For CTI O3400 Motors, where are the Grain Spacer O-rings Packaged?

[OverTheTop]

I am asking for a university team (USYD) I mentor about grain spacer o-rings for the O3400 motor. They have the motor parts currently, except for the fuel grains which are in a secure storage, but they can't seem to find the grain spacer o-rings in their parts.

So, questions:

1) Do the grain spacing o-rings get packaged with each grain?

2) Do the grain spacing o-rings come in the packet that contains the nozzle o-ring(s)?

3) What is the size of the o-rings please, in case they need to buy some if they don't have any.

It has been a couple of years since I have flown an O3400 and I can't remember where the o-rings were in the packaging.

Thanks in advance

 

[WILDMANRS]

They are with the grains

 

[OverTheTop]

Thanks Windman! They are looking at the grains in the packets, in the individual grain boxes currently and have been unable to locate the o-rings. I am doing this remotely with them unfortunately so I apologies for asking dumb question. I don't have the parts in front of me.

So, more questions:
Where EXACTLY are the o-rings in with the grains please? Packaged inside the plastic bag with the grain, inside the box that the grain comes in, or otherwise? Do they come in a bag all together or just one with each grain as needed?

 

[OverTheTop]

Also, do you happen to know what size they might be please?

 

[WILDMANRS]

Thanks Windman! They are looking at the grains in the packets, in the individual grain boxes currently and have been unable to locate the o-rings. I am doing this remotely with them unfortunately so I apologies for asking dumb question. I don't have the parts in front of me.

So, more questions:
Where EXACTLY are the o-rings in with the grains please? Packaged inside the plastic bag with the grain, inside the box that the grain comes in, or otherwise? Do they come in a bag all together or just one with each grain as needed?

The orings are typically in the bags with the grains,one per bag

 

[OverTheTop]

Thanks for that. Just got a call from my team who have somebody checking out their motors. The first motor they checked, of course, had zero o-rings with the grains . Checking the second motor showed all grains had o-rings attendant to the grains . So, they have three motors being held in storage currently and are checking the third of as to whether it has o-rings, or not. FYI the first two motors they checked were of different date codes. All are O3400.

Have you had any other reports of motors not having requisite o-rings provided with them?

Thanks again for your help!

 

[jimzcatz]

I could be wrong, but I believe grain spacer orings are relatively new to the hobby, say last 5 to 10 years? I don't know how old your loads are, check the included directions and see if they are called for.

 

[jsdemar]

The o-ring size is not critical. Nor is the material. Measure one and order the closest size from McMaster. (I've been using o-ring grain spacer for 20 years).

 

[Rocketjunkie]

Size 042, 3-3/8 OD, 1/16 thick. https://www.mcmaster.com/9452K131 $19.78 per pack of 100.

 

[OverTheTop]

Thanks RJ. Great info. The team had purchased three of the O3400 motors and, of course, the one they opened had the missing o-rings. The other two motors had the o-rings in with each grain. Got a good flight in the end.

 

[Steve Shannon]

Size 042, 3-3/8 OD, 1/16 thick. https://www.mcmaster.com/9452K131 $19.78 per pack of 100.

But to reiterate, as long as you get something between the grains to keep the faces from touching each other, the size of the o-ring isn’t critical. The o-rings can even be broken. You could probably get away with using weed eater line.