Thread size

[Paulprior]

Just about to refit this sensor but the threads are bad, any ideas on what size the screws are or how to find out ???

[rdl001]

They are a regular M4 thread - there is plenty of 'meat' in the plenum casting to take them to M5 if required

[Steve_D]

rdl001 said:

They are a regular M4 thread - there is plenty of 'meat' in the plenum casting to take them to M5 if required

Are you sure? Reason I ask is that the screws in the picture have a head style known as 'Cheese Head' which I would associate with imperial threads. The rest of the engine is imperial so my guess would be that they are BA thread.

Steve

[phillpot]

Steve_D said:

Are you sure?

While the original engine is of American origin and therefore imperial, I thought a lot of the later additions like fuel injection were metric threads?

[V8fan]

Remove the bolt from the TPS and check using a thread gauge is the ultimate. Or, try on a nut of a known thread, be it M4, M5, 1/4" etc. As a TVR owner, I had small bags with nuts and bolts of various sizes from various tasks and needs.

If imperial, it's more likely to be UNC or UNF than BA. But there's BSW to consider.

Edited by V8fan on Friday 28th February 08:52

[Jon100p]

It could be a UNF #8 (36 tpi), they are very close to an M4 x 0.7mm pitch (which is equivalent to 36.3tpi ).

Also yours look a little short, should be about 14mm or 9/16" of thread.

[Zener]

Jon100p said:

It could be a UNF #8 (36 tpi), they are very close to an M4 x 0.7mm pitch (which is equivalent to 36.3tpi ).

Also yours look a little short, should be about 14mm or 9/16" of thread.

This ^ I have a spare plenum on the bench that has longer M4 x 0.7 screws fitted , long story I was messing with alternative TPS units

[Paulprior]

I did try an M4 but that didnt work, if i new exactly what it was i would just buy taps and new screws, otherwise i have lots of metric stuff so i could try tapping to m4 or m5 if neccessary, the current screws are plenty long enough, its just the photo that makes them look shorter

[Paulprior]

I searched through all my taps of that sort of size, found one that looked the right thread and it screwed in easily, but I couldn’t make out what size it was, decided m4 also looked very close, so put those taps in with very little resistance, so m4 it is now, and maybe was before, it’s odd because the throttle assembly and stepper motor threads are imperial, but my plenum bolts are m8, so I suspect someone has had problems before and recapped a few threads to metric , but all sorted and going back together anyway, thanks for your help

[stevesprint]

I know what you mean as the block, heads & stepper are all UNC, oddly the plenum top long bolts are M8 therefore I’m not surprised the throttle POT can take M4 bolts and that’s what I’ve always used, M4s.

However, M4 (4.0mm) is interchangeable with 8 - 36 (0.164) UNF which are 4.1mm diameter and has the same pitch but due to the lack of 8 - 36 UNF choice I will continue using M4.

Here's a plenum top, stepper and 2 throttle POT bolts.

[Zener]

stevesprint said:

I know what you mean as the block, heads & stepper are all UNC, oddly the plenum top long bolts are M8 therefore I’m not surprised the throttle POT can take M4 bolts and that’s what I’ve always used, M4s.

However, M4 (4.0mm) is interchangeable with 8 - 36 (0.164) UNF which are 4.1mm diameter and has the same pitch but due to the lack of 8 - 36 UNF choice I will continue using M4.

Here's a plenum top, stepper and 2 throttle POT bolts.

And there it is ^

[stevesprint]

For the sake of a few pounds I bought a couple of 8-36 UNF bolts to try and could only screw them in a few turns by hand where as I could screw the M4s all the way in by hand.

As I’ve now tried the 8-36 UNF on two different plenums I’m going to accept that they are M4 and not try forcing the 8-36 UNF further in which I’m sure I could.

Left 8-36 UNF & Right M4

[Zener]

stevesprint said:

For the sake of a few pounds I bought a couple of 8-36 UNF bolts to try and could only screw them in a few turns by hand where as I could screw the M4s all the way in by hand.

As I’ve now tried the 8-36 UNF on two different plenums I’m going to accept that they are M4 and not try forcing the 8-36 UNF further in which I’m sure I could.

Left 8-36 UNF & Right M4

Well done Steve nowt queerer than LR/Rover