magnum 5.9 with aftermarket pistons

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Dragonbat13

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I got a magnum 5.9 out of the junkyard. Tore it down and found it had been rebuilt. It has Sealed Power 405P +.040 pistons in it. I plan on putting new rod and main bearings, along with moly rings on the pistons. I can still see the crosshatch in the bores, so I am hoping that everything will be OK on the bottom end after the build.

With the dish in the sealed power pistons, what is the average compression ratio that comes up when using stock deck heights, stock chamber volumes and felpro head gaskets of stock thickness?

Im just wanting to know if I have smogger 8.0 compression and need to fit some new pistons into the budget. I did some calculating on summits compression cal. and came up with 10.23. Seems rather high for what I am looking at.
 
Low compression for sure. Replacement for a stock 70's-80's 360. Definitely less than the originals in a magnum.
 
Measure how far down in the hole the slugs are. Then cc the head. Also find out gasket diamentions so you can add it all up I. A compression ratio calculator.
 
OK, the pistons are .170 in the hole. Using a .028 thick gasket and 60 cc for magnum stock chamber size it came out to 8:1.

This will not do. So I am going to revert to putting some KB 107 on Scat rods, re-balance assembly. Might as well.

Installing KB 107 pistons with the same setup and increased compression height will kick it up to 9.5:1. The KB107 will put the pistons at .071 in the hole, and give me some valve clearance as a bonus. Compression height on the current pistons are 1.576. The Keith Black pistons are 1.675.

I need to mic my cylinders to find out if I can just replace the .040 over smog mothers with the Keith Blacks. Should I clean them with anything more than some acetone and a rag? I have a three stone type hone, but I dont like using that thing cause it removes alot of material. I was also thinking about putting some scotch bright pads on the stones with some solvent and cleaning them lightly with that.

My concern is the piston to wall clearance. The cylinders look as though they could just use a cleanup hone to seat the rings. But I know that boring a block is matched to the piston. Would it be possible to swap the sealed power 405p smoggers to the KB107 pistons with just a hone? The present crosshatch is mostly around the head bolt areas in the walls, which seems odd to me. Wouldnt it be the other way around?

I could go .060 over after a sonic check, but I really dont want to do that.

Ill tell you one lesson learned: PULL A HEAD AND CHECK FOR STOCK BORE BEFORE PULLING A MAGNUM 5.9 OUT THE BONEYARD!

EDIT: I have to go to the farm to get my graduated burret, I am not positive that the heads have a 60 cc chamber. But in any case the current pistons have to go.
 
If you want clean, use ATF and a rag. But for measuring, they just need to be decently clean , not re-assembly clean.

Sure, you can just hone it. But it may or may not be any good. You gotta get some bore guages and check it for taper and roundness. If I saw bores that only had part of the hone pattern left, then I would assume some pretty significant wear has occured.

Can't specifically explain why the crosshatch is where it is, but block & heads warp in odd ways when torqued.
 
The KB's are .071 in the hole?! Wow!
Oh, I doubt there would be a problem with clearance with those pistons even at zero deck.
 
rumblefish360 said:
The KB's are .071 in the hole?! Wow!
Oh, I doubt there would be a problem with clearance with those pistons even at zero deck.
Click to expand...

The other ones are .17 in the hole! I came up with the number for the KB's by subtracting the difference in the compression heights.

I am also doing all this with a dial caliper. All I got. Not the best. I looked at the measurement fifteen times, thinking I was misreading. If this monsoon clears up I am gonna take some pictures.

Whoever did this rebuild used the wrong pistons for the application. They probably built it, and was disappointed that their "new" engine lost power. The engine could probably have run on Kerosene!
 
WHAT A WORM!!

I knew something wasnt jiving, thats why I posted those numbers. The 405p smogger pistons are NOT .170 in the hole, the are .107. I did misread.

That puts the smoggers at 8.75:1

That should put the KB pistons at .008 in the hole. With a .028 gasket thickness, that puts it at 11.3:1, with a .035 it comes out to 11.1

but I have been using 60 cc chambers. And from what I understand 62 is a more realistic number. With 62cc chambers, and a .040 compressed gasket it comes out to 10.75

I thought these keith black pistons were good street pistons. Am I off track?
 
nm9stheham said:
If you want clean, use ATF and a rag. But for measuring, they just need to be decently clean , not re-assembly clean.

Sure, you can just hone it. But it may or may not be any good. You gotta get some bore guages and check it for taper and roundness. If I saw bores that only had part of the hone pattern left, then I would assume some pretty significant wear has occured.

Can't specifically explain why the crosshatch is where it is, but block & heads warp in odd ways when torqued.
Click to expand...

I use a wire wheel on a drill to clean up the cylinders and pistons in the engine before removing. It works great.
 
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