Roddie tears-down his recent bench-run engine

Here's a different (bare) crankcase that shows the snap-on style reed-retaining cap.. and how far it's able to move forward in the event that it becomes detached. Exaggerated yes.. but could certainly bear on the crank-pin..

getback wrote:Hey roddie , the pin and piston skirt are showing some heat from running hot the bluing is proof. What fuel where you using ? I think in a boat where it will bee moving will help with that and not running wide open sitting .  

Hey Eric, I was using very old Sig "Champion 25" which probably doesn't have nearly the nitro that it did when fresh.

Here's a close-up of the piston and case..

From the look of the piston it was getting close to seizing up , the fuel is good enough to run it so i would say the heat is mainly the problem with a lot of speed lol I bet the reset will bee pretty hard to do . ?

Yes that "heat sink" works only if there is airflow through its fins..the mass of aluminum in it will heat up together with the cylinder, and contrary to its name it cannot simply absorb or sink the heat transfered from the engine unless it re-transfers it to the ultimate heat sink, which is ambient air..and heat transfer is minimal if there is no intense airflow around the fins.

Interesting experiment Roddie… Some high rpm for sure…. Agree some airflow is needed to help remove the heat….Also a little bit of a rich setting helps cooling…. Are you just wanting to see what the no load max rpm is?

rdw777 wrote:Interesting experiment Roddie… Some high rpm for sure…. Agree some airflow is needed to help remove the heat….Also a little bit of a rich setting helps cooling…. Are you just wanting to see what the no load max rpm is?

Hi Robert, I'm glad you joined the thread. The other guys think I broke my engine... (just kidding..) To answer your question; "Yes"... because there's the chance that a prospective marine engine app. could be subject to a no-load scenario if the vessel flips-over on the water. Is there a minimum weight/mass # for a drive-line; that would safeguard against engine damage under such a condition? Did Dumas, Sterling and others design their solid-metal marine flywheels with a specific mass to protect the engine from "over-revving"... or to aid in loading the engine with enough momentum to stay running within a specific power-band? I'm not asking you.. but just wondering for myself. There isn't a lot of info. on 1/2A glow-powered marine drives; whether submerged or surface type.

I'll reiterate two points; one being the Cox "Sea Bee"... which did not utilize either a heat-sink or water cooling for it's conventional submerged marine drive.



The Sea Bee's engine does have a buggy-type flywheel.. and a tab-actuated exhaust-throttle. Maybe that combo will prevent engine over-speed. Not likely that the Sea Bee would "flip-over" under normal circumstances either.

Again; when I removed the four case-screws from my bench-run engine; I expected the backplate to simply separate from the case.. as it usually does. It didn't... The retainer-cap and reed were stuck in the case.



I'm convinced that this is what abruptly stopped the engine.. and not overheating. Unfortunately; I don't have any "before" images of the internals of this 2nd-hand engine. The 5cc tank-bowl was so clean inside... I just swapped it out for a horseshoe carb.. and went with it. I could/should have... checked the piston-rod's ball-socket joint. It needs to be reset now....... if it didn't before.

To add/answer to your question; this was also a test of my velocity-stack mod. that was applied to the OEM choke-tube's throat. RPM #'s have been confirmed @ 22K+ on VERY OLD (might as well be FAI) glow-fuel.. which equates to zero-nitro.

Peter (robot 797) mentioned drilling-through a Cox heat-sink to install an aluminum tube to pass water through. That would be easy enough to try..

As I mentioned; there's probably zero nitro remaining in the glow-fuel that I'm using. Let's assume that's a fact. Could that be contributing to higher temperature runs? Nitromethane tends to "cool" the heat of combustion.. in my understanding. Should I be using fresh/spec. fuel?

