Correct Fit Drawbar Brackets Cub LoBoy

[kajun]

Men:


As noted in an earlier thread I abused Jack the Tractor my 1960 Cub LoBoy. As a result I pulled the final drives and asked a local friend with a small machine shop to keensert them at all-four holes to which the two drawbar brackets are secured. The keensert device has internal threads 5/8 x 11 and external threads that are screwed into the casting after drilling out old threads and tapping for new external threads.

My friend has tendered the final drives with keenserts that protrude from the castings about 1/8 inch . These prevent the drawbar brackets from laying flat against the castings. My friend does not believe that the protrusions will interfere with drawbar placement and drawbar utility -- as I understand his views the drawbar bolts do not have to be torqued very much to hold the drawbar and connected-belly-mower arms firmly in place . Indeed , he is of the view that the protrusions are an improvement over the original flat-surfaced-final-drive face. My view is precisely the opposite ; I have 26 years experience with this tractor and mower and experience teaches that if the drawbar brackets are not tight against the final drives the mower [ Woods 42 inch belly mower ] will throw its belt at the slightest uneven ground surface . These are the drawbar brackets as pictured on TM's site:

I would appreciate any and all views .

Kajun

[kajun]

Sorry about image . Here is link:

http://www.tmtractor.com/new/gb/554fp.htm

[John *.?-!.* cub owner]

I am not very experienced with the low boy, but the drawbar brackets do need to be flat against the smooth parts of the final, not standing off 1/8 inch. I disagree with your friend, thos bolts need to be torqued pretty tight to keep them in place, and having the bracket flat against the final gives them better strength. While that 1/8 inch on each side does not seem like much, it will make the drawbar or any other implement that reaches all the way across difficult to mount.

[Crimson Tim]

As just mentioned, a drawbar or anything that reaches all the way across now has to be 1/4" shorter to fit.
Also, anything that bolts on with only one or two bolt like the brackets pictured would now by supported on a sort of on a pedestal of the keenserts. Without lying flat against the final drive, this will substantially increase the forces applied to those bolts.

Put another way, for a given lateral load applied to the mounting plate that might try to pry out the bolts, the moment arm that was designed to resist that torque was the distance from the bolt to the edge of the plate. What? A few inches? Now the moment arm trying to resist that torque is the distance from the bolt to the edge of the keensert. A fraction of an inch. It's very easy to multiply the force by 8 or 10 times. This is why you can pull a nail with a crowbar that you can't pull with pliers.
Of course, the plate will soon contact the final drive and go back to the original moment arm distance, but by the time that contact is made, something has already deflected and probably over-stressed.

If there is some reason it is necessary that those stick out, I would look at counter boring the mating surface of the plate for clearance. Not sure if there's enough material to do that comfortably, though.

[Glen]

Hi,
I think you need to grind off the part of each coil that sticks out above the flat surface, down to the flat surface. I've never used the brand you are talking about, does it look like a regular thread repair coil ? That's what I'm thinking of anyway.
Use a small hand held grinder with small grinding wheel. You might need a very small triangular file to file the coil and fix the threads at the end, so the bolts will screw in after grinding them flat.
But if it's different than a regular thread repair coil, then I don't know if my method works for it. A picture would be helpful.

[John *.?-!.* cub owner]

Keenserts appear to be a solid sleeve with threads inside and outside rather than a coil like Helicoil. Here is a link to a site telling about the differences. It is trying to sell Acme threaded inserts, but you can get the idea.

http://www.acmeindustrial.com/insert_comparison.html

[Glen]

Hi,
Thanks for the info John. Do you think he should grind down the part sticking out of the hole, it's only a small amount sticking out.

[John *.?-!.* cub owner]

That is my opinion yes. May need to clean up the end of the threads a little afterward.

[brewzalot]

Agree, grind them off. If you have a short set screw that size put it in before grinding . Backing them out will help clean up the threads after grinding.

[Gary Dotson]

I don't know why your machinist would think it better for the inserts to stand proud. I've used Keenserts in the past and simply ground the surface flush after installation. The nice thing about Keenserts is that they can be used to repair a hole that is wallered out too much for a Helicoil.

[kajun]

Thanks , men . Wonderful and insisightful help from all .

I had forgotten about the limited left-to-right tolerance for the drawbar . That is a very close fit . The additional quarter inch is a deal-breaker .

Lateral loading and claw-hammer vs pliers . Exactly the point but I could not say it as well . Load magnification? What about the fence posts and tree roots I hit with the belly mower -- Talk about a load.
Grinding off is a good suggestion and the route I'll probably take but I was hoping for a like new repair .

Do appreciate all the help .

[Urbish]

Do verify that the locking keys have been driven all the way flush with the casting before grinding off the excess. Otherwise very little of the key will actually be locking the threads and you'll grind off the remainder. And 'ditto' on installing a set screw before grinding off the 1/8" as it will repair boogered-up threads upon removal.

[kajun]

Thanks swkinjim

Great guidance .

[Jim Becker]

To whatever extent is possible, position your grinding wheel so it throws the swarf away from the hole. That will put the major burr on the edge of the insert that is away from the new threads. That will minimize the deburring required to clean up the threads.

If you haven't installed the housings on the tractor yet, this should be pretty easy. If installed, you may not have much choice on how you orient the grinder.