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Triumph TR6 - Pressure relief valve

I removed my pressure relief valve out of the block to have a look at it. I noticed slight pitting on the plug end/edge (the face is very clean). I will replace it but ask a few questions.When I first start the car from cold, I get good high oil pressure and drops significantly when warmed up. This is normal but if I get "leakage" past the plug will the pressure at operating Temp be better?Does the face of the plug or does the round edge of the plug act as the mating surface for pressure relief?..in other words does the pitting on the edge make no difference to operation? The spring has static length of 1.5" which is spec. but will probably replace it also. Maybe just the spring needs to be replaced to what MOSS calls "HEAVY SPRING-provides some increase in oil pressure".
Thanks
Rick
Rick Crawford

A stronger or longer or a spring with spacers will help your pressure depending on the condition of the clearances, or the state of wear of your engine. I make an adjustable PRV for my racecars and when the adjustment doesn't work any more I usually need a rebuild.
Mike Munson

Ha Mike
Thanks for the reply. You obviously know a lot (understatement) more about the inside of a 2498 cc than I do. Had the head rebuilt and no blue smoke coming out the other end..so engine is not bad shape. Will do serious "recalibration" of timing and carbs this spring. I am not a red liner..just trying to get the pressure up a bit. With the slight pitting on the edge will oil pass by the PRV and reduce my oil pressure as seen on the gauge (and in the engine)? Is this what you refer to as clearances? FYI,I have installed the external oil line to the rocker arm.
Mike, what do you race? A 6 or 250? Bet you have fun!!
Thanks again
Rick
Rick Crawford

Rick,

Worn bearings are a significant factor in low oil pressure. Fortunately on the TR6, you can replace the bearings with the engine still in the car. Remove the spark plugs, drain oil and drop the pan, then check the thrust washers as outlined in the manual by moving the crankshaft fore and aft with a large srewdriver or pry bar. Now, pull a bearing cap to see what size bearings are installed and give the crank and the bearing shells a good visual inspection. If you see any copper coloring in the bearings, it is time to repalce. Inspect the bolts for necking down along the shank, which would indicate that the bolts are stretched. Replace the bearings and cap, then go down the line repeating the process and rotating the engine as necessary (why the plugs are removed, no need to fight compression). I have done rod bearings first, then mains. It is more important to do the mains one cap at a time that the rods. The gravitational load on the crank will ruin the seals if you left it with too little support.

Assuming that the crank was fine, buy replacement bearings, a pan gasket. There are those that say replace the bearing cap bolts everytime, but for a normal street engine that is pushed hard I don't think there is any need to replace them unless they are stretched. I have also replaced the little wooden wedges in the front sela block, but am not sure that replacing them is truly necessary. Now replace the bearings (and thrust washers if needed) the rod bearings are easy, the main bearing shell on the top side requires that you use the new shell to push out the old as you slide in the new. You may have to have more than one main cap loose for some so work clean and quick. Replace the little wedges (if inclined) reinstall the oil pan, fill with oil, replace plugs and you're done.

As a rule you will be able to replace the bearings unless they have been let go so long that you have scored the crankshaft. Do this and up comes the oil pressure.
SteveP

Steve
I wish I had asked this question in the fall. It is coming up to spring here and you know what that means. (you do not need to rub it in that you are still driving yours:) The actual pressure numbers are:COLD 50 LBS(3.5 Kg/cm2) and warmed up 30LBS.(2 Kg/cm2). Any comments on these #s? What about the PRV? Will this replacement help?
Thanks Steve
Rick
Rick Crawford

Hey Rick,
As far as I know 50lbs cold and 30lbs hot is not that bad.Of course more is better, so start with the easy
stuff. Replace the spring with a new one , replace the
plug or plunger with a new one as the pitting on the edge is allowing some leakage. Warm it up and see if it makes a difference. If not you have a nice winter
project for next year replacing the worn bearings.
The procedure that SteveP recomends sounds perfect.
If you hustle you could still do it before our warmth
returns. Good luck.
Christopher Trace

I'd leave it all just as it is. In my 3A, I change the bearing inserts about every 30,000 miles and the oil pressure is about 70 cold - then 40 hot when running. At idle it drops to 20 psi.

After, I rebuilt it all 11 years ago, the pressures were higher and I adjusted the pressure relief valve lower because I heard "the lower the pressure setting (still gettng good numbers) you get more oil flow through so the bearings etc are supposed to last longer".

Don Elliott
Don Elliott

Hi Guys
Thank you all for the comments. I will go the route of the new PRV and spring and see what that does. I can always experiment with the new "stronger" spring and the original. The interesting thing about the PRV is that if u look at a drawing depicting oil flow in the engine if the PRV opens then oil flows directly back into the sump. One would think this is a bad thing.Chris, time and $ prevent the hustle. as you said next winter.
I do have one question though...If I put some "plural possession" in my gas tank, will it make my TR6 go faster?
Rick
Rick Crawford

And to think that for all of this time I was operating under the impression that "Plural Possession" was a fragrance aimed at the polygamist market and not a fuel additive. Shows what I know. Guess that's why I'm not a hand picked honor student, eh?
SteveP

I have a 74 TR 6 with 93,000 mi. To my knowledge, the bearings have never been changed. My pressure runs at 50 to 70 cold and 25 to 35 when hot (at 2500 rpm). It will drop to 5 to 10 at idle when hot. I am considering changing the mains and rod bearings, but was told as long as they are not knocking and the pressure is least 10lbs for every 1000 rpms they are OK. What do you all think?
Regarding the pressure relief valve, isn't the purpose of the valve to reduce the pressure if it gets too high (as in cold startup condition)? I understood that it operates when the pressure exceeds a set amount. I don't see that it has any effect on low oil pressure. What am I missing here?

John
John

Hi John
Your numbers are virtually the same as mine. I started this thread in the thought that going from 50 down to 30 was a big drop and maybe I was getting some "blow by" in my slightly worn PRV thus reducing my oil pressure unnecessarily further. So far the replys say that this pressure is OK. John, you are not missing a thing on the purpose of the PRV. Remember that I am thinking the blow by(leakage past) at the valve that,as I said,may be reducing my normal operating temperature, oil pressure. Yes, that valve better NOT be open at low oil pressure (my leak question???). That is an interesting question John. If that is a true statement (10Lbs./1000RPM) then I am right on. Again, thanks guys. I will replace the valve and let you know if it makes a difference.
Rick
P.S. Thanks for the laugh SteveP...good answer.
Rick Crawford

Rick,
I had an EP TR6, sold it.Now I have an IT TR6,I haven't run it yet. Of course it is fun except when the rear axle breaks or the stock brakes give up.
I use the PRV to turn down the pressure when the motor is fresh (less engine drag)and turn the pressure up when it gets worn.
Nobody addressed the rocker assymbly. When the rockers and shaft get worn that is another place you lose oil pressure.

John,
It sounds like it is about time for a rebuild. You are correct about the original purpose, but we racers are always looking for another edge,and we are never ones to leave well enough alone!
Mike Munson

This thread was discussed between 30/01/2002 and 12/02/2002

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