I'm going to reset the piston's ball & socket joint to spec. and try running a different horseshoe carb that the choke-tube will fit. Some horseshoe carbs have an air-intake orifice that won't accept it. I'd like to think that the red (Killer Bee spec.) backplate will match-up.. but the three that I have are all mounted on airplanes.. and I hate to take an engine off an airplane.. just to check a part's compatibility.

It will be interesting to run this old translucent/white Delrin carb... with a copper-star reed and circlip.







All other variables unchanged..

roddie wrote:Peter (robot 797) mentioned drilling-through a Cox heat-sink to install an aluminum tube to pass water through. That would be easy enough to try..  

As I mentioned; there's probably zero nitro remaining in the glow-fuel that I'm using. Let's assume that's a fact. Could that be contributing to higher temperature runs? Nitromethane tends to "cool" the heat of combustion.. in my understanding. Should I be using fresh/spec. fuel?

I'm going to reset the piston's ball & socket joint to spec. and try running a different horseshoe carb that the choke-tube will fit. Some horseshoe carbs have an air-intake orifice that won't accept it. I'd like to think that the red (Killer Bee spec.) backplate will match-up.. but the three that I have are all mounted on airplanes.. and I hate to take an engine off an airplane.. just to check a part's compatibility.

It will be interesting to run this old translucent/white Delrin carb... with a copper-star reed and circlip.







All other variables unchanged..

Roddie my friend I have never had this and plate problem but maybe it was luck I used a motor with the choke tube in a way mine had the throttle control but the back plate is the same I would like to make you a suggestion you could maybe change for a new one but during installation you could use red lock tite. after that removing the ring would be difficult but for the best. you would avoid this problem.. Mabe ???... But I think the one you have with the snap ring will be perfect and for maximum performance you could widen the air inlet but no more than that of a black widow or even a kiler bee but may be more difficult to control the idle well wit a large air inlet but for a boat maybe it would be good for a car I find it more difficult to properly adjust the gas controls with the tube restriction Or even the cox tee dee .05 carburetor during idling the engine tries to flod it self wit fuel And the throttle response is slow so finding the perfect point where the engine has maximum performance is trickier and requires tricks to counter this effect. I have seen joint systems such as using an exhaust restriction ring with the choke tube carb air restrictor But better suited for an airplane It is for those different reason that I now like to use a wasp carb or system involving the exhaust gases but use a pipe to which the control valve is attached I like following the evolution of your project, I can't wait to see the results of the turbine in the water container Ha, that's right, what Peter (797 robot) mentioned: drilling a Cox heatsink to install an aluminum tube to pass the water. It's something that works. I did this to cool an ESC that wasn't really designed for boats and so far no problem with this solution. I never thought of doing this with a beetle engine but the odds are that doing it would have a beneficial effect.

Nitromethane's vapor pressure is quite low, meaning it doesn't evaporate easily. Methanol would evaporate much faster. Unless you left this can of fuel open, assume it's pretty good.

Was the engine broken in? break in runs with little cooling would be tough on the piston and cylinder. I would not try to lean it for max RPM without a load. Engines that can operate this way typically have some method of limiting RPM.

Do not put normal threadlocker on plastic! Most plastics will crumble. There are threadlockers for plastic which are essentially CA glue. The reed retainer fit must be a bit loose on the backplate. I have no experience with these. It should be expected that as the reed clearance increases at some point it just can't seat in time or correctly.

