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Old 08-15-2012, 09:59 PM   #1
slartidbartfast OP
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Heart transplant: DR-Z125 into Hyosung RX125

INTRO:

A year or so ago, I acquired a fairly clean, complete Hyosung RX125 rolling chassis (with paperwork) needing little except an engine. The intention was and still is to have a bike for my 16yo daughter to ride with me on some of the gravel back roads around here. An enduro is preferred but it must remain street-legal as these are public roads.

The project seemed as if it would be easy because of the parts bike I picked up at the same time. This turned out to be near worthless as it had a rusted up engine and even the head needs a lot of work, including cam repair to get it back. I can't justify the time or funds for such work on this bike so it sat, waiting.

Plan B came along a couple of weeks ago in the form of a Kawasaki KLX 125 parts bike (Same as DR 125) with a (supposedly) good engine. As the Hyosung bike is allegedly derived from a Suzuki design, I hoped I would be able to simply bolt the Kawa engine into the Hyosung frame.

I will document the process of making it all work here and am hoping someone with prior knowledge may be able to provide some pointers or helpful suggestions.
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
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slartidbartfast screwed with this post 08-27-2012 at 09:39 PM
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Old 08-15-2012, 10:08 PM   #2
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First steps: The heart transplant

The good news is that the Kawasaki engine bolts into the frame (sort of) - The critical rear mounts anyway. The Hyosung exhaust also lines up with no issues.


Difficulties I am encountering so far include:
The front engine mounts and head steady do not line up correctly. The front can probably be taken care of with some new mounting plates. The head would be more elegant if I modify the frame slightly. All I need is a good welder and a few beers.


The gearbox sprocket looks as if it might be slightly further inboard on the Kawa engine. This might be fixable with a different gearbox sprocket as there is room on the shaft to move it over. Maybe I can live with the small offset? Who knows?


The Kawaski carb pops into a rubber manifold but the Hyosung version bolts to a plastic stub. Either will bolt to the engine but the Mounts either leave the Hyosung carb tilted to one side or the Suzuki exiting on the wrong side of the rear shock (Airbox intake on other side and exhaust uncomfortably close.) There is probably a mount from something else that will make this all work - I just have no idea what. I might be able to cut and twist the Hyosung mount but I'm not sure how to reliably glue or plastic-weld it back together. Here's the Hyosung head with carb angled to the right side of the bike:


...and here's the Kawasaki head with the carb angled to the left:


Spacing of the Hyosung footrests is much wider. This would leave the gearshift in a very awkward, almost inaccessible position. The left footpeg can be modded to bring it closer but the Kawa engine does not have the six-inch unsupported (and bent) gearshift shaft that Hyosung employed. Some more welding will be required I think to make the Kawa offset linkage work.


I have the charging and ignition systems from both bikes (actually the Kawa has no charging system, only ignition). Eventually, I would like to try grafting the engine-side electrics from the Hyosung into the Kawa engine so the bike can have lights, etc. However, I'm not sure if things like ignition timing would be so different for the four-valve Hyosung engine that it might not run properly. If it seems to be a problem, maybe I can hybrid those systems - Time will tell
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
Summer 2009 UK to Alps ride
Summer 2008 UK End-to-End ride
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Old 08-15-2012, 10:14 PM   #3
slartidbartfast OP
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Will the heart beat?

The Kawasaki lump appears to have good compression when turned over by hand but that's about all that can be learned about it. Not wanting to waste too much time or money on an unknown engine, I decided that, if I can put an exhaust and carb on it and get it to start, I can worry about routing the intake and making engine mounts later. I don't want to invest in buying parts or welding, etc., until I know the engine is good, so I'm just doing things that can be done with existing parts and resources.

The rusty chain on the RX125 parts bike had a removable link so that has gone on the Hyosaki (as it will hereinafter be known). The chain alignment looks ok for now. I also found the Hyosung gearshift, which would not work well for riding but at least allows me to have a chance of push starting the thing. Fitting the shifter also gives me an idea of how much lateral gap needs to be closed to put it comfortably within reach of toes.


