MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG TD TF 1500 - Cubic capacity of head

Can anyone tell me please the cubic capacity of a standard (unskimmed) TF1250 head? In Hal Kramer's excellent article on tuning the XPAG engine he gives the cubic capacity of various heads, which he goes on to use in his various calculations, but does not indicate whether this includes the head gasket. A standard gasket has a thickness of 0.045" or 1.14mm which amounts to about 4cc capacity and makes a significant difference in calculation of compression ratio.
Dave H
Dave Hill

Dave,

You can find this information in the following document, Page 38 of the pdf or III - 6 of the book.

http://www.ttalk.info/WKF-Wood-XPAG-Engine-Book.pdf


John
J Scragg

XPAG - thickness - capacity of 4 combustion chambers.
Standard TBCD, 76.75mm, 182cc.
Standard TF, 75.16mm, 158cc.
Stage 1 TBCDF, 74.37mm, 146cc.
Stage 2 TBCDF, 73.58mm, 132cc.
Head gasket capacity for 4 combustion chambers, 18cc.
XPEG - thickness - capacity of 4 combustion chambers.
Standard TF, 76.75mm, 180cc.
Stage 1 TF, 76.25, 172cc.
Stage 2 TF, 75.5mm, 155.5cc.
Head gasket capacity for 4 combustion chambers, 21cc.
Simple check for compression ratio of standard XPAG 1250cc engine = (182+18+1250)/(182+18)= 7.25:1.
R A WILSON

Perhaps should have said 'capacity of 4 cylinder head combustion chambers'.
R A WILSON

Thanks, all good information. I'm on +0.080" bore, and knowing the head and gasket thickness I wanted to calculate the C.R. from basics.
Dave H
Dave Hill

8.56:1
(Possibly a slight variation if the combustion chamber surfaces have been smoothed, or the valves ground in too much)
R A WILSON

Yes, but in my case I have new hardened valve seats and valves, and the head has been skimmed to circa 2.91" giving a CR of around 9.5:1 or more. Won't know the exact thickness until I remove the head to install ARP studs - I was just contemplating whether a thicker head gasket might be desirable.
Dave H
Dave Hill

If 2.91", this would be 73.91mm, which not an 'MG' thickness as it is between stage 1 and stage 2. CR would be 9.4/9.5 to one - probably OK. (ARP studs ?)
R A WILSON

R A Wilson - If you go to mgtrepair.net you will see listed my ARP cylinder head studs, which are far superior to the factory ones and those commercially available today. Among other features my design adds a quarter inch of additional threads to compensate for heads that have been skimmed a few times.

Considering how often people seem to be blowing head gaskets, I would venture a guess that 50% of head studs are stretched, and provide inconsistent clamping forces to head, head gasket and block.

My ARP head studs are made of the finest 8740 nickel-chromium-molybdenum steel with preferred rolled threads, and are positively the best – and strongest – head studs available for the TB, TC, TD and TF Racers have found them (and my ARP main studs also) extremely consistent in their ability to hold torque values, and these studs have solved many head gasket issues in street cars.

I'm happy to answer any questions.

Tom Lange
MGT Repair
t lange

Tom, are the ARP studs reusable? Do they deform at the proper torque? Also, if you skim the head wouldn't a thinner head expose more threads on the standard or ARP stud? I'm confused.

Regards

Tim
TD12524
Tim Burchfield

Tim - yes, they are re-usable. The original studs are generally removed with pliers or pipewrench on the shaft, weakening and distorting it. Mine have a hex socket in the outer end, so that no brutal means are necessary to obtain the proper installation torque. They do not distort.

If there WERE threads, a thinner head would expose them, but the original studs run out of threads with a thin head. That's why mine have an extra quarter of an inch, so there is enough thread for virtually any head.

Tom Lange
MGT Repair
t lange

This thread was discussed between 07/09/2017 and 09/09/2017

MG TD TF 1500 index

This thread is from the archives. Join the live MG TD TF 1500 BBS now