MG-Cars.info

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

Recommendations

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 - Compression Woes

Realizing I'm doing everything ass backward, I do appreciated all the feedback, this is a fun and sometimes frustrating learning experience!

I finally got around to purchasing a pressure tester, My #1 and #4 cylinders (counting from L to R from radiator) are each producing about 120 psi, but my #2 and #3 are significantly lower at under 40 psi each. Is this a gauranteed engine rebuild for new rings or is there potential that a valve adjustment might fix this issue? FYI when I first got the car back from having the new suspension and brakes installed it seemed to run fine...how fast can rings go bad?

Thanks,

Steve
SD Denham

There is a guarantee that you have a blown head gasket between 2 and 3. 120# is still too low for the other cylinders, so a rebuild is probably in order.

You can always TRY new rings alone, but cylinders wear in a taper, so it is unlikely that rings alone will fix the problem.

Tom Lange
MGT Repair
t lange

Low compression betw en 2 and 3 is a classic headgasket.
D. Sander

According to Woods, a standard XPAG engine in good condition should give 145 psi on a compression test.
Dave H
Dave Hill

Headgasket. Make sure you are testing with a well charged battery and the throttle wide open or the reading will be too low. George
George Butz

Before you relie on a fixed compression of say 140 PSI as the standard give a look at the following. Since I live at 7000' there is no way I can see 140 PSI on a good running engine. He also discusses other issues effecting compression.

http://www.gregsengine.com/cylinder-compression-testing.html

Joe
JWP Policastro

Wow I can't believe it's the head gasket, it was just replaced a few months ago when I had engine work completed, not a rebuild but all new gaskets. I guess I'll find out when I pull off the top end and take a look :-)
SD Denham

There are a lot of question:

Did you always torque it cold?
Did you follow the correct torque pattern?
Did you torque it a second time after a few hours?
Did you torque it again after 100 and 500 miles?
Did you re-surface the block and/or head?
Did you check the head studs VERY carefully for stretch?

See mgtrepair.net under head studs for my observations, and the availability of high-quality ARP head studs.

Tom Lange
MGT Repair
t lange

When you get the head off, check it for flatness, too.

As for compressions, there are lots of things that can affect the reading (Joe gave you one), so don't take the 145 number as gospel. Here's another: there are a lot of compression testers on the market now that have a hose or metal tube between the gauge and plug hole. The valve is near the gauge, not at the plug-hole fitting. That means that the cylinder head volume is effectively increased, so the pressure will be lower. Mine is consistently about 135 psi with one such gauge, and I don't worry about it, as all cylinders are the same within a couple psi.
S Maas

This thread was discussed between 02/01/2016 and 03/01/2016

MG TD TF 1500 index

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