7 replies to this topic

[Tinkerbelle]

Hello,

Found reason for the severe oil leak on front of gearbox and transfer case. Third bolt up, the lowest one behind clutch has stripped its threads so will need helicoiling.

Question is as title.

Matt

[Cooperman]

Hello,

Found reason for the severe oil leak on front of gearbox and transfer case. Third bolt up, the lowest one behind clutch has stripped its threads so will need helicoiling.

Question is as title.

Matt

Yes, you can do this OK so long as the engine is out of the car. I assume it's one of the 5/16" UNC bolts into the gearbox rather than a 5/16" UNF into the block.
First of all you measure the ndepth of the transfer casing, i.e. to where the damaged threads start. Now drill using a clearance drill of just slightly larger than the outside diameter of the Helicoil tap to the depth of the transfer case thickness and no more. Then drill into the gearbox via the larger clearance hole with the tapping size drill for the Helicoil. Go to about 1/8" less than the depth of the existing hole. Tap the hole you have just drilled with the 5/16" UNC Helicoil tap as supplied with the kit. Fit the Helicoil insert ensuring that it is just fully engaged into the tapped hole.
Fit a new 5/16" UNC bolt of the right depth with a slightly oversize diameter flat washer. Torque it accurately. Don't use Loctite or you risk the insert coming out when next you strip the engine.
Although I've never done it, maybe you could do this with the engine installed, although it would need a 90 deg angle-drive drill and it would be difficult to go in as absolutely square as you must do. Depth measurements would also be difficult.

[1984mini25]

I had to do 3 of mine when I last split the box of the engine to sort out the oil pump, crank and bearings. It was hard enough doing it out of the car, what with making sure the holes are drilled out straight and all the swaft that it creates doesn't end up were its not wanted. I also couldn’t find the correct bolts, but the long mini water pump bolts are exactly the same length and thread.

[Cooperman]

I had to do 3 of mine when I last split the box of the engine to sort out the oil pump, crank and bearings. It was hard enough doing it out of the car, what with making sure the holes are drilled out straight and all the swaft that it creates doesn't end up were its not wanted. I also couldn't find the correct bolts, but the long mini water pump bolts are exactly the same length and thread.

The water pump bolts are 5/16" UNF. The transfer gear case to gearbox ones are 5/16" UNC. The transfer case to engine block are 5/16" UNF.
From the OP's description his bolt goes into the gearbox, so must be 5/16" UNC.

[1984mini25]

I had to do 3 of mine when I last split the box of the engine to sort out the oil pump, crank and bearings. It was hard enough doing it out of the car, what with making sure the holes are drilled out straight and all the swaft that it creates doesn't end up were its not wanted. I also couldn't find the correct bolts, but the long mini water pump bolts are exactly the same length and thread.

The water pump bolts are 5/16" UNF. The transfer gear case to gearbox ones are 5/16" UNC. The transfer case to engine block are 5/16" UNF.
From the OP's description his bolt goes into the gearbox, so must be 5/16" UNC.

Dam you are right, some how confused myself with there being two different threads. But then I did have to helicoil at leas 3 of the gearbox ones and replace a few of the block bolts for some other reason.

Also I don’t know if it’s just me, but I’ve vet to remove the transfer casing (done quite a few over the years) and not have to fix at least one of the gearbox threads.

[Cooperman]

Yes, it's not nunusual.
I recently did Helicoil one of the diff output cover plate 5/16" UNC holes in the diff casing with the engine in-situ using the method I just described, but that was with drive shaft and pot-joint removed. You blow the swarf out with a high-pressure air line if you have one.
I'm thinking of helicoiling all those 5/16" UNC threaded holes in the gearbox on the next engine/'box I build. On aircraft engines with alloy engine blocks it is a requirement that all threaded holes are fitted with wire thread inserts from new to allow for maintenance without thread degradation.

[Tinkerbelle]

Cheers all,

Looking at what is involved with doing them with the engine in situ, may aswell just remove the engine and do all of the gearbox/alloy/unc threads to make sure.

Just bugs me as I just got the engine in last night, but atleast I have had a quick play in it before it comes out again!


Matt

[PhilipGCaldwell]

the beauty of a mini engine is they can be removed and installed on a days graft