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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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 Posted: Thu Mar 08, 2018 11:25 pm Post subject: 85.5 B piston measurements |
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I got some 85.5 B pistons in the mail today but I'm concerned about the measurements I'm getting.
Cylinder: 85.45mm
Piston 180 degrees at the pin: 85.43
Piston at the crown: 84.61
It seems like these are milled too small at the top of the piston. Some 85.5 A pistons I have measure 85.0 at the crown.
These do have 2mm 2mm 5mm rings. Are these susposed to be a bit smaller at the crown? Anyone else use these?
Any opinions are welcome. Thanks. |
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modok
Samba Member
Joined: October 30, 2009
Posts: 27687
Location: Colorado Springs
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| Posted: Fri Mar 09, 2018 12:01 am Post subject: Re: 85.5 B piston measurements |
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| yeah that's ok, probably. |
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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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| Posted: Fri Mar 09, 2018 12:17 am Post subject: Re: 85.5 B piston measurements |
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Yeah by crown I'm talking about the diameter of the piston where the rings live.
Other than them being a bit smaller than I'm used to seeing there they seem nice. The pins fit well and they seem well made. They lack the AA stamp or any other so I'm not sure if AA makes these or just packages them with their cylinders.
The pins are a bit heavy at 112 grams though. No biggie as these are just going into a 1745 cruiser engine. |
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modok
Samba Member
Joined: October 30, 2009
Posts: 27687
Location: Colorado Springs
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| Posted: Fri Mar 09, 2018 1:07 am Post subject: Re: 85.5 B piston measurements |
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I figured so, just took me a minute... or two, to realize.
It's hard to say if that's intentional or not, because there isn't any specification for it, and no real problem that would result if it WAS .25mm smaller than usual. As a general trend, pistons geared for HD apps, and ones that run quite loose and/or with shorter skirts(thus more rock) they do have more clearance up there. |
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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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| Posted: Fri Mar 09, 2018 4:17 am Post subject: Re: 85.5 B piston measurements |
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| modok wrote: |
I figured so, just took me a minute... or two, to realize.
It's hard to say if that's intentional or not, because there isn't any specification for it, and no real problem that would result if it WAS .25mm smaller than usual. As a general trend, pistons geared for HD apps, and ones that run quite loose and/or with shorter skirts(thus more rock) they do have more clearance up there. |
That makes sense as these are about 1/2 as long as standard round pistons. They aren't quite slipper skirt nor full round. Kinda somewhere in between. You definitely could not use Teflon buttons. I think I'll just roll with it. It's a strange build anyway. |
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bugguy1967
Samba Member
Joined: January 16, 2008
Posts: 4368
Location: Los Angeles, CA 90016
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| Posted: Fri Mar 09, 2018 9:32 pm Post subject: Re: 85.5 B piston measurements |
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| Who still sells 85.5 Bs? I'm looking at 86mm pistons with a tight compression height right now. |
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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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| Posted: Fri Mar 09, 2018 9:36 pm Post subject: Re: 85.5 B piston measurements |
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| I ordered them from AC.net. Got them in like 3 days. They have them on sale, but they are a bit more than some of the more traditional size cast pistons but still cheaper than ordering directly from AA. |
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FreeBug
Samba Member
Joined: March 12, 2012
Posts: 4277
Location: deepest, darkest Switzerland
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| Posted: Sat Mar 10, 2018 2:06 am Post subject: Re: 85.5 B piston measurements |
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| Pruneman99 wrote: |
I got some 85.5 B pistons in the mail today but I'm concerned about the measurements I'm getting.
Cylinder: 85.45mm
Piston 180 degrees at the pin: 85.43
Piston at the crown: 84.61
It seems like these are milled too small at the top of the piston. Some 85.5 A pistons I have measure 85.0 at the crown.
These do have 2mm 2mm 5mm rings. Are these susposed to be a bit smaller at the crown? Anyone else use these?
Any opinions are welcome. Thanks. |
Are you comparing to stock 85.5s? The stock cast pistons had steel inserts to keep cold/hot tolerences closer, less expansion. |
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Frank Bassman
Samba Member
Joined: July 01, 2012
Posts: 903
Location: Miami
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| Posted: Sat Mar 10, 2018 6:49 am Post subject: Re: 85.5 B piston measurements |
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OP, any pics of the piston skirts?
