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do I have to bore to stroke?

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The1AndOnlyBug
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do I have to bore to stroke?

Post by The1AndOnlyBug » January 25th, 2020, 12:57 pm

So I'm rebuilding my sisters '00 TJ Sahara. It has a 4.0 with 211k with plenty of power, but the motor has a low end knock and gets warm under load. She gave me permission to stroke it, and I'm prepared to spend whatever money I have to, but will be trying to do it as cheaply as possible.
The ultimate goal is to increase drivability and to last many years without any work. 4" lift and 33's d44/d30 with 3:73 gears.

I found a 12 weight 4.2 crank for $125 but the guy said it needs to be turned.
I did a compression test on the engine and this is what I had for numbers.
Cylinder compression test, front to rear.
#1:160PSI
#2:163PSI
#3:150PSI
#4:145PSI
#5:155PSI
#6:160PSI

Spec is 125-150 PSI.

With these numbers I'm highly doubtful that the cylinders will need to be bored, but am I able to stroke it without boring them?

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Re: do I have to bore to stroke?

Post by IH 392 » January 25th, 2020, 1:03 pm

With that many miles I bet it will need to be bored.
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The1AndOnlyBug
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Re: do I have to bore to stroke?

Post by The1AndOnlyBug » January 25th, 2020, 1:24 pm

Ok, I'll know more once I pull the pistons and measure the cylinders. But on the off chance that the cylinders only need to be honed, would I need to bore it to stroke it?

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Re: do I have to bore to stroke?

Post by jasonb » January 25th, 2020, 2:18 pm

If that's the case, technically you could re-use your old pistons and make a short rod stroker. You'll need a set of 258 rods in addition to the crank, but most choose not to go that route anymore due to the advantages of the long rod setup. IMHO, the best approach is Russ's custom rod/piston combo... it will cost more up front though.

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Re: do I have to bore to stroke?

Post by Cheromaniac » January 26th, 2020, 12:01 am

The1AndOnlyBug wrote:
January 25th, 2020, 1:24 pm
Ok, I'll know more once I pull the pistons and measure the cylinders. But on the off chance that the cylinders only need to be honed, would I need to bore it to stroke it?
You don't need to rebore the cylinders when adding a stroker crank but with that many miles on the engine, I'd do it anyway for the sake of long term reliability. You'll need cylinders that are within factory tolerances for roundness and taper, and honed with the correct crosshatch pattern to ensure good cylinder lubrication while minimizing oil consumption.
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Re: do I have to bore to stroke?

Post by Russ Pottenger » January 28th, 2020, 12:16 pm

Cheromaniac wrote:
January 26th, 2020, 12:01 am
The1AndOnlyBug wrote:
January 25th, 2020, 1:24 pm
Ok, I'll know more once I pull the pistons and measure the cylinders. But on the off chance that the cylinders only need to be honed, would I need to bore it to stroke it?
You don't need to rebore the cylinders when adding a stroker crank but with that many miles on the engine, I'd do it anyway for the sake of long term reliability. You'll need cylinders that are within factory tolerances for roundness and taper, and honed with the correct crosshatch pattern to ensure good cylinder lubrication while minimizing oil consumption.
X2,

Considering the overall cost of time and investment building a new engine properly and assuming you’re going to have to buy new Pistons, The cost of of having the block professionally bored and honed to assure proper clearances would be wise.

The1AndOnlyBug
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Re: do I have to bore to stroke?

Post by The1AndOnlyBug » January 28th, 2020, 6:33 pm

Fair enough, I'll keep you guys posted by what I figure out :rockout:

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Re: do I have to bore to stroke?

Post by The1AndOnlyBug » January 31st, 2020, 8:12 pm

Still in the process of measuring, but this is what I've got so far.
You can still see some of the cross hatching on the walls 8-)
Cylinder dimensions
A = across B = front to rear
1A: TDC: 3.8769 1B: TDC: 3.8774
1A: BDC: 3.8779 1B: BDC: 3.8781
2A: TDC: 3.8778 2B: TDC: 3.8765
2A: BDC: 3.8776 2B: BDC: 3.8768
3A: TDC: 3.8768 3B: TDC: 3.8768
3A: BDC: 3.8783 3B: BDC: 3.8777
4A: TDC: 3.8778 4B: TDC: 3.8765
4A: BDC: 3.8770 4B: BDC: 3.877
5A: TDC: 3.8775 5B: TDC: 3.8764
5A: BDC: 3.8778 5B: BDC: 3.8776
6A: TDC: 3.8781 6B: TDC: 3.8778
6A: BDC: 3.8777 6B: BDC: 3.877

Main bearing bores:
1. A. 2.6898 B. 2.6893
2. A. 2.6894 B. 2.6901
3. A. 2.6911 B. 2.6910
4. A. 2.6901 B. 2.6908
5. A. 2.6905 B. 2.6908
6. A. 2.6910 B. 2.6909
7. A. 2.6920 B. 2.6910

The1AndOnlyBug
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Re: do I have to bore to stroke?

