There is no extention on mine. There is a special fitting that comes with the muffler that screws into the head. It traps a flange plate the mates with the muffler body. There is a red silicon Oring the goes on the adaptor and it seals the joint when the two screws are tight. It sounds like either they sent you the wrong muffler, or you are missing a part. If you can, post a photo of what you have and I can tell if it is right or not. The only other 4 stroke pits I have fits my O.S 1.20, but it uses a different arnagement at the head.

Actually, take a look at the YS 91 muffler. http://www3.towerhobbies.com/cgi-bin...?&I=LXFH03&P=7 The difference between the ony for the O.S/mag/TT 91 is that the flange shown on the photo at 3:00 has two holes vs one. The black fitting with the red Oring is shown.

Don

I've looked again and it's the same as yours. The only thing is that I think I can get it to fit without hitting the engine mount if I turn the right side of the mujffler towards the front. The muffler is not perpundicilur to the engine mount. Does that sound right? Would it be a bad idea to shave a little of the engine mount so that the right side of the muffler moves back a little?
Thanks

Chopper, can you send a photo?? What engine mounts are you using. I just took a closer look at mine, and the can of the muffler is tight to the engine mount. I'm using the stock mounts from a 4*60 kit. I think a set of Dubro Antivibe mounts would give you a bit better clearance. I'm not sure about my setup now, the heat from the muffler can may melt the side of the engine mount. GIRrrrrr.

Don

Mine looks just like Campgems' setup. What looks like an 'extension' is really just the exhaust port on the muffler. It is totally fine to swing the muffler forward a few degrees which would result in some downward clearance. The muffler pipes not being perfectly orthogonal to the airframe is hardly noticeable, especially with the cowl on.

Thanks. I'm headed out of town today and I'll try to get some pics tonight if I don't get back to late. Thanks again.

Chopper, a thought just popped up. If you could get a spacer, that woud stand off the fitting that screws into the head, that would probably give you enough extra to clear your motor mount. A flat washer may work, but don't short change yourself on threads into the head, they will strip out kind of easy. Also, the capture plate, the one that screws onto the muffler, needs to be able to turn slightly for alignment. I at first though of a nut off your old manifold, but I'm not sure that would leave enough threads. You may want to check it out though.

Don

Tower has a "late April" tag on one of their Slimline mufflers:
http://www3.towerhobbies.com/cgi-bin...?&I=LXFH04&P=7

I installed the muffler and tried to install the cowling with little success. I had to make major mods to the cowl and when it is all side and done not worth it. Had to remove way to much cowling. I'm going to order a new cowl and go back to the old way.

Depending on the model, an inverted pitts may work better. Like I said, that muffler is a lot of iron hanging under the engine and requires a big hole in the cowl to clear it.

Don

I think I want to use an inverted pitts on my Saito 100 in my Thunderbolt, the stock muffler would completely hang out the side of the cowl. The slimline looks like it is less than 2 inches where it goes into the exhaust port on the head, so it should stay inside the cowl, right?