High Butterfly Prototype

[Matt Blast]

I have received an interesting project that I thought I would post. If anyone has seen anything that resembles these High Butterfly throttles please let me know.

The story goes that these throttles were attached to a display board. The current owner has had them for about 10 years and the prior owner bought them on the same display board and owned them for at least 20 years. That owner also bought them on the display board and owned them for an unknown period of time. Any history before that is unknown. The throttles have had moderate use as evidenced by the worn bushings and small grooves in the barrels. The throttle shafts are still in good shape and other wear areas are not that bad so they haven't been beat to death like a lot of them.

When I first looked them over I thought someone had modified a set of the 2.5 throttles, but I couldn't figure out how they would have resleeved them to 44mm on top and about 40mm on the bottom. They don't look resleeved. There are also some crude areas on the castings and even some differences from one throttle housing to the other. It soon became apparent that these are factory throttles, but what their application was in the day is unknown. They look like they were used for developmental purposes. The later throttles were improved in many ways. Were these the very first High Butterflies? Any thoughts?

Matt

[Matt Blast]

The housings had been painted black as was some of the hardware. Here are some details after they were disassemble and the paint removed.

First picture shows the housing differences compared to a production housing. The prototype housing on the left has a narrower support rib. Both are magnesium.

Second and third show the casting around the air screws. This area looks like an afterthought. The fourth picture has a production housing to compare. Thread for air screw is smaller (5mm) compared to 6mm for the production housing.

Last pictures shows the steel inserts for the top studs. Production version has no insert.

Matt

[Rick Cabell]

I would say the only answer is they were prototype. Can't talk myself into anything else.

[Jim Calzia]

WOW! Very nice Matt!! I'll print your pictures and compare them to mine

[jcge]

Matt

They look like they were modified 'post casting' for some particular purpose or trial.

The grinding and quality of finish near the air screws is very interesting - its definitely not fettling (no apparent flash/parting line in that area of a casting, based on your known unit). Looks like it has been welded and ground in that region..an xray may reveal whats going on there (welded). I agree with your suggestion that the air screws were an afterthought / 'add on'.

As you know, 2R is an early pattern revision (have you ever seen 0R, 1R, 3R or 4R ??)

John

[Matt Blast]

I agree Rick. They look like they were used for development.

Thanks Jim. The 7R is the one in the comparison (like yours).

The castings look to me like they were made in a mold and then the air holes were added on later. I agree with you John. If this was done by welding then I'm thinking that it took a good bit of work and skill to make it look this good given the magnesium. Also the diameter of the air holes are 2.9mm on one housing and about 3.7mm on the other. So it looks like they were still learning at this point. The production holes are 3.9mm. (2R and 5R)

I don't know of other castings, only the 2R and 5R. What I find interesting is the castings numbers can stay the same but the castings can be different. For example, both the RSR and the SCRS were 911 110 107.5R castings. The SCRS had an extra boss for a throttle stop at WOT and the RSR did not. Also the SCRS had the cold start holes on the sides. I believe the throttles pictured here were the early developmental version which became the production 2R for the 2.5 ST

Here are more details.

Picture 1 Production version an right has a small hole for the return spring. Prototype with no hole and repair done to broken throttle return screw boss.

Picture 2 Spring hook on both prototypes. Getting them to look the same was not important.

Picture 3 Top housing 44mm, Bottom housing 50mm (production)

Picture 4 It appears that they learned to make the throttle return boss a little thicker (right side production version).

Picture 5 Details of rear of the housings. Bushing removed on prototype, left.

I have some hardware details on the way.

Matt

[mike curnow]

Matt

My RSR units are a 5R casting, and all my measurements, and other items are the same as your production units. Early in the thread you mentioned a casting number of 7R was this an error since you also said you had only seen 2R and 5R castings?

Mike Curnow

[Matt Blast]

Yes Mike you are correct. There is no 7R. I meant to say 5R. The entire casting number is 911.110.107.5R

Matt

[Matt Blast]

The throttle shaft couplers are a barrel type similar to what was used on a Weber carburetor. They were a bit different in that they are welded around the middle to make them rigid. Initially I thought they had been replaced at some point because these are different than the production type. But if you look at the throttle shafts they have no roll pin hole to secure the production type coupler so I've concluded that these are original couplers for the throttles. You can also see the marks on the shafts left by the set screws. The down side to using these couplers is that they don't work well if there is any shaft misalignment. The two piece couplers used on the production throttles solved that problem.

Picture 1 Misc hardware. Note the crude barrel type shaft couplers. Throttle arms with peened on ball pins rather than the threaded type.

Picture 2 Original throttle shafts. Note the marks on the ends from the coupler set screws.

Picture 3 and 4 Production throttle shafts top (roll pin holes). Prototype shafts below.

Matt

[gled49]

Matt, I assume that is the finish under the black paint. It looks like a coating not unlike Dow 9. It is interesting that the coating looks consistant. My experience with new coatings like Dow 9 is that any material difference in the base metal produces a different apperance, sometimes looking blotchy or a defined line where the welding would have been. Fuchs wheels that have been welded look good when polished but when anodized the weld is visible. Very interesting throttles. Gordon