Oversize Piston Clearance?

gnolan

Joined

Dec 2, 2010

Messages

107

• Dec 19, 2024

• #1

Capable machinist with proper equipment. I've bored many cylinders for Norton, BMW, HD.
Working on a T140 (76mm bore). Will be fitting Emgo cast pistons, Hastings (Emgo) rings.
The manual I have shows .0046 - .0061 skirt clearance. Is this what the experts recommend?

 

kommando

Joined

May 7, 2005

Messages

7,374

• Dec 20, 2024

• #2

The Emgo pistons are a very close copy of the original Hepolite pistons so working to the lower end of the manual clearance works well.

 

Triton Thrasher

Joined

Feb 10, 2009

Messages

3,078

• Dec 20, 2024

• #3

Mine’s a 650, but I’d never go tighter than 0.005”. The one I’m using now measured up at pretty close to 0.006” after a hone and it’s been good for 20,000 miles since then.

 

gnolan

Joined

Dec 2, 2010

Messages

107

• Dec 21, 2024

• #4

Thanks for the confirmation.
I'll shoot for the low end of book clearance.

Regards,
George

 

Triton Thrasher

Joined

Feb 10, 2009

Messages

3,078

• Dec 21, 2024

• #5

I don’t like to err on the close side. My experience is 650s not T140s, but I’d never deliberately go closer than 5 thousanths. A seizure is very inconvenient.

 

gnolan

Joined

Dec 2, 2010

Messages

107

• Dec 21, 2024

• #6

Thanks for the info.