Deadeye

I'm trying to find a reason for the failure on my Slimline Pitts muffler.

wjvail

My Feedback: (3)

Where did it fail?... and how?

Bill

Kmot

My Feedback: (24)

I don't have a scientific answer, but it gets darned hot! IIRC, a few times I have pointed my laser temp gun at the exhaust coming out of a Saito and it is in excess of 300°F.

w8ye

My Feedback: (16)

It depends on how fast the engine is running and the mixture as well as how much air is flowing over the pipe but I would think that they can get on up to at least 450F

They get hot enough to turn castor oil black

Castor oil boils at 595F

RCPAUL

My Feedback: (1)

I think the exhaust gases for a 4-stroke are a lot lower than a 2-stroke.

Paul

goirish

Muy Caliente sp?

Deadeye

It broke out from vibration, but Slimline is refusing to admit it. They are claiming the black ceramic coat I got on it weakened their 'aluminum brazing'. The ceramic coat was put on at 500 degrees, and I tried to point out that 4 stroke exhaust gets that hot to no avail. This is kind of a continuation of [link=http://www.rcuniverse.com/forum/m_8204864/anchors_8204864/mpage_1/key_slimline/anchor/tm.htm#8204864]this thread.[/link] They claimed back them that they would stand behind it, but after a few months, they made me order a new one yesterday...no replacement. The thing is, it didn't fail at a brazed joint, but right under the mount.

samtech

They refused to warrenty one of mine as well. Mine actully shattered and the two "out" pipes fell off. Slimline didn't return any of my e-mails or phone calls. I will never give them another cent, they don't stand behind their products.

Cherokee Flyer

Find a welder that will do AL and have them fix it; that is what I have had to do with all mine.
L.

XJet

Been there, done that.

The problem is that those "brazed" mufflers have the joins contaminated with that nasty hi-zinc welding material.

As soon as you throw a TIG torch on it the zinc boils and contaminates the tungsten.

Even if you grind it right back it's still a pig of a job.

I can see why they use brazing instead of true welding (it's cheap and even an idiot can produce a job that looks reasonably good) but I think it's pushing the limits of this low-melting-point stuff for a 4-stroke exhaust.

4-stroke engines seem to have a hotter exhaust than 2-stroke engines, probably because there's more complete combustion and there's no cooling from the inclusion of some intake charge (unburnt fuel) as you get with a 2-stroke.

Most of the cheap brazed mufflers that come with these Chinese gas engines also seem to fail pretty quickly once exposed to the heat and vibration produced by a bit of regular use.

It looks as if the brazed area develops cracks from vibration because the material is too thin and the modulus of elasticity and coefficient of thermal expansion of the aluminum is drastically different to that of the brazing material. This causes metal fatigue just beside the braze-line eventually creating cracks and ultimately, total failure.

rcdude7

My Feedback: (264)

Paul, I think you have that backwards there.

Two stroke exhaust is contaminated with some of the intake charge making it cooler.

Ram Jet

Yep.

Bill

Deadeye

Well, I got my replacement muffler today, minus the original one I paid for and paid to send back to them so they could deny any responsibility. When I called asking about it, they said they 'threw it away'. I said I would've liked to try to fix it, seeing as how I paid for two mufflers now, but I am SOL. I also inquired about side support, and they again said it is not needed on this muffler (of course, I will fashion something to support it). I also enquired about the ceramic coat (applied at 500 F), and they said 500 DEGREES IS TOO HOT FOR THESE MUFFLERS!! This is straight from the Slimline factory. I guess we are all really pushing it with our exhaust temps! And what about the brazing method? How hot does that get? I smell a big old load of crap! Please tell me if I am wrong here.

I love Saito engines, but I can't find anybody else that makes pitts mufflers for them. Do any of you guys have another source other than Slimline? I really don't want to throw my money away with any more.

dakotanut

If it is running lean then it will be hot. Rich and exhaust temps will be lower but not much. I can't see that brazing coming off at that temp. It takes a lot more heat than that to braze.

exeter_acres

My Feedback: (2)

Have you tried here?

http://www.jtecrc.com/pittsstylemufflers.htm

If not listed... give them a call

XJet

Actually, many of the low-temp aluminum brazing alloys do lose a *lot* of strength at temps as low as 500deg F.

But, often just as important is the fact that many of these brazing alloys have a very high percentage of zinc.

When heated, zinc expands at a 50% faster rate than zinc so every time the muffler heats and cools, enormous sheer-stresses are created along the braze-line where the two metals meet.

After a number of heating/cooling cycles, the aluminum around that area will begin to crystalize and fracture due to the metal fatigue that results.

This is why I'm *not* a fan of brazing mufflers. TIG welding is the most long-lived way to do the job but it takes longer, requires more expensive equipment and a skilled operator to achieve a good job.

XJet

I meant to say that zinc expands at a 50% faster rate than aluminum

BTerry

My Feedback: (8)

XJet is right as usual.

The other thing to remember when your engine is running the exhaust may reach a relatively hot temperature but the actual base metal temperature will be significantly lower, expecially if you have sufficient cooling air.

When the ceramic coating is applied they bake the muffler in an oven. The base metal temperature will be around 500 degrees F for over about an hour, followed by slowly cooling to ambient temp. This erases any heat treating originally in the base metal. Normally this isn't as much of a problem when using a thicker steel in a motorcycle or auto application, but with the very thin wall aluminum used in our mufflers any changes to the temper can greatly affect the overall toughness of the metal structure itself.