Valve/piston "kiss"

[llong66]

Hello everyone! Hope your still enjoying some of the goodies from Thanks Giving!
Over the last few months I have been slowly working toward putting the factory GM turbo on my rebuilt 6.5l
While doing the install, I had some other issues that have haunted me since I built and dropped this motor in last year, mainly smoking from the pass. side bank when accelerating and such. When I pulled the head I found two surprises waiting for me. One was that the No. 6 precup was cracked and needed to be replaced, that is a story in and unto itself.
The 2nd issue you can see pictured below, the intake valve has at some point just touched the top of the piston. there was some force to the "touch" as when you run a fingernail over the line left by the valve you can feel that the mark is there, not just some weird illusion. The valve itself does not look like it has been touched in the slightest. I removed all of the valves from the head and along w checking for straightness, I measured every possible thing you can thing of. Other than allowing for the human factor <0.0001" They are identical.
Everything reassembled fine and I have a buddy coming over Sun to help get the head and exhaust manifold installed. I plan on removing the hood, then, bolted only loosely together, place the head, turbo exhaust manifold on as a unit.
But, back to the reason for the post...ANY thoughts on this? I checked rocker arms, push rods and all. The lifters and cam are all new, only a year and maybe 1200 miles on them. The lifters are so pumped full of oil that I cannot get the lifter to "push in" but all of them on that side are like that.
I had thought about going back old school, taking the old head gasket and bolts, put the head back on with a thin layer of oil coated clay, the oil to keep it from sticking, on top of the piston, then turn the motor through a cpl of revolutions by hand, pulling the head and measuring the thickness of the clay. I don't know of anything else to do at this point as everything seems to be as it should.



When I was installing the precup, I had the opportunity to speak with one of the engineers at PTC power, where I got the precup and had what I thought was an issue with that. It ended up being the head itself, an SnS diesel, new pair, 2 years ago. I guess alot of these places that sell heads and such will mill them down to the absolute min. allowable as far as cover rail to deck distance so rather than having them reworked, you have to buy another. This is my case, I am literally 0.001 from the min allowable thickness, this an a set of "new" heads, the guy I talked to at PTC was curious as to whether the motor was loud or "clangy" and he said that I probably had to time the hexx out of it which, I think I do have it advanced pretty far to get it to run properly. These ARE interference motors so it could conceivably be an issue, but if so, I cant see it affecting only one cyl.
I had also noticed, as I was getting ready to take the head off that I had air blowing back UP the intake. With the original motor being NA, it had the dual plain intake, the puffs were coming from the pass. side of the plenum so I am guessing that it was either cyl 2 or 8. Again, I see nothing that could have accounted for this.Once I get the head back on, before I put the intake on, IF the problem still is there, it should be an easy manner to locate just hooking up the batteries and having my buddy crank while I check individual intake ports.
The cracked precup I think could have occurred last year, not long after I had reassembled the motor and had it running, but before I did the 12v glow plug conversion I had a cascade failure and had to replace a set of GPs. No.6 was particularly bad as, regardless of what ppl say, delco 60Gs WILL shatter! I had the typical swollen glow plug issue there, got it out, removed the injector and managed to fish out what I could from the GP and all seemed fine.
I do have several issues I have delt with or am currently dealing with, but that "kiss" on my piston really has me worried, but very curious!
From the info I have given does anyone have ANY thoughts as to this issue? I really think a lifter is the only possible cause.
I also want to put out a recommendation for PTC power, they are in Fairfax, Va. I am in no way affiliated with them other than being a happy customer. They are the ONLY source that the Gov uses for replacement parts for this kind of thing. Being as they are dealing with the military, they are not allowed to touch anything as far as head milling, etc. Their prices are right in line with most retailers ie: right around $400/ea for heads. They have new blocks, cranks, pistons, rods, everything!
Well, thanks for reading all of this and I look forward to ppls thoughts and ideas!

Take care,
Greg

 

[Ue413]

Valve to piston impact is due to non-specification geometry, either a part is out of spec (cylinder head, con-rod, etc) or something was modified beyond acceptable tolerances (machining of cylinder head fire deck or block, incorrect machining and replacement of valve seat as a couple examples)

 

[llong66]

Ue413,

I have gone over, in my mind, the things you had mentioned. The heads are as purchased from SS diesel, other than replacing the precup, they have not been touched, though as I mentioned in my OP, they were decked to the absolute max, there is nothing left to be reworked. I checked my rocker arms/shafts, they all look to be ok, though I do have another set I am going to replace them with for a just in case kinda thing. The rods are new, only thing done to them was the small amounts of material taken off by the shop when they balanced it. The block did not need to be decked, the machine work done to it was the boring and refinishing of the cyl and checking the line bore for the crank, cam bearing install. When I had the head apart, the seats all looked ok, and as mentioned above I checked all of the valves. Its weird to me that the valve in question does not have the slightest sign of any type of contact.
With all of that in mind I am leaning toward a lifter failure, I just cant see what else it could be. I pulled the lifters and they all LOOK ok, no signs of unusual wear, the guide plates and hold down clamps were all in place and when removing the hold down for the guide plates they were tight and had been torqued to spec when assembled. I also find it odd that as far as I can tell, it was only the one valve but I only have the one head removed.
I guess, unless someone has a different idea, I am going to go with my clay idea and see what that gives me.

 

[cucvrus]

Just a thought. Glow plug failure and a particle of glow plug lodged in the valve seat for a few revolutions? I have had a glow plug failure at 70 mph and it sounds terrible. I did not know what happened till the truck would not start the next day. The shaft of the glow plug was gone. I suspect that was the horrifying sound I had heard the day before on the turnpike. Just a thought that is all. Good luck with your search. Happy Holidays.

 

[llong66]

cucvrus, I had not thought of that! I was surprised to not see any apparent damage from the GP issue, but that may have been it! Thanks for that!!

 

[b4thundr]

Timing chain slop?

 

[m16ty]

I've seen that happen when the valve is sticking in the guide. It's a light hit because it doesn't take much force to push the valve back shut.

This is usually seen on engines that have been sitting for a long time and the valves have gotten sticky from lack of lubrication or the valve guides were too tight upon assembly. A bent valve can also cause it to stick.

If this is your problem, the stuck valve will also be accompanied by a miss on that cylinder.

To check this, remove the valve spring and make sure to valve is moving freely in the guide.

 

[gringeltaube]

I've seen that happen when the valve is sticking in the guide...

 

[gimpyrobb]

Have you thought about putting thicker head gaskets on? I just got a truck with a 6.5 and I've been doing a lot of reading. Seems a motor with a lower compression ratio and higher boost makes more powwer than one with high C.R. and blowing out head gaskets.

 

[llong66]

Hello all, thanks again for your thoughts and suggestions. I don't believe it is a timing chain issue as the whole set, chain and gears are brand new...or were last year when I rebuilt the motor. The motor has not been sitting and I checked all of the valves for being bent and they are all as perfect as you could ask for. I did not measure actual clearances but I don't believe the valve is to tight in the guide, it slides right in and the heads were new SS heads, only two years old and without checking, Ill guess 2500 miles or so, so guide wear is not, or should not be an issue.
Gimpyrobb, I use a +0.10 thicker head gasket as I had heard it is a good idea with a turbo install.
Its back together now, or at least the head and exhaust manifold are on, so soon I hope, we will be seeing if I have an issue or not. I know for me, Cucvrus's ideaa I think is probably what happened.
Again, thank you all very much and I will keep everyone updated as I get things finished and get that turboed beast on the road again!