oil tanks

[johnpl]

It seems to me I read a post on this forum stating that in 1966 the rocker arm lubrication for triumph Bonneville's was supplied by a line form the top of the oil tank as opposed to a connection from a tee off of the return line at the base of the oil tank. The author also indicated this design lasted only a year as the design proved to be unacceptable. He also recommended replacing the upper lubricating tank with the later (maybe earlier?) model with the tee from the bottom. Anybody familiar with this issue?

[Oggers]

Looked on my 66 Bonnie, and the rocker feed is as you say. Feed is opposite the the metered chain lubrication coming from the top of the discharge pipe from the scavenger pump. I am curious to undertand why is it considered unacceptable?

[Rex]

At a guess, insufficient oil supply?

[Oggers]

At a guess, insufficient oil supply?

I don't see that. It is essentially the same pipe from the scavenge, only the tee for the rocker feed is higher up. Any restriction is at the rocker feed pipe - which is the same for either arrangement.

[john.k]

The twins that have pressure feed from the motor nearly all suffered from oil flooding of the head........IMHO,the oil tank takeoff feed dosent work by any pressure at the tank,but oil is drawn into the engine by crankcase depression....Twin heads are generally lower than the tank,but the system also works on singles,where the rockers are higher than the oil tank.

[Oggers]

The twins that have pressure feed from the motor nearly all suffered from oil flooding of the head........IMHO,the oil tank takeoff feed dosent work by any pressure at the tank,but oil is drawn into the engine by crankcase depression....Twin heads are generally lower than the tank,but the system also works on singles,where the rockers are higher than the oil tank

On the Bonneville the tee to the rockers is on the scavenge plunger return line - which is pressurized by the plunger itself on the oil pump. 

[john.k]

But is it?.......once the motor heats up,the scavenge return is just spurts and froth.......and would need a positive restriction at the return pipe to raise any pressure at the tee.........I know I always used to put my finger over the return in my A10 on startup to pressurize the rocker oil ,but once the sump is cleared ,oil return is spasmodic ,and hot oil is thin as water ,so the return pipe has no resistance to flow..........There is a bit of gravity feed ,if the rocker shaft is lower than the oil pipe outlet.............but in the singles,the head is a lot higher than the oil tank,yet the oiling still works.

[Rex]

The return is pressurised by the pump and gravity doesn't come into it.
The restriction (to force oil down the rocker line) comes from the top of the tank return pipe having only a small hole for oil to come out of rather than a hole the dia of the return pipe.
The scavenge may be intermittent at tick over but rev the engine and the flow is continuous.

[TGR90B]

+1 for the above. It's how many four strokes effect the valve gear lubrication. I can't really see the point in any debate.

[Oggers]

The return is pressurised by the pump and gravity doesn't come into it.
The restriction (to force oil down the rocker line) comes from the top of the tank return pipe having only a small hole for oil to come out of rather than a hole the dia of the return pipe.
The scavenge may be intermittent at tick over but rev the engine and the flow is continuous

Agreed, but still does not answer why a tee at the base of the tank is considered an improvement over a tee at the top!

[TGR90B]

The farther the branch is from the termination of the main pipe, the higher the pressure available for the branch pipe.

[Rex]

Agreed, but still does not answer why a tee at the base of the tank is considered an improvement over a tee at the top!

This is one of those "how many angles dancing on the head of a pin" discussions.
Oggers, maybe the reason for the change is more prosaic than you think? Perhaps Triumph found that they could save two bob on every tank with the tee at the base?

[Oggers]

Rex - could be - and in addition who is to say the original poster was correct in his premise. I don't honestly know, just curious to understand the reasoning behind the assertion. Coincidentally I have just changed the oil, cleaned the filters and drained the sump. Needs a run now, but somewhat cool up here in the Tundra at present!