-Frank |
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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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| Posted: Sat Mar 10, 2018 10:27 am Post subject: Re: 85.5 B piston measurements |
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Yes I was comparing to stock pistons. These are definitely smaller at the crown. It just looked off when I fit one in the cylinder. But not having a steel insert could be another reason (along with more rock) to make the tops a bit smaller.
I'll post some pictures here in a bit. |
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AlteWagen
Troll
Joined: February 23, 2007
Posts: 8702
Location: PNW
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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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| Posted: Sat Mar 10, 2018 10:47 am Post subject: Re: 85.5 B piston measurements |
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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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| Posted: Sat Mar 10, 2018 10:48 am Post subject: Re: 85.5 B piston measurements |
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| The blank pistons weigh 349 grams. |
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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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| Posted: Sat Mar 10, 2018 3:26 pm Post subject: Re: 85.5 B piston measurements |
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| Anyone know if these need to be installed a certain way? Is the red dot indicate up? There is no directional arrow on the piston to indicate. |
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modok
Samba Member
Joined: October 30, 2009
Posts: 27687
Location: Colorado Springs
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| Posted: Sat Mar 10, 2018 3:55 pm Post subject: Re: 85.5 B piston measurements |
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I expect the pin is centered so it does not matter.
Check if the pin is centered |
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bugguy1967
Samba Member
Joined: January 16, 2008
Posts: 4368
Location: Los Angeles, CA 90016
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| Posted: Sat Mar 10, 2018 4:54 pm Post subject: Re: 85.5 B piston measurements |
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They're heavy! Jeez! Is the compression height 34mm?
Look up Chrysler 300 2.7 liter pistons. 86mm, 31mm compression height, moly-coated skirts AND crowns, comes with 22mm pins, rings, and clips for $80-$120 for six pistons. Bet they're around 180 grams bare. |
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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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| Posted: Sat Mar 10, 2018 5:53 pm Post subject: Re: 85.5 B piston measurements |
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| bugguy1967 wrote: |
They're heavy! Jeez! Is the compression height 34mm?
Look up Chrysler 300 2.7 liter pistons. 86mm, 31mm compression height, moly-coated skirts AND crowns, comes with 22mm pins, rings, and clips for $80-$120 for six pistons. Bet they're around 180 grams bare. |
Yes these are 34 mm pin height.
Have you used the Chrysler ones? Never seen them mentioned for use in aircooled before. 180g? Wow that's light in comparison. You would have to use some seriously long rods unless you went all the way to 82mm crank or something. These are going into a 1745cc so 76x85.5. |
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modok
Samba Member
Joined: October 30, 2009
Posts: 27687
Location: Colorado Springs
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| Posted: Sat Mar 10, 2018 6:26 pm Post subject: Re: 85.5 B piston measurements |
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If you don't mind....could you measure crown thickness?
If they are that heavy, maybe they can take a big dish....  |
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Pruneman99
Samba Member
Joined: February 22, 2012
Posts: 5013
Location: Oceanside
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| Posted: Sat Mar 10, 2018 6:34 pm Post subject: Re: 85.5 B piston measurements |
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| modok wrote: |
If you don't mind....could you measure crown thickness?
If they are that heavy, maybe they can take a big dish.... |
Sure I'll try to get a measurement tonight after work. |
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bugguy1967
Samba Member
Joined: January 16, 2008
Posts: 4368
Location: Los Angeles, CA 90016
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| Posted: Sat Mar 10, 2018 6:34 pm Post subject: Re: 85.5 B piston measurements |
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| Pruneman99 wrote: |
| bugguy1967 wrote: |
They're heavy! Jeez! Is the compression height 34mm?
Look up Chrysler 300 2.7 liter pistons. 86mm, 31mm compression height, moly-coated skirts AND crowns, comes with 22mm pins, rings, and clips for $80-$120 for six pistons. Bet they're around 180 grams bare. |
Yes these are 34 mm pin height.
Have you used the Chrysler ones? Never seen them mentioned for use in aircooled before. 180g? Wow that's light in comparison. You would have to use some seriously long rods unless you went all the way to 82mm crank or something. These are going into a 1745cc so 76x85.5. |
I've ordered a set. I have a guy that can hone barrels to my spec, so no big there...
Please know that there is no rule that says you need to keep your engine at stock width. Narrower is better. The engine is more stable, especially in the upper rpms. The minor modifications that come along with a narrow engine are trivial. |
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