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Triumph Repair/oil pressure & radio installation


Hi Howard, I was hoping you could help me with the oil pressure. What is the normal reading while cruising in my dream car?(1976 TR6) It starts out @ 15 and about 20 to 30 minutes later I'm sitting at 5 @ about 55 to 60 MPH on the highway. It runs excellent. It does not leak anything. Please let me know. Also if it is a problem, how to fix it. And, on installing the stock radio I bought for it. Can you tell me if there is a faceplate that should go to the front of the dash. There is an indentation in the dash and I do know that you can get a blanking plate(radio delete) that is in the same shape as the indentation but I can't seem to find a faceplate.  Thank You for your help.  Mike

Hi Mike,

Your readings are low and can be dangerous to your engine. It does not mean for sure that it is but it is an indication that you must do something right away.

Your oil pump has the capasity to pump 300 to 400 PSI easily but that is regulated down to a usable pressure. The regulator is mounted in the lower left side of the block below the distributor and oil light switch.

Oil pressure is built up when the pump can not push oil through the bearings of the engine. On a engine with good and normal bearings this pressure can build up to hundreds of pounds pressure so the pressure regulator valve is pushed open and the excess pressure it bled off by oil returning to the pan. If that regualtor spring is broken or weak or the valve is not seated well oil pressure will be bled off and you will have low pressure.

Where an engine is in danger is when the bearings get worn away so that oil goes through with little to no resistance, then not much pressure it built up thus low readings.

There are other possible reasons too. A faulty oil pressure gauge can give the wrong readings too.

When a TR-6 is brought to me in the dealerships I have worked in with low oil pressure there is a procedure I would go through.

First I ask what grade oil they used. 10w x 30 is ok for winter driving and 20w x 40 I recommend for summer driving. (never use 5w oil in it) Then I connect a known good hydraulic gauge to the block. (most auto parts stores have a universal hydraulic gauge that comes with an assortment of fittings.)They are not expensive and useful for all engine testing.

If I establish that the reading is low I remove the oil pressure regulator spring and valve to see if the spring is broken or the valve seat is damaged or somethng stuck in the seat area. (a small mirror and a strong light is useful to look into the hole when the spring and valve are removed) If the spring is not broken measure the free length of the spring to see that it is not compressed. It should measure about 1.53" or 40mm long. and there should be only one gasket washer on the valve body that supports the spring and valve.

Another thing I do is to remove the valve cover and watch the oil flow in the valve rockers to see if oil is being pumped up to the rockeer arms. The rocker arm shaft is hollow but there shoud be no oil coming out the ends of the rocker arm shaft and none from under any of the rocker arm stands. Oil should be coming out of the rockers themselves only.

If all of the above it correct, and I have low oil pressure I then remove the pan and examine the pick up screen and check that the oil pump is not loose. It is very rare for a TR-6 oil pump to be worn out like many older domestic cars. I then remove several rod caps and use "Plasti-Gauge" (available at most auto parts stores that deal with mechanics) (If your auto parts store does not know what that is, you should not be buying parts there anyway)

Use the "Green" Plasti-gauge and lay a strip across the baraing (not in line with an oil hole) and very carefully put the cap back on the rod and tighten the cap to specs. Being exreamly careful not to move the crankshaft or you need to start over with a clean piece of Plasti-gauge. Tighten the rod bolts to about 40 ft lbs. then remove the cap and use the paper gauge of the Plasti-gauge sheet to get a width of the crushed plasti-gauge and you want to see from 1.5 to 2.5 thousandths (.0015" to .0025")

With the loss of pressure you have, if it is a rod bearing problem, you would probably see much higher readings then that and even need to get the "Blue" Plasti-gauge to even read it. I would check several rod caps to see a pattern. I have been building engines for many years and it is very rare to find an engine with good rods and bad mains. (BE SURE not to turn a rod cap around or get them mixed up.)

If you find excess clearance in the rod bearings it is still not 100% sure that you need to rebuild the engine. In this case I push the rod and piston up into the cylinder and get mikes and measure the rod jurnal for size and roundness. If I find the jurnal within one half thousandths of being round and within one thousandths of diamaeter then is is possible to just install new bearings and you should get several more years out of the engine before an engine overhaul is necessary.

If it is bordor line you can just use the next heavier weight oil and a can of STP oil treatment and get some more time out of the engine. Keep in mind that the STP is not to thicken up the oil because it does look thick but the molacules are string shaped and it does not thicken oil. It changes the oil so as to help improve the viscosity index meaning it helps the oil not thin out so much when hot and the reason I like it is because hot oil normally runs out of bearings and off of cylinder walls and STP sticks there. (Most of the ware on an engine happens in the first few seconds of running on a start up due to this)

Let me know.


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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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