For the sake of argument,let's ***ume that you have a used engine.You tear it down to check it out.All the bearings look good and the crank mics out to spec.The cylinders look good also,maybe just a slight taper and a very slight ridge at the top.Just a turn or two with a ridge reamer and a hone cleans them up. Now here is the questions.How do you tell if the pistons are reusable?What is the best/easiest way to clean them? I have been in this situation a few times and always wound up buying new pistons.Let's also ***ume that this isn't a chevy and new pistons are very,very expensive.In the past,I've tried the broken ring to clean the grooves,I've also tried the ringland cleaning tool.It always seemed to leave too much carbon and would scratch.I've been told not to use a wire wheel.Can you sand-blast? Let me here what YOU do and why. Thanks.
Im no help everything you said is just what to do.The only thing I wire wheel is the tops of the pistons .
a quick measure of the bore and outer piston should give a an insight to wear from the engine spec chart..yep ol ring for the carbon trapment here to just be carefull to stay in the groove and remember old rings are sharp.
Back when bead blasting first came into general use around here back in the mid 60s, I cleaned quite a few with them. But now I'm told it's not a good idea, that it damages the ring lands and also is very hard to get ALL the bead residue off afterward. But I think a good scrubbing in hot soapy water should take care of that. I'm not so sure one way or the other about the damage to ring lands. Before bead blasters were available to me, I used the ring groove cleaning tool, just carefully adjusting it so as not to scar anything up. Then I soaked them in Gunk carburetor cleaner annd they came out pretty good. Had to do them one at a time in a one gallon bucket! Now the stuff is so weak I dunno how well it would work! Dave
a soak in carb cleaner will soften the carbon and make removing it MUCH easier. Measure ring side clearance in the top groove with a feeler gauge after cleaning. That is usually the location of wear and can cause 'flutter' with poor sealing and possible breakage. If that is OK and there are not cracks etc, you should be good to go.
Carb cleaner, broken ring, lots of care. It won't last as many miles as if you rebored it and bought new pistons....but if you're only gonna put a few thousand miles a year on it, it'll last a long time. Whether or not the extra cost to rebore is worth it, is up to you.
All the above is sound advice. I will add one more tidbit from the old days. If the pistons are otherwise OK but clearance at the skirt is out of spec, the skirts could be 'knurled' to increase their 'diameter' enough to restore clearances.....however, it is a budget fix that isn't as good as new pistons, but does offer extended life with decent results. Any older automotive machine shop should be familiar with this process and can further advise you about it. Just a thought. Ray
Thanks.I just figured that I was being overlly **** about getting the pistons spotless.How about a few more questions? Re-use old cam and old lifters? I was told that it's o.k. if you keep them in order.Or,what about old cam and new lifters? Another thing I've done, in the past,is to use a brake hone on the lifter bores when the block has set awhile and showing surface rust.Is this acceptable?I'vedone this before the final wash on the block. The reason I ask is that I might have another rebuild in my future,I hope.
What kind of engine? Unless it's something like a '55 Packard that new camshafts are both hard to find and expensive for, I'd put a new cam/lifters in it. If it's a sbc, you can find a new cam&lifters for less than a carton of cigarettes.
I've ben told all those new cheep cams are "smog cams" If you do a re ring job, I'd think about what cam you have. I got "talked into" changing a cam in my 330, 320 horse olds, It had the "toro" cam in it, nothing wrong with it......turned a runner into a smog dog!
If the pressure is kept down low with gl*** beads it works good, but by the time it's done, the pre-cleaning with solvent to keep from clogging up the 'bead machine, the actual blasting and subsequent removal of the dust, then mic-n the skirt and each ring groove all the way around, etc., the labor cost exceeds the price of a new piston. I would'nt even start unless I had to have the piston TODAY and immediate supply wasn't available. Then, the bottom line is, if a piston has been is service for a long time, it isn't going to p*** the dimensional inspection anyhow.
"chubbie",I,m familiar with Oldsmobiles too.I listened to those 'other guys' and had that problem with my 455 plus too tight piston wall wall clearance.Also I had a father who wnted to shift at 7500-8000 and it went BOOM! If I just would have changed the gaskests instead of "overhaulin" the motor I would still be driving it today. Thats part of why I started this thread.
I prefer the broken ring for carbon removal, more control. If not very careful with those ring groove cleaners you will gouge or remove parent material. Also if you think you can maybe see a slight taper in the bores with the naked eye, take it to someone you trust and have the pistons and bores miked, if you don't have the equipment to do it yourself. Then you will know what you have to start with. If you are in no big hurry set the pistons down in a pan of atf for a few days, it will soften the carbon.
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