NOS Pistons

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rx7171

rx7171

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Oct 8, 2007
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I bought these Standard 750 NOS pistons.
Except for some oxidation they seem fine.
I'm trying to figure out who made them and if there have been problems with the make.
They have 100 stamped on top and the RH and LH letters are raised as part of the casting rather than punched in.
They don't have the large slot of the early Hepolites so they should keep their tops on.
Can someone tell me the weight of the Hepolite 750 pistons so I can see how they compare.

Thanks
Bob

http://i924.photobucket.com/albums/ad82 ... CF9818.jpg

http://i924.photobucket.com/albums/ad82 ... CF9817.jpg

http://i924.photobucket.com/albums/ad82 ... 9816-1.jpg
 
I have a stock .020 over piston that weighs 252 grams without rings or pin.
 
Those are cast reproductions of the Powermax pistons. Do they have a name on the bottom? Jim
 
RennieK said:
I have a stock .020 over piston that weighs 252 grams without rings or pin.
Click to expand...

Rennie

252 grams converts to 8.889 oz
The pistons are 9.5 oz on a letter scale while is probably not real accurate.
I'll try to find an accurate scale.

Thanks
Bob
 
Bob, I have two new sets of those pistons left from many years ago. They came in a plain white box and I am not sure who made them but I got them from Sunset Motors. They weigh in at 252 grams- the same as a stock Hepolite and I used a couple sets many years ago in my racebike without any problems. They are a high compression piston similar to a powermax. Jim
 
comnoz said:
Bob, I have two new sets of those pistons left from many years ago. They came in a plain white box and I am not sure who made them but I got them from Sunset Motors. They weigh in at 252 grams- the same as a stock Hepolite and I used a couple sets many years ago in my racebike without any problems. They are a high compression piston similar to a powermax. Jim
Click to expand...

god to hear they hold up under heavy use.

When you say they are high compression any idea of precisely how much more than the standard CDO Hepolites.

Thanks

Bob
 
They were called 11 to 1 but they were probably closer to 10.5 without head milling. Don't put them together with a Combat head. jim
 
The following are weights in grams of several pistons and bits. I pasted them from a table I keep with a lot of weights for Norton rods, pistons, etc, and this is how it came out. If I could, I'd include the whole original table, in a better format, but I don't know if it's possible to paste it in.

Powermax 750 piston, 73 mm
235
Powermax piston pin
61
Powermax 750 +.020 piston, 73.5 mm
275
Powermax 750 +.020 piston, lightened, 73.5 mm
261
Powermax 750 +.020 piston rings, 73.5 mm
20
Powermax 750 +.040 piston, with larger valve reliefs, 74 mm
287
Powermax 750 +.040 piston rings, 74 mm
20
GPM 750 +.040 piston with pin, rings, circlip, unmodified, 74 mm
374.3
GPM 750 +.060 piston, 74.5 mm
289
GPM piston pin
55
GPM 750 +.060 piston rings, 74.5 mm
27
Norton 750 piston (keyhole design), 73 mm
241
Norton 750 piston rings, 73 mm
24
Norton 750 piston pin
72
 
comnoz said:
They were called 11 to 1 but they were probably closer to 10.5 without head milling. Don't put them together with a Combat head. jim
Click to expand...

Good to know.
I have a Combat with an Old Britts 0.028" spacer under barrel to get compression down.
Combining risk of catching valve with higher compression that I'm not really looking for I think I'll get some standard ones.

Thanks for the help

Bob
 
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