[BarryPJ]

Hi guys...I'm amassing various spares to begin the restoration of my (not used for 25 years) KE175D2. I have managed to find and buy (from Germany) a NOS original Kawasaki exhaust, after searching for years....very pleased as the old one I have has been welded and patched so many times.

I have noticed a fairly large (approx 4mm) hole in the bottom of the exhaust (see photo) - looking at forums etc it seems that this may be a drain hole to remove condensation etc. - but a) it seems quite big to me and b) surely this significantly decreases the back pressure needed for a two stroke to function optimally c) has someone drilled it for another purpose.

The exhaust is stamped with part number KH1K047.

Does anyone know for sure? Is this a 'factory' hole? Don't know whether to keep as is or seal it up......

Thanks
Baz

 

[WFO-KZ]

I don't think it is an OEM hole and I don't think it is a drain. Condensation would run to the lowest point and that hole is not anywhere near the lowest point when the exhaust is installed. It may have been drilled in an attempt to decarbonize.

If you want to retain it, you could weld a nut over the hole and fit a short bolt to plug the hole.

I would probably just weld a patch over the hole. Incredible find by the way. I would love to get my hands on a bike like that. They are so rare nowadays.

 

[BarryPJ]

Thanks very much - and a great diagram. Interestingly though, the hole is pretty much at the lowest point (exhaust upside down in picture)..and as the exhaust is unused (old stock but never used), not sure it can be related to decarbonisation. One thought I did have is did someone drill a hole to attach a wire to hang it up at some point in its 40+ year life on a shelf...surely no-one could be that dumb...!!

 

[WFO-KZ]

I don't have the benefit of seeing your bike, but from this picture (see below), it looks like any condensation would collect down near your exhaust port. And I don't see that condensation in the muffler could make its way make from the back to the front to the drain hole. But Like I said, I cannot see the entire bike. You are in the best position to judge. But I will say this, I cannot recall ever seeing an exhaust with an open hole like yours. I think it would make an odd noise and spew oil and hot gasses down onto the engine.

In regards to being that dumb, yes there are people who should never pick up a wrench. Maybe they thought that reducing back pressure was a good thing.

 

[9094]

I suspect it's a drain hole for condensation. I wouldn't plug it, If you did, Bet it wouldn't take long then to rust out the bottom of the muffler.

fwiw I have another bike with obvious factory holes in the bottom of the muffler system. It was stored for several months in Florida's humidity, When I went to get it ready to ride, took it off the lift I store it on, put it on the side stand and green anti-freeze colored stuff ran out of those holes. A bit of panic at that point... Then determined it was condensation that was growing things and would have normally ran out if on the side stand.

 

[WFO-KZ]

I dug through some of the archives on this site and it appears that some exhausts do indeed have drain holes as 9094 has said.

It seems like a weird location though because condensation should form on the coldest part of the system which is the back end muffler.

I don't recall seeing any such holes when I worked at a kawi dealership in the 70's but perhaps they rec'd too many complaints about rust in exhaust pipes and started adding drains.

To the OP, can you let us know what it looks and sounds like when you start the bike? I am curious to know if you can hear exhaust escaping from the hole. In the archives some suggest the hole actually allows air to enter which can lower the emissions. Not sure about that one.

 

[1981GPZ550]

It was not unusual back in the day for on off road Japanese motorcycle to have a drain hole. My 72 Suzuki TS125 had one. When present any I have seen were always a thick wall threaded bung welded into the pipe. Also I have never seen one on an expansion chamber, only muffled spark arrestor equipped exhaust. I am not saying one cannot drain condensation at this point but I do not believe that was their primary purpose. Another theory is draining after a failed water crossing but that also does not hold up as most machines would have flooded the engine before the exhaust tip was submerged. As far ass condensation, like all exhaust systems including modern cars the condensation would be quickly blown and cooked out. Back in that era I remember reading a how to article describing how to clean your plugged spark arrestor in the camp fire and I think that is related to the true purpose of the drain. Two strokes of that era, at least in the Northeast where I worked were almost universally set up and tuned incorrectly. Add to that some owners insistence on using the cheapest oil available and it was very common to see what was at that time referred to mung running down the head pipes and out the exhaust tip and down the bottom of the mufflers. Oil injection pumps were almost always set to deliver too much oil. I remember a low mileage GT380 that would not produce more than about 15hp, exhaust terminally plugged. I believe the plug was there to drain the unburned goo before it could foul the baffles and spark arrestor.

