[carlo]

I did a bit of clean up on the frames for my two Enfield twins, and decided to take pictures to show the difference between an Interceptor frame, and one set up for a 500 "Meteor Minor" engine.

Not trying to rain on any parades, but the fact that this was done in Redditch suggests that it's something that should be addressed for this type of conversion.

Here's a picture showing part of the frame backbone. Interceptor in the foreground with the lug for the head steady plates made of 1/8 or 5/32 inch steel. (to clarify; the plates are 5/32", the lug is cast iron)



Here's a closeup of the lug. Note that it's a fairly substatial casting, not just a piece of heavy gauge pipe welded to the frame. The 700cc frames undoubtedly also have these, since the cylinder heads on 700cc engines have the drilled holes for the plates to bolt to, while the 500 engine just has undrilled bosses inboard of the rocker boxes.



The other area that should be considered is at the swingarm mounting plates. This may only apply when using an Interceptor engine.

Here's the swingarm mounting plates for the Interceptor  and the 500 frame. Note the extra holes. The small one near the swingarm bushing hole is for some "cheesehead" screws that prevent the swingarm nuts from backing out.  Hitchcock's addresses this in the older bikes by selling nylon locking swingarm nuts.
The other hole is for the large aluminum piece that's bolted to the back of the trasnmission using extended length transmission  mounting studs.




Here's the rear mount used on Interceptors.



This, plus the head steady would really triangulate the frame, and give it much greater fore-aft stability than frames without  these  items. Even just using the head steady has to help in that area, and I don't know why the 500 lacks the head steady. I don't think the rod type head steady used on a lot of old style bikes would be as solid as these plates. (shoulda got a picture of those too!)
When you look at the two sets of engine  mounting plates used on these bikes, you can't help but think that's not much considering that the engine case is supposed to serve as part of the frame. It would be like bolting a couple of steel bars across the opening. There's no triangulation to prevent fore-aft flexing of the steering head without at least one of these extra mounting points.
(just noticed, I used one of the head steady  plates to prop up that aluminum piece, it's just peeking out  at the lower left)
(and in case anyone failed to notice, there's a scrollbar at the bottom of the forum  window, my pictures are way bigger than the pre-set width of window)


Anyhow, as my kids like to say....

"just sayin'"

[ScooterBob]

Carlo - That's QUITE an education for ME ...... Outstanding! Thanks so much for that! 

[bullethead63]

Thanks,Carlo...if I DO install this 700 Meteor mill in my Bullet frame,I will certainly use the head-steady plates,and probably beef up the frame in a few other places,as well...I'm going to look at a 1973 Triumph Tiger tomorrow,and if I get it,the Bullet frame will have to take a back seat!

[ERC]

They used the head steady plates 1960 up. The rod 1959 back.  ERC

[carlo]

They used the head steady plates 1960 up. The rod 1959 back.  ERC

Thanks for the update. I've got three other frames, one Interceptor and two of unknown model/year that I haven't had a look at yet.
My 500 Twin engined Tomahawk has no provision on the cylinder heads for even mounting a head steady. I'm thinking I should drill and tap holes for one when  I have it apart to rebuild the bottom end. Then I need to create a lug to attach to the frame. Not sure if those are brazed on or welded, but once I've got the paint stripped from the interceptor, I should be able to figure that out.

[Don]

It is also advisable to tie the heads together by inserting a steel plate, drilled to fit, over the 4 studs that bolt the heads to the head steady plates. I used 16th inch stainless plate. Carefully drill the 4 holes just large enough to be a tight fit over the studs, the head steady plates then go on top of this plate and the whole setup adds to the strength up at the top of the engine.
Don

[carlo]

Good idea. The idea of separate heads and cylinders added considerable strain to the crankcase. It's also the reason for oil leaks where the oilway to  the left cylinder head  feed passes through the joint between the case halves on the later model twins.
My Interceptor showed clear signs of "fretting" in the area between the cylinders when I took it apart 25 years ago to rebuild the bottom end.  (which rebuild is still solid 25 years later!)

I've heard that someone in France is building new "monoblock" cylinders for Interceptors, that would solve the problem for good.

[Don]

The siamese cylinder blocks are available from Alan Hitchcock in England for only 485. pounds. Shipping extra, of course.
Don

Good idea. The idea of separate heads and cylinders added considerable strain to the crankcase.

I've heard that someone in France is building new "monoblock" cylinders for Interceptors, that would solve the problem for good.