A7 1954-55 Pistons / Sleeves / Bore

[davgoustinos]

Hi All!

I am rebuilding my A7 1954 engine where (among others) the following are to be installed:

A) A new pair of original Hepolite sleeves (code FS.2207)
B) A new pair of original Hepolite pistons (code 11094) 66mm+010
C) SRM oil pump and SRM oil pressure release valve

I will very much appreciate your comments and advises, especially in piston to cylinders bore clearance issues where B.S.A. Service Sheet No 704 recommends (for pistons with split skirts as the ones I have) a clearance of 0.0011" - 0.0031". 

Regards,

Dimitris Avgoustinos

[RichardL]

I think you would not want to be any below the maximum (0.0031" listed for clearance and I would think 0.004 would be better. However (ωστόσο ??, you probably don't need the translation), I am greatly looking forward to someone else supporting (or shooting down) my advice, because I have an A7 to rebuild and I will be asking the same question.

Richard L.

[chaterlea25]

Hi,
Split skirt pistons run tight clearances compared to solid skirt 
the split closes up as the piston expands preventing siezure as would happen with a solid skirt  if the same clearance was used
My Ariel with a split skirt piston, has the same specified clearance as your A7
It was bored to 0.002in. clearance 30 years ago now
It has never given a problem and the piston is a lot larger than the A7

I would aim for 0.002in clearance

HTH
John

[RichardL]

...and I would take John's advice over mine on this any day.

Richard L.

[muskrat]

G'day Dimitris.
Ditto. My very first rebuild of my 51 A7 with split skirt pistons was given 0.0015". On a really hot day (38C) after 50 miles @ 60mph she nipped up. I then gave her 0.002" and she was great for another 30000 miles.
Cheers

[davgoustinos]

Many thanks my friends.

I will go for 0.020in - 0.025in, as stated into relevant documentation.
Hopefully my old Lady will be back on road  in 2-3 weeks, I will post same photos then.

It is a pleasure to be a member of this forum!!

Dimitris

[davgoustinos]

.... sorry I mean 0.0020 - 0.0025in!!

[davgoustinos]

Καλημέρα Richard , you are right 0.004in will be fine for pistons with solid skirts.
However, I will go with "muskrat" because of the split skirts....

Regards,
Dimitris