Does anyone have a new piston who could measure the width of the piston ring grooves? I need to know how wide the ring grooves were when new to check the ring clearance. I have an old piston that looks to be still in good condition but don't know how much the ring groove may be worn. I am measuring .006" clearance on the old piston with new rings.

Just to be clear, I am not asking about the ring end gap but the ring fit in the piston, top to bottom.



Bruce

Bruce the 'Standards Book' gives these figures for width of grooves :- Compression ring = High 0.097"- Low 0.096" Scraper ring High 0.127"- Low 0.126".

The manual quotes ring side clearance .002"-.004"

Ron

email (option): ronpier@talk21.com

PS Bruce. Some further figures from the Standards book so you can determine if you can use that piston.

Compression Acceptable at overhaul 0.098 condemned at 0.102

Scraper Acceptable at overhaul 0.128 condemned at 0.131

I calculate that .006" is too much according to BSA


Ron

email (option): ronpier@talk21.com

Have a new std heplex piston 4 top rings (above pin) listed as 1937/46 in 1948 hepolite reference book top groove in piston measures .0061" 2nd .0094" 3rd.0096" 4th oil .126 these are new sizes for heplex/hepolite original bsa may be different hope this helps mal mcs

email (option): malmotorcycles@gmail.com

Hi Mal,

The top groove in your four groove piston is not for a ring, it's a heat dam.

email (option): spacemonkeym@gmail.com

My piston is not a four groove but is a three groove. It is the original factory piston stamped BSA 66-1039. Cleaned up it looks to be in very good condition, just want to make sure it has no problems.