As I said Richard, my personal experience is:
1. A 1100cc sprite engine bored to take 68mm Hillman Imp pistons (~220
thou overbore).
That engine gave over 10 years of reliable service until a circlip broke,
and scored the bore. I still have that engine in storage.
I also had a 948 blocked bored to the same size.
2. My old 100/4 had Holden based pistons. That made it a ~3 litre
100/4 (~200 thou overbore).
That car/ engine is now owned by another active member on this list,
who has sleeved the block back to standard.
3. As I said, my BJ8 is 65 thou over.
Here are some Australians who run 3.3 litre 3000 engines, (~3.5 in
bore, which is ~ 220 thou oversize) - usually with Volvo based
pistons:
Cameron Sell; John Wakeling
http://www.natsoft.com.au/cgi-bin/results.cgi?22/03/1998.ARDC.E13
Neil Dunn (3.2 litre); Eric Rudd; Colin Rule; You'll also notice the 3
litre 100/4 of Peter Ford
http://www.natsoft.com.au/cgi-bin/results.cgi?25/07/1999.ORAN.R4
Road going 3.3 litre 3000's - to many to list.....
Typically, these kind of overbores require offsetting bores; and
decking blocks; and getting compression heights right. And not every
block can take that sort of oversize 50 years later, due to
corrossion/ casting irregularities.
However - you doubted it was possible. It clearly is....
Overbore at your own risk - but 60 thou is more than pretty safe.....
Chris Dimmock
www.myaustinhealey.com
On 04/12/2010, at 2:18 PM, richard mayor <mayorrichard@hotmail.com>
wrote:
> Ira, I'm a bit skeptical here. I know there's a lot of meat in those
> Austin blocks, but I would like some confirmation from someone, or
> two, down under that they have actually bored out their 3000 engine
> 120 thousandths (.120 inches) without having any issues.
>
> Richard Mayor
> BN7L-466 Vintage Racer
> Portland, Oregon
>
> > On Thu, Dec 2, 2010 at 5:00 PM, Chris Dimmock <austin.healey@gmail.com
> >wrote:
> >
> > > Ira,
> > > I have the Denis Welch 85mm cosworth pistons in my BJ8. That's
> approx 65
> > > thou oversize
> > > Many healeys in Australia have Volvo pistons to get 3.3 litres
> ie well over
> > > 120 thou oversize.
> > > I used to have a Sprite with Hillman imp pistons - again well
> over 120 thou
> > > oversize.
> > > BMC blocks have quite thick walls.
> > > If your block is at 40 thou, don't worry, it has plenty of
> birthdays
> > > left...
> > > ;-)
> > >
> > > On 03/12/2010, at 4:56 AM, I Erbs <eyera3@gmail.com> wrote:
> > >
> > > My BT7 engine is bored 40 over. I see on ahead4healeys' site
> that they
> > >> have
> > >> .60 over piston and ring sets.
> > >> I have always feared what would happen if I ever had to rebuild
> my engine
> > >> again?
> > >> So the question is can I use .60 over pistons safely in my 29D
> street
> > >> engine, if need be?
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