Another Busted Piston?

[DmaxMaverick]

Good luck, be careful, and remember.... That plexiglass shouldn't hold the pressure the cylinder should. I'm sure you know that, but if the repair was successful, it could have a different, bad ending. Looking forward to a positive report.

[joeq]

Thanx Gregg, (I think). If the rings hold, are you saying the sealant will blow out at 50lbs? I'ld like to think the little bit of air at that pressure, both will hold. If I see about 20% or less leakage, Ill be ecstatic. If it still shows almost nothing on the gauge, (and I'm confident the fixture isn't blowing out), then I'll try new rings. But I'll still question why they held pressure until the valve broke. I'm sure the other cylinder rings are in the same condition.

[joeq]

This morning I bring some good news, and some not so good.(Naturally).
The good news is the test was very accurate, and I'm confident of the results. The bad news is it was what we expected. The fixture did well, in that it didn't leak oil. But it did push the oil past the rings. At 1st I did it at the top of the cylinder, where there is some minor wear. I was able to pour a minimal amount of oil on top of the piston, and it did push out the bottom. once I got the pressure to 50lbs, I could stick my hand into the bottom of the piston bore, and feel the air leaking past.
Then I rotated the crank a few degrees to get the rings off the shiny spots, poured in more oil, (to the top of the bore), and retested. I put a rag on the crossmember to see the oil, and it was all there.

[joeq]

So I'll be taking the piston back out, and give it another groove inspection. These rings have a strange shape, in that they're not "square" or rectangular, but beveled both top and bottom sides. I wonder if the leakage isn't going past the diameter, or the end gap, but rather the inside of the ring and groove. Because the top and bottom surfaces aren't "loaded" in the groove, (on a P/T) maybe this is why the air is leaking out? On a static compression test the ring is shoved against the top of the ring land on the down stroke, and pushed up against the bottom on the upstroke. On this test, the ring is sitting stagnant.But I've done plenty of gas motor leakdown tests, and they work. I've never done one on a 6.2, or one with a beveled top ring. Not sure if it'll hold. I don't remember if I tried a leakdown test on the other side of the block, that I didn't remove the head from, and had 400lbs static compression, before I pulled the RHS head. I should give it a try for GPs.
If I don't see anything unusual in the ring groove once I take off the ring again, I'll probably end up doing as Gregg recommended, and buy another ring set. I see Robyn posted a link to a site that'll sell a set for 1 piston, so I'll probably be giving them a call. I can't believe the mark-up on rings now-a-days. Even our Napa can't supply "rings only", you have to buy a complete overhaul set. It's a conspiracy I tell ya.

[joeq]

I've spent an hour trying to find a single set of rings, but a .020 oversize seems to be as rare as an honest politician. And some of these websites have limited info, and they don't make contacting them easy.

[joeq]

I was fortunate enuff to find out Hastings carries these rings in +.020, in a single set, so I ordered them. No great bargain, but beats buying a whole set.
We'll see how they perform when they arrive in a few days. Got my fingers crossed, cause I'm running out of ideas.

['86 Dooly]

Bought a Beautiful 86 Duelly with 30,000 on a 2005 rebuild.Got a 400 turbomatic transmission and it loves 70-75 Mph. Don't know the mileage but seems ok.

[joeq]

Now that is some serious truck you got there Dooley. Talk about your "KingCab".

[Robyn]

That is one sweeeeeeeeeet ride

I love that body style.

[joeq]

OK people, sorry to be away, but I had some computer technical difficulties, and have fallen "way" behind in my up-dating. To do a quick recap, an exhaust valve broke damaging the #2 cylinder, and refreshing the heads didn't fix the problem.
So next I wanted to prove the rings defective with a leakdown test, but testing was sketchy to say the least. But I had enuff info to warrant pulling the piston, which I did, and you saw the stuck 2nd ring. I did get a single set of .020 rings from Hastings, and put them in. Here's a quick video of the results. It was actually the 3rd test, and my blooper was, the compressor valve was shut off at the time of filming, and the seal blew on the plate because of the amount of testing, but you can still see the results.
http://www.youtube.com/watch?v=3FIFATByon0

[joeq]

[joeq]

Well, seeing this thread is a dead end, and doesn't seem to draw any interest, I'll end it saying that when the exhaust valve broke on the #2 cylinder, it somehow upset the ability of the rings to seal, no matter how many attempts at cleaning and lapping them into the ring grooves. Even tho they weren't broke, there wasn't any static or leakdown test that would show them to seal even the smallest amount. Once I changed the rings to a new set, all was well.
So my goal was to prove what was broke, "really" was broke, and change "only" what was broke, and I did accomplish this with minimal cash expenditures, and for less than a couple hundred bucks, I got it back and running. I wish it didn't take so long, but I didn't spend all my waking, hours on it either. As mentioned B4, the truck is old and beat, but the motor has less than 50K on the rebuild, so I thought it was worth what little I did to it. I now have my "dump" truck back in service, and it was very inconvenient with it down. Now maybe I can move fwd on the cosmetics.
http://www.youtube.com/watch?v=s_sIrweVir8

[trbankii]

The lack of response is likely due to nobody else having any similar experiences. But it is good to hear that you’ve found a solution and will have your truck back up and running!