15 replies to this topic

[me madjoe 90]

I have found that the threads in the offside diff caseing cover for the bolt, that would normaly mount the exhuast bracket are worse for wear.
Since the bolt was gone i borrowed one from above but this wont tightent up.

So i was wondering what thread type they are and the bolt size ect. As i need a new bolt and need to get a suitable tap.

Would it be posible for me to drill the old threads out and use a metric tap and bolt that i have plenty off with out problems?

Edited by me madjoe 90, 11 January 2011 - 10:22 PM.

[Dan]

You should get the casing helicoiled. Anything else is a bodge. These are important fixings, you must use the correct grade rather than some screws you just happen to have.

[me madjoe 90]

You should get the casing helicoiled. Anything else is a bodge. These are important fixings, you must use the correct grade rather than some screws you just happen to have.

Whats wrong with M-8 bolts or some thing syimler the threads better, than w.e was standerd by the looks of it the standerd ones are abit fine.

I dont want this to sound like im arrguing as this is just a question but wasnt the caseing just taped alloy i dont see why it would need helicoiling if i drilled and cut new threads, I know its a bodge but its got to be better than what its hasnt got in it atm.

I cant realy afford a helicoil kit infact i can barely afford to run the thing and they say minis are cheap to run .

Edited by me madjoe 90, 11 January 2011 - 10:32 PM.

[mini13]

5/16 UNC,

Its well worth having the common mini helicoil's, 5/16 UNC, 5/16UNF, and 5/8 UNC (sump plug)

http://cgi.ebay.co.u...=item1e60bb31b3

[me madjoe 90]

The thread is 5/16" UNC

Thank you very much

Ill see if i can get a tap and new bolt then, before i try drilling it out.

[me madjoe 90]

5/16 UNC,

Its well worth having the common mini helicoil's, 5/16 UNC, 5/16UNF, and 5/8 UNC (sump plug)

http://cgi.ebay.co.u...=item1e60bb31b3

Thanks for the link thats not to bad but i still dont have £20 to spare... so ill just have to try with what i have for now and do it later whan im more finacialy equipt.

Seems like every time i buy it some thing new or fix some thing another thing breaks, like it dosent like its new parts getting tired of it now...

Edited by me madjoe 90, 11 January 2011 - 10:42 PM.

[Dan]

the threads better

Err, metric threads are actually the same as UNF/UNC, just based around metric base dimensions rather than imperial ones. The thread form is the same.

[MRA]

As above, however if I may clear up a possible mis-understanding..... the thread is the same but metric are NOT interchangeable with Imperial threads.

[Cooperman]

I must confess I once drilled and tapped one of the threaded holes, the to which the LCB clamping plate attaches, to 3/8" UNC. It worked well, but was a 'bodge' really. I had just run out of 5/16" UNC Helicoils and wanted the engine back in the rally car in a bit of a hurry.

[me madjoe 90]

I must confess I once drilled and tapped one of the threaded holes, the to which the LCB clamping plate attaches, to 3/8" UNC. It worked well, but was a 'bodge' really. I had just run out of 5/16" UNC Helicoils and wanted the engine back in the rally car in a bit of a hurry.

If it worked well whys it a bodge.

[Dan]

Anything that doesn't repair it to original spec, or improve the whole installation, could be considered a bodge. In this case the side plate now has one fixing that will develop considerably less clamping force at the same torque than the others, due to the screw being thicker and so stronger and so less able to stretch at the same torque. These side plates are a stressed component, they set the diff preload and if they aren't evenly clamped and accurately loaded they very frequently deform. This is a very common source of oil leaks that people commonly mistakenly attribute to the output shaft bushes. The same would apply if you were to fit one metric screw of a different size and material as the rest. There would be no simple way to calculate how much to torque this one fastener to match the clamping load of the rest, and since cars don't have exhaustive individual technical notation and histories llike aircraft do, there would be no way to easily and reliably record the change. So any future work on the same area would become more problematic. We have all found things that previous owners have done to our cars that we have cursed them for, and this falls right into that category. Can you imagine being under the car as the next owner, rebuilding this side plate, not knowing that one screw is different? That is a bodge. It may be considered an improvement to replace all of the screws with larger ones, but there would still be no way to be certain the diff was being preloaded to the correct level because the screws would be different.

