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General => Douglas Motorcycles - General Discussion => Topic started by: Ian on 09 May 2020 at 06:33

Title: OHV Head Torque
Post by: Ian on 09 May 2020 at 06:33
Hi folks, I am puting the OC motor back together. Its ages since I had it apart so can't recall what tensions I used. Should write things down !

Quick question. Anyone know what torque is safe to use on these for the head ? With the diamond ring head gaskets there is quite a bit of stress on the castings
Title: Re: OHV Head Torque
Post by: Doug on 09 May 2020 at 13:52
Ian,

I never used more than I could comfortably get with a six inch long spanner.

-Doug
Title: Re: OHV Head Torque
Post by: Ian on 09 May 2020 at 21:58
Good answer Doug ! Thatís how I do most of mine. Decided to try a different method this time !
Title: Re: OHV Head Torque
Post by: cardan on 10 May 2020 at 00:42
Hi Ian,

I'd be interested to see the head-sealing-technology you're using on the OC. A v-groove in the head face and a flat on the cylinder? And for the head gasket? I assume it was originally a copper-asbestos ring?

Cheers

Leon
Title: Re: OHV Head Torque
Post by: Ian on 10 May 2020 at 01:19
Hi Leon, there is a matching groove on head and cylinder. I use a solid copper square/diamond ring which is what they originally did i think. When we first built the motor we tried flat copper gasket but it didnít work. At that time I didnít know what was correct !
Title: Re: OHV Head Torque
Post by: cardan on 10 May 2020 at 01:53
Interesting. The RA barrels I'm using have no mating groove. I expect the trick in this case is to get a gasket that is suitably compressed when the cylinder and head faces are more-or-less in contact. Experimenting...

Leon
Title: Re: OHV Head Torque
Post by: Doug on 10 May 2020 at 05:14
Leon,

The diamond section copper ring was introduced (I think) part way through OB production. Early OBs are illustrated with flat copper wrapped asbestos ring. But I have seen plenty of OB heads with the grooves for the diamond section washer. I have seen those in both copper-asbestos and solid copper. The Works bikes in the thirties reverted to ta spigot head joint.

I make my rings from square electric motor armature wire. Welded slightly small and stretched over a mandrel to make it truly circular. I don't bother to roll the square on edge to make it a diamond section, they seem to seal fine in the flat, with the diamond grove crushing the edges of the copper square wire slightly. The square section does need to be a little smaller than that of the diamond joint rings. I found 0.127" (3.22mm) square worked well, about 0.131 (3.35mm) before the insulating varnish is removed. You want a slight gap between the head and the cylinder, to ensure the joint is sitting on the copper ring. I have heard of folk also using round copper wire for joint rings, but to my mind they would be harder to file the weld joint accurately. Though once you anneal and put the crush on it, it all evens out!


(https://www.douglasmotorcycles.net/aa-files/images/doug/2020/copper-joint-rings/joint-rings-1.jpg)
Rings after welding.


(https://www.douglasmotorcycles.net/aa-files/images/doug/2020/copper-joint-rings/joint-rings-2.jpg)
Welded, joint filed, annealed, and stretched on the left. Cut and rolled rings on the right, still with insulating varnish.


(https://www.douglasmotorcycles.net/aa-files/images/doug/2020/copper-joint-rings/copper-joint-ring-section.jpg)

-Doug
Title: Re: OHV Head Torque
Post by: eddie on 10 May 2020 at 06:47
Henry tells me he makes his own copper head rings from round wire with the joint TIG welded. Having annealed the ring, he then puts a knackered barrel in his hydraulic press (with the new ring in place) - he then inverts a second barrel on top of it, and applies enough pressure to produce the diamond section (about 6 tons!). Finally, he re-anneals the ring immediately before using it.

  Regards,
                  Eddie.
Title: Re: OHV Head Torque
Post by: cardan on 10 May 2020 at 07:47
Thanks gentlemen for the interesting info. Clearly it's possible to get a good seal, even on bikes that are pushed hard - good news for my modest requirements!

Cheers

Leon
Title: Re: OHV Head Torque
Post by: Doug on 10 May 2020 at 21:46
Eddie,

I like the press idea. Did not have a hydraulic press at the time I was making joint rings, but do have a 50 ton unit now. Round copper wire would be much easier to source than the square armature wire. At the time there was a local large electric motor repair shop nearby; now they seem to have all gone out of business. I do not have a ready supply of scrap cylinders to use as a die, but it would not be too difficult to turn a set of steel pucks to do the same thing for the 500 and 600cc heads when my existing stock of rings run out.

-Doug