V6 Troubleshooting question

[loose_electron]

Ah yes, the never ending saga....

OK, got a 2.8L V6 that was rebuilt, ported, with 2.9 valves, a Jose grind cam and many other goodies about 800 to 2000 miles of driving back. (guessing on the mileage, mostly a prior owner)

From what I can tell, engine was bored out .020" at that point in time with suitable pistons and rings done.

Coming up to the here and now, compression on 5 cylinders is over 120psi. One cylinder shows compression of about 90psi.

Cylinder with low compression is #4, front of engine, US drivers side.

Looking at the engine, there is also a slight leakage of coolant between block and head near that cylinder. Leakage is on the bottom edge of the head/block connection point.

Running a pressure test on the cylinder (valves closed, pressurize the cylinder via the spark plug opening) shows leakage of air by the cylinder and no leakage thru the carb (bad intake valve) and no leakage out the exhaust(bad exhaust valve)

Right now my guess is that the piston rings or cylinder wall is the problem, but wanted to throw it out there for other opinions. The coolant leakage in the same area might mean something else, they could be related or two seperate things.

Advice, ideas or comments?

Thanks,
Jerry

 

[belmateo]

Sounds like you have a blown head gasket to me. When you pressurize that cylinder, can hear the air going into the crankcase maybe at the PCV valve?

 

[Fergusonic]

Blown Head Gasket would be the easy fix...... could be the dreaded cracked head.

 

[loose_electron]

The coolant leakage says blown head gasket for sure, but the pressure leakage is past the cylinder into the oil pan. Like I said, they could be related but could also be seperate things.

 

[belmateo]

Are cracked heads a weakness in these motors, or happens after you overheat it?

 

[loose_electron]

Sounds like you have a blown head gasket to me. When you pressurize that cylinder, can hear the air going into the crankcase maybe at the PCV valve?

Yes, the air leaking path seems to be into the crankcase-oil system. Could be a leak between between cylinder and oil galley due to the head gasket. Am getting the head off now, so will know more fairly soon.

So on the list: Failed head gasket, cracked head, bad rings.

Usually, rings take a while to die, and they go with a high mileage situation across all cylinders. But considering this engine is under 2000 miles since a rebuild the prior owner could have messed up one cylinder in the rebuild.

 

[loose_electron]

Latest and greatest:

Head gasket is good, valves are good, no cracks in the head, it seems to be a leaking ring set.

The coolant leak was a badly attached head gasket underneath the center piston, so it was an unrelated thing.

Considering the engine is low mileage since the last re-build going to pull the pan and take the one piston out and R&R just that ring set, after cleaning up the cylinder walls a bit.

Always open to ideas and suggestions!

 

[belmateo]

hmmmmm, badly attached head gasket and a leaking ring set. What else could have been assembled wrong? Since you have it this far apart, I would check everything and if you still see a crosshatch pattern in the cylinders new wrings would be in order. Just my two cents.

 

[Fergusonic]

No coolant in the engine oil?

 

[loose_electron]

No coolant in the oil, correct.

Right now I am going to R&R the rings in the one cylinder since everything else seems to be ok. Hopefully can get the one piston out the top without having to drop the crankshaft. Cylinder walls look good. Trying to avoid taking the whole engine out of there.

The engine rebuild was by a prior owner so I am second guessing the quality of the work there.

 

[DanR]

Jerry, While at it check to see what the engine was re-bored to. Some overbore the 2.8 from what I've read.

 

[Fergusonic]

Shouldn't the .020" over pistons have .020" stamped on the tops of them?

 

[loose_electron]

Jerry, While at it check to see what the engine was re-bored to. Some overbore the 2.8 from what I've read.

Original bore should be 3.6616 to 3.6630.

All cylinders were bored out to 3.6910 (got notes from prior owner rebuild)
New pistons in are all measured at 3.6890 (from rebuild notes)

According to Haynes engine manual on the V6 the .020 bore out should be 3.6821
And the .040 bore out should be 3.7018

The rings put in were +.030 (Hastings 2C4205030)
Pistons put in were +30 (from rebuild notes)

My perspective here is that they bored the engine out .030 and rebuilt with the proper pieces for that.
With the exception of the one cylinder compression everything else looks good.
Cylinder walls look good as well.

My guess is that the one cylinder has a bad ring set in there, and maybe the installation had a "file to fit" not done right, or the rings in that one piston got twisted in the install. All guesses of course.

Present plan is to drop the oil pan and see if we can get the one piston out the top. Inspect and clean things up, Fresh rings on the one piston, and lightly clean the cylinder walls to get that little edge off the top and bottom of the cylinder wall you get after an engine has been running a bit. Put the piston back in, and hopefully not mess the re-install of the rod bearing to the crank up in the process. Rod bearings go back in the exact same place and same orientation as they came out.

Gaskets and rings have been ordered, need to hand cut another Offy Intake manifold gasket. For this build the Offy standard gasket is too thick, and last time we had this apart we found a slightly thinner gasket got it to all line up nicely and seal well.

Last time I got this deep into an engine rebuild was a 404 Peugeot, so it's been a few (!!) years. Thankfully I have a mechanic who likes to work on classics doing most of the heavy lifting for me. My HOA would freak out if I had an engine apart in the garage. When I re-wired the car 2 years back, I was really careful to not open the overhead door and let anyone see that I had a car up on jackstands.

Waiting for the parts to come in...

 

[DanR]

need to hand cut another Offy Intake manifold gasket. For this build the Offy standard gasket is too thick, and last time we had this apart we found a slightly thinner gasket got it to all line up nicely and seal well.

Jerry take special note on the length required on the four bolts ( 1 about 1/4" shorter than the other 3) and the position the shorter one goes. I have it covered in my PDF.

 

[loose_electron]

Jerry take special note on the length required on the four bolts ( 1 about 1/4" shorter than the other 3) and the position the shorter one goes. I have it covered in my PDF.

Yup, you taught me about that last time this was apart. Thanks!

Any idea what is the max people bore this engine out to?

 

[DanR]

Sven P recommended less than 60... As I recall. I think his best was 30 Max.

I'll go back to his Book and let you know.

 

[belmateo]

You may want to run a quick glaze buster on a drill for that one cylinder before installing the new rings.

 

[Fergusonic]

Also may want to check for concentricity of the cylinder making sure that it is not oblong..... altho it's doubtful that it's out of whack. Peace of mind.
Pictures would be interesting...... we love pictures.

 

[Barry]

Any idea what is the max people bore this engine out to?

There is undoubtedly a Ford specification somewhere, but the real world answer is what oversize pistons and rings are available.

Hastings is about as mainstream as it gets and lists +020, +030, +040 and +060 rings for the 2.8 engine.

 

[loose_electron]

You may want to run a quick glaze buster on a drill for that one cylinder before installing the new rings.

Yeah, need to carefully prep the cylinder and also properly fit the rings.