Hello again,
I measured one combustion chamber at ca. 36.5 cc. Factory manual specs 43
cc for the 1622 engine. This thread is getting a little messy so will post
a separate note on my methodology immediately after this one.
Thanks to all for the advice and encouragement. I will continue to follow
up on this, but am signing off of the list tomorrow (Monday) night as I
must travel to Minnesota for a week. After that I am hoping to go to NAMGAR
GT in Grapevine, but I won't have time to put the car back together so will
go sans MG. Anyone who likes can email me directly and I will catch up with
you later.
More follows:
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>
> >> Perhaps ... your 1588 was overbored to 3" and fitted with a set of
> >> HC 1622 pistons and rods.
> >
> > That's what I first thought until I removed the carbon buildup. The
> > pistons are clearly stamped "+.030", Made in England," but no mfr
> > name. I'm familiar with the piston configurations and these are
> > definitely flat.
>
> Hmmm ... could be your 1588 is overbored +.062 and fitted with 1622
> +.030 pistons/rods. Is the bore 2.998" or 3.030"?
The bore measures 3.001" +or-
>
> Took a look at the BMC "MGA 1500 and 1600 Special Tuning" booklet
> ... as you are probably aware, BMC did offer 'flat-top' pistons for the
> 1588 (BMC Part No. C-12H-173), but they required the use of the Twin-
> Cam rods (BMC Part No.s C-AEH-642 and C-AEH-644).
>
> According to "Tuning BMC Sports Cars", the BMC Special Tuning pistons
> rods are no longer available (th book was printed in 1970), but Hepolite
did
> make a piston with a 3.8cc dish (Hepolite Part No. 14986), in lieu of the
> stock 7.75cc dish, and a 'flat-top' piston (Hepolite Part No. 15059) for
use
> with the stock 1588 rods ... perhaps you have the later.
There is a No. stamped on the piston head, this is from memory, but I
believe it is 15755.
> >>> ... [snip] ... and someone has ported and polished the head
extensively
> >>> if not expensively. [snip] ... Now I have it back and am concerned
that
> >>> it may be excessively milled by the cumulative amount of machining it
> >>> has had over the years. ... [snip]... I do not have the burette setup
to
> >>> accurately measure the combustion chambers, but I may have to devise
> >>> one in order to answer my questions. Does anyone know the factory
> >>> dimensions for head height? I am probably milled at least .095"
(2.4mm)
> >>> from stock.
>>
> >> The rule of thumb is that removal of .010" equates to a 1cc reduction
in
> >> the combustion chamber capacity, but the chambers have been modified
> >> so your right ... you will have to cc the chambers to determine what ya
> >> have.
> >>
> >> Assuming a 3" bore with 'flat-tops' ... my WAG is that 37.5cc equates
to a
> >> 10:1 CR ... 35.5 is a 10.5:1 CR.
> >
> > I am jury-rigging a measuring setup now. If it works, I will describe it
> > later.
See next post: MGA cc
> Anxious to hear your findings ...
>
> >>> Is this excessive? Should I consider double-gasketing the head? Will
I
> >>> be able to burn 92 octane fuel?
> >>
> >> Seems a bit radical ... did you have problems with pinging/detonation
> >> prior to the valve work? If not, there are several of us that would
love
> to
> >> know the size the combustion chambers. ;^)
> >
> > A slight ping was sometimes present, pulling a long hill in top gear at
> > WOT, e.g.
>
> With 92 Octane fuel?
Yup.
>
> Safety Fast! ... larry.g.unger@lmco.com
> '61 MGA 1600 MkII
>
>
David F. Darby
Long time no cc.
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