Valves and Guides on 2 3/4's ?

[phil_h]

I think my 1913 has some oversize-stem valves and guides.
They are 5/16 diam, with a step at the end of the valve so the spring retainer will fit.
Unfortunately, not only does (at least) one exhaust valve need replacing because it was made in 2 pieces screwed together ...
but (at least) one inlet guide also needs replacing because it is incredibly loose.

I am hoping everything will work well enough for the Pioneer Run, but I need to understand what dimensions of parts should actually be fitted !
I have a nice list of parts that the club sells, but there are no dimensions to let me know exactly what I need.
Looking at a couple of odd loose heads of unknown vintage, one of them appears to have guides cast integral to the head, and the other shows a really small thickness of head to locate on !
Looking at loose guides, it looks like they must be machined down to the required length.
All help gratefully received.

[Chris]

Hi Phil
  The standard valve's stems are nominally 0.275" diameter for 2.3/4hp. Samples of used valves I have show measurements on unworn portions of between 0.274" and 0.278". I have a set of manufacturing drawings somewhere for most Douglas valves but cannot find it at present. Veteran machines pre Jan. 1915 had integral valve guides and these were superseded by detachable guides through to 1926. When wear has taken place in the integral guides, a usual "cure" has been to ream out the guides and then find/make valves to fit. I have done this in the past by taking an oversize valve with the correct stem diameter to fit the reamed guide and then turning the head of the valve to match the standard 2.3/4hp valve head profile. A better solution in the long run is to have the integral guides machined out to take the standard replacement valve guides. There was a tool, whether it was factory supplied or made by dealers I don't know, but the only one I was aware of was lent to someone some years ago and has never been seen since. This located in the threads of the valve cap and ensured that the bore left in the cylinder head for the valve guides was concentric with the valve seat and ensured that ovality and wear in the old guide did not influence the position of the valve unlike that of reaming the integral guide. In the absence of the original tool it should not be beyond the capabilities of a good engine reconditioning workshop to carry out this work. When the new guides have been fitted it will almost certainly require the valve seats to be re-cut as frequent regrinding of the seats from the worn guides will have left the seats out of square with the new valves and guides. You should be aware that there is no need to machine the new guides available from LDMCC spares as they are purpose made for each application. The inlet guides like the inlet valves being shorter than the exhaust guides and valves. A frequent problem with engines that have had a lot of use and frequent overenthusiastic regrinding of valves in their seats is valve seat recession. The solution to this problem is to fit new valve seat inserts. This is extremely difficult on these engines but can be done. The difficulty arises from the fact that access to the valve seat is only via. the valve cap threaded hole and the inside diameter of this is critical in terms of the outside diameter needed for an insert.  Chris.

[phil_h]

Thanks Chris, that is a very exhaustive explanation. (sorry - no pun intended !)
I've had my exhaust valve carefully bazed together, and I took the bike out for short tootle again, backwards and forwards along my road, on saturday, and managed to get back home under power.
It was extremely hard work keeping it going in these lovely temperatures we're having !
The very loose inlet cannot be helping in those circumstances, but things are looking up !
Hopefully I'll be able to go out for a longer run next weekend.
I'll have a word with an engineer friend to see what the best way of working out what stem size the guide could accomodate, and then look for a suitable valve.
At the moment I really dont want to take the cylinder off, as the front inlet joint is very problematical too !

[eddie]

Phil,
       To overcome leaks between the induction pipe and cylinders on my 2¾, I used Viton 'O' rings. The ones I used were originally for the cylinder head end of the induction pipe on a Dragonfly. They are slightly smaller in diameter and have to be stretched over the pipe - but this ensures a good seal on the end with the loose flange.
                               Regards,
                                          Eddie.

[phil_h]

Thanks for that eddie, it sounds like a good move.
Unfortunately I have worn theads on the front cylinder to fix first !
I'm guessing that the best fix is to cut off the old threads and get a new threaded collar welded on.
However, theory and practice are often quite different, and it would be really nice to find someone who has had the job done.

[eddie]

Phil,
        Trying to get 97 year old, oil soaked cast iron welded may be problematical. If it was mine, I would have the thread recut undersize and a new collar made to suit. I know this will mean having to remove the flange from the induction pipe and then fix it again - but it's better than ruining an otherwise good barrel.
                                      Regards,
                                                Eddie.

[phil_h]

Hmm ... cutting a custom thread on an 'interestingly' shaped casting does not sound like an easy job though !

[phil_h]

Hmm ... cutting a custom thread on an 'interestingly' shaped casting does not sound like an easy job though !

Or is it a size with 'readily' available split dies ?

[Chris]

Hi all
   The thread size of the inlet and exhaust stubs on the cylinders is 1.1/4" x 20 tpi. and circular split dies for the stubs and taps the for the locking rings are available. (to the Whitworth thread form). I don't know about "readily" but they can be obtained (at a cost). The die especially is extremely useful for cleaning up the threads which invariable show signs of corrosion and in the case of the exhaust, some carbon build up.
Chris.

[eddie]

Phil,
       The present poor fit of the locking ring is probably caused by wear on both the threaded stub and the ring itself. With a bit of ingenuity, you should be able to rig up a guide with a thread chaser clamped in it that will allow you to 'scrape away' at the thread until you get back to the full form (in which case, any 20 tpi chaser will do - ¼whit or 3/8 BSF). Then you will have to screwcut the thread in a new collar to suit. I think you will be pleasantly surprised at how little undersize the finished job will be!
                                   Regards,
                                              Eddie.

[phil_h]

from ebay ...
1 1/4" x 20 tpi TAP SECOND HAND 20tpi 20 TPI   £39.50
1 1/4" x 20 tpi DIE second hand 20tpi Whitworth HSS   £165.50

1 1/4" x 20 tpi TAP second hand 20tpi     £30.50
1 1/4" x 20 tpi DIE New 20tpi     £87.50

Gulp !

[Doug]

Phil,

Port thread repairs are not too difficult. Just turn the whole stub as a separate piece in the lathe. No need to awkwardly chuck up the cylinder or head in the lathe and trying to turn that. As for preparing the head, you just need to saw off the damaged thread reasonably square and drill a shallow hole down the center of the existing port. Turn a spigot on your new stub to suit to avoid any steps on the inside, and braze in place. The picture below is a repair done on my A31 rear exhaust thread prior to brazing, but it is the same idea for other models. After brazing you can contour and blend the inside and outside surfaces.



-Doug

[oily bloke]

I have recently bought new taps and dies in odd sizes from 'Tracy Tools Ltd' In Devon UK for my ongoing EW350 rebuild, among others. They seem to stock a plethora of sizes and pitches. For example 11/4" x 20tpi tap £20. Same size die £25 (plus vat & carriage). All new and a choice of first, second and plug taps. I have no connection with the above company other than that I am a very satisfied customer. They have a website too.
Cheers
Andrew

[phil_h]

Thanks for the pic and info Doug,
That sounds like the kind of thing I was imagining needing.
The pic is especially useful as it clearly shows what the replaceable guide looks like.

[phil_h]

Thanks Andrew
those prices sounds much more comforting.
The cost of making a new trial collar is suddenly much less than I feared, as I am obviously hoping to find a 'minimal' solution that leaves everything looking as original as possible.
What is a tap of that size like ? Did you get a plug to fettle an old collar ?