stunthanger.com
General control line discussion => Open Forum => Topic started by: BOB ALLAN on December 16, 2015, 06:44:58 PM
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Having just added a new “big case” Johnson 36 BB to my collection, I got to reading the spec sheet which has left me wondering where exactly the BB fits in to the Johnson line-up. Put simply, it appears to be a slightly heavier (by 0.7 oz.) and slightly de-tuned Combat Special. According to the factory paperwork, the BB shares the same crankshaft and con-rod with the J-RC 36, but all three engines (BB, CS & J-RC) have identical piston & liners. The Stunt Supreme and the Combat Special share the same con-rod (which is different to the one used on the BB and J-RC) but use different cranks. The SS also sports a different piston/cylinder to the BB, CS & J-RC. With a 0.020 in. shorter stroke, the SS displaces 0.348 cu. in. against the other 3 at 0.358 cu. in. and the compression ratio on the SS is 6.5 : 1 compared to 10.8 : 1 on the other ones. In theory at least, the ball races on the BB (with less friction) should put it not that far behind the CS in power output. Would be interested to hear any user comments on the Johnson 36 BB and what it was used on. BOB
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The rear bearing on the BB is nearly impossible to find, and they don't hold up that well. That plus when you can find one, they are very expensive.
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The first BB I saw was on Carl Berryman's Big Iron. It didn't seem detuned at all. It would be interesting to see what timing the CS and BB had.
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The ones Carl and I had were exactly the same, and all the ones I did R&D work on were the same. I liked the CS better but Carl liked the BB...
I still have one brand new, never run left over from the R&D engines.. Just wish I had a new box for it but I never got them in boxes. Also have one of the small case CS with 6 bolts holding cylinder plus different venturi (sp) that were never produced.. I kept one of each new....
RW
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The first BB I saw was on Carl Berryman's Big Iron. It didn't seem detuned at all. It would be interesting to see what timing the CS and BB had.
Howard, as quoted above - the CS and the BB have identical parts numbers for the piston & liner, only the cranks are different. They also share the same size venturi insert. It's a wonder to me why Hi didn't market the BB as a "Combat Special with Ball Races" which would have given it a more de-luxe upmarket appeal. Either that or dropped the compression ratio on the BB, and with a smaller insert market it as a "warm" SS ! Mr. Wooten, do you know if any late model Johnson's left the factory with different piston metallurgy ? My BB's piston is very shiny and appears to have a different molecular structure (ie. not sintered) to my other big case engines.
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It has been so long, but if there was a change I was not made aware of it and I think Hi would have told me. That said, the later engines had a lot more problems with pistons coming apart and cracking. After Hi was bought out quality control went to pot and they were using (unconfirmed) reject parts to assemble engines.... Again, this was the rumor and I don't know if it was true.
RW
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That is one of the reasons I quit using Johnson engine was the pistons kept coming apart.
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Who was it that bought out Johnson at the end?
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Dynamic
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As I had a .36bb and used it in combat, maybe somebody would be interested in my experience. Mine didn't run very fast and was hard to start due to poor piston fit. Mike Haverly suggested that we swap engines, my Johnson for his Series '61 K&B, as he had some Foxes and Johnsons and I had another K&B Series '61. Simply having fewer bolt patterns to hassle with was the incentive.
We traded engines at a summer club meeting (at the old Flying Tigers field in Issaquah), and bolted them into our current combat planes. The K&B snapped the crank at the front bearing and the ensuing shaft-run made the crank pin work it's way out and into the backplate, sending aluminum through the piston/cylinder. I believe that was the incident where the post in the middle of the exhaust port in the cylinder went missing. I sent it off to the factory for repair under warranty. They updated it to '64 specs and improved it a lot.
Mike's new/used Johnson .36bb also "blowed up" that evening, with the piston skirt falling off. I don't believe Mike ever had it fixed, and eventually gave away the remains. We still laugh about it. y1 Steve
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That is what happened to my K&B series 62 engine. Cranks would not take the turns a combat plane would make.
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Who was it that bought out Johnson at the end?
Found this on the net -
"AMT, which stands for "Aluminum Metal Toys", was making high quality 1/25 scale plastic static models in the early 1960s. Dynamic Models Inc. was making model airplane parts and had just developed a successful line of slot car chassis components and accessories. In 1964 these two companies entered into a joint venture in which Dynamic became a subsidiary of AMT."