What size nut for lambda sensor on VZN185

[Shaft120]

On coming back from a long trip to Inverness, I got a sudden blow from the exhaust system. I figured a hold in the exhaust or down pipe as it was so loud, but on inspection later, it appeared that the lambda sensor had come out. Not quite sure how, as it is held on by two nuts, which improbably must have worked themselves loose and dropped away.

Anyway, good news in a sense as should just be an easy fix back. However, I cannot for the life of me work out what size nuts I need to replace. I thought it was an M8, but the nuts start to go on, but stick almost immediately. I've done a wire brush and oil on the threads, but this hasn't made any difference. M10's were too big, so I presumed M9 as I had heard these are sometimes used on motors / bikes. So bought a pack of these on Amazon, but they arrived today, and they are too big as well.

Does anyone know what size I need? Also, does anyone know where I can get a new gasket for it as well? If not, I'll have to use a liquid gasket I guess.

[BUSHWHACKER]

They're M8X1.25. (The 1.25 is the thread pitch. )

The nuts you tried are probably M8X1.0. A more common size found elsewhere on the truck.


Ask at an exhaust shop for a couple.

[Shaft120]

Cheers Bushwhacker

Have found the OEM part number as well in case anyone searches this thread (excuse the punn!) :

90179-08059

The original has a locking feature, (which clearly is designed to stop what happened to me - and I presume whatever was on there before was a replacement which worked loose)

However, I think buying a pack of M8 1.25 pitch will cover me for a long while. I have learned more about nut dimensions today than I knew existed!

[BUSHWHACKER]

Get some M8 spring washers as well to stop the nuts vibrating loose.

[Shaft120]

Ok, popped down to kwik fit local and they gave me a couple of nuts, which they said were M8 1.25 pitch, but asked if 'coarse' was ok, or if I needed 'fine'?

I said no idea, and they only had coarse, so I took those but they seem to get as far as the other M8 nut's I've tried before.

What s the difference between coarse and fine and do I need to get fine ones?

[Shaft120]

Hmm - seems 'coarse' on an M8 just means it is a 1.25 pitch, where as 'fine' means 1.0 pitch. So these should be working. Not sure what to try next. Don't really want to force them (any further than I have tried) and the threads seem pretty clean on the exhaust.

[BUSHWHACKER]

Yes it's the fine thread you need, sorry should have pointed that out.
Fine threads are more resistant to vibrating loose because there's more material between the threads. Coarse threads are deeper cut and more common.

[Shaft120]

Ok - So had a chat with a local engineering company, who insist there is no such thing as an "M8 1.25mm Fine" Nut size, as the Coarse is 1.25mm and Fine is 1.0mm

Anyway, I popped down and found that a "5/16 UNF" nut fitted, so have chucked those on.

Very, very strange.