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MG TD TF 1500 - Remove broken layshaft locating screw(?)

Any suggestions on how I can remove the broken tip of the "layshaft spindle locating screw" from my TF gearbox? How can I do it without damaging the threaded hole? (Moss TD/TF Gearbox illustration #78, part #441-260)

It looks like part of the threaded shaft of the screw plus the tip are still in the threaded hole in the gearbox. The tip is not wedged onto the locating hole in the layshaft ... the layshaft can move a little.

I can't remove the layshaft until the broken tip is removed.

Thanks,

Lonnie
TF7211

LM Cook

Lonnie, do you have a new locating screw? Compare it to the broken one to get a quantitative idea of how much is missing. If it's just a sukoshi bit you may be able to do a 'damn the torpedoes' and drive the layshaft out with the villain still in place until that part of the layshaft clears the housing. Good luck. Bud
Bud Krueger

I don't have a new screw to estimate how much is broken off of the old one. The screw is 1.199" from the base of the head to the edge of the jagged thread in the photo. It is 1.185" at the shortest part of the screw.

Lonnie
TF7211
LM Cook

I make drill guides. They center a smaller drill bit and you can drill into or through the broken part and use an EZ-out.

If it will not come (softly) with an EZ-out, as long as the pilot hole is centered you can keep going with larger drills.

It may help to use Left handed drills. (Available from McMasters)

You could make a guide, if you have access to a lathe, out of the broken screw, although they do not need threads.

I suppose if you can get to a lathe you can make one out of rod.

If you try to drill out the broken piece, increasing the drill diameter in smallish steps the initial drill must be centered.

Normally the guides are hardened but for a one time use soft guides are OK.

If you do not have access to a lathe, guides can be purchased from Victor Machinery.

http://www.victornet.com/departments/Drill-Jig-Bushings-Headed/270.html

Jim B.

JA Benjamin

Nope, I would not drive the layshaft out, it will take the gearbox casting with it, as it looks like the tip goes through a blind hole and then into the layshaft, Neils site shows a good sectional, copy below.

bit of a pig, good luck maybe with a drill as Jim suggests

mog

As Jim B. says... use a drill guide. I have made these out of bolts so they thread in. It is easier to drill a small center hole in a vice with good lighting than using the threaded hole to use as a guide. I had the same problem with that locator bolt. I ended up using a short section of copper tubing in the casting to center the drill. One time use only.
... CR
C.R. Tyrell

Thanks for your advice and experience. Looks like I have only hit a bump in the road and not fallen off of a cliff.

Hopefully I can find a good local shop that can drill out the broken screw. If not, I may try it myself -- with some help from club members.

Lonnie
TF7211
LM Cook

Here's an image of a worn screw and a new one. It may help to determine how much is still in the hole. Lonnie, how many threads are still on the screw? Bud

Bud Krueger

Bud

The screw has 15 threads remaining on it. The ones in your photo have 19 or 20 threads plus the tip. Rough estimate is about 5/16" to 3/8" broken off inside the case including the smooth tip.

Lonnie
TF7211
LM Cook

I know it's not helping, but I'd love to know how on earth the screw broke. Did it feel as though it broke when you tried to remove it?

David
David Provan

What ever you do don't use one of the tapered, left hand threaded "easy outs". They are hardened and if one snaps off - very easy to do - you can't drill it out. The only solution then is to use spark erosion.

Jan T
J Targosz

David -

I don't believe that I broke the screw (?). I didn't feel it snap. The remaining screw turns very easily in the threaded hole until it is almost seated; then I can feel resistance in the threads. The break is smooth but not shiney.

The lay shaft can move 0.101" back and forth. It is retained by the tip of the broken screw, but not locked solidly by it.

Lonnie
TF7211
LM Cook

Jan

Good point about the EasyOut. The hole is over an inch deep before reaching the broken tip. That's a long space for a small diameter bit or tool.

It's a job for a good shop; not for me.

Lonnie
TF7211
LM Cook

Am I correct that the threads are 6X1 metric?

Lonnie
TF7211
LM Cook

Hi Lonnie,

You could drill down the centre of the broken bolt with a 1/8" pilot drill but this would have to be done in a lathe. Using this you could pilot drill the bit of broken bolt and then using larger drills clear out what remains. You wouldn't need to buy one of the Hotchkiss metric taps - just retap the hole in the casing with a BSF or modern metric thread.

