more expensive had the cheaper rings I think. I have silvo 2229s which are standard, and I got moly rings for $38.14.

[Shark]

i believe '96 and up use metric rings and '95 and before use standard. on XJs anyway.

[oletshot]

by seanyb505 on March 24th, 2008, 10:10 am

Your Compression ratio and quench will go up, so youll probly have to use premium gas.

How can you be sure? Static compression only goes up .33 from 8.76:1 (stock 4.0) to 9.09:1 (his 4.5 spec.) and quench stays the same as stock (I'm not sure what "242 pistons" means, to me it means stock pistons). Plus, he didn't mention a cam, so there is no way of knowing what the real compression ratio his engine will see is.

My guess is with the right cam you may be able to run 87 octane.

[riversidefort]

i was going to stick with the stock cam. and indeed i meant the stock pistons, machined to have a 22cc dish volume. i figured stick with the stock cam because i figured it would make it easier for me to fine tune the engine. as i already know how the stock 4.0 acts. i try to stick to changing one variable at a time.

[seanyb505]

How can you be sure? Static compression only goes up .33 from 8.76:1 (stock 4.0) to 9.09:1 (his 4.5 spec.) and quench stays the same as stock (I'm not sure what "242 pistons" means, to me it means stock pistons). Plus, he didn't mention a cam, so there is no way of knowing what the real compression ratio his engine will see is.

My guess is with the right cam you may be able to run 87 octane.

Yes, static compression will only go up to 8.94, but thats still up If he uses 258 crank and rods, 4.0 pistons, .043" HG and no block decking his quench will be at .0815". Not by much, but both go up. I used the handy dandy stroker calc for those numbers. At any rate, I have not completed any motor yet, so this is just my reasoning speaking. Im sure you could get away with mid grade.

[oletshot]

Yes, static compression will only go up to 8.94, but thats still up If he uses 258 crank and rods, 4.0 pistons, .043" HG and no block decking his quench will be at .0815". Not by much, but both go up. I used the handy dandy stroker calc for those numbers. At any rate, I have not completed any motor yet, so this is just my reasoning speaking. Im sure you could get away with mid grade.

I don't think the numbers your using are correct, or mine aren't. I've drawn this up in a cad program and run it on a couple calc's, and all come up quench is same as stock with the .043" gasket. That includes our calc. Here are the numbers I used.

Head volume: 57cc
Bored over: 0
Decking: 0
Planing of head: 0
Custom piston: -22. cc
Rod length: 5.875"
Piston height: 1.601"

Using an .043: gasket yields

Compression ratio: 9.09:1
Quench: .0725"
Difference from stock: 0

"How can you be sure?" , referred to the need for premium fuel, not compression going up. Static compression is just a fancy number to throw around, it doesn't really mean anything. Now that he has stated he plans on using the stock cam, Dynamic (real) compression can be calculated and a real "on paper guesstImate" can be made.

I've also never completed a motor, yet. My mouth (fingers) is also writing checks my ass can't cash.

[seanyb505]

I was using the pin height of 802 or 825 replacement pistons, 1.592". I think theres our difference.

[oletshot]

That's it.

[Flash]

That's it.

Hay, Oletshot..........specking of stilling signatures.........check out mine