Taper pin reamer

[Hugh Barnes]

I'm trying to reassemble the Chummy bottom fan pulley after fitting a modern lip seal instead of the felt version in the starter dog housing. I have, through the kindness of a fellow forumist, now got a couple of 1/4" taper pins that can replace the rather ugly long thin nut and bolt that was previously used. To do this properly, I think I need a taper pin reamer - the existing bottom pulley has just been drilled in a couple of places to take the nust and bolt. Am I right in thinking that imperial taper pins are at a 1:48 angle and that any suitable reamer to that spec will do?

I also have a roll pin, gifted by another forumist, that I could use, so I have options.

Advice from the experts please!

[Hedd_Jones]

The roll pin will be for parallel hole.

The starter dog will have started life tapered. What is it now? As indeed would the pulley.

If its all parallel. and the roll pin is suitable size go with that.

If all tapered, go with taper pin.

The one I did here, I welded up the holes in the pulley. And re drilled. I just drilled the holes the same diameter (within reason) as the diameter of the holes at each face of the dog. I have a large tin of drills and simply tried them till I found an acceptable one. You of course could just index the pulley round a bit too and re drill

I actually aimed for a drill slightly smaller than necessary. So when I belted in the taper pin it made itself fit the soft ali, while fitting the dog well.

[Parazine]

I did this on the Top Hat engine. Near the bottom of page 14 of the thread "Restoring a Top Hat" has details but I used a letter D on the large side and a number 2 on the small side. The ally is soft enough to form a taper when you hammer the pin through.

[Stuart Giles]

Imperial taper pins are 1:48 so 1/4" per foot taper. So you just need an imperial taper pin reamer to finish the hole -the sizes of these reamers and pins are quoted using the large end.

Metric taper pins are 1:50 and sizes are quoted using the small end of the taper.

[Robert Foreman]

The starter dog has a parallel hole through it and the pulley was originally fitted with a split taper pin.

[Hugh Barnes]

Thanks Stuart (and others) that is particularly helpful and bears out some of the reading I have done this afternoon. In the meantime, a pal has offered me a 1/4" taper pin reamer that is coming in the post. I've tried the pin on the starter dog and it isnt't 'comfortable' so I will be able to temporarily place the pulley in place and then run the reamer through the two to ensure a perfect alignment and an easy placement of the pin when I tap it into place..

[Hugh Barnes]

Thanks Robert - for some reason, even though your post preceded mine, I have only just seen it. As a result I have double checked the starter dogs on the 2 engines I have. They are both parallel. I had assumed taper as that is what I had been led to believe. Interestingly, the spare engine has a dog that will permit a 1/4" drill bit to pass with ease, whereas the engine in the car will allow a 7/32" to pass through it but not a 15/64th" A 1/4" stands no chance.

From what you are saying, it seems that the Roll pin is the better option, though I may need to clear the starter dog with an appropriate reamer (awkward with it being in the car). Having just measured the Roll pin I have been given (by a trusted source) it measures 0.2585" so would seem to be correct for the application.

[Hedd_Jones]

The starter dog I fitted to my engine had a tapered hole. 

No idea of its source. I found it in a tin. It certainly wasnt a recently manufactured item.