Gregg Baker (gbaker@customcpu.com) wrote:
> All,
> I'm rebuilding my 69 MGB and am going to need to bore my cylinders. The
> cylinders have already been bored .030 and I'm wondering about going to .040
> or even .060. I see Moss has pistons that are.060 over and I was wondering if
> this starts to exceed the safe size without possibly getting into the water
> jackets? What is the overbore on the 1950cc engines? I've read in several
> places that even though the warning is always given about the 1950 overbore
> that the blocks very seldom have problems. If the overbore on the 1950 blocks
> is much less than .060 I would feel much better about trying it. I realize
> that boring this large will ruin the chances of another rebuild without using
> liners and I willing to deal with that.
> Anxious to hear any responses.
Gregg, I've asked the same question here before. The reaction was mixed.
The 1950cc engine is an 83mm bore. which is considerably more than .060, if
I'm not mistaken.
The pistons for sale by Moss and VB are, I believe, repurposed Lotus
pistons which require the block to be shaved as the pistons are too short.
This causes problems with valves fouling the block and requires even more
work to reshape the valve clearance "notches". And this often (always?)
results in a compression ration which is very high, making pump gas a
crapshoot.
It also is not possible on every block, as many will go right through to
the water jacket.
Doug Jackson sells a set of pistons specifically designed to be used in a B
series engine with an 83mm bore. His site is at http://www.mgbmga.com.
I've thought alot about it and have decided not to go this route with my
block when I get it redone, yes it would make for a zippier engine, but it
definitely makes it harder to rebuild in the future.
_______________________________
Chris Thompson
1974 MGB Chrome Bumper Roadster
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