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[KNO3]

Hello, I have recently acquired this very nice Cheddar Gemini engine and would like to add the original water pump, which I also have.
Cheddar supplied the Gemini pump with 6BA screws and half-nuts. However, on my Gemini the supplied nuts foul the crank disk. That's why I can't use them and would prefer to use screws that fit the tapped holes marked with arrows in the picture.

Can somebody please confirm what threads are those?
They are slightly over 3 m  diameter (an M3 screw can be just pushed inside).

And happy New Year everybody!

[ooyah/2]

Hi Calin,
If the C/sk screws are the same thread as the tapped holes in the base bed ( 6ba)why not cut the screws to a length when screwed up doesn't foul the crank web.
With a spot of Loctite 243 on the thread it will never move and a lock nut will not be required.


Have a Happy New year.


George. 

[KNO3]

Thanks George. I need to know what thread those holes have, if somebody has the same engine and could check. They are not 6BA but larger, a little more than 3 mm.
 (Looks like the question was missing from my original posting,  I have added it now).

[ooyah/2]

Calin,
I would suggest then that you give Jerry at Clevedon steam  in the new year a call and he will possibly know what size the tapping is for, it could be 5ba  Possibly a member who has this engine can let you know what thread it is.


George. 

[KBIO]

Good evening!
I'll have a look at mine tomorrow. Too bad that I just set the pump back up. It used to stand inside the hull as I di not have the intention to use it.
I wonder if mine is not tighten with some flat nuts of the back! My memory is falling apart !
I can only tell if it is 5 or 6 BA as this all the taps&dies I have this size. Just above , I have 1/4''x 40 TPI or 36 Tpi. So not too much choice to help.
Time to get back to the workshop !
Cheers !

[KNO3]

That would be great Yves!

[KBIO]

While I think of it! As you are registered on my forum you can go there and have a look at the engine.You have access to the photos.

https://modelismenavalvapeur.forumactif.com/t162-gemini-engine
Just to confirm what I thought ! There is a counter nut to hold the pump in place. You can see it on the attached pic : bpptom right of the skid !. So the thread is not that important as long as you have the bolt & nut.
But still I'll check for you tomorrow !
Byyyye !

[KNO3]

Hello again, thanks for the picture. I have the half nut, look in my first posting and the picture. The problem is that it does not fit in the space between crank disk and bearing, it is to thick.

Anyway, I want to know what thread the holes are and find a suitable screw.

[KBIO]

Hello !
As promised, I took the pump away from the engine.
What I can say , is that there is no thread on the frame itself on mine. No trace of any and the paint is still on. Does that mean that there was no thread originally ? Can't tell !
My pump is held with a 5BA nut and and thin counter nut (2mm thick ) . I inserted a 2.1 mm drill between the frame and the crankshaft disc to show the space available. The nut has been filed to make it thin.
Note that the caliper reads 102/1000'' = nut size.


An option will be to re-thread the frame in order to screw a bigger nut to hold the pump. Someone familiar with BA can tell which size comes just above 5BA. This will avoid the use of a counter nut . Eventually a 4x0.50 metric will do it.


Everything is back on place ! Days over !
Cheers!

[KNO3]

Thank you for the measurements Yves!

It looks like my Gemini is "special" having those holes threaded. I think it came like that from the factory, because there are no signs of it being threaded at a later date, the original paint also goes a inside the holes a little. The holes are a little over 3 mm, so I think they could have 5BA threads, but I don't have any such screws here to check.

Anyway, I have two solutions:
1) Find some 5BA screws to check if they fit,
2) File down the nuts supplied and make them fit between the crank disk and bearing.

[SteamboatPhil]

I can send you some 5 BA c/sk, cheese  or hex head if you would like, and 1/2 nuts if you need them

[KNO3]

Thank you Phil, that is very kind! I'll PM you.

[KNO3]

I have finally found the time to mount and test run and make a video of the new water pump attached to my Cheddar Gemini steam engine.
The water pump was original and unused. However, I had to file down the fastening nuts and screws supplied with the kit to make them fit in the very tight space between the bearing and the crank disk.
With a few drops of oil, the engine runs with pump as good as it ran before. The pump doesn't seem to have excessive friction. Of course, that will change when it will be actually pumping water.


Phil, thanks again for your help!


https://www.youtube.com/watch?v=BQ3ZeM2keZs

[KBIO]

Excellent Calin!

[KNO3]

A few pictures of the Cheddar Gemini with the water pump: