4.0 Compression on 2001

[Shadowranger]

So, still waiting for my mechanic to have an opening to do the timing chain work on the '01. It's at 140,000 miles and runs very good. I've been assuming the compression is good as I wait for this job and it's going to be a big one. 4x4 automatic and I have quite the list of things for him to do. Main seal, transfer case seal, heads off and valves ground, new radiator, alternator, drivelines, u joints, water pump etc.
Can I assume the compression on this motor is good? I'd hate to have to have him tear it down even more and do a complete rebuild from the ground up. Engine doesn't smoke nor use oil other than the main seal.

 

[franklin2]

You can make that assumption based on it running good with little oil consumption. But that begs the question, why are you pulling the heads and having them gone through?

 

[Shadowranger]

It was something the mechanic suggested. Probably because it would be easy since the engine is out. At this point I don't care about the added cost but if it isn't necessary why bother, huh?
I have complete trust in the mechanic having known him about 10 years now so that's not an issue, hopefully...
Appreciate your thoughts, though. Thanks

 

[RonD]

Yes, if there was no excessive blow-by and oil use then pistons and rings are OK

Doing a valve job at 140k should give you another 200K+, pistons and rings are usually 400k+ so full rebuild at that time

Remember to change the 2 timing chain tensioners every 100k just for piece of mind
Upstream O2s need to be changed at 100k or 12 years, which ever comes first

 

[Shadowranger]

Got it. Thanks, Ron. Will give him the ok on the valve job

 

[Blmpkn]

Having a 5 angle job done would be beneficial.