TM Top End Interchangeability

[Anthony Herpolsheimer]

I have a K9b that I recently stuck.  I haven’t pulled it apart yet, but if I do have a cracked cylinder I can’t find a new K9b jug to replace it with (for a reasonable price).  I know I can get it repaired but I’ve also heard it’ll never run quite the same.  Either way, I want to make sure I can still get parts for my engine.

With a little research I have found that the KZ10 jug will bolt on.  Obviously to get the most out of that I will need the proper pipe too.  What I can’t find any info on is if anything else should be changed.  Do I need the KZ head insert?  Reed cage?  Piston?  What about the ignition system?  Is the timing different between the 2 engines?

I see posts saying swapping jugs will work, but I haven’t been able to find anything about someone successfully  doing it and what was needed to make it work well.

I’m just a local club racer out to have fun, so I’m not worried about the potential mixed homologation issues.

2008 GP 8 Honda 125 / TM K9B
Building F125 Enduro

[Glenn L Riggs]

Have not done a kz10 but have done kz10b and c the cylinders interchange the only difference is the outer o ring is larger an not compatible. Now on those cylinder is a 4 degree piston dome  instead of  6 degree and to go with the difference the insert has been changed, doesnt mean you have to change these to run it.  These newer cylinders do seem to wake up the engine. Timing is the same for the most part. jetting also except it needs to be closer if it is rich seems to be more effected as the 9 b an c dont seem to be as fussy. If using a kz10b cylinder it has holes in the base that should be plugged so as the block doesn`t have holes when using the hose on the side, for whatever reason on the newer engine they went back to the hose on the side. Hope that helps.

[Anthony Herpolsheimer]

Glenn this does help.  When you say timing is the same for the most part, is it close enough to not have to switch to the newer ignition?

2008 GP 8 Honda 125 / TM K9B
Building F125 Enduro

[Glenn L Riggs]

As far as i know the ignition is basically the same have not tryed to watch the curve so not sure but wouldn`t be to worried about it.

[Daniel Wendel]

My wrist pin circlip decided it wanted to break in half this weekend, and damage the cylinder, VHM flat top piston and head insert on my K9b.
So I am in the same boat as Anthony, my rules also allow mixed homologation.

I am thinking about doing the KZ10c cylinder, VHM FT piston, and KZ10c pipe.

[Glenn L Riggs]

I wouldn`t worry about ignition, if the insert got damaged you can just replaced the insert. up to the kz10c the inserts are interchangeable, the c is all different. a kz10b pipe or c is fine the c seems to have a little more off the corner and the b pulls a little stronger at the end. For what ever reason have had a couple of clips break over the years have also had piston cracks so is not a bad idea to check those on occasion. Hope this helps.

[Anthony Herpolsheimer]

Glenn L Riggs wrote:

I wouldn`t worry about ignition, if the insert got damaged you can just replaced the insert. up to the kz10c the inserts are interchangeable, the c is all different.

What do you mean when you say the c is all different?  Different combustion chamber design or that the insert won’t fit into older heads?  Or am I just reading this wrong?

2008 GP 8 Honda 125 / TM K9B
Building F125 Enduro

[Glenn L Riggs]

The kz10c head is a 2 piece unit with a copper gasket sandwiched in between. Havent tryed to put an old head on a new c may work not sure. Do not see much difference between  the b or c cylinders, the c costs a couple of bucks more.

[Anthony Herpolsheimer]

Ok, makes sense.

Another question I have is about the reed cage.  I think I have heard that the new style will fit into the k9.  Can you confirm this?  Is it worth changing up to the supposed better flowing design?

Thanks again

2008 GP 8 Honda 125 / TM K9B
Building F125 Enduro

[Glenn L Riggs]

good question never tryed to switch them . I believe the c is different than the b but may work someone may have done this and can advise, you can use the shorter intakes available to make better top end

[Anthony Herpolsheimer]

Daniel Wendel wrote:

My wrist pin circlip decided it wanted to break in half this weekend, and damage the cylinder, VHM flat top piston and head insert on my K9b. So I am in the same boat as Anthony, my rules also allow mixed homologation. I am thinking about doing the KZ10c cylinder, VHM FT piston, and KZ10c pipe.

Daniel,

Can I ask why you run the flat top piston?  From my understanding changing piston design can change the dynamics on the engine in a negative way unless you also change head shape and possibly the pipe dimensions.  That’s what kept me from running the RS piston in my Honda 125.  Do you get better results with the flat top?  Seems like with a bigger combustion chamber you would have less compression so less potential power.

Now I have another dilemma.  I was just offered a fresh complete K9c with all the running gear and a spare cylinder is included. That would pretty easily give me 2 engines ready to rock.  Now I can decide if it’s worth going that rout, or upgrading my top end to the KZ10b/c to get the better power and more current parts.  Cost either way would probably be the same.

2008 GP 8 Honda 125 / TM K9B
Building F125 Enduro

[Daniel Wendel]

The flat top piston is from VHM. You would need use their head insert for the flat top piston, which brings it correct combustion chamber volume.
The flat top allows about 2% more airflow at low exhaust port openings vs the 4 degree TM “special”.
I found it made a more power compared to the K9B standard.

[Joey Guyon]

Fyi guys I did a billet VHM piston and head kit on a K9B this winter and compares to the stock cast piston an increased piston to wall clearance is recommended. Be certain to have a kart shop or nikasil specialist measure your bore and likely open it up .0005″ or more. Also likely order the smallest VHM piston to save some hone time and extend the life of your jug.

[John parker]

I cracked a cylinder on my K9C, I sent it off to Millenium with a new piston. They welded it, renicked it for $190 and worked amazing all year.

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