When to replace head?

I finally checked the compression on my '96 2.7 with ~260k today.

152 / 139 / 130 / 160

These are pretty good numbers for such an old motor, but it seems like either the head is warping a bit, head gasket is wearing, or it's slightly cracked between #2 and #3.

I'm wondering how long I should wait before I slap a new head on this thing. I've noticed a small decline in power, but nothing drastic. I don't want to be driving around in a slug, though.

Doesn't use any oil, so I don't think rings are the problem.

When would you replace the head?

 

Was dry and wet testing both done? (only one set of numbers, assuming that's dry?)

Did you do a leakdown test?

Compression lost from warping or gasket issues is AFTER other serious problems, such as a major overheating, coolant in the oil, hearing the exhaust in the radiator, etc.

It's much more likely to be rings, valve seals/guides, worn valves/valve seats, or even, believe it or not, carbon build up in the higher # cylinders.

It's possible that a refurbished head would be in order. Or that your current head just needs it's own refreshing. But it would be good to complete the testing before starting some serious work and $.

 

My mechanic buddy (40+ years experience) and I both agreed that the rings are probably good if I can drive 7000 miles between oil changes and lose almost no oil. As for carbon build-up, this thing has been decarbonized with distilled water and seafoam. Seriously doubt that's the problem, although there's no way to rule it out without pulling the head off.

I can see it being valve problems - but at that point, I'm going to need to replace the head anyhow. The truck is my DD and work truck, so I don't have time to send the head off to a machine shop....and there isn't a machine shop that does that kind of work in my area anyway.

So I guess the question is how low can the compression go before it's such a slug that it's better to just put a new head on there?

 

Time to pull a rebuildable head out of a yard and get it done right...or you can simply order a head from one of the online rebuilders...

 

Fair guess. But a wet test will prove it. Oil ring could be fine and compression ring worn a bit, or bound in the groove.

Recall I said the 'high' compression cylinders. And I agree, it's unlikely, but not impossible, and always worth a check. Easy to do with a borescope. They are pretty inexpensive now, most quality shops have them. Or they are likely rentable in some places. Point is, you don't have to pull the head to examine them.

It may be that the head is the correct solution. All I'm doing is encouraging proof before diving in, and it is provable.

Here's the place I bought my last one http://www.cylinder-heads.com/ It's local to me (not affiliated, yada yada) so I didn't have shipping issues, but it was a well done piece, bolt on ready, and the vehicle it went on is still doing fine 6 years later. In my case the need was due to overheating from a failed water pump resulting in a blown head gasket and warped head (another family members vehicle)

 

Have you checked valve clearance? Low comp. Could be as simple as a couple valves need adjusted

 

He has solid lifters? Or adjustable hydraulics, aka mid 90s' Honda like, in his mid 90's truck?

 

What Vern said. 3rz uses shim over bucket. Check your clearance, do the math and go to your local stealership for the correct shims. You may want to invest in sst(special service tool), makes the job a bit easier.

 

Yeah guys...I adjusted the valve clearances about 1 year/30k miles ago (last June). Got them all within spec, none were super far out of spec (a few off by .003). I think I had to buy about 5 new shims. I plan to check again this summer, but I doubt the current valve clearances are the root of this problem.

From reading about this motor a ton, and from all the work I have done, I strongly suspect that my head has small cracks between #2 and #3. I suppose it could be valve damage from the PO driving it for a long time with valves a little out of spec, but the end result is the same: I will buy a new head and slap it on there. I'm not so much curious about diagnostics as I am wondering how long I have before I have to bite the bullet and replace the head on this thing? How low do the compression readings have to go before the truck is a total slug? How fast will this progress if I keep the valves in spec?

 

The factory head does like to crack. I drove mine out of spec for for way to long. I believe below 120psi is considered dead hole

 

Thanks man - great info. Sounds like I'm getting close on #3....I'll probably try to plan a new head in the 6-12 month budget.

 

I think $600 gets you a head shipped to your door. Valves included

 

Yeah, another great reason to not mess around with trying to find a machine shop. I figure I'll have to do a head gasket and studs as well - probably around a grand to get it running like a young buck. Wish I could to the same for myself that cheap...