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MG TD TF 1500 - XP Engine Enlargement Question

Hello


While understating the MG XP engines were an old pre-war design by the time the 1466cc XPEG appeared in the 1954 MG TF, was there any further stretch available to enlarge the XPEG closer to 1600cc or would that have required an updated design produced on new tooling? Have read rumors of the XP engines being capable of further enlargement in a scenario where BMC never came into being though not sure how accurate that titbit is.


Am interested in knowing whether the XP engines were a solely in-house design or like the 918cc Morris Sidevalve / Wolseley OHV were copies? The latter for example was said to be a copy of the Ford Sidevalve engine from the Ford Model Y.


Kind Regards


Ben M
Ben M

Ben - You might want to purchase the booklets, Living with the XPAG - The Morris 'X' series Engines by Neil Cairns and Engines for M.G's Their Story after 1935 also by Neil Cairns. Both of these booklets should be available from the MG Car Club. Cheers - Dave
DW DuBois

My understanding is that the max non-standard rebore is plus 60 thousandths of an inch, as otherwise the gap between bores 1 and 2 and 3 and 4 leaves too little metal in the block.
N D Wallace

Thanks for the replies.


What caught my interest regarding a further enlarged XPEG was via The XPAG Engine - Data, Service, Super-Tuning, WKF Wood, 1968 PDF below. Which on page 37 mentions overbores of both .060 inches and .125 inches allowing for the XPEG to be enlarged to 1528cc and 1598cc respectively.


In the absence of the B-Series, could Morris have fully productionized either the enlarged 1528cc or 1598cc XPEG engines in the same way the 1466cc XPEG was derived from the 1250cc XPAG or would that entail new tooling as well as likely a new clean sheet design by that point?


Kind Regards

Ben
Ben M

From memory, I think the 1/2 and 3/4 cylinders are 'Siamesed" on the XPEG (no water passageways in between), with a very thin strut of metal between the cylinder bores. To go any larger the cylinders would virtually touch, with minimal head gasket sealing area and/ or no support to the block deck. So I think a clean sheet with wider bore spacing would be the answer. George
George Butz

My XPAG is bored out to .120. It was .100 when I bought it. The machine shop sonic tested the cylinder walls and said there was plenty of metal left to safely go to .120. I've only ran the engine for tuning and short road tests. I hope to have the car finished this month and will be driving it at highway speeds. I'll report back if I have any problems.

Tim
TD12524
Tim Burchfield

XPAG had 66.5mm bore (2.618") and XPEG had 72mm (2.834").
We have an XPAG that was bored out to 72mm, .216" overbore. I physically measured the wall thickness through the core plug holes as low as only .10" so I dared not rebore again. It had a lot of good miles normally aspirated and I sure hope it doesn't mind a few more horses with a blower.
JIM N

This thread was discussed between 06/09/2017 and 09/09/2017

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