Jan T
J Targosz

Use a "C" lock pin (roll pin) to centre the pilot drill. I always do this to centre drills, slowly go up in size until you are able to punch out the layshaft. You will feel the difference when it clears the locating tip and hits the shaft.
I am a retired mech eng and this has got me out of trouble many times.
Ray TF 2884
Ray Lee

Ray -

The roll pin is a good idea. Even if the machine shop can remove the broken screw, I'm filing your suggestion in my "memory bank", 'cause I know that I will need it sometime.

Lonnie
TF7211
LM Cook

"The lay shaft can move 0.101" back and forth. It is retained by the tip of the broken screw, but not locked solidly by it. "


"I don't believe that I broke the screw (?). I didn't feel it snap."

Further suggestions;

1)
If the trany is out of the car, lay it on its side with the screw hole down and try wiggling the lay shaft back and forth to see if you can work the broken nib back into the hole.

2)

It has been suggested that the screw might be a 6 mm by 1 mm pitch. If so a 3/16 rod should fit into the hole.

First center the lay shaft in its travels.

File the end of a 3/16 rod flush. Put a dab of the jellied form of super glue on JUST the end. Carefully insert it in the hole and but it against the broken nub.
Let it sit for an hour to cure. Then try pulling and/or rotating back. Not too much force.


Jim B


JA Benjamin

lONNIE.
Why not try a dremel tool with a small flat headed grindstone. All you have to grind is enough off the stub to clear the shaft. You don't need to remove the complete pin.
At worst if you damage the threads in the gearcase it will be only the two or three at the bottom of the hole. Take care and slowly grind away and the shaft will slide out.
If it's only a minor bit holding you up you could possibly flatten it sufficiently to clear.The pin stub is soft and you might be able to push it further into the layshaft.
Sandy
SANDY

Great idea Jim. I would use carb cleaner or something first to remove the oil from the broken off part, and let it dry completely. Then try the glue. A tiny dab of JB weld would do the same thing.
George Butz

I would try to simply put a tune up screw driver against the broken remains in the hole. If the shaft moves it should mean there is no pressure on the remains. you might be able to put enough pressure on what's left with the screwdriver to back it out. it's happened a few times that way for me on other projects. It has probably been broke for years

Good luck

Bill Chasser jr
TD4834.
W. A. Chasser Jr

Bill may have something there. Looking at the image of the broken screw gives me a bit of optimism. I can envision an image of the reverse of the broken end. What I see is a sharp edged break that is raised at its barbed end. This would be going in a clockwise direction and then falling off. If so, it means that a flat, sharp edge would put pressure against it while being rotated in a counterclockwise direction. Picture one of these tire valve core removal tools with one tang removed. You might be able to 'simply' drop it down and rotate it CCW. It might just rotate the broken piece out of the hole. Just MHO. Bud
Bud Krueger

A club member came to my house today and showed me how to remove the broken screw. Too easy!

Glad he offered to help. I didn't have the experience or the nerve to do the job.

We sat the gearbox on my drill press table. Chucked a 15/64" bit. (1/4" was too big.) And drilled into the broken screw. Checked our progress a few times. It was evident when the bit broke through the tip of the screw.

The locating screw was good quality steel, but not grade 8. A standard twist titanium coated bit easily cut into the screw and chewed up the screw and tip. The hole in the case guided the bit perfectly into the center of the screw. The bit didn't wander, so no damage to the threads in the case. Cleaned out the swarf with a 6X1 tap.

Inserted a dummy layshaft and pushed out the real one.

The layshaft is spalted and will be replaced. Everything else looks OK so far.

Lonnie
TF7211
LM Cook

Good news Lonnie! hope the rest of the build goes without a hitch.

Cheers

Bill Chasser jr
TD4834
W. A. Chasser Jr

I think you mean that the shaft has galling, not spalting (i.e. spalling).

Glad we know how it finally came out; a reverse drill bit would have also done it, it sounds like.

Tom Lange
MGT Repair
t lange

Thanks Tom -

I'm still trying to learn "machine shop" terms. I've spent too many years working with wood, so my fingers typed "spalted". Rotten wood / rotten steel ... kinda similar.

Lonnie
TF7211
LM Cook

Well done, Lonnie. Bud
Bud Krueger

Bud -

Your photo of an intact screw helped us judge how deeply we had to drill.

Thanks,

Lonnie
TF7211
LM Cook

Happy to have been of help. Bud
Bud Krueger

I suggest you take out the layshaft, pull the laygear, and measure each roller inside, if the shaft is toast, then the needles will be also.
mog

This thread was discussed between 12/05/2015 and 16/05/2015

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