davidll1984 wrote:
Roddie my friend I have never had this and plate problem but maybe it was luck I used a motor with the choke tube in a way mine had the throttle control but the back plate is the same I would like to make you a suggestion you could maybe change for a new one but during installation you could use red lock tite. after that removing the ring would be difficult but for the best. you would avoid this problem.. Mabe ???... But I think the one you have with the snap ring will be perfect and for maximum performance you could widen the air inlet but no more than that of a black widow or even a kiler bee but may be more difficult to control the idle well wit a large air inlet but for a boat maybe it would be good for a car I find it more difficult to properly adjust the gas controls with the tube restriction Or even the cox tee dee .05 carburetor during idling the engine tries to flod it self wit fuel And the throttle response is slow so finding the perfect point where the engine has maximum performance is trickier and requires tricks to counter this effect. I have seen joint systems such as using an exhaust restriction ring with the choke tube carb air restrictor But better suited for an airplane It is for those different reason that I now like to use a wasp carb or system involving the exhaust gases but use a pipe to which the control valve is attached I like following the evolution of your project, I can't wait to see the results of the turbine in the water container Ha, that's right, what Peter (797 robot) mentioned: drilling a Cox heatsink to install an aluminum tube to pass the water. It's something that works. I did this to cool an ESC that wasn't really designed for boats and so far no problem with this solution. I never thought of doing this with a beetle engine but the odds are that doing it would have a beneficial effect.

Hi David, It may have been "luck" (bad luck..) having the cap separate from the reed-housing. I'll try the "circlip" style carb next. I'll also run the jet-pump drive when I get the chance. I've modified some of my 2mm to 2mm (shaft) couplings to accept a 5-40 threaded stub-shaft for the engine-side for use on my out-rigger.



I may have to use one of these on the jet-pump.. if there's any vibration in the current set-up.

Water-cooling the Cox heatsink is also on my "to-do" list.. but first things first..

gkamysz wrote:Nitromethane's vapor pressure is quite low, meaning it doesn't evaporate easily. Methanol would evaporate much faster. Unless you left this can of fuel open, assume it's pretty good.

Was the engine broken in? break in runs with little cooling would be tough on the piston and cylinder. I would not try to lean it for max RPM without a load. Engines that can operate this way typically have some method of limiting RPM.

Do not put normal threadlocker on plastic! Most plastics will crumble. There are threadlockers for plastic which are essentially CA glue. The reed retainer fit must be a bit loose on the backplate. I have no experience with these. It should be expected that as the reed clearance increases at some point it just can't seat in time or correctly.

Hi Greg, Thanks for your interest. You taught me something about glow fuel today. I'm glad that I haven't resorted to using old fuel for cleaning-purposes as I've read that some people do. I've always been super conscious about keeping my fuel tightly capped.. and stored in a dark/dry environment. I even keep a cap on my primer-bulb's hose.

I don't know much about the engine's history.. but I suspect that it was run before.. because of the the way it was configured when I received it. A later-model Babe Bee; it had a 5cc tank-bowl with a single fuel-fill nipple zamac backplate; re-oriented 90 degrees. It was also missing its needle and mesh-screen for the air-intake.





There was some evidence of having been fueled/ran at least once.. but who knows beyond that. It was very clean inside when I swapped-in the horseshoe carb.



Here's a vid of my first bench-run of that engine..



I didn't get too crazy with it; ran it rich and peaked it a few short times.

As I mentioned; I noted a good degree of "slop" in the ball & socket joint when I tore it down following the abrupt-stop where I thought I'd seized it. I've got it in a little bag with a note to reset it.

I can and maybe should mount an aero-prop the next time I bench-run it. I will run the choke-tube with velocity stack though.

I guess one needs to test-run a marine engine on the boat and in the water.. to provide the necessary resistance for the engine. I sourced some 22mm 2-blade nylon "surface-drive" propellers which I plan on running on a straight 2mm wire-drive. There wasn't any pitch-spec. provided with the props.. but there's both; left and right-hand versions. Those are planned for my outrigger project. I'm not sure how much drive-mass will be required to run one.

Roddie wrote:I can and maybe should mount an aero-prop the next time I bench-run it.

I think that would be a good way to collect the data you’re after Roddie….If you are shooting to find max rpm you could clip (and re-balance) the prop a little at a time until there’s no return…. You’ll get cooling that way too…. Running one for all she’s worth may show tripping points of main components as I’m sure you’re aware …. Regardless, Your unusual experiment is interesting