BIGPORT PISTONS

oldae82
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BIGPORT PISTONS

Postby oldae82 » Wed Jul 13, 2022 7:22 pm

I need a set of pistons for a largeport 4age, 81.5 bore, with rings and wrist pins if possible. 20 mm wrist pins.

I bought a set quite some time back. Every piston has broken lands between the middle ring and oil ring. The "why" I don't know yet, but the pistons are goners.

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oldeskewltoy
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Re: BIGPORT PISTONS

Postby oldeskewltoy » Fri Jul 15, 2022 5:25 pm

budget??

As to why stock pistons break ring lands it all has to do with poor ring land support

Image
OST Cyl head porting, - viewtopic.php?f=22&t=300

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sirdeuce
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Re: BIGPORT PISTONS

Postby sirdeuce » Fri Jul 15, 2022 11:18 pm

If you do need, I have a set of aftermarket pistons, High comp style.
One shot, one kill.

oldae82
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Re: BIGPORT PISTONS

Postby oldae82 » Sat Jul 16, 2022 4:57 am

oldeskewltoy, I think you nailed it. The pistons are slotted behind the oil ring, not drilled as in your example of a stronger design. They all broke on the intake side, if that information makes any difference. Highest load? It's been a long time since I bought them, but I believe they were 10:1 compression.

sirdeuce- I do need pistons. The ones I see on ebay are in the 11-12 c/r range. I'd like to go a little lower, if possible. I'd also like to avoid paying 1K for pistons, rings and wrist pins.. You can answer here or dm me if you like.

Thanks to both of you.

jm

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Re: BIGPORT PISTONS

Postby sirdeuce » Sat Jul 16, 2022 9:21 am

These are just cheap stock replaccement pistons. I've used them in the past for stock rebuilds without issue. BUT. If you are breking ring lands maybe your tune is off or your use is a tad bit harsher than the stock offerings can deal with.

If you want to use these I'll dig them up and see if I can find the rings I had for them as well.
One shot, one kill.

oldae82
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Re: BIGPORT PISTONS

Postby oldae82 » Sat Jul 16, 2022 10:57 am

If you would I'd appreciate it. I don't feel I ask more of the engine than it's designed to do- no long romps at high rpm or such like. I have changed the cams to a slightly more aggressive profile. I'm hoping that's not a problem. The wrist pins are 20 mm diameter.

sirdeuce
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Re: BIGPORT PISTONS

Postby sirdeuce » Sun Jul 17, 2022 12:20 pm

Ok, I'll go look around for them.
One shot, one kill.

oldae82
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Re: BIGPORT PISTONS

Postby oldae82 » Sun Jul 17, 2022 4:47 pm

Thank you kindly

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Re: BIGPORT PISTONS

Postby sirdeuce » Thu Jul 21, 2022 9:34 am

Found the pistons, can't find the box the rings are in.
One shot, one kill.

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oldeskewltoy
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Re: BIGPORT PISTONS

Postby oldeskewltoy » Fri Jul 22, 2022 10:02 am

Not $1000, but for $700 you get pistons, rings, pins and locks in the bore size (and compression height) you want.

Image


As far as smallport rings are concerned... you might get an OEM set from Partsouq. Aftermarket smallport rings are currently tough to get, I've purchased a few 81.5mm sets for my own inventory (directly from Grant Ring)
OST Cyl head porting, - viewtopic.php?f=22&t=300

Building a great engine takes knowing the end... before you begin :ugeek:

Enjoy Life... its the only one you get!

sirdeuce
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Re: BIGPORT PISTONS

Postby sirdeuce » Fri Jul 22, 2022 11:22 am

I'll keep looking, save a bit of hassle.
One shot, one kill.