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MG TD TF 1500 - C40 Dynamo rear bush lubrication

I was assembling the dynamo today after checking and cleaning.
I am surprised to find that the rear bush is grease lubricated (according to the manual)as it has a bronze grease tube with felt sprung loaded insert on the rear casing over the bush.

However, on inspection I can see no hole in the bush for grease to get to the rotating parts !

Is this normal ? Do you think that I should drill a small hole through the bush ?

Or, is grease a mistake and the felt should hold oil that can soak though the bush. Other Lucas models have an end oiling hole for this ?

Simply puzzled to find this !!
Mel Pascoe

Hi Mel - the bushing should be an oilite sintered bronze bushing (which is actually porous).

The theory is that the grease will migrate through the bushing to the rotating shaft. The bushing itself is impregnated with lubricant prior to installation.

I am not sure how well the concept actually works. But I lubricate the spring loaded greaser with a low temp grease.
DLD

I have always thought that the felt should be oil soaked, and the oil lubricates the bushing,, I don't agree with putting grease in there,,,

Steve
Steve Wincze

The Operation Manual is pretty clear on when and with what to lubricate the bushing.

Tim
TD12524

TW Burchfield


My experience is that the grease hardens and does not lubricate as required. I prefer to soak the felt in oil, put a small amount of oil in the lubricator, replace the pad and spring and then screw the unit to the dynamo. I check for sufficient oil about once a month.

The alternative is to have the bush replaced with a sealed bearing.

Jim

James Neel

I don't have my manual here,, what does Ref D Recommended Oils say,,,

Steve
Steve Wincze

Here you go.

Tim

TW Burchfield

OK,, That's what it says,,,,

but I'm stayin' with oil, it just makes more sense to me,,,

Steve
Steve Wincze

The grease recommended by the manual is not the same grease we use today on bearings and bushings. It melted at temperature and flowed through the oilite bushing, lubricating the rotating parts. Today's greases will not melt and therefore will not penetrate the bushing or lubricate the shaft. I use a heavy oil and lubricate the felt pad every now and then to simulate the original lubricant specification.
Steve Simmons

An additional point about the sintered bronze bushing - if I remember correctly, the instructions state that the bushing should be soaked in oil for 24 hours prior to installation. If you all are like me, you see that instruction mere minutes before installing the bushing, throwing your reassembly schedule into a tailspin. Here is a procedure to complete the 24 hour soak in minutes. Set one open end of the bushing on your thumb, fill the bushing until the oil brims over the open end, put your other thumb on the top opening (it helps to be somewhat double jointed here) and push your thumbs together. When you see oil oozing through the pores of the bushing (mere seconds) you have completed the 24 hour soak and you can proceed with the installation. Cheers - Dave
DW DuBois

The recommendation of my mechanics who rebuild my C40 was:

Take of the tacho gearbox and inject some oil onto the generator axes. That is better then oiling by nipples or lubrication cap.

Bela

The late Jim Holcomb, owner of Holcomb Armature, in Atlanta often told us in the SE MG T Register to just add a drop of oil from the dip stick to the felt. Jim could still wind armatures by hand and drove, really drove, an award winning TF and TC. We all miss him.

Gary
G B McGovern

I believe grease is a better option. As the shaft rotates oil is forced against the bushing by centrifugal force. This isn't a problem with non porous bushings because the oil has no where to go. But because the bushing i the generator housing is porous the oil can be pushed back into the bushing. This lessens the microscopic layer of oil between the bushing and the shaft. This is especially true where the lubrication orifice is located. When the spring loaded cap is screwed on to the lubricating tube the oil will just migrate up around the felt pad and up into the tube. The oil in the tube will move downward but only by the force of gravity. High temp grease, on the other hand, will not easily migrate around the felt pad but will be pushed against the bushing by the force of the spring loaded pad. I believe the factory recommended high temp grease because they wanted a lubricant used that would not liquefy easily and suffer the shortcomings of oil. Hi temp grease would not be easily forced back into the bushing by the rotational shaft as oil would because of its much greater viscosity and the hydraulic pressure of the spring loaded felt pad. The engineers picked grease over oil and I suspect the had a good reason for doing so.
TW Burchfield

Today's common grease will not penetrate the bushing. It's far too thick. Oilite bushings are designed for liquid to permeate through. As the oil works its way through to replenish oil lost at the armature shaft, the felt will wick oil downward by absorption, not by gravity. It works the same way as an ink marker - inside is a long piece of felt-like material soaked in ink.

If you use common modern grease on an oilite bushing, the pores of the material will be sealed solid, and the grease you put in the oiler will never go anywhere. The grease specified for use in the generator oiler is not the same as what you're buying at the auto parts store today. It would melt at temperature and flow through the bushing. Think of butter in a frying pan. Melts slowly from the bottom up, oiling up the pan.
Steve Simmons

Gary, would you mind sending me your email address? Have some GA questions. Bud
Bud Krueger

This thread was discussed between 22/03/2016 and 24/03/2016

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