Cox powered jet-pump for model Sprint Boat

looking good!!!

robot797 wrote:looking good!!!

Thank Peter!  Assuming that this will work.. and in anticipation of that... I'm going to make a "spray-baffle". I think I just made a new word. Basically just an angled plate to box-off one end of the tub.. about 6 inches on the spray-side.. and about 2 inches off the floor. Maybe just a  "flap" mounted just above the pump nozzle made from thin clear plastic? Easy enough to do.. and might help keep me and the surrounding support equipment dry. Wishful thinking....

That was an easy one...

so close!!!

robot797 wrote:so close!!!

I've been waiting to run some of this Sig fuel.. unopened since 2018... (really glad I got it when I did...) The castor is for "doctoring" small fuel batches of 10-22 Powermaster fuel, for old vintage glow plain-bearing/steel-fin "stoves".. of which I have a few of.. and I love them.



The Sig "Champion" blends are for my Cox engines.. exclusively.

I recently reworked my marine flywheel/O-ring set-up for more positive "grip".. and less slip for two prospective marine engines.. as well as the flywheel on my electric starter.




In the process; I noticed excessive run-out in the drive couplings on my jet-pump-to-engine connection that absolutely needed to be addressed.. or else the vibration would wreak havoc in the drive-bushings in no time.

Talk about a PITA..  (um.. fiasco..) I'm using X2 couplings which is not ideal.... but it's the way I did it. The pump has a 3mm dia. input-shaft.. so I sourced a 3mm to 3.17mm (1/8" dia.) adaptive coupling. I had to source a 2nd coupling so as to clear the pump-housing around the input-shaft.. and also the bulkhead that the housing's flange mounts to. A 3.17mm to 3.17mm (1/8" to 1/8") coupling. The Cox .049/.051 engines accept a #5 (5-40) machine-screw which must be utilized in the set-up. I used a 1" length 5-40 cap-screw with the head cut off to achieve this.. and filed a flat for the coupling's grub-screw to bite-into. Then I made a stub-shaft from 1/8" music-wire to connect the two couplings.

The adaptive "pump-coupling" utilizes real small grub-screws which require a 1.5mm hex-key. A lesser quality hex key strips in short order. I sourced a good quality hex-key to deal with this issue. Well.. it turns out that those little grub-screws aren't of the highest quality either..   The couplings came in a package of 8.. so I replaced the pump-coupling having fresh screws and my better quality hex-key. OK... then the stub-shaft connects the engine-coupling. The engine coupling has bigger/better grub-screws and seems to be spinning "true" from the pump-side. The connection to the engine was where the run-out was happening. I needed to face the coupling up "flush" with the 5-40 hex-nut on the flywheel to alleviate the run-out. (are you getting all this?)






I'll be building a single-coupling surface-drive for my rigger project.. and will drill/tap the coupling 5-40 on the engine-side to avoid this issue. Unfortunately I have to run two couplings with this jet-pump drive.