View Full Version : TR6 TR6 - Secondary oil feed to rocker shaft

11-25-2004, 03:25 PM
Has anyone used one of these aftermarket oil feeds to the valve train?

In looking at the original engine oil flow diagrams, it appears that this installation will 'rob' oil from the main gallery just before it would normally go to the rear cam bearing. This almost seems a bit self-defeating in that we get more oil to the rockers, but we take the chance of damaging the cam bearing. That is of course unless the pressure and volume of oil in the main gallery are high enough to overcome the loss of some oil to the rocker shaft.

Did I answer my own question?? Any thoughts??

mike crane
11-25-2004, 03:37 PM
I think you answered your Question. For street use most TR owners that I have talked to feel they would rather not reduce the oil supply to the bottom end and unless your oil galleries are clogged you have sufficient oil supply to the top end. Just my humble opinion.

11-25-2004, 04:42 PM
I've seen more than a few stock rocker assemblies that are mucked in the front section because of poor oil flow. I don't think that the auxillary flow line creates a problem.
Too, I have a large oil cooler and get an extra quart of oil in the system, not that that matters. Am running GoodParts roller rockers and upon checking (setting valves) everything is very well oiled. Experts say (of which I am not one) oil starvation is not created with the auxillary oil line, especially with a later oil pump.


11-25-2004, 04:55 PM
Don, I run one on my GT6, and have had no problems at all. I ran one on the 1500 Spit race motor, for the added advantage of more oil on the valve springs, to promote cooling. That one had roller rockers, the GT6 has a stock valvetrain.

11-25-2004, 05:53 PM
Thanks for the input.

The engine in the wife's '75 had about 80k on it when this rebuild started. I went through it and found virtually no wear, so aside from gaskets and seals, nothing has been replaced. I had thought seriously about adding this secondary supply line but based on the wear, I just could not justify it. Being that it will be a Sunday / summer driver, I think I'll pass on it.

BTW Bugeye, your tag line was worth the price of admission to this board!

Rick O.
12-02-2004, 09:36 AM
A worthy compromise is to install the external feed with a suitably sized roll pin inserted in the end that attaches to the block adapter. That will reduce the feed flow a bit, but still provide extra top end oiling without a significant drop in flow to the lower end bearings. I would not install the feed line on a worn (low oil pressure) engine.

12-03-2004, 12:32 AM
I dont believe that any pressure is being "robbed " from anything. The oil pump puts out a volumn of oil that reaches a certain pressure before the excess is bleedoff by the relief valve. That lets you take some oil off at this junction and feed it up to your rockers so they can bathe in plenty too!!! It cant hurt anything, and some of the 2.5's need a little help in this area(mine did).
MD(mad dog)

Rick O.
12-03-2004, 10:40 AM
Yes, the pump is a positive displacement type, meaning that it always moves a certain volume of oil regardless of the pressure (except for a little internal leakage). It produces a specific amount of flow at a given rpm. The resistance to that flow produces the pressure. A large increase in pressure will NOT give you a large increase in flow (pressure increases exponentially with flow). However, the pump's PRV spring setting is pretty high (I think in the 90 psi range) and most of our engines don't normally operate in that range. The result is the PRV doesn't unseat and no excess oil flow capacity is available. Tap in the feed line and simple hydraulics tells you that the pressure has to be reduced a bit to accomodate the additional flow to the rocker gear. Does this matter? Absolutely not. What does matter is that every bearing, bushing, and lifter surface maintains a miniscule oil film (I've read that some Rolls Royce engines operate with less than 5 psi oil pressure).

[A useful diagnostic: If an engine (including the rocker bushings) has excessive clearances in anything but rod bearings, the oil pressure will be uniformly low throughout the rpm range. If the rod bearings have excessive clearances, the oil pressure will be low at idle and will get worse as the rpm increases. Rod bearings turn in a circle rather than on an axis, so they are subject to centrifugal force trying to pull the oil out of the bearing.]

My experience has been that a consensus on the merits of the feed setup does not exist. I used to run with it, but it now sits in a box (removed to solve an excessive oil consumption issue). This proved to me that the feed line was supplying a healthy flow of oil to the rocker gear. Sounds wonderful, but was this additional flow useful? I certainly don't believe it established a better oil film on the bushing or push rod/lifter surfaces. Until someone provides real data on the decreased wear benefits purportedly offered by the feed line, I will not be convinced that it is necessary. I do know that the kit provides an inexpensive psychological benefit.

Simon TR4a
12-03-2004, 11:09 AM
I'm always impressed when someone can back up an opinion with a logical explanation, wee done, Rick!

12-03-2004, 11:39 AM
Hello Rick,
my feeling is that if the PRV valve is not unseated to a degree then the pump must be undersized.
My car will go to 75 psi when cold and 50 psi when hot at above 2000 rpm. I think the reason that there is a difference is down to viscosity and the PRV is not large enough to dump the volume of oil when cold.
Incidentally I had to shim my PRV as I felt that I had too much oil pressure, near 100 when cold and 70 when hot. To me this is also additionl reason to believe the PRV does regulate the oil pressure and that there is excess capacity for an extra oil feed to the rockers. Whether it is necessary I don't know, it certainly won't help if the oil channels are blocked in the rocker assembly.


Rick O.
12-03-2004, 01:08 PM
wee done, Rick!

[/ QUOTE ]
Thanks Simon. I'm just a 'wee' bit anal about such things!

Rick O.
12-03-2004, 01:19 PM
Unfortunately, everyone's experience is different. I have a fairly tight engine that consistently hits 90 psi cold idle, so that's why I think the PRV unseats there. The lowest stuck-in-summer-traffic idle pressure I've seen is in the 50's. That's with my brew of 2 qts Rotella-T synthetic 10W-40, 2 qts Castrol 20W-50, and 1 qt 10W-30 synthetic. At the beginning of the year, I R&R'd the #4 main bearing cap (to install bronze thrust washer) and noted the lower bearing shell was as-new. I have about 15K on the engine and it has always behaved that way. So I'm not inclined to shim the PRV based on that experience but . . . YMMV.

I have not doubt the oil pump has sufficient reserve to supply the oil feed; just not convinced the feed adds more surface film where it counts.

Rick O.
12-03-2004, 01:39 PM
And one other thing. It is a remarkably common misconception that bearing surfaces rely ("ride") on the oil pump's pressure for longevity. What matters is the single layer of oil molecules between the surfaces, not your oil pump being able to support bearing loads. The loads on the rod bearings are tremendous (thousands of psi), but it is the oil film that offers the protection. This loading is why the 10,500 psi Vandervell bearing material was superior (until they were discontinued; Clevite 12,500 psi tri-metal rod bearings are a good substitute). The commonly available Glacier bearings are only rated to 6,500, so expect a more frequent changeout with them.