Scratching head over head gasket?

[Vincent Waldon]

(100% my opinion only)

If I measured:

- all four cylinder bores, at 3 places each
- the skirts of all four pistons
- all 3 ring gaps, on all four pistons, several places on each gap, especially by the top two gaps, injector side
- wrist pin wobble, all four pistons

and everything was within spec, I might be inclined to reuse those pistons.

My guess, however, is that with that kind of erosion other things have also been going on in that engine... things that the measurements above may reveal.

[joat]

balance pistons by weighing all individually ( after cleaning and no rings ) take the lightest and put aside ( your reference)

then take each other piston and grind away the bottom of the skits (by the wristpins) till you are within spec of your reference piston... smooth out any burrs .....

con rods repeat weighing as above to get reference ROD ... remove material from the SIDE of the rod between the big and small end till within spec ...

reassemble rods / pistons / wrist pins ( matching heavy rods with light pistons ... ) and re- weigh you should be within spec by now ....

[CoolAirVw]

I did a google search for balancing an assembly and one website said to balance the pistons to within .5 grams of each other....

That is a very "tight" specification. Probably that would be for a super high revving engine. My machine shop told me that within 1 gram is their standard for a passenger vehicle. Take into account diesels do not rev high compared to gas.

... and another one (Ford engine) said to balance to within .05 grams of each other. I wonder if this last one is a typo, as it doesn't take much to equal .05 grams of weight.

Probably typo, and would be very difficult to make them match that closely. Probably impossible to grind off .05 grams. What would end up happening is you would grind off too much then have to grind off the others, then you would grind off too much... ect...

The <a href="viewtopic.php?t=6550&start=15&postdays= ... ht=balance" target="_blank">Engine Pull thread</a> has my piston balance story... Last post on pg 1....

..... everything was within spec, I might be inclined to reuse those pistons.

I would try to reuse them as well.

[HOPPING DIESEL]

Thank you for the info guys. I will get them weighed and see where things stand. Just to clarify... If I matchup the pistons and rods, I will be okay as long as I keep the pistons with their cylinder and the rod bearings with their correct crankshaft journal.

I had a broken ring in number 3. I am guessing the timing was off a little and I think the injectors were overdue for a tuneup. I already have new injectors.

[82vdub]

Just to clarify... If I matchup the pistons and rods, I will be okay as long as I keep the pistons with their cylinder and the rod bearings with their correct crankshaft journal.

How worn are the cylinder walls and what is the clearance with the pistons and cylinders? To use the same pistons in the same hole probably isn't necessary, but I'd plan on doing it that way. You will have to hone the cylinder walls if you want the new rings to have any chance of breaking in properly. Keep that in mind when you determine your clearances, and make sure they are within spec.

I, personally, would not reuse rod bearings. I mean if they were nearly obsolete or $100 a bearing pair, then that's another story. But, you should at a minimum find out how worn the journals are, and have the crank turned or polished and use a properly sized new bearing. Do this thing up right. It will cost a little more money to get things back in spec and use some new parts, but why reassemble a used engine?

[HOPPING DIESEL]

I have not checked cylinder specs yet or pistons, next on my list. I agree on the bearings. Oddly enough, all the crank and rod bearings have been well within new specs (.002-.0025). So I thought I would re-use them.