Expansion tank thread

[hoofa]

Anyone know what the thread size is on the expansion tank with the blue cap ?

[Belle427]

No idea but spares are available.
https://www.racetechdirect.co.uk/car-parts/cooling...

[LucyP]

It's an old VW/Audi part. This is what the sellers of the part number for VW/Audi say:

443 121 321 VAICO, TOPRAN Expansion tank cap, Coolant ...https://www.autodoc.co.uk › ... › Expansion tank cap
Expansion tank cap with OEM number 443121321 in original part quality ... Inner diameter [mm]: 33; Diameter [mm]: 58; Weight [g]: 47; Thread Size 1: M3.

[hoofa]

Need the thread as Clive f was going to make one in stainless hence the thread question , some has to make the weld on boss

[mk1fan]

Send him a blue one.

[BIG DUNC]

Is the blue cap not a pressure relief cap, or is that what Clive is making?
I would be very interested in one of these as well, unless the cost is silly.

[hoofa]

Guys the topic is trying to establish the thread not Clive making a cap, I want him to make a nice polished stainless tank and he has to get the boss made but needs to know the thread

[TwinKam]

Point is, there's a chance that it may not be a 'standard' thread (eg M40 or whatever), with a 'standard' pitch, or a 'standard' thread profile, so it may be that a machinist has to copy one from an existing tank.

[BIG DUNC]

Sorry, I mis-interpreted your post as Clive was making a stainless cap. I take it then you are putting a blue bit of plastic on top of the lovely shiny expansion tank?
I would suggest buying a new cap and sending it to Clive and saying make a thread to fit this.
As said above, it may not be standard.

[mk1fan]

Hhhmmm Clive F stainless expansion tank.

[Zener]

TwinKam said:

Point is, there's a chance that it may not be a 'standard' thread (eg M40 or whatever), with a 'standard' pitch, or a 'standard' thread profile, so it may be that a machinist has to copy one from an existing tank.

Wise words ^ all I can add is VAG been using this style cap/thread since 1974 minimum

[TwinKam]

Zener said:

TwinKam said:

Point is, there's a chance that it may not be a 'standard' thread (eg M40 or whatever), with a 'standard' pitch, or a 'standard' thread profile, so it may be that a machinist has to copy one from an existing tank.

Wise words ^ all I can add is VAG been using this style cap/thread since 1974 minimum

You've been in this game long enough to remember the story behind the A-Series crank thread, Simon... folks were scratching their heads and arguing over it for years, until it transpired it was copied off a random bolt that a prototyper at Austin 'found under a bench' that was 'just the right size' for the job...
But would that happen at VW?... could be a barrel/ flagon/bottle thread...

[mk1fan]

https://www.ebay.co.uk/itm/284984063625?hash=item4...

Buy it. Get it sent to Mr F and he can determine size.

Racetech have the these in stock - https://www.racetechdirect.co.uk/car-parts/cooling...