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MG TD TF 1500 - Tightness of tach gearbox to dynamo

Before I re-attach the tach gearbox to the dynamo and route the cable from there to the tachometer, I just wanted to get the groups input on how tight the brass coupler should be when screwing it on the back of the dynamo. I want it tight enough so it doesn't loosen up and the gearbox then starts flopping around, but at the same time, I don't think I want it too tight either. The brass coupler has some thin knurling on its upper outer portion. Should that be finger tight only...or cinched it down somewhat using a pair of ship-joint pliers?

Thanks!

Jim
Jim Rice

Jim, I've been around a long time and even spent 5 years in the Navy, what are ship joint pliers? Never heard of them! PJ
Paul S Jennings

Oops!

Should be slip-joint pliers....or really any type of tool that would fit the O.D. of the coupler to tighten.
Jim Rice

I tightened mine with gas pliers. How many know what they are?

Jan T
J Targosz

Gas pliers?? Not a clue!
Jim Rice

I also use a dab of locktite.
-David
D. Sander

Gas pliers are the same as slip joint pliers (with just two positions). Cheers - Dave
D W DuBois

I found, many years ago, when the TD was running that you did need to tighten it with something more than your fingers.

I must admit, that in those days, I used slip joint pliers and of course buggered up the knurl on the nut.

When I put it back together I made a new nut.

Now I do not recommend using pliers on anything that is not round and smooth, but you do need more than fingers.
I believe I have seen some units that had a hex, but mine was a knurl.

Either put a piece of leather between the pliers and the knurl or there are special pliers (expensive) that have plastic inserts to prevent marring the surface.

Jim B.




JA Benjamin

Photo of gas pliers. Very old but ideal for tightening circular collars/nuts. Re the original thread I tightened mine by hand but the nut unscrewed itself and there was a ticking noise. After adjusting the clamp on the gear box input shaft and nipping the nut up tight it now appears to be OK.

J Targosz

Thanks guys. I had busted the old coupler drive. Not sure if it was because the replacement drive cable that I installed (perhaps too tightly),or because I may have over-tightened the brass coupler...but nonetheless ended-up shearing the dog-ear drive that inserts into the end of the dynamo. Now I have the new coupler kit attached AND another new cable (original type) that I will use, and I didn't want to screw up the installation a second time.

Jim
Jim Rice

have you got/tried a shake proof washer inside the coupler?

Try it, and then you can feel it bite nicely and no need to overtighten.
mog

Mog:

I don't have one, but that would seem to be a good fix. The new tach drive cable I got from Moss came with a fiber washer that has the same feel/effect. May take a quick trip to the automotive/hardware store and see what they may have in that regard. Any idea what thickness would work best?

Thanks in advance,

Jim
Jim Rice

Search around in the archives, lots in there somewhere. See Moss tech note on the cable also. Make sure the drive snout is a passive fit and not forced into the armature. I think best to lock down the rest of the parts (knurled nut and split bushing), then tighten the clamp screw. Washer has to be thin, or it will space everything out too far. There is a picture somewhere of a support bracket that attaches to the grease fitting and then to a generator screw that will help keep it from flopping around. Also make sure your rear dynamo bushing isn't worn, or it will trash your new drive mounting. George
George Butz

Here it is, George: http://www.ttalk.info/picture_this.htm#Tach%20Box%20Stabiliser it came from John Twist via the late Gordon Lawson. Bud
Bud Krueger

And, it looks like this:


Bud Krueger

And, this:


Bud Krueger

Thanks Bud..That's pretty clever!
Jim Rice

Finger tight with a drop of loctite. No need for bracket modifications or pliers of any type. No disrespect to the inventor, but the bracket is unnecessary. Regards, tom
tm peterson

The original used a fiber washer such as Moss supplied. This works for a time with finger tight. However I have found that a rubber washer works better .
Over time the fiber washer (the one that Moss supplies more so) looses its elasticity and you can't get it tight enough. It is often omitted by the DPO and you can't get it tight by any means.

The rubber washer provides more friction to rotation of the drive and keeps its elasticity to maintain the friction.

I have used one about 1/16 in thick for over 25 years in my TF

A perminent solution to the occasional grounding of the distributor terminal by the tach drive is to rotate the distributor 90 degrees.

If they had intended to use some sort of wrench or pliers on the coupling they would not have used a fine knurled brass fitting. FINGER TIGHT!!

By th way, I found a range of rubber washers at the local hardware store
Don Harmer

Slip pliers, channel locks or water pump pliers
David
D. Sander

Thanks for all the replies! Quite impressive in such a short time. Don's idea of a rubber O-ring may be worth a try. The frictional properties of an O-ring in this application seems very plausible. Of course the reason for all this, was the Tach had needle float. I thought perhaps the cable might be binding causing the problem, so I promptly screwed up most of the parts trying to locate the cause. With my luck I'll get all the drive components to work flawlessly...and then discover what really needs to be done is to have the Tach re-built!! Thank you all so much for your input. I'll advise how thing turn out!

Cheers!

Jim
Jim Rice

Just put a thin o-ring in the brass nut before you put it on. Then tighten with hand pressure only. Mine has been that way for tens of thousands of miles, never a problem.
Steve S

Jim, you might want to glance at the thread Tach Gear Box from 2013:
http://www2.mg-cars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=8&subjectar=8&thread=201308211418479239

In addition to the tach needle swinging wildly due to the non-meshing gears corrected by the box rebuild, the box itself was flopping around on the end of the ginny. I fixed that by making and installing a thin rubber gasket inside the knurled connecting nut. The gear box has remained stable for almost two years and a couple of thousand miles. Jud


J K Chapin

If you do a finger tight, when sputter, backfire, and die, first check that your tach gear box has not flopped toward the engine and shorting the distributor. Been there. Not brave enough to try rotating the distributor.
R W Hinton

RW

Put some insulator covering over the distributor terminal

and use the flat rubber washer inside the coupling

Don H
Don Harmer

Jim
This is how I fixed mine once and for all.
Easy fix. Shake proof washer the right size - to takes up any wear on the collet. File the clamp jaws to get it to fit tightly. Drill it for a slightly larger screw to hold the clamp really helps.
It no longer comes loose.
Rod.


R. D. Jones

All:

I went with the rubber O-ring/dab of Loctite method. Everything went together like clockwork, and the Tach indicator arm doesn't have the "float" anymore.

Thanks again for all your inputs.

Best regards,

Jim

BTW....the O-ring I got at Lowes in the kitchen/bathroom faucet area where they sell the re-build kits. BrassCraft # 0584. Measures 9/16" I.D. (3/4" O.D.), 3/32" height. Fit's perfectly inside the brass coupler.
Jim Rice

This thread was discussed between 06/03/2015 and 09/03/2015

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