On old worn engines it is always wise to bore out the absolute minimum
possible. There is not much to gain in BHP with slightly larger bores.
Pay attention to the head and manifolds. A substantial gain can be had
when these are even blueprinted and polished, while further widening up,
larger valves, free flow exhaust, Dell'Orto's or Webers, HC pistons,
balancing etc. will show a much more effective performance increase.
John Harper schreef:
> You might be lucky but my personal view is that the risk of failure
> having committed a lot of time and effort is that it is just not worth
> There appears to be a variation in the quality of the castings. I had
> problems with taking an original 100 block out to only +040". After
> testing a pin prick was found in one bore and the only way to recover
> the block was to bore out further and fit a sleeve. As the extra metal
> was removed a significant hole emerged. The engine appears to be OK
> after 10,000 miles but I have always since been anxious that the
> engine might fail.
> The other issue is corrosion inside the water jacket. The rough
> internal casting surface appears in some cases to attract corrosion.
> After 50+ years and inhibitors not being the 'in thing' it is
> surprising how much extra pitting there might be. It rather depends on
> how the engine has been looked after during its life. Something you
> most likely will not know anything about.
> So it is not just how much metal is available. Something that it
> somewhat marginal but also the state of the metal that will be left
> after boring.
>> Are there any issues reboring an A70 motor (2.2 lt) out to 100 spec.
>> Q1 Is there enough "meat" in the bore to do this ?
>> Q2 Any other pitfalls apart from no tacho. drive
>> Keith Taylor
>> Wamberal OZ
>> 100M....if I ever finish them
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