Post by The1AndOnlyBug » February 13th, 2020, 5:48 pm

So I changed directions with this build and am saving the 4.2 crank for a build in my own jeep :twisted:
I also swapped engines with one that I bought several years ago previously rebuilt, and I tore it down to measure everything and rebuild.
This engine is the same few years '00-'02 TJ/WJ block everything looks much better number wise.
The engine I removed out of the TJ ended up having 3 pistons that were cracked on the left side skirt, front and rear. (#3, 4, and 6.)
Here are the measurements of the other block (if anyone cares), I still have to crunch the numbers, and I still have probably another half-day of measuring some remaining things.
Cylinder dimensions
A = across B = front to rear
1A: TDC: 3.8722 1B: TDC: 3.8722
BDC: 3.8765 BDC: 3.8756
2A: TDC: 3.8772 2B: TDC: 3.8760
BDC: 3.8761 BDC: 3.8761
3A: TDC: 3.8775 3B: TDC: 3.8768
BDC: 3.8754 BDC: 3.8761
4A: TDC: 3.8776 4B: TDC: 3.8765
BDC: 3.8765 BDC: 3.8765
5A: TDC: 3.8779 5B: TDC: 3.8770
BDC: 3.8753 BDC: 3.8762
6A: TDC: 3.8793 6B: TDC: 3.8762
BDC: 3.8772 BDC: 3.8763

Main bearing bores:
1. A: 2.6886 B: 2.6885
2. A: 2.6915 B: 2.6915
3. A: 2.6902 B: 2.6909
4. A: 2.6869 B: 2.6921
5. A: 2.6896 B: 2.6884
6. A: 2.6919 B: 2.6903
7. A: 2.6916 B: 2.6917

Main bearing journals:
1. A: 2.4998
B: 2.4989
C: 2.4992
D: 2.4990
2. A: 2.4991
B: 2.4995
C: 2.4990
D: 2.4993
3. A: 2.4989
B: 2.4989
C: 2.4989
D: 2.4989
4. A: 2.4989
B: 2.4900
C: 2.4989
D: 2.4989
5. A: 2.4989
B: 2.4988
C: 2.4989
D: 2.4990
6. A: 2.4990
B: 2.4989
C: 2.4991
D: 2.4990
7. A: 2.4990
B: 2.4991
C: 2.4989
D: 2.4989


Behind oil ring: A: 2.6305 B: 2.6309

Rod bearing journals:
1. A: 2.0944
B: 2.0944
C: 2.0943
D: 2.0943
2. A: 2.0941
B: 2.0938
C: 2.0941
D: 2.0939
3. A: 2.0947
B: 2.0944
C: 2.0938
D: 2.0940
4. A: 2.0941
B: 2.0943
C: 2.0940
D: 2.0941
5. A: 2.0941
B: 2.0943
C: 2.0941
D: 2.0940
6. A: 2.0941
B: 2.0944
C: 2.0942
D: 2.0946

Crankshaft runout (no spec): 0.002 old New .0005

Connecting rod bearing bore:
1. A. 2.2082 B. 2.2081
2. A. 2.2085 B. 2.2081
3. A. 2.2085 B. 2.2081
4. A. 2.2081 B. 2.2080
5. A. 2.2081 B. 2.2082
6. A. 2.2082 B. 2.2081

Lifter bores:
1. E: I:
2. I: E:
3. I: E:
4. E: I:
5. E: I:
6. I: E:

Ring gap clearance (Brand new rings):
A: Top B: Bottom
1: A: .026, B: .022
2: A: .026, B: .022
3: A: .027, B: .024
4: A: .025, B: .023
5: A: .026, B: .023
6: A: .026, B: .024

Piston ring groove clearance
1. A: .002 B: .002
2. A: .002 B: .002
3. A: .002 B: .002
4. A: .002 B: .002
5. A: .002 B: .002
6. A: .002 B: .002

Piston Diameters:
1. Top: 3.8708 Skirt: 3.8745
2. Top: 3.8711 Skirt: 3.8733
3. Top: 3.8701 Skirt: 3.8740
4. Top: 3.8711 Skirt: 3.8762
5. Top: 3.8706 Skirt: 3.8738
6. Top: 3.8728 Skirt: 3.8759

Now not all of my measurements may be perfect, but I promise that the are all very close.
While I may not be stroking this engine, I am putting a comp cam in it, for now I am going to keep the 0330 head (I have 2 now with neither of them cracked), I know I need mopar performance valve springs and retainers, can anyone tell me if I need the keepers as well? Looking at them they don't look like they are the 3 groove like the oem valves?
I'm upgrading the exhaust with 2.5" the whole way (still have to find what header I want to use) and am going to port match the head/intake best I can. I will also see if it's possible to get the machine shop to bore out my throttle body, but we'll see.
I also ground my valves today to 46 degrees (from 46.5) and my seats to 45 (from 44.5)

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