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MG TD TF 1500 - Exhaust Valve two block clearance

Hi,

Does anybody out there have an original 7.25CR XPAG cylinder head sitting on their bench. If so, would you be able to measure the distance from the exhaust valve to the face of the cylinder head in the area that the face of the block covers.That rear of rear, front of front, or in the middle of middle, cylinders.
I have searched the archives but not found anything.

Thanks
B W Wood

I can't help you with your stock head measurement but I had one that had been shaved and the chambers measured 42cc. The measurement was .460 from the seat to the block deck. I would imagine you would get different measurements from stock heads depending on where the valve seats are sitting
L E D LaVerne

Can't help either-
But did a head here a while back with 1500 valves and shaved right down till the sparkplug hole started showing- can't remember but think it was about .125" off it and it had 8mm from the valve face to the head deck and had just over 1mm clearance between the valve and the top of the block at full lift-
from that i'd reckon a std head would be about 11mm face to face--?
willy
William Revit

Thanks Guys,

Bit of history, TF1250 with Laystall head(bought new 2006) ran fine but eat a cam lobe. Decided to fit one of Lens roller cams. Allready had one in TD with Laystall head(bought new about 8 years ago) runs great. When I fired he up I heard a crack, rocker pillar broke. So far broke 6 pillars while investigating, finally decide to pull head and saw exhaust valves had been hitting head. Started taking measurements and fishing out old heads from both cars. Measurements and picture in enclosed file. Don't know what original specs were for Laystall head, but my measurements indicate barely any clearance for standard valve lift at 8.3, let alone 10.5 for Lens Cam. The question is what to do with it now. Machine out the combustion chamber to set valves 3mm lower, but that will mess up a whole host of things. Don't want to use thick or multiple head gaskets as that is just hiding the problem. Put the original steel head back on. I have asked Brown & Gammons for comment but have not heard back yet.
B W Wood

Thanks Bernie
B W Wood

Bernie
Best option would be to flycut the top of the block a couple of mm to get some clearance for the valve at full lift---not a fan of sinking the valves into the head
willy
William Revit

DITTO Willy!
BTW the deck of the block is .220" thick.
Also Bernie you will need the machine shop to calculate the Dynamic as well as static compression ratio for your S/C engine.
Len
Len Fanelli

Hi Guys,

Pulled the rest of the valves out and all OK. Had a look and due to the way they profiled the inlet tract there is not enough to mill head out and set valves lower. Not heard back from B&G but as these heads were manufactured by George Edney and there has been no update to his website or facebook page since 2010, chances of finding out why this head was machined as it was are pretty slim. So I have decided to refit the original steel head which has sufficient clearance for the 10.6mm valve lift and it has had a 0.020"skim so will give me a 8.9CR which is not too bad for a show car. I'll sell the Laystall head and maybe buy a new one at some time in the future, maybe not.

Regards Bernie
B W Wood

Bernie,

If you want to more info on your Laystall head you can try Peter Edney I assume that he has taken over the firm from George. https://www.mg-parts.co.uk/

John
J Scragg

This thread was discussed between 23/09/2022 and 27/09/2022

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