Hi All,
I have three planes (AeroWorks Edge 540, H9 P-51 and GP Minnow). OS 91Surpass is installed on all three. On the H9 P-51, I have an alluminium mount but on the other two, I have the regular nylon mounts that came with the kit. No issues with the muffler on the H9 P-51.

On the Minnow and the Edge 540, I have been having serious muffler issues. Either the muffler comes loose or the ELBOW that connects the muffler to the cylinder completely breaks apart. This is what I have done to the muffler in case many of you have questions:

1. I sent the mufflers to Clarence Lee to have an additional brass fitting glued to the muffler and the elbow.
2. Propellor is balanced
3. On both muffler end and the cylinder end I used Locktite before I tighten them
4. The spinner runs true when the engine is running
5. None of these engines have been in a crash, in fact they are fairly brand new. I would say I have about 20 flights on each of them
6. Using the TAC meter, the engine runs about 8700 RPM

Usually it takes about two to three flights before they come loose or break apart. Yesterday I flew the Minnow and after the second flight, I lost pressure and as I started to land I noticed the muffler hanging on the fuel line. When I landed, the elbow completely broke from the cylinder end.

I must say I have been working on these issue since last season. This has been very frustrating to say the least.

Question for everyone is, have any of you had these issues? Is so what do you do to solve to the problem. I am thinking of getting the Flex Pipe. Not sure this solution would help.

Any help would be apreciated!!

Kris

I had the same problem years ago with an O S 1.20 FS. Nothing seemed to fix the problem. I finally J B welded all the fittings and never had another problem. But if you use J B Weld, you aren't ever going to be able to take the exhaust system apart. To use the J B Weld, you will have to clean all fittings extremely well. Might have to take them to a machine shop to get all the gunk off, or use a Dremel wire wheel. It's got to be very clean or the weld epoxy will not stick.

pmw

Pmw,
Thanks for the reply. I sent the muffler to Clarence Lee. He had JB Weld the a brass fitting to the muffler. But the issue with mine is Elbow actually breaks apart.

Thanks
Kris

Try supporting the muffler with a metal retaining strap. It sounds like you are getting engine vibration that's causing the elbow to crack. I finally took my muffler off and ran a straight copper pipe for the exhaust. That stopped my elbow from cracking. I never could support the muffer because the vibration kept breaking the strap. A brass or copper exhaust is much lighter than the muffler. The noise difference is not noticable and since you don't need muffler pressure to the fuel tank, it might solve the problem.

pmw

pmw,
How do you connect the Brass pipe to the exhaust? Do you thread the bass pipe? By exhaust do you mean the cylinder where the elbow connects to the engine? Also my club has a sound limit of 92db. Also, I do need to back pressure as evidence from yesterdays flight when the elbow broke with the muffler, I immediately started to loose power.

Thanks
kris

I used a thick wall copper tube and had a machine shop thread the inside of the tube to fit the male threads of my elbow. I J B welded the threads as I screwed it on. Then I tightened the elbow nut down to the copper pipe, again using J B Weld between the nut and the pipe. Let it set for a couple of days. Never had any more problem. If you need the back pressure, you can squeeze the end of the tube until the engine is where you want it. But... the elbow itself might provide enough back pressure. Mine worked fine just running the tube open. You might also try an aluminum tube from Lowe's or Home Depot. They weren't around here when I made mine.

pmw

This makes a lot of sense. I am going to thry this one out. Thank you very, very much. I will report back if I am succesful. Thanks again.

Kris

You're welcome. Good luck!

pmw

The two different mounting styles step right up as culprit.

The two aircraft with the standard nylon mounts...are the mounts installed dead even so there is no torquing of the crankcase when secured ? Is side clearance present between the mounts and crankcase? Just a thought.

This is interesting. I will check tonight when I get home. I know for sure there is enough clearance between the mounts and crankcase.

Thanks you..

Kris

Hi pmw,
Quick question...how long is your brass copper tube?

Thanks
Kris

This was true of the earlier Surpass engines, but the newer versions (The ones that have a piece of fuel tubing that runs from just forward of the hed to the intake header) DO require muffler pressure!

MinnFlyer,
Are you saying that pnw suggestion will not work? You have a point because when my muffler came off in-flight, I immediately started to loose power.

Thanks
Kris

Kris,

It is about four inches long. I determined the length to clear the cowling on my Aeronca Champ. By the way, here's another way to mount the tube to the elbow that I've used. I cut a slot in the tube about 1/2 inch long. This alowed me to slide the tube over the threads of the elbow. I then clamped around the slotted portion of the tube with a small radiator clamp to hold the tube onto the elbow. It worked, but the clamp interfered with the cowling. The threaded method was what I liked best. But, both methods worked fine.

pmw

Ksubram,  <font size="4">IF</font> your engine is the newer version with the hose that I described, you can not run without muffler pressure. But if it's the earlier version without that line, you only need to do a little tweak of the needle valve and it will run fine without pressure.

I have also had this problem with a couple of os .91s I have. I am a strong believer in safety wire, even if a motor is not known to kick off the exhaust. Also, I use the copper color gasket maker, and as a last resort.... Get the motor good and hot then try to tighten down all the fittings. This won't help your cracked elbow, but it might keep your engine from ejecting your exhaust.

MinnFlyer,
Both the engines are the ealier versions. So I would need the muffler pressure. Thanks.

Kris

pnm,
I found the copper wire from Lowe's and now calling some machine shops to see if they can do the threads for me. I am kind of excited with your idea. Will keep you posted.

Thanks
Kris

This is the tube I'm referring to. If you have this tube, you must run muffler pressure. If you do NOT have this tube, you can run a straight pipe with no muffler.

Don't take this as a negitive reply. Make sure the valves are properly adjusted and the carburator low and high speed needle's are correct. I had an older version O.S .91
that would shake like heck, till I got if adjusted.
good luck with the engine.

MinFlyer,
Yes, both my engines are just like yours. I just returned from the Machine shop to have the copper tube threaded to fit the elbow. I had also tapped a hole so that the nipple can be fitted for the back pressure.

Hope this solution works.

Thanks
Kris

pmw,
I just got the copper tube threaded. Should I cut the length of the copper tube to about 4" just like yours?

Kris

When my engine runs, the engine does not appear to shake at all. It look pretty sturdy.

Thanks
Kris

Kris,

I don't think the tube length is critical. I just used a length that would clear the cowling. All the tube is doing is directing your exhaust, so choose a length that works for your set up.

pmw

PMW,
Great! The machine shop guy did a great job. I am going to try it out tonight and will keep you posted. My only concern is the noise issue. I guess I will know tonight. I can't wait to see the results. Will keep you posted.

Kris