It's "only" a 125 but I would like a little control over it in the event it actually starts, so I also rigged up the clutch, which required carefully transferring all the switch internals from the "good" bike to the switch housing from the Hyosung parts bike, that does not have a smashed clutch perch but had mashed, corroded switches. I just happened to have a new clutch lever on the shelf which fit perfectly.

The clutch action is light and there's very little drag. I was able switch up and down through the gears and push the bike down the driveway with the engine turning over. Initial efforts appear to show very good compression, which is encouraging.
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
Summer 2009 UK to Alps ride
Summer 2008 UK End-to-End ride

slartidbartfast screwed with this post 08-16-2012 at 07:06 PM
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Old 08-16-2012, 07:48 AM   #4
Kawidad
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Quote:
Originally Posted by slartidbartfast View Post

Difficulties I am encountering so far include:

The Kawaski carb pops into a rubber manifold but the Hyosung version bolts to a plastic stub. Either will bolt to the engine but the Mounts either leave the Hyosung carb tilted to one side or the Suzuki exiting on the wrong side of the rear shock (Airbox intake on other side and exhaust uncomfortably close.) There is probably a mount from something else that will make this all work - I just have no idea what. I might be able to cut and twist the Hyosung mount but I'm not sure how to reliably glue or plastic-weld it back together. Here's the Hyosung head with carb angled to the right side of the bike:


...and here's the Kawasaki head with the carb angled to the left:

Can't you flip the Suz/Kawq intake manifold upside down to change the side it points toward?
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Old 08-16-2012, 10:39 AM   #5
tntmo
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I was just going to say to flip the manifold, so I guess it's a consensus. Looks like the engine mounts are pretty close, the top one may just need a pair of brackets manufactured from the fame to the head.

Is the rear brake a drum unit? If so, you may be able to fab up some new spacers for the rear wheel to move it a bit to the right to line up the sprockets.

Looks like a fun project. I like making something useful out of leftover junk.
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Old 08-16-2012, 06:32 PM   #6
slartidbartfast OP
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Quote:
Originally Posted by Kawidad View Post
Can't you flip the Suz/Kawq intake manifold upside down to change the side it points toward?
I looked at this and it might work. The port on the head is not flat to the head, however, it is angled slightly to the left. Also, the manifold compensates for the slight forward lean of the cylinder so the carb would end up not far enough to the right and angled up slightly. I MIGHT be able to make it work if the stub was longer and more flexible. Might also go the the local breaker and see if there is another manifold that would work, although most of them appear to be straight. Another possibility would be to buy/make a short metal inlet stub and look for a section of curved radiator hose in the right size

Quote:
Originally Posted by tntmo View Post
I was just going to say to flip the manifold, so I guess it's a consensus. Looks like the engine mounts are pretty close, the top one may just need a pair of brackets manufactured from the fame to the head.

Is the rear brake a drum unit? If so, you may be able to fab up some new spacers for the rear wheel to move it a bit to the right to line up the sprockets.
Do you think the bottom mount would be ok with only one bolt into the frame instead of two? It is going to make that area less rigid than was intended but I don't know how much it will matter.

Rear is a drum brake. I am thinking I could space the transmission sprocket a bit further out on the output shaft, or perhaps mill down the sprocket carrier on the rear wheel. I'm not too concerned about making irreversible changes.
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
Summer 2009 UK to Alps ride
Summer 2008 UK End-to-End ride

slartidbartfast screwed with this post 08-16-2012 at 07:07 PM
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Old 08-16-2012, 07:09 PM   #7
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As I am about to embark on my annual round of brake system flushing and maintenance on the bikes in my stable, now seemed like a good time to have a look at the front brake on the Hyosaki. It had absolutely no resistance at the lever. The reason for which became apparent when I removed the cap. I have never actually seen brake fluid literally turned to dust before.
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
Summer 2009 UK to Alps ride
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Old 08-17-2012, 06:40 PM   #8
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Front brake resurrection

I dumped out the dust, rinsed everything in hot water and set about disassembly. Once I had got the slightly crusty snap ring out, the piston came out fairly easily. A couple of hours in an ultrasonic cleaner with warm water and a good splash of vinegar got everything looking much cleaner.


Somewhat surprisingly, the piston bore looked to be in good condition, as did the seals.


