M6 Fine Bolts?

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SteveW
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M6 Fine Bolts?

Post by SteveW » Sun Dec 22, 2019 2:50 am

I need to mount my TC engine on a stand so that I can strip and rebuild it. This is normally done by bolting the engine stand mounting bracket to where the gearbox bell housing bolts to the engine block. On a TC engine I understand that these are M6 fine threads. Due to the dimensions on the engine stand mounting bracket (it's one of those where the fixing is through tubular sections), this means that I need some M6 fine thread bolts that are at least 85mm long. The internet is awash with M6 standard thread, but try as I might I cannot find any fine thread of that length or longer (or even any threaded bar that I can cut down). Does anyone have any ideas/recommendations? - given postage costs, this is probably a UK only question.

Merry Christmas
Steve

Tom Lange, MGT Repair
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Re: M6 Fine Bolts?

Post by Tom Lange, MGT Repair » Sun Dec 22, 2019 4:24 am

I think M8x1.0 bolts are used to support the engine, not 6x1. The length of the bolts will be determined by the length of the bolt tubes on the stand head, but if you can only find longer bolts, you can always use washers to reduce their effective length. It's awkward, but do use all 4 arms for support; I reverse one of my arms to better fit.

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bloodysalmon
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Re: M6 Fine Bolts?

Post by bloodysalmon » Sun Dec 22, 2019 5:29 am

great to see youre thinking about the engine now ... I've sent you a note offline Steve
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Steve Simmons
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Re: M6 Fine Bolts?

Post by Steve Simmons » Sun Dec 22, 2019 8:39 am

I use the bell housing holes, which are 8x1mm. The bolts I use are high strength socket caps, with a few hardened washers under them to adjust for length. I'm in the USA but I buy them from McMaster-Carr.

These are the bolts I use: https://www.mcmaster.com/96144a239

With my engine stands, a 70mm bolt is required to fully engage the threads in the block. The above bolt is 80mm so I use the aforementioned washers to take up the slack. Be sure you don't bottom out in the hole!
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SteveW
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Re: M6 Fine Bolts?

Post by SteveW » Sun Dec 22, 2019 10:03 am

My bad, both Steve and Tom are of course correct, it's 8x1mm that I need. I can easily buy these on e-bay.

However, I have one further question. Like a lot of engine stands, the bolts to the engine block pass through four tubes on the engine stand mounting plate. These tubes are of much wider diameter than the M8 bolts that are needed. This doesn't seem to make for the most robust fixing to me as there is potential for the shafts of the bolts to move relative to the tubes as I rotate the engine on the standand the load shifts direction (it would just be the clamping force stopping this). I've never used this engine stand before, so am I missing something - e.g. should it have sleeves so that the internal diameter of the tubes can be ajusted to match the diameter of the bolts?

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Steve Simmons
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Re: M6 Fine Bolts?

Post by Steve Simmons » Sun Dec 22, 2019 10:22 am

In my experience, the engine doesn't move so long as the bolts are tight. You could certainly make a sleeve but I don't think it's really necessary. I do however like to make sure the bolts are up against the top of the tube before tightening. I would think that if the size of the tube was truly important, the stand would come with sleeves for different sized bolts since most are smaller than the tube I.D.
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1949 TC8975 / XPAG 9609
1949 TC9849 EXU / XPAG 10507
http://www.mgnuts.com

Ray White
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Re: M6 Fine Bolts?

Post by Ray White » Sun Dec 22, 2019 3:17 pm

At a push four manifold studs and four big end nuts should suffice with tubing and washers to suit. A new use for those discarded items, perhaps?

I do wonder, however, if there is not too much strain put on the threads in the casting with the weight of the engine hanging from them. ?

SteveW
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Re: M6 Fine Bolts?

Post by SteveW » Mon Dec 23, 2019 3:22 am

The strain on the threads in the casting worries me as well, but it does seem to be a standard way of putting an engine on an engine stand so I'm going to go with it. If it's done up tight it should be ok, but if it's wobbling on the stand then I suppose that it could tear the threads. I guess that an old cast iron engine block can probably stand up to the strain better than a modern aluminium block.

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Re: M6 Fine Bolts?

Post by ROGER FURNEAUX » Mon Dec 23, 2019 3:54 am

This discussion came up not long ago on the main Yahoo TABC list, now superseded by the new io group thing, so once again we seem to be split between the two, a bit of overkill!

Anyway, I can provide long 12.9 grade cap-head bolts re-threaded to 8x1.0mm for this job. I would not trust old manifold studs, they are probably only mild steel...

As too the strain on the block, clean out the threads and make sure you go to the whole depth (usually 20mm) and that the threads have not been damaged by a PO using UNF bolts!

ocTagonally

Roger

Tom Lange, MGT Repair
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Re: M6 Fine Bolts?

Post by Tom Lange, MGT Repair » Tue Dec 24, 2019 5:16 am

When cleaning the threads do NOT use a shiny, new, crisp tap, as it will remove enough metal to weaken the threads. Use either a dedicated clean-out tap, or an old tap that has been vigorously sand-blasted.

I offer this suggestion because one Australian owner bought and used a new tap on his head stud holes, and pulled four studs right out of the block before he even reached the proper torque! A new tap will remove enough metal to require the use of thread inserts to repair, as the chap on Oz did. While there is relatively little stress on a bellhousing/engine joint, there is quite a bit when you hang an engine on an engine stand from those same 8x1 holes.

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Ray White
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Re: M6 Fine Bolts?

Post by Ray White » Wed Feb 12, 2020 2:05 pm

In the end I chickened out of hanging the engine from those 8x1 holes and hoisted it onto the bench. The block is supported on wooden blocks until I am ready to fit the sump. Each to their own I say.

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Re: M6 Fine Bolts?

Post by timberstone » Wed Feb 12, 2020 7:19 pm

Wonder whether the short block (only) can be worked on while upside down on the bench?
The pistons can be installed from the bottom and the bench does not interfere with the fitting of sprockets on the front of the block -- just have to remember that the timing chain marks as shown in the illustration 30 in the "Brown Book" on page 56 will be in mirror position.
Octagonally yours, Boxley (Robert and MGTC0820)
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Tom Lange, MGT Repair
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Re: M6 Fine Bolts?

Post by Tom Lange, MGT Repair » Wed Feb 12, 2020 7:49 pm

I hear that you feel reluctant to hang the block from the four 8x1 bolts, but I have done so with literally hundreds of engines, and have never had the slightest problem. It's all a matter of aligning the four brackets so they support the block and distribute the weight as evenly as possible. I have a 0% failure rate and a 1`00% success rate!

It is certainly possible to assemble an engine on the bench, but it is MUCH easier on a stand.
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Ray White
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Re: M6 Fine Bolts?

Post by Ray White » Thu Feb 13, 2020 10:06 am

As it happens, the engine was already most assembled. With the block screwed to a couple of deep wooden runners, all I had to do was fit the camshaft and followers and the head. Once the oil pump is rebuilt and the timing done I can hoist it up, remove the runners and attach the sump which I have cleaned and painted.

With the benefit of hindsight I would probably have used the engine stand. In the past my engines have had far more substantial fixings to work with. I just felt nervous; better safe than sorry...... apparently I need not have worried.

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Re: M6 Fine Bolts?

Post by frenchblatter » Thu Feb 13, 2020 10:15 am

I have a stand but the crane won't go up to the stand becaue the stand wheels are too wide. I always remove the head studs and build the lower engine parts on the bench, then, when the sump is on, crane the engine to the fllor and refit the head.
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