Your thoughts please

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trmorrisminor
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Your thoughts please

Post by trmorrisminor »

Hi all, am currently in the process of rebuilding a morris minor van, currently am working on the underneath of the van and have noticed that the bolts the 3 bolts that hold the engine steady wire and bracket to the gearbox - 2 have clearly been overtightened in the past and spin/ wont tighten up correctly - i know with these bolts you have to be very careful not to over tighten them as you are going into aluminium. One appears to be ok and two spin, can i ask what I should do, only two logical options I can see, is to re-tap hole with a slightly larger thread and put a new bolt in that relates to the new tap thread or secondly buy some metal weld and glue the bolts in situ - what would others do please?
Many thanks
Murrayminor
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Re: Your thoughts please

Post by Murrayminor »

If you can tap it then that would be easiest no need to go overboard with the size just a step up from the current size.

If you "glue" the bolts in they may damage the casing if you ever try to extract them.

A mechanic once told me don't forget the next man, meaning the next person to work on the car, he always put copper slip on bolts etc and made sure any damaged nuts were repaired or replaced.
A glued in bolt will cause all sorts of issues.
Proud owner of my first Morris Minor
ManyMinors
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Re: Your thoughts please

Post by ManyMinors »

I would think that you'll have to go up a size. They are a bit marginal as standard and I don't think any sort of adhesive/metal weld will be strong enough if you ever need this to do its job :wink:
les
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Re: Your thoughts please

Post by les »

Glueing would be a big mistake ! The next preferred tapping size would be 5/16”. A 9/32” tap might be difficult to find, even so may not be big enough.

alawrence10360
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Re: Your thoughts please

Post by alawrence10360 »

I would helicoil it provided there is enough material around the original fixing
Have done this many times in both steel and alloy
You can then use the original bolt
Commonly used in industry for repairs
If you can tap a thread you can do this
Using “glue”would be crackers. Drilling and tapping epoxy liquid metal would only be on option on low stress fixings
Helicoil can be as strong as the original thread if carried out correctly
https://en.m.wikipedia.org/wiki/Threaded_insert
Sleeper
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Re: Your thoughts please

Post by Sleeper »

+1 for Helicoil.

Stronger than original.

John ;-)
philthehill
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Re: Your thoughts please

Post by philthehill »

The fitment of the steady wire was an after thought by BMC to stop the engine/gearbox moving forward.
BMC typically used what was already there - that is the three 1/4" UNF bolts holding the gearbox tail housing to the main gearbox casing.
The 1/4" x 28TPI UNF threads are too fine for this application. For this application the threads should be coarse and I would recommend using 5/16" x 18 TPI UNC bolts.
This has been used successfully many times by myself and other MM owners.
You need to drill the existing holes in the gearbox casing to 6.60mm as the tapping size and then use a 5/16" UNC 1st tap followed by a 5/16" UNC 3rd tap.
Make sure that you do not drill too deeply - gauge the depth of the existing holes first and go no deeper with the 6.60mm drill. Keep the 6.60mm drill in line with the existing holes.
You will need to drill the three holes in the gearbox wire attachment out to 5/16"
Once the bolts have been increased to 5/16" UNC you will have no more problems. It is what BMC should have done in the first place.
An alternative to the bolts is to fit three 5/16" UNC studs - thermostat housing studs can be used which have 5/16" threads for fitting into the head - use with 5/16" UNF nuts and spring washers. I would also Loctite the studs/bolts in place.
Good luck.
Phil
Last edited by philthehill on Wed Apr 29, 2020 4:16 pm, edited 1 time in total.

alawrence10360
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Re: Your thoughts please

Post by alawrence10360 »

It seems that the original design on this was flawed and so fitting a helicoil to return it to “original” was never a good option
I would not consider a UNF thread in soft alloy unless the overall length was say 3 x the diameter of the fixing
There is a lot to consider when choosing the pitch of a thread not least is the amount of tension required which is limited the courser you go
I think in this application Phil has identified the most expedient solution as usual
philthehill
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Re: Your thoughts please

Post by philthehill »

As regards threads in alloy. I am in the process of replacing the steel front bracing bars with alloy items, the bracing bars have rose joints at either end. The originals rose joints are 3/8" x 24TPI which is too fine for alloy. To achieve the required hold I am having to use rose joints with M10 x 1.5 threads which is a coarse thread not un-similar to UNC.

noidea
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Re: Your thoughts please

Post by noidea »

sometimes heli coil is a nightmere to do if you cross thread the bolt when you screw it in but is the proper way to repair a hole as the coil is stainless steel but what phil says to use a stud will also work perfect .have repaired in the past both ways
dave
trmorrisminor
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Re: Your thoughts please

Post by trmorrisminor »

Many thanks to you ALL for your input, am very grateful for all of your comments. Ok so it sounds like the easiest option is going to be to redrill the three holes with a 6.60 drill bit, and re-tap holes with a 5/16 unc tap ( 1st and finishing tap) and job done. Have looked on ebay and i can get all the bits on there taps, drill bit and bolts. Am very grateful to you all, and thankyou aswell Phil, will run with what you have suggested.
Thanks again
Richard
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