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MG TD TF 1500 - Metric Bolts

The bolts that hold the flywheel housing to the engine are 8mm. Are these the same threads as modern metric nuts and bolts?
Bob Marshall
R J Marshall

https://www.mg-cars.org.uk/mgtd/mgtd_engine_fasteners.htm
Christopher Couper

Yes, see attached photo - the set screws (full thread) are M8 x 30mm.
They are plated HT steel, and being 30mm long, they reach the unworn threads at the inner ends of the threaded 'bosses'. However, with the thickish washers shown, they do not reach the starter ring gear.

R WILSON

NO! Modern 8mm metric is 1.5, the fine thread on our engines is 8x1.0. Very fine thread, which is why many of the bellhousing to pan bolts strip, also timing chain cover. Do a good google search on the various thread types used on our cars. Link above great for engine and gearbox- most fine metric, except for the exhaust hanger threads…... George
George Butz III

I should have said that the set screws are M8x1x30mm - see attached enlargement of original photo. They are standard metric fine threads, and are readily available - at least in the UK.
As they go all the way through the threaded bosses, the grip is excellent.

R WILSON

Perhaps I should say they are normal metric fine threads. Standard M8 threads, also called coarse, have a pitch of 1.25mm. 1.5mm pitch is not a recognized M8 option.
R WILSON

You are correct- 1.25 coarse. The 1.0 pitch can only be found at a specialty dealer like Fastenal in the US. Parts and big box store here only have the coarse threads. No matter how deep the boss, several cars I have worked on had most of the aluminum threads stripped. A too long bolt makes a really bad noise when it hits then spinning flywheel! George
George Butz III

Mr R J Marshall, who started this thread, lives in the UK. I think the washers are just over 1.5mm thick, but I will measure one to make sure.
R WILSON

The washers are thicker than I thought - they are 2mm thick.
Regarding stripped threads, it is possible (well, over here) to buy Helicoils for M8x1mm.
R WILSON

There's a lot of misunderstanding about metric threads, specially in USA for some weird reason
Basically using the words course and fine creates issues-Toyota for example tend to use finer threaded bolt more that other makers but they're still metric

With imperial fasteners we refer to the thread count as tpi. (threads per inch) Course thread bolts have less threads per inch than fine threaded bolts but we have to be carefull with fine threaded imperial bolts as well as they might be UNF -national fine, cycle thread, etc all having different thread counts for a particular diameter-

Basically the same applies for metric but it's simpler, all you need is a thread gauge and you're in business.
Any sized diameter bolt can have any thread count, The bolts are described as diameter x thread count x length
eg. an 8 mm bolt with 1.5mm pitch(distance between each thread in mm) and 30mm long would be M8x1.5x30
Any sized bolt can have any pitch, it has to be measured/matched
A small fine threaded bolt could be right down to something like 0.25mm pitch whereas a larger courser bolt might be 2mm--We'd possibly call 2mm course thread but 1.5mm is course as well---you have to measure the pitch
It's the same deal really as with whitworth and UNC--basically the same but some sizes like 1/2" have different thread counts
William Revit

ACE Hardware dealers typically have these bolts on the shelf. However for higher grade bolts must go to specialty distributors.

Since many of. our engines have been rebuilt probably more then once, by different individuals of varying muscular torque capabilities, I have found the need to use Helicoils all over in many places.

In particular one edge of the threaded oil pan flange was broken off completely. Using a Helicoil, high tensile epoxy steel JB Weld, reinforcing it with wire rod drilled into the flange, wrapped in soaked wire screen -- made it possible to rebuild and finish it so that the gasket seals and there is no leak. Of course the particular bolt going in to the repaired flange is tightened only after all the pan bolts have been properly tightened and very gently - just snug.

Did then same proceedure many years ago in winter on a broken flange of the differential housing and it ran for 11 years without leaking.

Miracle stuff
Michael Balahutrak

Time Serts are a better option compared to Helicoils,
particularly with reference to the aluminium sump flange.
Rob Grantham

I have never seen a big box hardware store that carries 8x1.0 bolts. Only 8x1.25. If you have one that does, then consider yourself lucky! Also keep in mind that the original bolts on these cars had British heads, not Metric. So you will need to carry more tools if you start using standard Metric bolts on the engine.
Steve Simmons

This thread was discussed between 28/10/2025 and 08/11/2025

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