Hey guys,

I'm doing my first motor rebuild and am totally new to this stuff. Before I started taking everything apart I did a compression test on the motor and cylinder 7 was at 90psi while everything else was at 350+. I then continued to do a leak down and cylinder 7 showed comparable numbers to all of the other cylinders.... strange.... I've got most of the engine taken apart now and noticed this (see attached image) inconsistent carbon buildup above the rings on cylinder 7. Could this be from a blown head gasket? I guess I could imagine hot exhaust gases flowing past the gasket on this section of the cylinder could clean up the carbon buildup.

I'll embed the image tomorrow if facebook decides to allow me to create a link to the uploaded image.

Thanks for the help guys,

-Lyle

 

Should be able to look at the decks / headgasket to see if it was blown or leaking. I would check cam, lifters, pushrods, rockers, valve tips on cyl. 7. The carbon is no doubt from the the lack of compression. At 90psi i would imagine it was missing on that cyl. could be washed. Can see some crosshatching though, so all might be well.

 

I looked at the section of the heads and block right above where that "missing" section of carbon buildup was at and it looked consistent with all of the other sections of the head and block. I too would assume I would be able to see something different, but idk.

I have not looked that deep into the other pars of the head (lifters, valves) and suppose i will do that next. Perhaps the section of valve that is closest to that side of the cylinder is not sealing properly? I'll check that next and report back.

-Lyle

 

Maybe the piston is buggered up (thats the technical term) in that spot and scraped the carbon off. Might be worth pulling the pan and inspecting.

 

Um... Look at that photo again(if you haven't already). That entire side of the piston looks like something /chewed/ on it!
So, you are definitely on the right track here.

A chunk of steel of some sort must have gotten in there and buggered things up; you wouldn't see that sort of damage from anything but that.

 

I see that now. Maybe it melted the piston in that spot.

 

Y'know... I'd pull the oil pan on this engine. I wonder about a rod or main bearing issue, or at least just a cracked or broken ring. Somethings totally wrong with that cylender, and unless your plan is to just run as is, you will want to get that taken care of and a new piston installed.

 

My jaw dropped.... What do i do now???

-Lyle

 

Gulp.....

-Lyle

 

Looks like time for a ring and bearing job.

 

How bad does the cylinder feel? Can you feel gouges with your fingernail?

 

I definitely feel something. The word ripples seems more appropriate as the edges are not sharp. When talking about boring and bigger cylinders are the +.020 of an inch over figures talking about the diameter or radius? If I had to call it i would say that the damage on the cylinder is no more then .010 inches deep.

I was planning on putting new rings and gaskets in this motor, turbocharging it, and putting it into my 85 F350 Crewcab. But another option would be to pull that trucks 6.9 and possibly rebuild it... It runs fine but has crazy blowby, is constantly smoking from the tailpipe, and i have ran it a gallon low on oil a few times so the bearings and other components might be shot.

What do you guys think about rebuilding and turbocharging a 6.9 vs a 7.3? and how much do you think it would cost to fix the damage on this 7.3?

Thanks fellers,

-Lyle

 

When I had my motor redone, I had a shop do everything(long block). It cost $2800, of which $~1000 was parts.
Of course, if you can simply drop the block ready-for-boring at a shop, it shouldn't be too much.
I'm not sure if you are supposed to bore every cylinder to the same thing, or if you can mix-and-match. It would probably /work/ just doing the one.

I know you can bore these blocks .030 over(.015 per side), because that's what my block is.

 

That piston is marked .030, so likely that block is done unless you have it sleeved.

 

damn you guys are observant..... Its kinda embarrassing on my end.

Thanks so much for the help. I think what i will probably end up doing is tearing down the 6.9 that is in my truck now. It has really bad blowby and eats/drips a bunch of oil but i am hoping it will be a better candidate for rebuild then this 7.3.

This has been quite an experience!