I recently picked up a set(8..plus one extra) of used 951 pistons.

What things would you look for as far as inspection for overall condition?

They appear to be in "OK" shape..but i want GOOD shape. To me there are a few questionable nicks and marks on them. Some of the skirts seem in better shape than others. I plan on take them down to a local shop to get a good diagnosis.

Any input? Ill shoot some close up and personal pics of them later and post them.

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I'd get them checked for cracks before I would use them, paying particular attention to the ring land area if they came from a boosted engine.

 

They came ALL came from tolerance group 1 . When i get time later ill have a closer look for any visual irregularities

thanks
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Tony-

I agree - a close inspection is critical. I had planned on having my 968 pistons bead blasted and then having a liquid penetrant exam performed on them for any cracks/defects.

Let me know what route you take...

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I'd check the weight of each piston if you use 2 different sets.

 

That is a good point tresamore. I'm not certain about the 951 pistons, but the 968 pistons are supposed to be 762 grams +/- a couple (I have the info - just not in front of me at the moment).

 

Tony,
Overall measurement (micrometer) and ring lanes/groves/conditions - The last is important, that's the place for piston wear, and if not Ok, the new ring will get a short life-time

 

Jay 968 pistons should weigh about 700 grams plus or minus 4 grams. I don't think I would bead blast the pistons because if you remove the iron coating or even so of it you'll be in big trouble.

I investigated some coatings myself and have found out that some coatings will never detach which of course is a worry with chrome. These people I spoke with apply a crown coating and it goes on at 15 degrees C, very spiffy. Their 105 mm pistons also weigh in at less than 500 grams, which includes the pin and rings.

 

You mean that bead blasting will remove the finish? Hmmm.....

Disclaimer - I was quoting off the top of my head regarding the 968 piston weight.

 

Jay,

In addition to possible coating damage - bead blasting can cover up a crack. Bead blasting should always be done after penetrant inspection, not before.

 

Good stuff guys, thanks.

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Tony-

Something else to consider is that the skirts on the 951 Pistons will require some minor trimming around the lower sections due to interference based on the crankshaft stroke.

btw - looked @ my notes - the 968 pistons are 704 grams +/- 4 grams.

 

Personally i think i have a set of matching paper weights....too many questionables even in with my limited knowledge.


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I guess it all depends if you are thinking about building a "like new" rebuilt engine, or just "reassembling" some used parts, which will give you the compression ratio you want... I think used 951 pistons, etc, will work just as well as the *used* pistons currently in your shark. Chances are, your 928 pistons probably look just as banged-up, but they work fine.

It just seems like if you are taking the time to take your entire engine apart, and rebuilding it from the ground up, you might as well do it right, so that you have new parts, tight tolerances, and so the engine will last hundreds of thousands of miles....

But if you are really trying to do things cheap, and just want to rip out one set of pistons, slap in a used set, and throw the motor back in the car with a supercharger, it will still probably work fine. It just will not have the same lifespan... I would say that using used parts, makes your engine just like supercharging any used 928 engine. It will be questionable, in terms of long-term durability.

And yet, on the other hand, if you do something wrong with supercharging, and blow the engine, you will be really pissed off if you just rebuilt the thing with all new parts...

If you are experimenting with supercharging and stuff, I would use used parts too. But if I knew I was building something for the long-haul, I would use new parts...

 

Get rid of those, The ring lands have had the rings gouged out of them. If you use then, blast them first,(do NOT blast the sides or the ring lands, it will create a tolerance that will destroy the compression) manaflux for cracks then, very carfully use a fine file (small, jewelers file) to cut down any burs that will keep the rings from floating freely in th lands. If they bind they will get stuck, and the engine will get blow by, lose compression and may even burn oil and smoke. They are low compression. That pocket in the top is the same as my 83s I'm thinking your car is a turbo.
Blaa blaa blaaa, I think those pistons are wrecked, bottom line. If they are "stock bore" You dont need them anyway.... when you pull your old ones out you will bore it out and hone it to the next size up anyway. This will require a larger piston. You will never use a stock size piston again unless you resleeve the cases.
Hate to be the bearer of crappy news man. I hope you didnt have too much $ invested in them. They could be used for a quick fix if one in your car went out that there was no sleeve damage. But thats the kinda luck drag racers talk about over beers in the pits scratching their heads. Not too often haha. I'd keep them ( the two best ones) Just in case. But they will probably be better off as ashtrays for conversation.
When you have to tear the motor down in your car, take advantage of being inside the thing and punch that baby out!!