BMW K bikes (Bricks)

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1Back to top Go down   K75 Muffler Life Expectancy Empty K75 Muffler Life Expectancy Wed May 25, 2022 3:08 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
For the past couple years my K75RT(which has 100,000 miles) has been annoying me with the volume of the exhaust.  Even with good earplugs I am finding it to be too damn loud, especially around town at low speeds where there is no wind noise to drown it out, and even the wind noise doesn't totally cover the exhaust note at highway speeds anymore.

I have tightened up the exhaust connections and replaced the copper gaskets to no avail, and even went so far as to replace the original muffler with a lower mileage(~61,000 miles) unit.  But, alas, there is still a lot of exhaust noise coming out the hole in end of the muffler. 

My question, is there a life expectancy for a brick muffler after which it's ability to tame the exhaust noise decreases allowing the sound level to increase?  Has anyone ever dissected one to see if the internal baffles are burnt away over time?  Is it worth $700+ to install a new one?  I can't believe it was this noisy when it was new.  Has anyone installed a new muffler and achieved a reduction in sound level?

Also, looking at the parts lists at MaxBMW I see that there is a muffler for the K75 that has a catalytic converter noted in it's description.  How do I know if that is the one I might need?


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

2Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Wed May 25, 2022 5:27 pm

MartinW

MartinW
Life time member
Life time member
Gryph I've got 180.000 K's up on mine and it's still quite.  It would be interesting to find what's inside them and whether they are repackable.
Regards Martin.


__________________________________________________
K75s Hybrid
    

3Back to top Go down   K75 Muffler Life Expectancy Empty Muffler Wed May 25, 2022 5:46 pm

daveyson

daveyson
Life time member
Life time member
Dunno about the insides of mufflers but I'll guess converters were required by law sometime during k75 manufacturing. Maybe compare it's production date against your brick, if it's stamped somewhere.

I'm thinking the exhaust is another example of the brick being even better quality than cars, how many cars use stainless? My k75 lived on the coast most of its life before I got it and it's fine. A neighbour of mine with a similar vintage Japanese cruiser with a rusted out exhaust can't even get a replacement, new or second hand.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

4Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Wed May 25, 2022 7:37 pm

MartinW

MartinW
Life time member
Life time member
Some mufflers relied on fibreglass packing, I don't believe BM went down that track. It probably relied on metal baffles and perforations. It may be that over time one of the baffles or perforated tubes has come adrift causing less muffling. With the muffler removed can you detect rattling when shaking the muffler? Some of the café modifiers  have shortened the 75 muffler and could probably shine a light on their construction.
Regards Martin.


__________________________________________________
K75s Hybrid
    

5Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Thu May 26, 2022 12:09 am

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Most U.S. auto exhaust systems are stainless these days.  Corroded exhaust allows air leaks that mess up the emission control.  I've had exhaust systems on autos go over 15 years and 350,000 miles.  I've never had the noise increase on a car like my K75RT.

As far as packing, I don't think OEM's use it to quiet the exhaust.  To many warranty issues with that approach.  Packing rarely lasts more than a year or so. 

I suspect that the interior of these units consists of baffles, perforated tubes and two or more chambers.  What I am wondering is how long it takes for the exhaust gases to burn through the baffles and enlarge the perforations in the interior. 

All I know is that my bike wasn't as loud as it is now when it left the dealer.  It is noticeably louder than my 16 valve K100RS that only has 44,000 miles.  Since I have a spare muffler that has the same noise level I will probably have to cut it up to see what is going on.  I have to get this fixed, I am not enjoying my time in the saddle on this bike anymore.  I suppose I could just drop the $768 on a new muffler, but what if it doesn't fix the problem?


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

6Back to top Go down   K75 Muffler Life Expectancy Empty Muffler Thu May 26, 2022 2:21 am

daveyson

daveyson
Life time member
Life time member
I don't spose any support bracket are broken, like some on mine, but would also make it louder at those spots, but might cause burning the gizzards out there.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

7Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Thu May 26, 2022 9:02 am

Point-Seven-five

Point-Seven-five
Life time member
Life time member
No external damage to either muffler.  Also, the gasket is in excellent condition and I have tightened and replaced all the copper O-rings.  The noise is all coming out the end.