 

[WFO-KZ]

Yes, I remember threaded bungs on various bikes back in the day. Even my 2011 has them, but as stated, they are mounted back on the muffler section, not near the engine. According to my manual, they are there for decarbonization.
Perhaps that is the true reason for hole in the KE175? My manual says to remove all the bungs, run the bike while you beat the on the muffler with a soft face hammer.

But a hole in the expansion chamber you would think would mess with the flow and back pressure, but I am not an expert, although I did study the theory and formulas for expansion chamber design ages ago. They did not address drilling of holes for any reason.

 

[1981GPZ550]

The drains I am talking about were at the low point of the exhaust. Look at a photo of any early TS125, the plug was at the bottom just before the exhaust starts to rise. Roughly in line with the swing arm pivot. I agree with you assessment regarding expansion chambers, that was why I specifically stated I have never seen a drain in an expansion chamber. Basic motorcycles are sold to please and be maintained by the masses, by the time someone buys an expansion chamber I believe the engineers had every right to expect a higher level of knowledge and tuning expertise from the operator. An expansion chamber equipped motorcycle is highly likely to spend a very high percentage of its time in the upper rev range mitigating much of the loading up and production of mung. I have worked extensively with Suzuki, Kawasaki and Yamaha 2 stroke motorcycles. Again the vast majority of poor running and catastrophic failures were due to misunderstanding 2 stroke theory and tuning. I once subscribed to a national magazine, there was the typical tech. write in question section. I read this for perhaps one to two years, the magazine expert was clearly that, an expert. However at one point a reader wrote in asking about a problem with an H2 triple, the answer was purely 4stroke. So many highly skilled mechanics simply do not understand 2 strokes. So yes a hole in an expansion chamber would likely interfere with both back pressure and the reflected pressure waves necessary to prevent loss of pressure out of the exhaust port.

 

[1981GPZ550]

Just an interesting point of reference. The 71,72,73 Suzuki TS125 was rated at 13hp. Removing the drain plug, and we all tried it, made no discernable difference. Suzuki offered a hop up kit, this contained a new cylinder, piston, head, carb, airbox and expansion chamber, no drain. HP went from 13 to 20. Of course at this level of tune the engine was far less tolerant of mishandling.

 

[BarryPJ]

Thanks for all your comments guys...I appreciate them. It will be a while before I get the bike running - as it has stood for 25 years - so a lot to do before then. Once rebuilt etc I think I'll just have to run it first with the hole in the exhaust - and see what happens - if it spits out loads of gas/unburnt fuel etc then I'll seal the hole up (perhaps with a removeable bung of some sort...if it doesn't spew out crap then I'll just keep it with the hole. My gut feel is that it will need sealing - it just seems too big a hole not to spew out exhaust gases etc - also wouldn't be long before the hole starts to rust out I reckon.....

 

[1981GPZ550]

If you are not going to weld it closed or weld in a bung be sure the edges of the hole are very smooth. Any small imperfections will cause stress risers and with the natural vibration of the pipe be likely to crack. I have seen pipes crack on both motorcycles and snowmobiles, once the crack starts it advances quickly. If you are not familiar with stress risers I suspect you can quickly find info on the web. It's hard to tell from the photo but that does not look like any oem hole I have ever seen.

 

[BarryPJ]

Thanks - that's a good point re stress risers (and not something I was previously aware of) - on balance then I think I'll get it sealed up - I reckon getting the hole brazed up or a small plate welded would look cleaner than a bung etc. Thanks again.