marcw
Senior Heliman
Location: Southern California
My Posts This: Topic Forum | Not sure what they are selling at the home improvement stores, but the material specified for the Cricket’s cross struts was .125 x .50 x 11.88 6061-T6 aluminum bar, and .375 OD x .032 wall 6060-T6 aluminum tubing for the skids. The angle pieces don’t have a specific grade of aluminum specified.
On the topic of “acceptable time period correct” engines for the Cricket, there seems to be some somewhat contradictory period literature out there.
The Cricket instruction manual only talks about .25's and .28's
The very first Cricket Customer Bulletin (Jan, 1981) does indeed list a “K&B 40 Standard” as a “tested” engine for the Cricket.
But then fast forward to Cricket Bulletin # 2, which lists all of the previously tested engines except the “K&B 40 Standard” !
By Cricket Bulletin # 4 (May, 1981), GMP was only carrying the OS .25 FSR and Super Tiger X25, with possible plans to also carry the K&B .35 soon.
Cricket Bulletin # 6 then says:
We have tested several more engines with "Cricket", and in particular, the new “K&B 0.35 ABC” engine is proving to be a real powerhouse...naturally, of course, the old faithful “OS 0.25 MAX FSR” still does an excellent job, as do many of the other 0.15-0.25 “car” engines available today. The new 0.25 British “Irvine” engine also seems to be a great performer and they also have a 0.30 in a 0.40 case. Wish it was a 0.30 in a 0.25 case!
Then, bulletin # 6 goes on to talk about the Hughes 300, which is based on the Cricket:
since the "Hughes” is heavier, don't expect it to fly well at 5,000 with a 0.25 engine. Fit it with a 0.40 and it should do fine.
So, it seems as though a .40 was not a preferred choice by GMP at least for the Cricket, but by the final comment in that first quoted paragraph from bulletin 6, I bet John would have been really happy with a modern OS .32 or .37 in a Cricket, since those engines are the same “case” size as the old OS .28’s.
Bottom line, while not "time period correct", that OS .37 you have should be considered a suitable modern replacement for the old .28 and be just fine for your Cricket. It was much more reliable running in the Viper with the enclosed fuselage and cooling fan assembly than the original .28, so I think you will be more than happy with it on your Cricket.
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And it is easier to tune down a throttle curve than wish you could push it up 
