• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

6.2l piston question

S

Skittlesquad

New Member
Messages
9
Reaction score
0
Location
Spencer ,ohio
Hi, i got a 86 6.2l engine out of a military blazer recently that ran good , saw with my own eyes it fire up and run, so i was going to regasket it and throw it in my truck, but after i got the heads off i notices quite a bit of carbon built up on the pistons and i notices i could shimmy them slightly inside the bore, all of them, my question is , is this bad? or is it ok, the cylinder wall is smooth with no ridges, thank you
 
The only way to tell is to measure the ring gap.
Unless I knew 100% that the engine had less than 70,000 miles on it, and had measured the compression before tear down, there is no way I would put it back together without putting in new rings.

If you can afford I would suggest a set of gapless rings, as the added engine life, added engine oil life , tended time before blowby starts is worth it.

Also how are your bearings while you are there?
 
IMO rings and bearings are cheap insurance. As far as piston play you would need to measure the pistons and cylinders.

A brass cone wheel on an angle grinder made my piston tops spotless.
 
Can you see the "crosshatch" on the cylinder walls? If not you have some wear and will need to deglaze the cylinder walls as well as measure. Check the mains for cracks before spending 10 cents on the engine.
 
I've always referred to the flat ones as wheels and the others as cones or cups. 6 of one half doz. of the other sort of thing.
 
thanks everyone for the replies,i will go ahead and measure the ring endgap,there doesnt seem to be any cracking in the main web and the heads look good too other than a little carbon build up,thats a great idea on the brass cone to clean things up,im going to pick one up today, Thanks everyone!
 
You mentioned being able to rock the pistons. This is completely normal! There is .004" clearance on these pistons, but that is measured about 3/4" from the bottom of the piston skirt. The piston is tapered, especially near the crown. Most likely to deal with carbon build up issues in a normally running Diesel engine. Remember black smoke = carbon, these engines do not burn clean under all operating characteristics. Just roll the engine over and inspect the bores. I think you'll find it's in good shape.

The only thing I'd do to an engine like this is re-seal it.

Replacing rings and bearings when it's not necessary only leaves room for error in sizing an assembly. Installing rings if you haven't done it before is a chore and lots to damage in the process.
 
uniquediesel said:
You mentioned being able to rock the pistons. This is completely normal! There is .004" clearance on these pistons, but that is measured about 3/4" from the bottom of the piston skirt. The piston is tapered, especially near the crown. Most likely to deal with carbon build up issues in a normally running Diesel engine. Remember black smoke = carbon, these engines do not burn clean under all operating characteristics. Just roll the engine over and inspect the bores. I think you'll find it's in good shape.

The only thing I'd do to an engine like this is re-seal it.

Replacing rings and bearings when it's not necessary only leaves room for error in sizing an assembly. Installing rings if you haven't done it before is a chore and lots to damage in the process.
Click to expand...

With respect the engine is out and it's a major PIA to remove the engine and do this later. Most surplus engines I got needed a ring job to help blowby. Rings are cheap for normal rings and give you lots of blowby free miles when changed. The last operator could have easily overheated the rings and ruined them. Gapless rings are a complete new ballgame actually keeping the oil cleaner where you can see the marks on the dipstick under the oil after 3000 miles of use: My gapless 6.2 hot rod is still like this thousands of miles later.

Rings are not that hard to swap and if you pulled the engine one has the ability to do rings.

Bearings that matter most would be the cam bearings for wear and oil pressure. I am a fan of not touching the main bolts at all to eliminate the possibility of cracks or making cracks worse. You will see the rod bearings when doing the rings and this will let you know the general condition of the mains.
 
Very true, it's basically up to what's found.

I always remove one rod bearing, usually cylinder #1 and check for wear, since it's the furthest from the oil pump and usually an indication of worse case wear. Since I'm there I'll do #1 and #2 for an inspection with plastigauge.

Gapless rings can be great, but can be a source of failure.

If you just buy replacement rings from Total Seal these rings are not pre-gapped. They have to be manually filed/gapped. This is a very tedious process and requires a lot of finesse to remove all possible sharp sealing edges that will gouge the cylinder wall and cause a worse problem. These rings usually come with almost no gap, which when run will score the ring and bore if not filed for the proper gap.

Now, rings that come from say a Sealed Power or Mahle set that have been sent to Total Seal to be converted work good for just throwing them in the hole and moving on. I know Mahle rings that I have used on many 6.5 builds have been spot-on on the gapping. Just need to be sure they're straight (some get a little warped in the conversion process).

Just lots to look out for...
 
I agree.

Get that engine on a stand and flip it over and rip the pan off.

The rods are not marked at the part line, so stamp them on the outside facing part line before you take them apart.

Left side 1 3 5 7 Right side 2 4 6 8

Not only do you need to check the bearings, get the crank out and check the middle 3 main webs for cracks around or emanating from the outer bolt holes down the web.

A gentle wash with brake clean and dry with a rag, then heat the areas around the outer holes with a propane torch to get them hot.

Watch for oil bubbling out of hairline cracks.

Easy way to tell if the block is good.

You can then clean and reassemble things fresh with bearings and rings.

Check the wrist pins to be sure there are no loose ones (in the rod bushing up top)

End up with a nice clean fresh job.

New head gaskets and bolts too.

Good luck and have fun

Missy
 
You must log in or register to reply here.
Back
Top