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

8Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Thu May 26, 2022 11:52 am

Laitch

Laitch
Life time member
Life time member
Point-Seven-five wrote:Has anyone ever dissected one to see if the internal baffles are burnt away over time?  Is it worth $700+ to install a new one?  
This customizer posted some images as he modified the oem exhaust during his work.


__________________________________________________
1995 K75 81,000 miles
K75 Muffler Life Expectancy Usa-lo10
    

9Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Thu May 26, 2022 8:09 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Thats' what I expected the internals to look like.  I'm thinking that the perforations are burned out and not putting enough back pressure on the exhaust.


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

10Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Thu May 26, 2022 8:38 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Can anyone say how to tell if my bike can use a catalytic muffler, the one with the part number 1 464 505?   There is one in Germany, brand new for about $200 shipped.  It doesn't seem to have ports for a lambda sensor and I don't think any K75's came with the catalytic Motronic controls.  If I use it would the engine need retuning?  The MaxBMW parts list shows no special part numbers for engine control components for a catalytic muffler or cop bike.

MaxBMW makes reference to an RP model associated with the catalytic muffler.  Was this used on cop bikes?  Real OEM lists four different part numbers for mufflers for my VIN.  Confusing!


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

11Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Thu May 26, 2022 8:41 pm

Rick G

Rick G
admin
admin
AFAIK none had Cats and none would have had O2 sensors as they all ran L-Jetronic.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 2004 K1200GT 1998 K1100 LT, 1986 K75 GS.
    

12Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Thu May 26, 2022 11:03 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
That's right, but how to explain the part number for a catalytic muffler, and a Reference I found that said the '95 K75 was the first motorcycle to have a catalytic converter.

https://www.bmw-tech.org/wiki/BMW_K75


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

13Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Fri May 27, 2022 8:18 pm

MartinW

MartinW
Life time member
Life time member
Gryph a members of our group of K Kronies lust after Staintune mufflers to get a lustier note. It may be possible to swap your noisier OEM muffler for a quieter one. Maybe as encouragement to do a swap post what sounds your muffler is producing. I only occasionally lust after more better note, mainly happy with the stealth approach. 
Regards Martin.


__________________________________________________
K75s Hybrid
    

14Back to top Go down   K75 Muffler Life Expectancy Empty Muffler Fri May 27, 2022 9:51 pm

daveyson

daveyson
Life time member
Life time member
I'd say the reference about the first catalytic converter refers to the K, not the '95 k75, cause the K1 had it earlier. 

I'll guess it's a brick with an early primitive cat without a closed loop control. 

I'm trying to remember if your K75 is one of the many with a backfire issue on overrun, I'm thinking it is. If it is, maybe that's blown or melted a hole in the cat, especially if the muffler has the later part number. Then an earlier muffler would be better, or reducing the number of holes in the cat version. The cat version probably has more holes in the tube.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

15Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Sat May 28, 2022 1:24 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Daveyson, my mufflers are not the catalytic version, the part number ends in 291.  The catalytic muffler I referred to was posted on eBay by a German seller.  It's brand new and with shipping is under $200, so it could be a nice deal if it works. 

My bike has not had the backfire problem, just the occasional burbling when I don't close the throttle completely when engine braking.

I think that the next step will be to check sound levels with the db meter on my phone.  I need to do some research on the test procedure which I think involves drive-by acceleration in 3rd gear at some speed at a distance of 30 meters or some such. 

Where is TWB?  I'm sure he could shed some light on the subject.


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

16Back to top Go down   K75 Muffler Life Expectancy Empty Replace the muffler - No cat... Sun Jun 05, 2022 11:17 am

dbier

dbier
active member
active member
With all that's been posted it seems pretty clear that your muffler needs to be replaced. Maybe you can find a less expensive after-market muffler or a used one from a bike that has been scrapped/modified. I'm scratching my head at why you would want to add a catalytic convertor on a bile that didn't come with one. I believe in keeping it simple - or you'll probably just be giving yourself new problems since the engine wasn't designed/tuned for a cat.



Last edited by dbier on Sun Jun 05, 2022 11:17 am; edited 1 time in total (Reason for editing : typo)

    

17Back to top Go down   K75 Muffler Life Expectancy Empty Re: K75 Muffler Life Expectancy Thu Jun 09, 2022 11:13 am

JohnnyMac

JohnnyMac
New member
New member
I have a good used one kor sale if you are interested. Johnnymac

    

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