Great engine - the exhaust "funnel" is a condenser - very nice item.
On the t-part there should be a cap - but that should also have the
same Marklin thread - I remember the size is close to 8x1 mm. Very
strange that you can not remove the whistle/gauge - how was it fixed
to the t-part once?
A very nice and rare engine - just fantastic.
Congrats,
Arnold
Arnold
The gauge / whistle combination only looks like it is together. The whistle is screwed all the way down but the gauge is only 1/4 of a turn in. If you look at the pictures you will see that the whistle cannot rotate out without hitting the gauge, and same for the gauge it cannot rotate out without hitting the whistle. To take it apart I have to turn the gauge 1/4 turn CCW and take it off, then the whistle can be removed. I am sure that is not what Marklin designed.
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I got a surprise when I decided to check out your recollection of an 8 x 1 mm thread. I have a lathe that I can single point a metric thread, so making a cap would be relatively easy. Just to check everything I got my metric thread gauge and a digital caliper. I measured the diameter of the whistle thread and the filler plug thread from the 4150, the readings were 7.78 and 7.81. Close to 8mm and threaded sections are usually smaller. Next I took the thread gauge and clearly 1 mm did was too course. I tried .75 it was too fine. Next .8, which was too fine, and .9, which was, too course.
I thought that maybe it was an imperial thread. I used my TPI gauge and it registered 32 TPI exactly. Next I switched the readout to inchs on the caliper and the diameters measured .309 and .310 for the whistle and filler cap. That dimension is close to .312 or 5/16 inch. I have been making models since the mid 1970s and have many taps and die. There is a series of taps and dies called Model Engineer which uses 40 tpi for 1/8 1/4 and 32 tpi for 1/4 1/2. I have a 5/16 32 tap. I drilled a tap hole in some 1/4 brass and tapped it.
Both the whistle and filler cap screwed in perfectly no wobble, no tightness, no slop. You can see from the pictures the fit. The last photo shows the bottom of the filler in the thread, nice and firm.
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I had a 8 x 1 mm bolt and tried screwing it in both the filler hole and the whistle hole on the gauge T. It went in about 1 turn then got tight. If I wanted to force it I am sure it would have gone through the filler hole being brass or copper, it would have reformed the threads. The 8mm diameter or the bolt was actually 7.85 mm or .309 inches virtually identical to diameter of the whistle and filler plug. The real difference is the thread 1 mm vs 32 tpi. 1mm is .0390 inch and 32 tpi is .0313 inchs ie the measurement of the thread pitch. They are only about .008 inches difference. That is why screwing the 8 x 1mm bolt in seems to go for a bit ie 1 turn and then gets tight. It almost fits.
Why Marklin used that thread pitch is a mystery to me. I believe that thread came into existence in the late teens to early 1920s. I have model engineering books from the 20s that reference the thread as being used for model steam engine fittings.
I hope this information is useful to everyone.
Bob