What is the normal compression on a 1995 RRC 4.2. My mechanic said I have 142-147 on the cylinders. Just checking what most people find they have. The truck has 196,000miles on it. Maybe its time for a diesel conversion.
compression
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I bought it at 175000 miles. I don't know if or when it was done. Will the timing chain cause the compression to be lower?
I don't think I see them that high. I figured his 145 was pretty good. But then I usually just do cylinder leak down tests anymore.
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Is there a difference between the GEMS and 14CUX trucks? Don't the GEMS have a higher compression head? I'm pretty sure my 4.0 was testing out around 170-180 but my 3.9 was a bit lower maybe the 155 range. Maybe it's just an age thing.
Buddy the rods are a little longer on the 4.0 vs the 3.9 and the cam is advanced a few degrees so maybe a 4.0 will read a little higher than a 3.9. Comp ratio is still the same. It's been so long since I've had a real 3.9 that I don't remember. I'd expect a 4.2, just like a 4.6, to have similar readings as the 9.35:1 4.0. Now on my 4.6 with 4.0 pistons I'm seeing around 215 psi
Interesting, I have a 4.2 and possibly a 4.6 (not 100% confirmed it's a 4.6 yet) sitting at the house now. But I've never tested either of them. I've only tested my 4.0 and 3.9. Maybe if I get really bored one weekend. I might see how the test out.
Sounds like a similar build. I did the crower 229 cam. A 228 might have a little higher psi. Which did you do?
Might want to go by this advice. One of the main things to keep in mind is difference between cyl readings. If varies less than 20% rather normal.
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Not familiar with a cylinder leak down test. I'll have to ask my mechanic about it.
I did order the timing chain, gears, and gaskets. Not expensive and only one days work.
I did order the timing chain, gears, and gaskets. Not expensive and only one days work.
Whatever Mark at D&D sent me. The pistons are aftermarket and have cutouts for the valves. I didn't know any of this until I tore it down to rebuild after spinning a bearing.
ptschram
Well-known member
I wish I lived on the planet you guys do. at 196,000 miles, that's fantastic!
I guarantee you that you will need a cam gear in addition the the chain!
You also need a camshaft, which will improve compression as well.
My '95 DI at ~225K has one cylinder at 90 PSI
I guarantee you that you will need a cam gear in addition the the chain!
You also need a camshaft, which will improve compression as well.
My '95 DI at ~225K has one cylinder at 90 PSI