Cracked Phenolic Liner

Background: I am a high power noob. I have flown a total of 4 flights using 38mm AT "H" reloads.

Tonight I sat down to put together my first "I" motor, a I225FJ. When a got all the parts out on the table I noticed that the phenolic liner was cracked at one end.

I was not totally hosed, since I had ordered several different motors that fit the 38/480 case I figure I would just "borrow" the liner from one of them. I opened up the first one (an I154J) and discovered that liner was cracked at one end as well :bang: I opened another one (an I211W) and finally got a liner that was intact.

All of these reloads were mail ordered, and appeared to be packed well.

Is this a common problem? I haven't heard it discussed much so I am wondering if I just got unlucky?


If the liners are cracked on my new I59s tomorrow I'm gonna hurt somebody :hot:

You can use the cracked liners. I would recommend using them on the J and FJ loads as this propellant burns cooler than White Lightning. I have seen J350s with cracked liners fly successfully many times with no damage to the case. Do not use the liner if there is a gap. Do not use a cracked liner with an I59 as this is an end burner and needs all the insulation available. Make sure the grains fit easily, peel if necessary to prevent the crack from spreading open. I would put the cracked end toward the nozzle.

I flew an H250G back in July with a liner that had about a quarter inch long crack with no problems.

I placed the cracked end of the liner at the nozzle end of the motor and I had also applied a liberal amount of grease on the crack as well. Since this reload requires the use of the 29mm RMS seal disk, I could not have placed the cracked end at the forward end as the disk and O-ring would not have been able to seal properly.

Since this motor burns so fast, .9th of a second to be exact, I didn't think it would cause a problem.

When I removed the liner during cleanup, I noticed that it had cracked the entire vertical length starting at the original crack site but the casing was perfectly fine.

I had on break in parts after getting stuck. I glued it with heat tolerant epoxy sanded it and used with a J350W. It worked fine.

I have used thin CA to seal a crack, but I would e-mail AT and see if they would prefer you to replace the liner.

5x7 said:

I have used thin CA to seal a crack, but I would e-mail AT and see if they would prefer you to replace the liner.

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Just to follow up on this...

I sent an email to AT customer service on Tuesday pretty much repeating the info I gave in the first post of this thread. I got a reply from customer service the next day asking for some more information (lot numbers, who I bought them from, how were they shipped, etc.) and for my address so that they could send me new liners.

Later that morning I also got an email from Karl Baumann from AT addressing my questions about using the cracked liner, and the possibility of the grains swelling (I still don't believe that the grain I had to break out of the liner could have been installed that way). His reply is given below for everyone's benefit.

I would have to say that ATs customer service and commitment is at least as good as I've always heard it to be. :clap:

Hi Matthew,

Do not use a cracked liner, the flame front will exploit the weakness and cause a burn through of your case. You were correct in removing the Glassine outer layer to fit the propellant grains into the liner, you want them to slide freely in the liner to promote equal end burning.

The propellant grain did not swell as you suggest...the liner probably had an imperfection in the I/D. We try and cull out these liners with imperfections. As for the liners being cracked, some of them have a weak point along their linier axis and are prone to splitting when handled less than optimally.

Thanks for the support of our products,



Best Regards,

Karl Baumann
Director of Operations
RCS RMC, Inc.
Cedar City, Utah

Buckaroo said:

Do not use a cracked liner, the flame front will exploit the weakness and cause a burn through of your case. You were correct in removing the Glassine outer layer to fit the propellant grains into the liner, you want them to slide freely in the liner to promote equal end burning.

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That's pretty much the answer I expected you to receive from AT -- I know I wouldn't fly with a cracked liner.

The removal of an outer layer of paper, to get the grains to slide, is also pretty much a standard answer. FWIW, while I've seen this primarily on AT reloads, I've seen AMW grains require peeling.

-Kevin