So, I lubed up the piston with some fresh fluid and put it all back together. The only minor problem was this thing:


It looked like it should press into the well in the bottom of the reservoir, presumably to keep dirt out but allow fluid through. It wouldn't quite fit however, and as I didn't see it on the fiche it must not be essential so I left it out.
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
Summer 2009 UK to Alps ride
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Old 08-18-2012, 07:28 AM   #9
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Quote:
Originally Posted by slartidbartfast View Post

Do you think the bottom mount would be ok with only one bolt into the frame instead of two? It is going to make that area less rigid than was intended but I don't know how much it will matter.
It should be easy enough to modify the existing mount to fit, or to make some new plates to use all the mount bolts.

I'm wondering how close the charging system will fit. I have heard these motors are copies of Japanese engines, and they look close ot the same but I'm sure a lot of things aren't bolt on. Sort of like how this motor is close to fitting in the frame.
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Old 08-18-2012, 07:55 AM   #10
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Sorry, but to my eyes judging from the photo, that master cylinder looks totally gone. I'd not run it. I'd just pick up a cheapie on FleaBay and throw that away.

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Old 08-18-2012, 08:09 AM   #11
slartidbartfast OP
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Sorry, but to my eyes judging from the photo, that master cylinder looks totally gone. I'd not run it. I'd just pick up a cheapie on FleaBay and throw that away.

You may be right. To my eyes at the time, it appeared scruffy on the outside but the critical internal bore was fine. The photo appears to show some surface marks inside that were not obvious to the naked eye. I'm a couple of days behind updating the project but the front brake seems to be working fine. Hopefully it will continue to do so - Time will tell! If I get the bike running, I will strip a lot of it back down for some cleaning and painting. May take another close look at the master cylinder then.
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
Summer 2009 UK to Alps ride
Summer 2008 UK End-to-End ride
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Old 08-18-2012, 08:14 AM   #12
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Hah hah hah

I just realized the engine says "Suzuki" on the cases. Probably was not the original KLX engine. The finished bike won't be a Hyosaki but a Hyosuki. A bit of research based on the engine number (F445-111XXX) indicates the engine is indeed DRZ/DR125, probably late 90's/early 2000's vintage.
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
Summer 2009 UK to Alps ride
Summer 2008 UK End-to-End ride

slartidbartfast screwed with this post 08-18-2012 at 10:04 AM
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Old 08-18-2012, 09:51 AM   #13
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More front brake!

I got the M/C back together and hooked it up with some fresh fluid in the reservoir but could not get the brake system to bleed. I eventually realized the bleed hole was still blocked but a little attention with a dental pick fixed that and I was able to bleed/flush the system quite easily.


The fluid that came out of the caliper was some of the nastiest I have ever seen - but at least it was liquid, not dust.


Several days later and the front brake is tight, with nothing binding and no leaks . Fingers crossed it will stay that way
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
Summer 2009 UK to Alps ride
Summer 2008 UK End-to-End ride
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Old 08-18-2012, 11:56 AM   #14
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Have you considered just getting a pod filter on it for now? You could give Robi a call with the measurments and I'm sure he could get one to fit it fairly easy.

On a side note I have a welder and a drill press, may be able to get my hands on a few bits of 1/4" plate to make you some brackets out of.
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Old 08-18-2012, 12:48 PM   #15
slartidbartfast OP
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Originally Posted by RedRaptor22 View Post
Have you considered just getting a pod filter on it for now? You could give Robi a call with the measurments and I'm sure he could get one to fit it fairly easy.

On a side note I have a welder and a drill press, may be able to get my hands on a few bits of 1/4" plate to make you some brackets out of.
I have indeed thought about a pod filter. For now, I just want to see if it will run (with open carb). Assuming positive results, I will get serious about fitting it all together properly, and finally tidying it up.

Thanks for the offer of help. 1/4" plate may be heavier than necessary but cutting, bending, drilling and, yes, possibly welding will be required.
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MSF Ridercoach IBA: 35353 95 R1100GSA, 93 GTS1000, 85 R80RT, 93 DR350/435, 99 RX125, 78 DT100
January 2010 New Zealand South Island ride
Summer 2009 UK to Alps ride
Summer 2008 UK End-to-End ride

slartidbartfast screwed with this post 08-18-2012 at 12:54 PM
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