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 How to repair worn gearbox threads 
Description Inserting a recoil kit to provide a strong engine mount thread
Author Ian Geary Date Sat Jun 12, 2010 5:28 pm Type Picture How-To

Category Engine
Viewer Comments [1 - Post your comments]
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How to repair worn gearbox threads
Inserting a recoil kit to provide a strong engine mount thread
This article is aimed at strengthening the 2 threads on the front of the E153 gearbox that hold the front engine mount bracket in place.

But it can really apply to any stripped or worn threads that need replacing with a bolt of the same size.

Why were they stripped?
- Old age making aluminium soft?
- Extreme heat and cooling?
- Force of acceleration ripping the threads out?

Or
- Knackered torque mounts allowing engine movement to stress them (my theory)
- using the wrong Toyota bolt to secure bracket. If the bolt used is too long, it will reach the end of the hole. Then, when you tighten it, you’re just pulling the threads against themselves (Peter Gidden theory)

If its the engine mounts, get them sorted, as it will eventually have your flexi pipe too.


I am using a recoil kit. It’s a competitor to a helicoil kit. It’s like a spring, with threads both on the outside and inside. Kits are specific to bolt sizes. The inside threads are M10 – 1.5 pitch, the outside slightly wider. The kit has a specific drill and tap to fit the outside threads.

You also need a 90 degree drill attachment, a drill, 2 new bolts, as well as tools to get the mounting off. Disclaimer – this guide will require you to drill into your gearbox, and this is done at your own risk.

But the alternative to repairing these threads involves getting the gearbox out!


Here’s a picture of the kit.




You have the inserts at the bottom. At the top left is the tap – which cuts the thread in the gearbox, and some unknown rod next to it.

Next to the kit is the drill – it’s short already, but I hack-sawed about an inch of the bottom to help clearance. There’s a full size drill next to it in the shadows - bought seperately.

The hook thing is both the handle for the tap, and the winding in tool for the insert.

Finally there is my 90 degree drill attachment, from Machine Mart. The first one I bought screwed up straight away, so my advice is to keep the receipt...


First off

Jack the car up, take of under tray, remove the front engine mount, undo gear cable connectors, and the slave cylinder (3 bolts on top) and push it all out of the way. The BGB will give you all the info you need.

You should now have clear access to the 2 holes in the gearbox.

Before the recoil kit can be used, the hole has to be widened. The drill is 10.3mm, so only a bit wider than the 10mm existing hole. This is the advantage of using an insert kit, rather than say moving up to a M12 bolt – which would need a 12mm drill.






Make sure the drill goes in straight, it will tear through the aluminium gearbox, and you want it to line up when the brackets are back in place. You don’t need to go in too deep – say 4 or 5 centimetres.


Next

Insert the tap into the square hole on the hook tool. Simply wind this into the drilled hole. Again, make sure you do this straight – steel is stronger than aluminium. Every few turns, un-wind it a bit to clear the debris out.




You need to wind the tap in about half way down – say 5 centimetres or so. If it gets really tough, stop – you’ve probably reached the bottom of the drilled hole.


Next

The inserts have a tang across the base. Take the tap out of the hook tool, and slide an insert over the end of the tool. The tool has a slot in it, and the tang in the insert needs to sit in this. the tang should be at the end of the tool - i.e. go into the gearbox first.




The insert is a spring. You have to wind it in under force to stretch it. This makes it grip the inside of the threads you’ve just cut, and will stop it unwinding when you take the bolt out.

You line up the tool into the hole, and start turning whilst applying pressure. This will cause the first loop to catch in the thread. Keep turning, and it will simply wind the insert into the gearbox.




Keep winding until the end of the insert has gone half a turn or so past the lip – i.e. completely inside. This is where you find out if your hole is deep enough.

Taking inserts out needs a special tool, which I don’t have. Google will have the answer though. Don’t break off the tang until you’ve got the insert fully in



Next


For a long bolt to fit in, the tang has to go. Remove the winding tool, turn it 90 degrees, and insert it back in, and give it a sharp push. As the slot won’t be lined up, it will shear off the tang, which should fall out.


Job done

It’s now ready for your bolt. The kit I have is a normal pitch – 1.5. Wind a bolt in to check its all working. The inserts look quite slim, but they are stronger than original apparently. Don’t forget, the clutch slave bracket and engine mount bracket add depth, so your new bolt has to be long enough to reach the insert properly. The bolt can go through it – you just don’t want it hitting the bottom of the hole.








Replacing master cylinder

A bit tricky. I’d take off the heat shield to help access the bolt on the left (cam belt side). If it goes on easy, check you’ve actually got the actuator rod into the clutch fork! Also, make sure the 2 engine mount bolts you’ve just fixed are in loosely, as the slave cylinder bracket needs to line up.

You can now re-connect the gear cables up, and replace the engine mount, doing the bolts up to full torque.


Kits cost about £35 (tooled-up) and the drill £23 (machine mart)

If anyone has symptoms of this i.e. not being able to torque up bolts, or them shaking out - and fancy a go at this, drop me a pm and I can lend you my kit.

You’d have to pay postage each way, and say a £1 to buy replacement inserts that you use.





Ian
  

 User comments 
toxo: Tue Jul 20, 2010 12:12 pm    

I had this happen on my car... Original Toyota bolts, engine mount was fine, my money's on expansion and contraction of 15yr old aluminium breaking the threads up. It ate my flexi too, as you suggest, as well as destroying the rear engine mount once the front one wasn't connected anymore, as this took all the rotational force of the engine [Sad]
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