Good or bad Idea to re use old pistons
Discussion
Hi,I want to re use my old pistons but with new rings and a deglaze/light hone of the bores.What puts me off doing it all properly is that I will have to buy new pistons,camshafts,bearings,timing chains,oil pump,valve seats,rod bolts,head bolts,clutch,etc etc, plus all the machine work it will be a good 5,000 pounds,then the rest of the car would really have to be rebuilt to the same level.What Id like to know has any one re-ringed an engine and what were the results.I have to say the worst part of my pistons is not the diameter but a worn larger top ring groove by about .25mm which would allow the top ring to move up and down a bit,but I dont know if that would give me any problems.
The vertical clearance of a ring in its groove should be a thou or so when new. 4 or 5 thou would be considered badly worn. If you're saying there's now 0.25mm (10 thou) clearance then those pistons are toast. The only place for them is in the bin.
Ring groove wear is normally very low on properly specified pistons and rings but it accelerates greatly with a number of factors. The ring thickness limits the rpm at which the groove will work without wear and thick rings (2mm or so) on stock OE pistons from older designs of engine do not like high rpm. 1mm race piston rings will operate at much higher rpm for longer.
Piston material is also key. Stock cast pistons made from LM13 or similar alloys with 13% or so silicon content resist wear quite well. Hypereutectic pistons with even higher silicon content do better still. Forged pistons might be either 4032 alloy with similar silicon content to cast pistons or 2618 with almost none. 2618 will wear its ring grooves out like the clappers and should be reserved for race engines with frequent rebuilds.
You don't say anything about what type of engine, or pistons you have but wear that drastic means the pistons are not properly specced for the engine's use.
Ring groove wear is normally very low on properly specified pistons and rings but it accelerates greatly with a number of factors. The ring thickness limits the rpm at which the groove will work without wear and thick rings (2mm or so) on stock OE pistons from older designs of engine do not like high rpm. 1mm race piston rings will operate at much higher rpm for longer.
Piston material is also key. Stock cast pistons made from LM13 or similar alloys with 13% or so silicon content resist wear quite well. Hypereutectic pistons with even higher silicon content do better still. Forged pistons might be either 4032 alloy with similar silicon content to cast pistons or 2618 with almost none. 2618 will wear its ring grooves out like the clappers and should be reserved for race engines with frequent rebuilds.
You don't say anything about what type of engine, or pistons you have but wear that drastic means the pistons are not properly specced for the engine's use.
rob07 said:
Hi,I want to re use my old pistons but with new rings and a deglaze/light hone of the bores.What puts me off doing it all properly is that I will have to buy new pistons,camshafts,bearings,timing chains,oil pump,valve seats,rod bolts,head bolts,clutch,etc etc, plus all the machine work it will be a good 5,000 pounds,then the rest of the car would really have to be rebuilt to the same level.What Id like to know has any one re-ringed an engine and what were the results.I have to say the worst part of my pistons is not the diameter but a worn larger top ring groove by about .25mm which would allow the top ring to move up and down a bit,but I dont know if that would give me any problems.
"Properly" is relative.You only replace major components if they need replacing, not for some misguided reasoning that you must do it.
If the pistons are in good condition and measure up, then there is little need to replace them, unless it really is an extreme application which will have a limited service life ( like WRC, F1 etc )
What engine, what application, what sort of spec etc ?
Thank you for the very informative response.The engine is a 2.0 v6 fiat dino,which would rev to close to 8,000 rpm and only for road use, with original pistons(dont know if cast or forged).was smoking heavily ,found all top rings thinned and broken.Piston ring groove should be 1.503 with .013-.027 ring clearance.Apart from the smoke it seemed to run well.As I said before it is the potential very large expense that puts me off doing all of whats needed.what would happen if I did just put in new rings.
Pumaracing said:
The vertical clearance of a ring in its groove should be a thou or so when new. 4 or 5 thou would be considered badly worn. If you're saying there's now 0.25mm (10 thou) clearance then those pistons are toast. The only place for them is in the bin.
