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MG MG Y Type - Bell housing to engine bolts

I have just fitted a drip tray to my YB, necessitating the removal of the three lowest bolts between the bell housing and the engine. These bolts were in poor condition and partially stripped. I want to replace the damaged bolts but I am confused about the thread size.

I understand that all of the engine and gearbox tappings on the XPAG engines are metric, for historic reasons. The bolt data sheet on this website states that these bolts should be 8mm with metric threads. However, the bolts that I removed are definitely 5/16" BSF (22tpi) and of the correct diameter, although the difference between 5/16" and 8mm is very small and probably not measurable with confidence even using a digital caliper. French metric bolts have 25.4 tpi.

Has anyone else had reason to measure or replace these bolts and can offer an explanation for the apparent anomoly? I presume that I should buy some new BSF bolts.
M Long

These should be 8x1mm ie as you say 25.4TPI. I expect someone has forced BSF bolts in and hence why they looked stripped! Best to get the correct 8x1mm bolts from say MadMetrics and if the sump threads are too damaged use Helicoils to repair the thread.

Regards
Brian
B R HOUGH

I second Brian and would advise to (heli)coil all three threads.

On my engine I thought some threads were usable, but some stripped anyhow. Probably because the DPO used a BSF bolt.

The bolts used to fasten pedals to the pedal axle on most bicycles is often 8x1mm, so a trip to the local bicycle shop may yield some useful (hi tensile) bolts.
Willem van der Veer

Hi - I am surprised the bolts are stripped, as the sump is aluminium, and it is normally the sump threads that get stripped. You probably have incorrect bolts because that is what a previous owner thought they were, or were all he had at the time. You need to obtain 8x1 bolts (plain shank max length 11mm) or set screws (full thread) 30mm long. Then with one flat washer they will go all the way through the sump threaded bosses, but still not touch the flywheel (even without the washer). However, they will use the full length of each boss, and importantly the unworn threaded rear of the boss, rather than only the well worn, often stripped, front section. If the bosses are totally stripped, 8x1 helicoils should be fitted, but 30mm bolts/screws should still be used. In my case I use old, but not stripped or stretched, little end bolts, and run a die down to extend the thread, then cut the length to 30mm.
Be careful buying from a hardware shop or ironmonger, as they normally sell coarse series metric fastners, which for 8mm have a pitch of 1.25mm.
R A WILSON

Good advice above - I have nothing more that I can add other than to re-emphasize RA Wilson's comments about being careful about where you buy your stuff from to ensure you get fine thread - 8 x 1 not 8 x 1.25.

Paul
Paul Barrow

Thanks to all who responded.

I got some M8 x 1 bolts of the correct length from a local fastener supplier, rather surprisingly, although he has helped me in the past with some 'odd' sized bolts.

I am concerned though because the one good BSF bolt that I have screws in relatively easily and tightens, but the metric bolts will not screw in without considerable force from a spanner, which I am reluctant to do. I wonder if a previous owner has either retapped the thread in the bell housing, or, possibly fitted BSF helicoils. I will get some BSF bolts and see how they tighten before doing anything more drastic.

Mike
M Long

Oh, the joy of tinkering on tinkered on cars!
Willem van der Veer

Whilst on the subject of David Pelhams aluminium drip trays, when a friend of mine bought one I have to confess I copied the development from it and have recently got round to making a couple of trays up for my cars. The problem was always how to join the corners as the originals were welded. I used “Miliput” a wonder material that is seldom seen advertised. It is two sticks of putty that when kneaded together can be sculpted to any shape and will stick to anything and goes rock hard. Very clean to use just like plastercine, every handy person should have some on their shelf. It certainly did the job for me on the trays and by the way I did tell David I had copied his design.
Interestingly I had the same problem with the set screws and had to replace a BSF with a longer metric fine.
Peter
P W Vielvoye

It may be that all the fasteners into the sump have been changed to BSF by using helicoils. If, in the future, you want to use the correct 8x1 metric fasteners, you will have to take the sump off, remove the helicoils, then have the bosses welded up, and drilled and tapped 8x1mm. This is what I did to my TD sump, but I admit it was a lengthy process.
The timing chain cover is also aluminium, and has four tapped threads which can strip, so you might want to check what is being used there.
R A WILSON

This thread was discussed between 24/09/2014 and 01/10/2014

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