CYLINDER HEAD

[geni]

Sur la culasse du twin- cam les 2 filetages 3/8 - 18 NPT sont arraché et fortement abimé
Se sont ceux sur la culasse de la liaison avec la sonde de température eau et celle du robinet de chauffage Je voulais effectuer la réparation avec des inserts a filetage rapporté Helicoil ou Recoil mais il reste difficile a en trouver et très onéreux a l'achat avec l'outillage de pose
Qu'elles sont les autres moyens a utiliser pour réparations ?

On the cylinder head of the twin-cam the 2 threads 3/8 - 18 NPT are torn off and badly damaged
I wanted to repair with Helicoil or Recoil inserts but they are difficult to find and very expensive to buy with the tools to install them
What are the other ways to repair?

[h20hamelan]

Time sert is an option i think

[rgh0]

Not sure which ones your talking about but all the pipe threads in the head are BSP not NPT. If they are stripped its probably because the wrong threaded components were fitted.

cheers
Rohan

[geni]

Not being a mechanical engineer, I don't think that it can harm the assembly so I think, and know my conviction that either NPT or BSP should work properly. Am I wrong?
NPT can help because of the advantage of the taper.
So if you could help me find the tool that would be a plus

[rgh0]

Not being a mechanical engineer, I don't think that it can harm the assembly so I think, and know my conviction that either NPT or BSP should work properly. Am I wrong?
NPT can help because of the advantage of the taper.
So if you could help me find the tool that would be a plus

The thread pitch is different and also the thread form putting a NTP male into a BSP female will strip the thread

cheers
Rohan

[nmauduit]

Not sure which ones your talking about but all the pipe threads in the head are BSP not NPT. If they are stripped its probably because the wrong threaded components were fitted.

cheers
Rohan

This is about the two horizontal BSP threaded holes coming out of the thermostat (one for water temperature pickup, the other for interior radiator take off hose)
https://lotuselan.net/forums/viewtopic.php?f=39&t=37754&start=
https://lotuselan.net/forums/viewtopic.php?f=39&t=44698

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Gérard, as mentioned perviously by Rohan and others, an issue may arise from the angle of the thread itself (BSP 55° vs. 60° NTP), other than the shape of the fitting (both type come in parallel and conical),see online for instance https://www.valvesonline.com.au/references/threads/

An helicoil would be the cheapest imho, if deemed reliable enough (I would not think easy to do it with the head in situ, or at least without a setup to make sure the repair is square) - you may also get it welded and retapped, or drilled clean plugged and retapped, for a proper, durable repair (unlike quick a fix played by side-of-the-road butchers who would retap with whatever tap he has in hand and glue everything back to see you out of the shop).

[rgh0]

I believe the female threads in the head are both BSP straight, though hard to confirm as now all are some what worn, I must research the original design a little more on this. The original adapter for the temp sender is also BSP straight male and very short originally and Aluminium and sealed on the head face with a Aluminium washer these often corrode and are replaced with different designs. The heater control valve is BSP male tapered and sealed on the threads with sealant. Screwing it in to get it to seal and also have the correct horizontal alignment is somewhat challenging and also leads to thread damage

Using a Helicoil would be problematic due to leakage past the helicoid but possible. I would need to see the actual thread damage to recommend a repair method with any confidence

cheers
Rohan

[Andy8421]

If anyone is interested, some historical context here:

https://arthurharris.com/news/npt-vs-bsp/

[lotusfan]

Another piece of interesting information that may help geni is that the ISO standard 228 G thread is the same as BSPP. It surprised me to learn that the G threads are in inches and fractions of inches and are used widely in Europe.

[nmauduit]

Another piece of interesting information that may help geni is that the ISO standard 228 G thread is the same as BSPP. It surprised me to learn that the G threads are in inches and fractions of inches and are used widely in Europe.

yes, in France it is commonly depicted as "pas du gaz" (nat gaz thread), mostly restricted to a specific niche...