My mufflers aren't muffling.

October 31, 2006 2:17 PM

Any way to quiet a set of motorcycle "mufflers?"

I bought a set of mufflers for my old Beemer off of eBay and it turns out that the baffles had been removed. I like the look of the mufflers, but they are too loud for my tastes. Is there any way to quiet them down just a tad? Like reintroducing baffles or something like that? I don't mind a bit of loudness from the pipes, but it's just too much as it is now. They rattled my teeth out the other day when I put them on and fired up the bike.

posted by NoMich to travel & transportation (7 comments total)

You sure they're not rusted out inside?

Seems a new baffle set will run you $274... what kind of beemer do you have? What was the can taken off of?
posted by SpecialK at 2:31 PM on October 31, 2006

Removing the baffles on a standard set of classic boxer mufflers will get up to 10% more horsepower (if you couple it with a low-restriction air filter, and heavier fuel jets). Even more if you do the double plug head modification. So it's a very common and easy to do modification, and they are the first thing to rust out in classic boxer mufflers.

But putting the main baffles back in securely if they have been forcibly punched out is tough to do, without screwing up the chrome plating. I have seen people who needed to quiet their machines for road inspections stuff a ball of coarse steel wool down the muffler, to about the point that the baffle would have been. It doesn't last, and if your fuel mixture is lean, it can even burn in the muffler, but while it is there, it does quieten things some what. Don't use fine steel wool, as that will burn immediately. At a minimum, you want #4 grade, and if you can get some of the coarser grades made for industrial applications, so much the better.

I've also seen guys do this with the fiberglass packing from inexpensive automobile "glaspack" type mufflers. The "fiberglass" in these things used to be made of asbestos and glass fiber mixed together, but today's "glasspack" mufflers don't use asbestos. The fiberglass in these things is fairly coarse, and you wouldn't want to use fine fiberglass of any kind, for obvious reasons.
posted by paulsc at 3:59 PM on October 31, 2006

You could try Predator "Silencer" pipes, which would have to be imported from the U.K.
posted by Smart Dalek at 4:04 PM on October 31, 2006

You could post your question on boxerworks.com message boards, if anyone knows the answer, they will. (PS. I drive an 83 R100)
posted by BillsR100 at 5:47 PM on October 31, 2006

I'm afraid that mentioning what kind of bike I'm riding has thrown people down the wrong path. I still have the stock /5 (1972 R75/5 to be precise) mufflers and they are in great shape. I just wanted a set of cafe style mufflers that are bit louder, but I didn't expect them to be baffless. The new mufflers are in fine shape, they're just obnoxiously loud and I'm wondering if there is a way to quiet them down a bit.
Sorry for causing the confusion.
posted by NoMich at 6:30 PM on October 31, 2006

Some aftermarket mufflers for R75/5 are 38mm megaphones, that had an optional disc stack down the main tubes, that let you put in one or more oversized star washers, sandwiched between nuts on a threaded rod that was inserted into the muffler, from the header end, when assembling the exhaust system. The number and configuration of the discs in the stack created a variable resistance to the straight through action of the megaphones, and could divert substantial portions of the exhaust flow into the outer sections of the megaphone, where it is turned back by a peripheral baffle to cancel the standing waves in the main megaphone straight through path (that's actually also how the stock mufflers work, when the main baffle near the header end is in place, and hasn't be drilled, but the stock mufflers aren't megaphones, and don't have the tuned effect on horsepower curves proper cafe megaphones will have). So, you could see if the maker of your megaphones offer a disc stack kit. But frankly, the steel wool or glass fibre on a coat hanger does pretty much the same thing.

One other thing to check is that your megaphones are designed to be used with crossover style header pipes, or not. Many of the big volume classic megaphones of Rennsport style do not use the crossover pipe, and if you use them with crossover headers, you do not get the full megaphone matching action to atmosphere, because the megaphones don't see the sharp individual gas pulses from the short header pipes they are cut to work best with.
posted by paulsc at 8:39 PM on October 31, 2006

"baffless"? I meant baffleless. heh
paulsc: I'll look into your fiberglass suggestion. Thanks.
posted by NoMich at 7:23 AM on November 1, 2006