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MG Midget and Sprite Technical - Wee maching job

Hi folks, long time no see. It seems very quiet around here.

Would anybody be able to help me out with a wee machining (lathe) job? I would like to modify this 1500 front gearbox scroll seal housing (left) to accept an oil seal (right).

My regular guy is currently indisposed. Bad form!

Cheers,
Malc.


Malcolm Le Chevalier

i have a lathe and could help, do you have a drawing to work to, or is it just a question of machining the diameter to accept the ring ?

P Bentley

This is what I am looking for: 32mm diameter (+/- 0.03), 10.2 mm (+0.3/-0.0) deep from the outermost face. The diameter is obviously more critical than the depth for the fitting of the seal, along with the concentricity of the bore.

Breaking the sharp corner with a small chamfer would also be nice, but of least importance.

Cheers,
Malc.


Malcolm Le Chevalier

Malc
My machine is a 1930's Atlas and is not great for this sort of precision. With the run out i have i wouldn't want to take this on without you knowing that.
I am happy to try it for you, but you may prefer to wait for someone who is more confident in their machine.
Let me know
Peter
P Bentley

Thanks for the offer of help Peter. Realistically I am in no rush to get it done, it is more just the satisfaction of getting the job complete. It is the last bit in my gearbox rebuild but I won't be installing the box for a while so it's not holding anything up. So if you aren't confident I can wait and see if I can get it done elsewhere.
Malcolm Le Chevalier

Peter,

I can do that for you on my Harrison M300, but I live near Oxford. Is that any use?

What is the actual seal reference? Is it a nominal inch or metric seal?

Richard
Richard Wale

It's a metric seal, 32mm.
Malcolm Le Chevalier

Understood Malcolm
P Bentley

You could pop down to Clevedon and do it yourself !

R.
richard b

Malcolm,

I don't know very much about the Triumph-based 1500 gearbox, was is made to metric dimensions?

What is the diameter of the input shaft where the new seal will go? Does it already have a well polished surface to give the seal a good chance to do its job?

Richard
Richard Wale

Hi Richard, a copy paste from a comments I made on a previous thread on the 1500 gearbox front seal:

" There was a thread a couple of months back started by "SJY" about modding the scroll seal at the front of the 1500 gearbox and converting to a lip seal.

It was something I was also pondering at the time, although I didn't get chance to post on that thread. I have thought about the problem a bit more and wanted to present the solution I will be using on a gearbox I am building.

I intend to machine the scroll type housing to take a 24 x 32 x 4 mm lip seal.

I chose a metric seal as the imperial seals that are readily available in the UK are larger in diameter and thicker. This would have resulted in too much material needing to be machined away.

The scroll seal type shaft (the later lip seal designed shafts are different) is 15/16" diameter. This converts to 23.81mm. The recommended minimum diameter for the 24mm seal is 23.85. So the shaft is nominally 0.04mm too small. But it is still a tight fit when pushed on the shaft so I think it should seal OK, certainly better than the scroll seal! :-) "

Cheers,
Malc.
Malcolm Le Chevalier

Hi Malcolm,

The nearest imperial seal is a SKF CR 9244 double lip seal, which is 15/16" ID, 1 3/8" OD and 1/4" thick, but not usually available ex-stock.

The metric seal 24x32x4 is more available, and also in the 'R23' version, which is a double lip seal and available from Wych Bearings or Simply Bearings. 4mm is quite thin for a double lip seal, but there is also a 7mm deep version - if the bore is to be 10mm deep, could the wider and maybe more robust 7mm version be fitted?

Happy to machine the front cover, unless you get a better, i.e. closer, offer?

Richard

Richard Wale

Hi Richard (if you are still there!)

I looked into a few imperial seals and there wasn't really enough meat in the housing to machine out to accept the seal. The 4mm deep seal leaves approx 2.5mm wall thickness, so the 1/4" (6.35mm) leaves nothing!

The bore has to be 10mm deep from the outside face to ensure the seal runs on the smooth part of the shaft. This is the part of the shaft that would ordinarily run within the scroll seal section of the housing.

The seal I have is R23 and from simplybearings. I love that company :-)



Malcolm Le Chevalier

Hi Malcolm,

Being a bit thick! I don't understand why a 1/4" thick seal leaves nothing in a 10mm deep bore? Is it that the 1/4" thick seal is imperial, so a slightly bigger OD?

My only concern is that 4mm thick seal is very thin, and that is why I wondered if the 7mm thick version might be better?

Am around a week on Saturday (14 Oct), so if you would like a trip to deepest Oxfordshire (no passport required until post-Brexit), we could do the job 'while you wait'?

Richard
Richard Wale

does the drawing in the 3rd post explain it? Looks to my untrained eye that if the seal was too thick then some (half?) of it would be seated in thin air.
David Smith

Yeah, it's 10mm from the outer face (the face I assumed someone would use as the datum when machining). There is a domed area (green in attached) of approx 6mm which gives clearance for the bearing/spacer/circlip on the input shaft.

Only the red area needs machining, approx 4mm, to allow the seal to sit in the correct location on the shaft and also not sit over thin air as David says.

Hope this clarifies.

Malc.


Malcolm Le Chevalier

Malcolm,
NOT wanting to pour cold water on the idea but I have a recollection of the bearing guide tube section shearing off the base plate on one of these. It was certainly quite a few years ago and due to vague memory I cannot be absolutely sure that it was on a 1500 box, though I think it was. I can't think what else it would have been on! The only other gearboxes I have dealt with over the last 25 years have been ribcase and T9s. I do recall that it didn't cause a whole lot of problem, - just a bit of a rattle as the tube bounced about on the input shaft.

It may be just that your drawing is diagrammatic and that there is more metal in the region of the root of the tube than in your sketch.
GuyW

Yup, being thick!

I did not notice the attached picture to the 3rd post!

All explained now and 4mm is the only solution.

I think some careful measurement first, and also put a radius (governed by the seal shape) at the bottom of the counterbore to reduce stress concentration as much as possible.

Richard

P.S. 14th October still free if you would like to use it?
Richard Wale

Oxfordshire is a big place, whereabouts are you exactly Richard? Then I will have a look-see whether I can make it across then.

Cheers,
Malcolm
Malcolm Le Chevalier

Malcolm,

OX

5

2

SG

Hope that works?

Otherwise:

richardl dot wale

at gmail dot com

Richard
Richard Wale

Malc
Just to make your job interesting----You could post it and the seal out to me and I'll send it back machined and covered in Aussie postage stamps for your collection-
Only joking------------It would cost, but would fit the timeframe ok

14th Oct -- that's nearly 3 weeks for a 2 min job--good thing you're not in a hurry

willy
William Revit

Hi Richard, sorry for the delay in responding. I was waiting for wifey to finalise her plans for Saturday - I am afraid I won't be able to make it. Shame, the midget needs a good run.

Willy, as much as I love Australia, it's probably a bit excessive :-)

Malc.
Malcolm Le Chevalier

Hi Malc,

Thanks for the update - my next free weekend at the moment is 11/12 November. Does that work for you?

Richard
Richard Wale

This thread was discussed between 25/09/2017 and 10/10/2017

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