[me madjoe 90]

Anything that doesn't repair it to original spec, or improve the whole installation, could be considered a bodge. In this case the side plate now has one fixing that will develop considerably less clamping force at the same torque than the others, due to the screw being thicker and so stronger and so less able to stretch at the same torque. These side plates are a stressed component, they set the diff preload and if they aren't evenly clamped and accurately loaded they very frequently deform. This is a very common source of oil leaks that people commonly mistakenly attribute to the output shaft bushes. The same would apply if you were to fit one metric screw of a different size and material as the rest. There would be no simple way to calculate how much to torque this one fastener to match the clamping load of the rest, and since cars don't have exhaustive individual technical notation and histories llike aircraft do, there would be no way to easily and reliably record the change. So any future work on the same area would become more problematic. We have all found things that previous owners have done to our cars that we have cursed them for, and this falls right into that category. Can you imagine being under the car as the next owner, rebuilding this side plate, not knowing that one screw is different? That is a bodge. It may be considered an improvement to replace all of the screws with larger ones, but there would still be no way to be certain the diff was being preloaded to the correct level because the screws would be different.

All this is great but dosent solve the problem. I was asking if it would work and have found from cooperman it should. And in my eyes its better than not having a bolt at all, like it has done fore the past year and a half. The diff seems fine also and if the person in the future comes to strip it down, which would probbly be me. They would be inteligant enought to put the bolts in an order so they go back in the same place they came from.

my car is no concourse nor is it a droping to bits wreck but id rather fix it by any means than none at all. Yes it is also leaking oil slightly but i like to keep an eye on my oil and its not as problem. The engine probly wont be in the car when im done with it or will need replacing.

I also know how it feels to be fixing somes bodge that hasnt worked but thats a differant matter and explains my reason for asking if it would work as then it wouldent be a problem.

All i wanted was to know that it would work not wether you think its in apropriate However thank you for sheareing your advice and knolage.

[MRA]

If you go down this route as Peter will tell you there is a reduced amount of matel holding it all together, it really only requires a gentle tweak to tighten it up, and if you are hanging your exhaust off it go for the older bracket which uses 3 fixings.....

[Cooperman]

If you go down this route as Peter will tell you there is a reduced amount of matel holding it all together, it really only requires a gentle tweak to tighten it up, and if you are hanging your exhaust off it go for the older bracket which uses 3 fixings.....

As I say, I never like 'bodge jobs', but I had no option and it's now been like it for about 5 years without problem. I do indeed have an LCB bracket which picks up on 2 diff cover bolts, one of which, the normal one for single bolt fixings, is now 3/8" UNC. I've not had any oil leakage of diff pre-load problems, but the tensile stresses on those 5 off bolts is not really high, especially at the RH side, which this is. I used Loctite on that bolt and just 'nipped' it up to avoid any risks.
It's worked OK, but I don't like non-standard installations. I've never understood the desire of some to drill out and re-tap the gearbox to block boltings from 1/4" UNF to 5/16" UNF. Do you get better clamping? Do you need better clamping there? The tensile strength of, I think 12 off, 1/4" UNF bolts is very high. (Sorry, that's another issue).

[MRA]

Although another issue still relevant to this type of topic, you can get movement between the engine and gearbox.....

Think of it like this, the bolt, fixing call it what you will is there to hold it together to form a clamping load, if the forces exerted on that joint are higher than it can withstand movement will occur.

This is why I say change to a 3 point bracket, as the exhaust can exert quite a lot of force

Ideally secondary fixings should be outlawed, however in reality we would need lots more bolts / fixings if that were the case, the downside to secondary fixings is the issue highlighted by the OP.