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MG TD TF 1500 - Oil pressure goes away

I have a TD in the shop thats giving me fits. The engine was compltly overhauled and ran as such with 50 lbs of oil pressure. The engine lost pressure when the oil pump rotor gear broke and bent the shaft away from the cam. The pump was repaired to spec. The cam looks good. car leaves my place with 45 lbs of pressure and running fine. Now the car comes back with no oil presure again. remove the pump and everything looks good but find the back of the cam gear was warn .072. had it machined with a thrust washer. now the engine has only 11 lbs of pressure and when rpm are increased the oil pressure drops to 8lbs. checked the check valve in the pump, OK. engine sounds good, no knocking. I'm about to remove the pan and check the bearings but I'd thought I might get your input
Jim Pelletterie

Jim

I just spent a good year plus tracking down oil pressure problems in a new engine. I had a very similar experience in that I also bent the pump shaft upon startup. But in my case I also tore up the cam gear. Then, while replacing the cam, I knocked the back cam cover off. (that is a whole nother story)

First thing is take the valve cover off and see how much oil is coming out of the rockers with the engine running. If you are getting any spurting above the rocker, the pressure is good. (word of advice, put towels down all around the head to catch the spray if it is spurting)

In my case, it was my oil pressure guage - even though it had been working fine prior to putting in the new engine. I spend $12 and purchased a new oil pressure guage to check it and found the guage was the problem.

BEC Cunha

jim, i have the same thing going with my newly overhauled motor...at idle i have 70 psi plus in the main oil galley and 8 psi at the block to head pipe. my machine shop friend reads in his XPAG overhaul manual that oil pressure to the head is metered pressure from the rear cam bearing. before you drop the pan i would suggest you do what bruce says..see what oil flow you have out the rocker assembly when the engine idles...and note how soon after start you see that flow.. i would also tap into the main oil galley at the galley plug closest to the rear generator mount. i just took a bolt with the same thread as the galley plug, drilled a hole down the center, cut off the bolt head and cut a slot in the end for a screw driver. thread the "fitting" you just made into the galley plug hole and connect to an oil pressure gauge with hoses and hose clamps. now you know EXACTLY what oil pressure is being supplid to your main bearings. regards, tom
tm peterson

I have a remote guage in place and there is a restrictor in the fitting to the head. there is oil at the rockers but not excessive. Tom I will try your idea, stay tuned
Jim Pelletterie

took toms advise and made a tap from a extra banjo bolt. drilled a 5/16 hole and tapped with a 1/8 pipe tap. replaced the bolt with the pump outlet and get 60 lbs and rizing when rpm is increased. moved the bolt to the outlet of the filter where it enters the block and get 14lbs. The filter is a new replascement from moss. with the help of the guys from napa I was able to find two shorter filters with the same diameter as a direct replacement was not available. upon start up the pressure is 48 lbs and shows 45 on the original guage. If you are having oil pressure problems check the filter first. My cousin stopped by and told me that they had problems with the sock type filters on diesel engines especially when the oil is cold. it seems the filter cannot pass enough oil thru when its 20w50. I will be looking for a pleated filter as a direct replacement.
Jim Pelletterie

Jim;
I had a problem with a customers TD.It was a completely rebuilt engine with 1000 miles or so. He changed the oil and sock type filter. What he did wrong was he installed the outside perforated screen on the wrong end of the sock. The sock itself unprotected by the perforated screen was pulled into the oil outlet. This lowered the oil pressure down to about 10PSI.
Sandy
Sandy Sanders

I am having an oil pressure problem as well and I haven't really identified the problem. The motor is back at the machine shop for new cam bearings and line boring (something I should have done in the first place). I also have a rebuilt oil pump ready to go in. If after all this it turns out to be the filter I'm going to cry! All of this background to ask a question - That is, I would assume that if the oil filter is 'plugged' the oil would flow through the oil filter relief by-pass? Wouldn't you still have good oil pressure and flow? The only way this wouldn't happen is if the main oil pump relief valve opens first....??? Does this make sense????

Have fun!

Jim
Jim Budrow

Jim, The pressure by pass in in the pump not at the filter, so if there is an obstruction the excess oil get diverted back into the pan from the pump. I have been fighting this problem for some time and I knew it was something other than the bearing clearences. The line bore will only center the crank in the block.
Jim Pelletterie

jim, where did you get the info that the emergency relief dumps into the pan. the maint manual says.."If the filter element gets clogged through negelect, an automatic safety device is prvided. .....It consists of a spring-loaded ball valve which allows the oil to by-pass the filter, ths maintaining engine lubrication until a new filter is fitted." regards, tom
tm peterson

There are two relief passages. One past the filter to the block and one going back to the sump if oil flow is restricted from the pump gears. All gear pumps have this one to prevent damage (positive displacement pump).

Again, I think that the pump relief valve going back to the sump could open before the filter by-pass valve if the filter is too restrictive.

This maybe a good arguement for using an adapter with a spin on filter. Spin on filters have a bypass relief built into them I believe.

Best regards,
Jim

PS - I agree that line boring will not affect the oil pressure but while the block is in the shop I decided to have it done - I was annoyed with myself for not doing it the first time! Budgets....
Jim Budrow

This thread was discussed between 01/06/2007 and 06/06/2007

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