"First for existing built rockets I have several that have very tight MMTs. I have difficulty getting Estes BP engines in them to the point where I feel I am going to damage the rocket, any suggestions on how to deal with this? Some are 18mm some are 24mm, The rocket affected are both Semroc and Estes and or components from either company.
Second, are there better/looser MMTs I can use for engines in general that will fit all engines?"
Some replies suggested peeling layers off the engine casing.
From Solomoriah: "Estes engines are often a bit tight in Estes tubes. Quest engines (both the old German and the new Chinese) are smaller and never stick. Rockets with Centuri-sized #7 tubes work better with Estes engines, because the ID is just a hair bigger; makes flying most of my Semroc fleet easier.
Getting the engine in doesn't usually trouble me, but getting the casing out is sometimes a bit of a bear. I have a pair of pliers with curved jaws that I got as part of a gift years ago, which is darn near perfect for removing 18mm engine casings, but even so it's still tough sometimes."
I agree with you on engine fit being easier in the stronger ST-7 tubes.
Estes engines (especially the 13mm engines) bulge above the nozzle area.
I don't peel the engines, sometimes a peel can get away from you and you can take off too much.
I'll sand down the bulge a bit with sandpaper on a block.
Fred Shector gave out some great advice about engine removal -
Remove the engines right after a flight while it is still warm.
You'd think it would be easier to remove when the engine cools down but it is removed easily right after the flight.
This is especially true when an engine has been friction fitted.
All Estes motors are slightly larger at the nozzle end. You can easily insert the front end of a motor into BT-20 or ST-7 but you cannot insert the nozzle end. Go ahead, try it. The solution is very simple: Sand the first 1/4 to 3/8 inch of the inside of the motor mount tube with a tiny piece of 220 grit sandpaper over your fingertip. The rest of the motor mount tube will hold the motor perfectly aligned.
ReplyDeleteHi Lonnie,
DeleteSorry, I have to disagree on this one.
I wouldn't sand the inside of the engine mount tube, the BT-20 and BT-50 tubes are thin enough already. That might make them weaker.
If there is a turned under burr at the open end of the engine mount you could roll it back with a dowel.
Sometimes the front end of the engine can have a burr and it could make the engine hard to slide in. The burr could be sanded off and the top of the engine rounded.
The ST-7 tube has a larger inside diameter than the BT-20. Engine fit in the ST-7 is usually a little loose and tapes one wrap of tape. Not to friction fit, but to seal up the sides.