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MG TD TF 1500 - oil pressure help

I rebuilt my XPAG (#12942) engine about 1 1/2 years ago. It currently has about 900 miles on it. From the start it has had low oil pressure. It will be 40 psi when it starts but drop down to 20 when hot. I pulled the engine this weekend to see if I could find out what the issue is. The main, rod and cam bearings are in very good shape. I miked the main and rod journals and came up with the following numbers: rod bearing journals 1.762" 1.760" 1.763" 1.762 and main bearing journals 2.036" 2.035" 2.035". In the last rebuild I used .010 bearings. The rocker shaft bushings are new. Oil pressure/water temp gauge was rebuilt by Nissongers.The oil gauge pipe is on the lower oil feed on the block. I had the oil pump rebuilt. Is there something I'm missing?

Tim
Timothy Burchfield

Have you checked the oil pressure relief valve located in the bottom of the oil pump cap.
A weak spring or damaged ball/seat will mess up your pressure.
PS, is this running or tickover pressure.
Ray TF 2884
Ray Lee

Ray, I just checked the oil pressure relief valve and the oil bypass valve Both are to specs (at least as far as Moss parts are to specs). I bought both valves new from Moss when I originally rebuilt the engine. The oil pressure is about 40 at speed and 20 at idle when hot. I just found the item below and it is making me rethink my oil pressure problem. Thanks for the input.

Regards

Tim

Timothy Burchfield

Hello Tim. use plastigauge and check the clearance of the bearings. If necessary feather shim them.

Butch
R Taras

I have been running with 10/15 psi at tickover with 40/50 psi when running hot for many years. Nothing has broken and I do not hang around,3.9 axle and 70 mph cruise(3500rpm)
Ray TF 2884
Ray Lee

Butch, I plan to thanks.

Ray, that matches my driving style and numbers except the high figure is around 40.

Tim
Timothy Burchfield

Butch. Can you please explain feather shimming is it for tight bearings
R D Thompson

The TF Workshop manual states the oil pressure should be 50psi cold and 40psi hot. I interpret this to mean during operation and not at idle. My TF shows 50psi on a cold start and 40psi hot at 2,500rpm. At hot idle on a very hot day it can drop as low as 10psi, but generally idles at 15psi hot. I see nothing wrong with these numbers. I have a 3.9 rear end like Ray’s TF 2884, and limit my RPM to 3,500. Like Ray, I have been driving my TF a number of years with no sign of a loss of oil pressure which would have indicated wear. I use a separate, calibrated, third party gage to monitor my oil pressure.

I read that some owners add restrictions in the oil feed pipe to the head to artificially boost the pressure recorded by the gage, above the pressure recommended in the WM. This is detrimental as it reduces the oil flow to the top end. 50 and 40psi on the gage are the correct numbers during normal operation.
TF 1500 9194

What oil are you running Tim
William Revit

I have always presumed that when all the gauges are at mid-point then all is well with the world.
Ray.
PS. I don't limit it to 3500, in traffic the occasional burst up to 4500 has not broken it.
Ray Lee

William, I'm using Valvoline racing oil 20W - 50.

Butch, I too would like to know what you mean by feather shim?

I bit the bullet and took the crank in for a regrind. Someone mentioned on another site that a difference of .003" between the rod journals would never be corrected with just new bearings.

Thank you everyone for the excellent advice and comments. I'll report back when the engine is back in the car and running.

Regards

Tim
Timothy Burchfield

Hi Tim. A feather shim is a shim material that each layer is .0005 thick. The one I have is 4 layers thick. The center layer is about 1" wide the second layer sticks out about 1/4" on each side, repeat until you get 4 layers. The idea is you can peal off the layers you don't need. You get the thickness you need in the center of the bearing and half the thickness on each side of the bearing to make up the full thickness. You only shim the cap. The shim goes between the cap and bearing. The ones I have were from Blaisdell 2149 Pound Drive Placentia, Ca. 92670. I don't know if they are in business anymore. Today the grinding machines have gotten more accurate. So this isn't a problem any more.

