Simplon UN Gearbox Leak Fix
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  1. #1
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    Default Simplon UN Gearbox Leak Fix

    Consider this a sanity check with a consensus on the fix.

    I am sprucing up an old Summit branded Simplon UN Horizontal/Vertical mill.

    01313_8b7vtulin2t_1200x900.jpg

    When I started the paint job, I was not aware of any leaks in the main gear sump. However, after the first coat of primer, I noticed one corner of the gearbox had just enough oil seeping to keep the paint from drying. I promptly drained the gearbox (was going to replace oil anyway), wiped the area the best I could, and applied the two topcoats.

    summitheadstockcover.jpg

    First thought was to remove the plate and use gasket maker to reseal. I pulled the speed adjustment knob and dial and realized that I could be opening pandora's box if I pull that cover. Especially for a leak that has to be extremely minor (the headstock has been full of oil for 6 months with no noticeable change in oil level). Anyone know how these are put together? Is the cover easier to remove than I am anticipating?

    Also, I am not actually sure that the cover gasket itself is leaking, or simply oil is seeping by the threads on the cap screw. (the screw countersink had the most oil collected).

    So I pulled the screw, and sure enough, it appears they drilled and tapped it all the way into the gearbox chamber.

    Just in case it was the seal, I added a little extra paint to the joint in hopes that if it is leaking there, the paint may catch it. (wishful thinking) Second, I would like to seal the screw in case oil is simply leaking around the threads/countersink.

    First thought was rectorseal 9 pipe dope. Second thought was to dip the screw threads in Ultra Grey RTV. Any thoughts on a right way to fix this? I'd play the guess and check game, but once I dump the 2.5 gallons of fresh oil in this, I"d rather not redrain for a repair.

  2. #2
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    Quote Originally Posted by Gundraw View Post
    Consider this a sanity check with a consensus on the fix.

    I am sprucing up an old Summit branded Simplon UN Horizontal/Vertical mill.

    01313_8b7vtulin2t_1200x900.jpg

    When I started the paint job, I was not aware of any leaks in the main gear sump. However, after the first coat of primer, I noticed one corner of the gearbox had just enough oil seeping to keep the paint from drying. I promptly drained the gearbox (was going to replace oil anyway), wiped the area the best I could, and applied the two topcoats.

    summitheadstockcover.jpg

    First thought was to remove the plate and use gasket maker to reseal. I pulled the speed adjustment knob and dial and realized that I could be opening pandora's box if I pull that cover. Especially for a leak that has to be extremely minor (the headstock has been full of oil for 6 months with no noticeable change in oil level). Anyone know how these are put together? Is the cover easier to remove than I am anticipating?

    Also, I am not actually sure that the cover gasket itself is leaking, or simply oil is seeping by the threads on the cap screw. (the screw countersink had the most oil collected).

    So I pulled the screw, and sure enough, it appears they drilled and tapped it all the way into the gearbox chamber.

    Just in case it was the seal, I added a little extra paint to the joint in hopes that if it is leaking there, the paint may catch it. (wishful thinking) Second, I would like to seal the screw in case oil is simply leaking around the threads/countersink.

    First thought was rectorseal 9 pipe dope. Second thought was to dip the screw threads in Ultra Grey RTV. Any thoughts on a right way to fix this? I'd play the guess and check game, but once I dump the 2.5 gallons of fresh oil in this, I"d rather not redrain for a repair.
    We used a product called " Hylomar " to seal screws in those sort of locations. For really troublesome leaks you could get " Dowty " washers. They were a bit thicker than a normal washer, made out of a softer material with a rubber lipped seal on the inside. They cure most leaky screws. It's not unusual for the tapped holes to go straight through the casting.

    You can normally remove those style of milling machine gearboxes quite easily without removing the dial etc. The secret is knowing which speed to set the dial at to bring all the selector forks into a central position for ease of removal. I used to take the four corner screws out and screw in lengths of threaded rod in their place. Then remove the dowels and the rest of the screws.

