Aluminum head spacer for '72 combat (2018)

Status
Not open for further replies.
ILLF8ED said:
Macca70cmd.
Do your domed pistons look like these. This is what was in my ‘730 750 when I bought it in 1981. View attachment 83404
Click to expand...
Hi Illf8ed, power max were THE performance piston back in the day.This bike came back from the USA so looked at US suppliers, looked very similar to ones sold by Baxter Cycle .Exchanged a few emails, he offered me +10 rings(they take standard 3 piece oil rings) but Andover had them in stock.
Believe they are forged and must be between 10-1 and 11-1.We will aim for 10-1,PW3 cam and a pair of 32 Amal mk 1 1/2’s. Cheers Paul.
 
My Combat came with the standard composition head gasket. No flame rings. I tried a copper gasket once but it leaked like crazy.
I really don't see any need to reduce the compression on a stock Combat.
 
Macca70cmdo said:
Hi Illf8ed, power max were THE performance piston back in the day.This bike came back from the USA so looked at US suppliers, looked very similar to ones sold by Baxter Cycle .Exchanged a few emails, he offered me +10 rings(they take standard 3 piece oil rings) but Andover had them in stock.
Believe they are forged and must be between 10-1 and 11-1.We will aim for 10-1,PW3 cam and a pair of 32 Amal mk 1 1/2’s. Cheers Paul.
Click to expand...
I thought those powermax pistons were 10.25 -1 but I'm not certain ?
I remember the compression rings are narrower but you can turn the grooves wider for stock type rings
 
chaztuna said:
David, regardless of if the head gasket is made of copper or aluminum, during manufacture, all the holes are made by broaching. Even when using annealed metal, the broaching process will work harden the metal along the edges of all those holes. This is why annealing is recommended. One thicker copper head gasket would be preferrable.
Click to expand...
No.
 
I raced a set of Hepolite domed pistons way back. They didn't make it through the season before the ring lands pounded out and loosened so much that the rings broke. With the thick heavy Hepolite rings - the high RPM/piston speed was too much for them. Even back then they were so rare that I couldn't find replacements for them.
 
Last edited:
baz said:
I thought those powermax pistons were 10.25 -1 but I'm not certain ?
I remember the compression rings are narrower but you can turn the grooves wider for stock type rings
Click to expand...
I believe you are correct 10.25:1 compression ratio with Powermax pistons with a standard 750 engine. That would change depending on which high compression head is used. The RH-6 head for example on 1973 750s which is what I had.
Aluminum head spacer for '72 combat (2018)
 
  • Like
Reactions: baz
Status
Not open for further replies.
Back
Top