Butch
R Taras

Butch, thanks. I would have made a wild guess at the meaning of shimming in this context but was not sure. Reminds me of bearing scraping, another technique I've never been exposed to. I imagine those .0005 sheets were difficult to handle.

Regards

Tim
Timothy Burchfield

I've used a .001" shim on a Morris Minor with success. Always Plastigage after to verify the actual clearances. And most importantly make sure you DO NOT cover the oil gallery hole. I use a bit of spray trim adhesive to hold the shim in place while assembling.
John Quilter (TD8986)

I cannot understand how shimming the mains and big ends will improve oil pressure. Surely it will make the bearings loose and reduce pressure. If I was concerned about the dimensions I would have the caps skimmed and then the rods / block line bored. I would never shim the bearing caps.

My TF running on Comma 20/50 shows 45-50 psi when running hot and 15-20 at tickover. The pressures improved significantly when I rebushed the rockers as part of a stem seal update.

Jan T
J Targosz

Hi Tim. Not bad to handle. John the problem that you get with using plain shim stock is you get .001 on the bottom, but get .002 on the sides. unless you go all the way around and punch a hole for the oil squirt hole. The feathered shims allow you to only need to shim the cap. An old technique I was shown many, many years ago.
I googled it and saw some for sale on ebay.

Butch
R Taras

Tim,
You must have a TD, a TF owner just puts up with slightly low pressure. To get the unit out of a TF without damaging something is a nightmare
Ray
Ray Lee

Tim. Try the old penny trick. Put a penny under the oil pressure relief spring. If the pressure goes up, it is a weak spring. I changed to the Moss adjustable relieve valve. It made all the difference.
Bruce Cunha

Ray, I actually looked at a TF before buying my first TD. I asked the guy why the side panels didn't lift up like the TD. I thought he had modified the bonnett somehow. I decided I was too old to contort myself for routine maintenance.

Tim
Timothy Burchfield

modern high revving engines don’t even give you a light until in the 9-11 psi range. A similar technology long stroke engine designed, built and operated during the same period by Hudson Motors uses a splash lubrication system. There is no oil pressure at all at the big ends. Higher oil pressure is NOT required for long engine life. It is NOT oil pressure from the pump that keeps the bearings from contacting the moving parts. If oil is delivered to all moving parts at ANY pressure it is dynamic film lubrication that keeps the moving metal parts separated. The pressures between the moving parts FAR exceeds the pressure provided by the pump.

Oil pressure as a tool to determine engine health and wear is ONLY valid when looked at as the pressure changes over time.

As a side note, the condition of the oil bypass relief should have a nominal effect on oil pressure as the oil that bypasses is dumped into the gallery.

Regards, Tom
tm peterson

Tom,
I agree with you that flow is more important than pressure but it is the filter by-pass that dumps to the gallery. The oil pressure by-pass shunts into the pump suction side limiting output.
To show my age, I sailed on a ship with a splash lube steam piston engine, mind you max revs was only 100rpm.
Ray TF2884
Ray Lee

Tom, are you saying that an XPAG engine with 10 psi of oil pressure at 3000 rpm will last just as long as an XPAG with 40 psi at 3000 RPM? I'm not talking about a new and a worn out engine. Let's say you rebuild two XPAGs and control the oil pressure (i.e. modifying the pressure relief valve, modifying the pump, etc.) to provide 10 psi on one engine and 40 psi on the other at normal operating speed. You seem to indicate that, everything else being equal, the engine life will remain the same for both engines. Is that what you are saying?

Tim
Timothy Burchfield

Tim,
The pressure is a function of flow,if you modify the pump to a lower pressure you will have reduced the flow. As you wear out the bearing/journal the pressure drops with exactly the same flow.
Ray
Ray Lee

Ray, regarding the bypass, that is what I stated in my post.
Tim, if you have adequate flow to all bearings the pressure delivering the oil has no effect on the dynamic oil film that keeps the rotating parts from touching.
Regards, Tom
tm peterson

This thread was discussed between 07/04/2019 and 14/04/2019

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