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Hi All,
New to this forum and it is very impressive. Hoping for some help on an exhaust problem. I bought my 1975 KZ900 Z1b new in 1975. Wonderful bike with 26,000 miles now. A very conservative rider, I replaced the original tires three years ago. They had lots of cracks in the sidewalls. But now there is a muffler problem. I am on my third set of orignal 4 into 4 mufflers. The two on the right side keep rusting through until they separate at the rear mounting bolt. The left two are never any problem. I have one more brand new factory OEM set that I saved from 1977. They have become expensive so I am really hoping to learn if there is anything I can do to stop the corrosion on the right side before I replace them. Any thoughts or suggestions will be truly appreciated.

does bike get ridden often?might be condensation in pipes thats not getting dryed out;) ive never had a z1 with stock exhuast but thats been my personal experiance with exhuast in general;)

Does the bike sit for extended periods in an unheated/high humidity environment?

Seen this before on stock Z1 pipes.

oh yeah,almost forgot! welcome to z-jungle and we need lots of pictures those pictures from pts barmitzfa(SPELL CHECK! )back in 1954 are getting boring,we need bike pictures!

No winter riding. The bike is stored in a dry garage that has been heated for the past 15 years. Prior to that it was in an unheated, sometimes humid garage. The odd thing is that the left two pipes have zero corrosion but the right two rust completely through at the middle and end of the mufflers. Could it be jetting, poor carb adjustment or timing? The exhaust pipes are not blue or brown.

Sorry about the lack of photos. I can post one in a few days. It's a nice bike. 100% all original.

RandallS1 wrote:

No winter riding. The bike is stored in a dry garage that has been heated for the past 15 years. Prior to that it was in an unheated, sometimes humid garage. The odd thing is that the left two pipes have zero corrosion but the right two rust completely through at the middle and end of the mufflers. Could it be jetting, poor carb adjustment or timing? The exhaust pipes are not blue or brown.

Been thinking about this while squashing bugs in other forums...

Running various notions and ideas around - moisture traps, electrolytic rust prevention (sacrificial anode-type and capacitive coupling), and the spot welding process on the muffler seams.

One oddball idea that popped into my head regarding why the right side only is problematic - and this may sound far fetched - but where are the battery vent/drain tubes routed? In the stock battery box, the vent is located on the right side of the box, and I've seen the overflow tubes routed a number of ways.

It's possible - if unlikely - that small quantities of acid find their way on to the pipes via the overflow and congregate around the mount pivots. Just a guess, but it's the only idea that comes to mind regarding an environmental difference between the left and right side of the bike.

As part of the year-end ritual, especially since those pipes have become so bloody expensive, might be worth taking them off, washing and drying them down, coating them with wax and standing them in a corner...

Thank you Wireman and Peterosaur for your ideas and help. Never thought about the battery vent. In the past, the right side mufflers have shown streaks of discoloration on the chrome as if something corrosive ran down over them. The battery vent tube does extend all the way down past the kickstand but not sure if air currents could be causing problems. The corrosion does appear to start on the inside and work it's way through to the outer skin. It always appears in two locations. First at the muffler tips as rusted through holes and then near the center mounting bolt but somewhat towards the rear of the bike. Eventually they corrode all the way through, and about one foot or so breaks off. Tried welding them back on. Worked for a little while. The left side is always perfect.

Got me wondering about the battery acid thing. Never thought about that. I will try installing a longer vent tube and routing it further back.

Is there any possibility it might be heat corrosion even though the exhaust tubes are not brown or blue?

Thanks again for your help. It is very much appreciated.

do you store it on its kickstand, or centrestand? If the kickstand, is it possible that the moisture in the left side pipes drains out, but the right side stays in and keeps acting to rust the cans out?

Hi Pyxen,
Thanks for the reply. The bike is almost always stored on the kickstand. Even in the winter. The right side mufflers are higher than the left ones when it is on the kickstand but now I am wondering if it might be possible for water to accumulate in them with no way to drain out. Maybe this problem has more than one cause. Thanks for the help.

RandallS1 wrote:

Thank you Wireman and Peterosaur for your ideas and help.

No problem.

Never thought about the battery vent. In the past, the right side mufflers have shown streaks of discoloration on the chrome as if something corrosive ran down over them.

There's a clue. It's worth remembering here that chrome is a POROUS, electrolytic metal.

...The corrosion does appear to start on the inside and work it's way through to the outer skin. It always appears in two locations. First at the muffler tips as rusted through holes and then near the center mounting bolt but somewhat towards the rear of the bike.

There's a number of things going on here, and it's no mystery why that appears to be so.

Strangely enough, for an outfit that operates steel mills, Kaw motorcycles has never been known for the quality of theirs. It's worth a thought that those mufflers showed up at the mill on a scrap barge. There's something over 2000 recipes for specialty steels, and I'd bet that the mix they picked was one of the cheaper ones.

Ditto for their plating.

The steel in the pipes is the most reactive metal in the structure, and especially since it is subjected to the repetitive thermal shock and exposure to exhaust gases, my bet is that acid is getting through the chrome/nickle plating, oxygen binds to the steel, then it's off to the rust races - hence the initial discoloration.

Is there any possibility it might be heat corrosion even though the exhaust tubes are not brown or blue?

That's certain to be *part* of the problem - but not the sole cause. If that were the case - that one side was running that much different than the other - there'd be other evidence - either the pipes would dis-color, or the motor'd be running like a *Wireman Special* - so wheezy, whiny and asthmatic that the problem would be obvious...

RandallS1 wrote:

Hi Pyxen,
Thanks for the reply. The bike is almost always stored on the kickstand. Even in the winter. The right side mufflers are higher than the left ones when it is on the kickstand but now I am wondering if it might be possible for water to accumulate in them with no way to drain out. Maybe this problem has more than one cause. Thanks for the help.

Moisture-trapping is certainly part of the problem - the complex curves, seams and mount pivots on those stock pipes is a veritable Club Med for condensation.

Those stock pipes are somewhat famous for turning into little piles of oxides right before the owner's eyes - they're complex, big and not made of the best stuff. Spot welding processes are also notorius for what they do to corrosion resistence.

The ends of the pipe going are no mystery; they're an open inlet to air, moisture, whatever. One weak spot in the end of the pipe, and off we go. That's common to many other bike exhausts than Zs alone.

But there's something else going on here - otherwise there's be at least some balance to the effects side to side.

So far, that "discoloration" seems to be the smoking clue.