Hello guys,

i have a Katana 36% by Aeroworks (World Models) and powered by an Evolution 116CC twin.
Let me first say that me and my friends are not beginners, and that i pre-blanaced my prop and aluminum spinner on a Dubro high point balancer.

since i bought the first Evolution in Israel, and one of the first ever, there were no other mufflers available besides Jtec, so i ordered a set of 2 cans for 140$ + shipping.

after a few flights (i have balanced the propeller and spinner) - both cans broke at the welding joint between the neck and the mounting flange, and Jtec has agreed to immidiately send me a new set (at my shipping cost) - and i agreed (since they recognized it had a bad weld), and the owner also noted to me that i can easily re-weld the broken ones and keep them as spare, so i did.

2 flights later (after the re-weld) both cans broke around the neck (the can this time, not the weld!) (see pics) so i knew a bigger fix was in order. i had a friend who is a machinist mill me 2 thick mounting flanges from solid t^ aluminum blocks, and weld them onto the can, and also weld in 2 aluminum tubes for the bolts to go through (kinda like DA mufflers) and this seems to work good so far. see pics for the new flange we made.

after 2 more flights with the new mount, the rear can caps both broke, one flew off and the other one is cracked at the joint. Jtec knows about everything at this point.
in the meanwhile, i got the new mufflers they sent me (thanks guys) but they have 2" cans rather then 2.5" cans (they say theyre fine for the Evo116cc though theyre smaller), and im not so sure about using these, since i feel they will break in their mounting like set #1 (look at the pics of them when they were new, the mouting flange is weak).

anyway, i made a new design on my own and Jtec told me its around 200$ for a set, and if i send the #2 set back (new) at my cost, add 70$ + pay for the shipping back to me, they could make me a set like that.

The reason im not using the #2 set is that i know theyre going to break just like set #1 since the design is very weak around the mounting joints, causing it to break (see pics)

I ask you guys is it fair that in order to get a decent set of 200$ worth i need to pay:
A. shipping to me of set #1 (35$).
B. shipping to me of set #2 (35$).
C. shipping back to them of set #2 (15$).
D. shipping to me of set #3 (35$).

Thats 120$ just in shipping charges, not to mention the weeks down time.

How do you guys feel about this ? who needs to do what ? Please help me decide what to do here.

i know it is down time but i would keep sending them back till they make a set that works

But would you pay 120$ for shipping charges ? []

Yes I would because you have little choice. Just like you, I also don't live in the USA and suffer the same problems when I need to return something. The guys in the USA get it easy but that good luck to them.

If you decided to move to Mars should all the vendors pay your shipping charges??

20 years ago it was difficult to find vendors in the USA that were interested in shipping internationally. Now everyone does and those of us outside the USA benefit. The shipping on warranty items is just the price we pay.

In any case I would be having a real close look at your engine and set-up for any other sign of vibration. The failures you have are unusual and make me wonder if there is a vibration issue.

Where would you suggest to look ?

im going to try starting the motor without the spinner to see if it makes any difference.

Is your engine hard mounted on the firewall? Is the firewall and engine box sturdy enough?
If your engine is soft mounted, that's why you're cracking mufflers.

The engine is just bolted to the firewall, no soft mounts of any kind.

the engine box seems strong, its a stock Katana (AW) but i added fiberglass on the whole box and aluminum 90 degree corners on the front, so it should be pretty damn strong.

BTW, mufflers were initially installed reverse by mistake (it was late night hehe) but i flipped them afterwards.

The three sided "box" is not stiff enough. You need to make it four sided. Just make a "top" for the box and only cut out for the carb clearance.

I would bet that if you ran the engine with the cowl off you would see a lot of motion of the engine at certain RPMs.