Normal piston movement?

[MIKE_JAMES]

Ive pulled the heads off my 1985 6.2l to try and find why No's 3 and 6 had low compression, head gaskets appeared fine, no cracks in the heads, but there appears to be 1mm to 2mm movement with the pistons in the bore, the motor ran strong with no blow by or smoke till it snapped a rocker arm bolt and lost a couple of push rods, is this piston movement normal? Also i found a plate rivetted to the left hand door with shipping info for an M1008 ? is this a military vehicle

[5.7L oldsdiesel]

The movement your experiencing is totally normal.Don't worry about it.You'll be fine. smile.gif Every engine has some piston movement.It's nothing to be concerned about.

Good luck.

[john8662]

First off, a M1008 is a military truck. What is your truck, is this a 1 ton 4x4 single rear wheel truck? If so, its probably then M1008. Anyways, are the sloppy pistons the ones with low compression? How do #'s 3, 6 compare to the rest? Usually #8 and #6 are pretty loose (with wear and miles), and thats going to be an indication that there is some wear.

The main thing to look at is how much of a ridge ring do the cylinders have. Basically your looking for the wear ring that will be at the top of the cylinder, this is where the rings on the piston stop. Also, can you see any of the cross-hatching in the cylinder bore? This is from the hone at factory, if it's still visable it usually doesn't have that much wear.

I'd take the heads to a reliable machine shop and let them examine them, especially where you had the rocker shaft bolt break leading to the bent pushrods. You could possibly have a bent valve stem or bent valve for that matter causing the compression loss.

By the way, what were your compression results?

[MIKE_JAMES]

The truck is a 1 ton 4*4, single rear axle, 6.2l, TH400, NP208 and dana rear diff (8 stud)the piston with the most movement is No 2,3 and 6 have very little movement. there is a small ridge at the top of the bores but it appears to be carbon, not wear there is no cross hatching visible, will do with the heads, he biggest problem i have found here (New Zealand) is finding mechanics or machine shops who know these motors,One that advertisers as American Diesel Specialist said " bring it on over, but its going to be expensive", Not much chance of going there. Thanx for the input