    I had a sharpened painters pallet knife for getting the gearboxes moving if they'd been sealed. Just tap that in carefully all around, trying not to damage any gaskets that may be there. After that some fox wedges. Some of the better thought out gearboxes had tapped holes in each of the four corners so you could use the screws to get the gearbox moving. If you do remove yours drilling and tapping it may be a big help if it needs to come out again in the future.

    Once it's out an inch or so you can look inside to see if there are any obstructions, oil pipes leading to that sight glass etc that may prevent you getting the gearbox all the way out.

    Then it's just a question of rigging it. I used the threaded rods to slide the gearbox back into place when the job was done.

    Regards Tyrone.
    Last edited by Tyrone Shoelaces; 11-16-2019 at 03:42 PM.

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  4. #3
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    Quite a the writeup Tyrone.

    It seems this Hylomar is similar to Permatex "Form-a-Gasket" #2 non hardening sealant that I use on engines. Any thoughts on using that instead?

    I figured I would try just sealing around the screw first. Perhaps I could even fill the headstock with a good layer of oil and see if the joint leaks again.

    Let me ask you this, as it is apparent you have dealt with these kinds of gearboxes before. What would the gear-change mechanism behind this look like? I was hoping that this cover simply interfaced with a shaft that did all the shifting, so once I removed the handle and dial, I could remove the plate, inspect all of the gears, fix the gasket, then re-install the plate.

    I can tell you that when I removed the handle, the gear change shaft was preloaded back into the gearbox (ie, it pulled back into the column with the handle removed). The dial is a ring gear driven by a single (planet gear) gear on the cover. The handle installed with a tapered pin that allows the shifting shaft to be pulled outward while installing the handle. This is what made me nervous, not know what was all going to be dis-assembled when this cover was removed.

    Naturally, I have no manual or other hints as to how this all works, so if you have any insight, I would love to hear.

  5. #4
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    Well can I just preface this by saying I've never worked on that particular machine. Different manufacturers have different methods of selecting spindle speeds. Ranging from the most basic to the sophisticated IE Speed pre select etc. Looking at that single photo I'd say your machine fits into the basic category.

    What I would expect to see on the other side of that plate is a circular disc with paths cut in it. There will be a structure of some sort that holds several selector forks in position, most likely there will be three forks. One end of the forks will engage with the paths in the circular disc. The end business end of the forks will in turn be slotted into reliefs in the gear clusters that run on shafts inside the gearbox. When you turn the dial the disc will revolve and the paths will move the gears along their shafts into the required speed positions.

    On some machines as you select certain speeds the forks will move outwards so they take up a bigger space than the aperture the gearbox fits into, making complete removal impossible. There will be a speed were the forks all come to there innermost position, making removal easy. That's the speed you need to be in. If you had the handbook it would tell you what that speed is.


    If you're very careful you can ease the cover plate out slightly on the screwed rods until you can just see what's going on and then turn the dial until the forks move to where you need them to be.

    I've never used " Permatex ". " Hylomar " was developed in conjunction with " Rolls-Royce " so as you can imagine it's pretty good. We normally called it " Rolls-Royce " blue. It comes in a smallish tube with the consistency of runny toothpaste, dark blue in colour, you just smear it on thinly and it sets but it doesn't go hard. Just sort of tacky, you can remove it easily with a way scraper. There is a liquid remover you can buy but we never bothered with that.

    Many years ago I installed a brand new " Asquith-Archdale " 6ft radial arm drill. They were made in Halifax, West Yorkshire and Yorkshirmen are renowned for being very careful with their "brass", ( money to you ).

    After about a month or two the rep from the makers came around and asked me if I was having any issues with the drill. I said " It's a really good machine but one or two of the panels have started leaking, you could do with a tube of " Hylomar " to seal them on assembly ".

    He replied " Neigh lad, yon stuff's £1.50 a tube tha knows !"

    Translation from Yorkshire speak - " No way lad, that stuff's £1.50 a tube you know ! "

    This is on a new drill that possibly cost about £5,000 plus back in the day.

    Regards Tyrone.


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