Engine Block Placement

[Keseimron]

Hello everyone, I have just got to building the motor mount section for a custom-designed rocket, and a rather subtle problem hit me. When placing the engine block into the MMT, should it be placed right where the total length of the motor ends? I am talking specifically about the G80-7T, which is 124mm long. Should the engine block be placed (start) exactly 124mm from the end of the tube where the retainer is placed? This question got to me, because of the shape of the motor itself - on both ends is a nozzle, so the diameter is reduced on both ends of the motor, thus if the block is placed exactly 124mm from the end of the tube where the retainer is placed, the motor will have some free space to slide. Is that tolerable as long as the motor doesn't burn inside the MMT? I don't have my hands on the motor right now, that´s why I'm reaching out to you guys for your thoughts on this.

Sorry for the stupid questions, this is my first scratch build.
Thanks a lot!

 

[rharshberger]

Best place for a motor/engine block is in the spare parts bin for other uses, put a thrust ring on the motor and leave out the motor block, that way you have max flexiblity if you want to fly longer motors. At one end is the nozzle (end with thrust ring to prevent going all the way inside motor tube), the other end is the charge well that holds the black powder ejection charge.

 

[Rex R]

A G80 has an engine "block/thrust ring" molded into the case, all you have to worry about is the motor ejecting.

 

[Keseimron]

Ah okay, but won't the thrust ring collide with the retainer?
The design currently encompasses the Estes 29mm retainer. If this one doesn't work well, is there a different one I could turn to?

 

[rharshberger]

Ah okay, but won't the thrust ring collide with the retainer?
The design currently encompasses the Estes 29mm retainer. If this one doesn't work well, is there a different one I could turn to?

It should be fine with the Estes retainer, the thrust ring on the motor it held between the retainer cap and the retainer body. The retainer cap/ring will screw on until its tight preventing either forward or backward movement of the motor case.

 

[Keseimron]

Okay, thank you so much

 

[jimzcatz]

we don't use blocks in anything other than Estes motor rockets.

 

[MALBAR 70]

we don't use blocks in anything other than Estes motor rockets.

...and with the 18mm retainers I'll leave them out sometimes too.