Ring groove wear is normally very low on properly specified pistons and rings but it accelerates greatly with a number of factors. The ring thickness limits the rpm at which the groove will work without wear and thick rings (2mm or so) on stock OE pistons from older designs of engine do not like high rpm. 1mm race piston rings will operate at much higher rpm for longer.
Piston material is also key. Stock cast pistons made from LM13 or similar alloys with 13% or so silicon content resist wear quite well. Hypereutectic pistons with even higher silicon content do better still. Forged pistons might be either 4032 alloy with similar silicon content to cast pistons or 2618 with almost none. 2618 will wear its ring grooves out like the clappers and should be reserved for race engines with frequent rebuilds.
You don't say anything about what type of engine, or pistons you have but wear that drastic means the pistons are not properly specced for the engine's use.
Ring groove wear is normally very low on properly specified pistons and rings but it accelerates greatly with a number of factors. The ring thickness limits the rpm at which the groove will work without wear and thick rings (2mm or so) on stock OE pistons from older designs of engine do not like high rpm. 1mm race piston rings will operate at much higher rpm for longer.
Piston material is also key. Stock cast pistons made from LM13 or similar alloys with 13% or so silicon content resist wear quite well. Hypereutectic pistons with even higher silicon content do better still. Forged pistons might be either 4032 alloy with similar silicon content to cast pistons or 2618 with almost none. 2618 will wear its ring grooves out like the clappers and should be reserved for race engines with frequent rebuilds.
You don't say anything about what type of engine, or pistons you have but wear that drastic means the pistons are not properly specced for the engine's use.
rob07 said:
Thank you for the very informative response.The engine is a 2.0 v6 fiat dino,which would rev to close to 8,000 rpm and only for road use, with original pistons(dont know if cast or forged).was smoking heavily ,found all top rings thinned and broken.Piston ring groove should be 1.503 with .013-.027 ring clearance.Apart from the smoke it seemed to run well.As I said before it is the potential very large expense that puts me off doing all of whats needed.what would happen if I did just put in new rings.
I'd imagine the rings would move around a lot in the groove, wear out quickly and allow oil past causing smoking. You need a specialist in this engine really to give you the tolerances and to tell you how much you can really get away with.rob07 said:
Hi,I want to re use my old pistons but with new rings and a deglaze/light hone of the bores.What puts me off doing it all properly is that I will have to buy new pistons,camshafts,bearings,timing chains,oil pump,valve seats,rod bolts,head bolts,clutch,etc etc, plus all the machine work it will be a good 5,000 pounds,then the rest of the car would really have to be rebuilt to the same level.What Id like to know has any one re-ringed an engine and what were the results.I have to say the worst part of my pistons is not the diameter but a worn larger top ring groove by about .25mm which would allow the top ring to move up and down a bit,but I dont know if that would give me any problems.
Can I ask why you feel you'd need to do all that additional work if you swapped pistons? It's around £900 for a full piston set and it has to be costing £300+ just to get the rings??If the only real problem with the engine is ring sealing, then really all you would need to do during that rebuild, assuming pistons measure up ok, is a quick hone of the bores, and install new rings.
The only expenses will be labour, some parts, gaskets, oil etc.
Yes it is always nice to replace lots of other bits at the same time, but in many cases it is also a waste of money. If it aint broke, dont fix it !
The only expenses will be labour, some parts, gaskets, oil etc.
Yes it is always nice to replace lots of other bits at the same time, but in many cases it is also a waste of money. If it aint broke, dont fix it !
It seems that there is wear in alot of places beyond specifications.If I was going low budget,I wouldnt do all thats worn.However once I start spending big bucks it doesnt make sense to not do other worn items,which means the more I spend ,the more I sensibly should spend again.For example Pistons at 960 plus ~250 bore/hone,so now I should do the small end bushes ~250 inc machining,then definatly replace main and big end bearings ~350,then clutch~280,then camshafts(beyond regrind)~1,150,then line hone cam bearings ~500,then big end bolts~430,then main bearing studs and head studs~400.So now I cant leave out the oil pump,cam chains and sprockets,valve seats,balancing,polishing crank etc,not to mention rebuild the gearbox.
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