Quandry. Comments wanted

[bespander]

I just cracked a piston in my 6.2 with 270k miles and I am looking for a quick fix that will get me to warmer weather, another 10k miles. Oil consumption is 500 miles per quart. I am considering several options: 1) pull the glow plug on the bad cylinder and vent cylinder into air box; 2) pull the head and slip in a piston from a dead 6.2 sitting on the floor of the garage; or 3) put my ’93 6.5 turbo into the ’82 Sub. Option 1 should be the quickest.

I will be building a new engine from a ’82 red block with less than 100k miles, using the heads from a ’83 J series with less than 80k miles (the heads are from the original engine in the truck but a coolant leak hammered a cylinder, six good pistons.) Heads are flat to +/- 0.0015 and they have no cracks. I bought the red block and installed in my ’74 Jeep CJ and it proved to be too much if there is such a thing. Unfortunately, I don’t have access to a shop to work on this and at 10-20 F it is too cold to work on things outside very long.

Option 1) Drill out glow plug and run copper tube from glow plug core into turbo air box appears to be the easiest. This will minimize piston blowby and I will limp along on seven cylinders. I don’t think it will have enough compression to ignite the fuel and will blow excess fuel into turbo air box.

Option 2) Pull the head and pan to pull out cracked piston and stuff in a piston from ’83 J series. Down side is freezing my butt off. I did this about 100k ago when a glow plug was melted off by a miscreant who held the manual glow plug switch in excess of the 5s limit I gave him.

Option 3) This was my summer project. The ’82 sub has a dead 350 and I bought the ’93 to install. Four inch exhaust, big tires, etc. Again, an outside project and it is cold out there. I must be getting old.

Comments??????

[More Power]

I vote for installing a used piston... if you intend to drive the vehicle for the next 10K.

Jim

[redbird2]

I will second the used piston

[SimonUK]

Fit the used piston before you even consider starting the engine again. If that cracked piston decides to turn itself into shrapnel then the resultant loose connecting rod will do its best to turn itself and a whole load of other good components into shrapnel as well.

[Robyn]

Howdy
First off, how do you know you have a cracked piston??
The 6.2 is not known for cracking pistons under most circumstances.




If indeed its cracked I'm for getting the head off and seeing whats up in there.
A good used piston will work fine. Just be sure the size is the same.

These pistons have a letter code on the pin boss area, Usually a two letter code. This is paint type letters. (JT) is an example

If the rings are good you could simply clean everything well and reinstall the good used piston/Rod assembly and bolt it back together.

Going with used rings is not a great idea but if they are clean and otherwise not damaged they will work until your rebuild this summer.

Just be sure there is no carbon at the top of the hole and or a big ridge.

Be sure there are no other issues in there while you have the top off.
I would recommend using a fresh bering shell on the assembly thats going back in.

Now the bearings in these engines are all select fit so be sure the size is the same. The numbers will be on the back of the shell. Generally unless the crank has been ground a standard (STD) will work. The bearings came in .0005" and .001" Under size (This will be noted in metric though as these engines are all metric)
I would not suggest swapping bearings that have been run from one rod to another, BUTTTTTTTTT in a pinch as long as you keep them as a set it will work.

Once a piston fails it is really a matter of time before it scatters.
Running the engine with one dead hole is not a good idea, the extreme dynamic forces generated with one hole not working could spell doom and gloom to your little beast.

I know its not fun to do an engine in the winter but I think it best to patch it up with a good piston.

This is not a bad job to do just a little tedious to get the head off.

If you have not had one of these apart before there are a couple things to think about.

The head bolts are a one time use only and must be replaced after use.
The term is TTY or torque to yield. This has become a standard on many engines of late.
I dont agree with it but thats the way it is.

Be sure the copper collored ends on your pushrods go up toward the rockers. ( Just the ball end has the copper color and it may be worn but it will be there)

Other than these things its pretty straight forward.

OH when you bolt the head on, be sure "no" pistons are at the top.
Then bolt the rockers on without moving the engine. This allows the lifters to settle and eliminates the possibility of hitting a piston with a valve and having problems.
Once together you can rotate the engine by hand a few turns to be sure all is well.

Good luck

Robyn

[bespander]

Head is off and I found two cracked pistons and one melted crown. One cracked piston is attributed to a glow plug failure. Compression on the second cracked piston cylinder was 400 psi, so I have deemed that the piston is not completely cracked. Bad piston was 250 and the remaining were 375 to 390. This engine is a 88 Goodwrench and the piston codes are either C or D with over and underscore marking. The 83 pistons are C or D with a color code, or or bl. How do I select the appropriate candidate? I would like to replace all three but I am not comfortable until I find out what piston size code means.

[HillBilly2]

If there are three bad ones on one side I think I would have to pull and check the other side just because I would have to. I couldnt stop myself. Gotta feel some level of confidence. Besides you can't just buy one head gasket, can you?

[Robyn]

I personally would have the other head off in a heartbeat.
Yank the pan off and get the assemblies out.
Now be sure to mark the rods and caps as they are not marked.
I usually stamp them with number stamps above and below the part line.
One does not need to get overzelous with the stamp but just get the numbers on there so you can keep the caps with the rod it came from and oriented right.

Now as far as piston codes I would just mic the bores and see what the sizes are and then use a set of pistons that get you in the clearance range called for. (004" is about right)

I have a set of new in the box standard 6.2 pistons with rings that I have no plans for.

The spec of .004" is about in the middle of the road. The rear two cylinders are speced with a tad more clearance than the rest of the lot but the .004 will make it plenty happy.

Now the cause of the messed up pistons must be addressed.
If the engine has been turboed and the horse pressure screw twisted too far will cause it. OR if the injectors are messed up and peeing off into the corner this can do it.

Let me know if I can help

Robyn

[bespander]

Thx for the help. I will put in two or three slugs and button it up. I also plan on turning the IP all the way up, producing some black smoke, and having fun. I have a '82 red block, ~100k miles, that will be opened up and inspected. If it looks good it will get the '83 or '88 J series heads. Otherwise, I will use the '83 J series block, bad crank, and salvageable internals from red block and '88. I am worried about the bore taper on the '88 block which has 270k miles. Will replace engine with assembly of best parts this summer.