Author Topic: Low compression pistons...  (Read 1098 times)

Offline Resto-Rob

  • A's Good Friend
  • ***
  • Join Date: May 2014
  • Posts: 54
  • Karma: 0
Low compression pistons...
« on: 29.06. 2014 18:25 »
Hey guys,
Since i am forced to rebuild half my 53 plungers engine i was thinking i might as well have a bit of fun with it.
I currently have low compression pistons and have been thinking about running standards insted.
And yes, i have thin flanged barrels, hence the hesitation to just bung them in.

What do you guys think?
Is it safe to run the standard pistons or should i stick with the low comp?

I am just looking at improving the crusing speed a fraction.

Cheers :)
When life throws you a curve..... lean into it!!
1953 BSA A10 Plunger
1927 BSA S27
Austria

Offline muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8850
  • Karma: 113
  • Lithgow NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: Low compression pistons...
« Reply #1 on: 29.06. 2014 21:20 »
G'dat Rob.
7.5:1 and a 356 cam would be a safe upgrade.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online orabanda

  • Wise & Enlightened
  • *
  • Join Date: Nov 2008
  • Posts: 1085
  • Karma: 22
Re: Low compression pistons...
« Reply #2 on: 29.06. 2014 23:54 »
I agree with Musky.

Online Brian

  • Wise & Enlightened
  • *
  • Join Date: May 2007
  • Posts: 1742
  • Karma: 42
  • Mt Gambier, South Australia.
Re: Low compression pistons...
« Reply #3 on: 30.06. 2014 02:18 »
I would also recommend that combination. You will still have a nice smooth engine but with just that bit more go.


Offline Resto-Rob

  • A's Good Friend
  • ***
  • Join Date: May 2014
  • Posts: 54
  • Karma: 0
Re: Low compression pistons...
« Reply #4 on: 30.06. 2014 05:05 »
Brillient!  Then thats the way i will go :)
Thanks guys! :)
When life throws you a curve..... lean into it!!
1953 BSA A10 Plunger
1927 BSA S27
Austria

Offline Resto-Rob

  • A's Good Friend
  • ***
  • Join Date: May 2014
  • Posts: 54
  • Karma: 0
Re: Low compression pistons...
« Reply #5 on: 14.08. 2014 05:15 »
I am finally ready to start my rebuild!! But first another complication made me question the "power" upgrade... i have a SJ crank that has been taken down to -40.  Is it still recommended to up the compression?
When life throws you a curve..... lean into it!!
1953 BSA A10 Plunger
1927 BSA S27
Austria

Offline muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8850
  • Karma: 113
  • Lithgow NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: Low compression pistons...
« Reply #6 on: 14.08. 2014 21:09 »
I don't think it would be a problem for day to day riding, just don't try to do the TON too often!!
My A7SS racer had a SJ crank running 13:1 on methanol and reved to 8k. In 9 years only broke 3. *problem*
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Offline bonny

  • Valued Contributor
  • ****
  • Join Date: May 2010
  • Posts: 262
  • Karma: 1
Re: Low compression pistons...
« Reply #7 on: 14.08. 2014 21:35 »
Speaking of low compression pistons (6:1) , is there anywhere where these can still be bought or is anyone reputable making them ? 

Offline trevinoz

  • Newcastle, N.S.W. Australia.
  • Wise & Enlightened
  • *
  • Join Date: Jul 2006
  • Posts: 3004
  • Karma: 71
Re: Low compression pistons...
« Reply #8 on: 14.08. 2014 22:07 »
Why would you want them? I think that they were 6.5:1 and were suited to the low octane fuel of the day.
Eventually BSA went to the flat top 7.25:1 pistons as standard which are quite suitable today.

Trev.