I have recently purchased a shifter kart roller and a KZ10C engine package to start racing in my local autocross KM class. The engine I bought was claimed to be freshly rebuilt and from what I have seen so far everything checks out. I have been scouring the internet for as much knowledge as I can about these motors so I hopefully don’t have any problems. I have found some good resources like the KZ cost of ownership thread on this forum and the PowerRepublic rebuild series, but nothing as comprehensive as I would like. Currently, I have the cylinder off and I plan on inspecting the cylinder, ring gap, and squish. I have a few questions going forward:
If one of you more experienced guys were to get a claimed “freshly rebuilt” engine, what would you check on it before you run it?
Are there any resources for knowing the recommended ring gap, squish, torque specs, nominal cylinder bore, etc.? Are these generally applicable to all modern KZs or are the model-specific ie. KZ10C?
Best way to get comfortable with operating and maintaining these engines? Currently concerned about missing or forgetting one thing that leads to failure.
Should I run the same oil and fuel that the previous owner ran or any recommendations for those? Also recommendations for mix ratios?
Recommendations for gearbox oil?
I could probably come up with a lot more questions, but these are some of my bigger ones. I am excited to learn how to work on these engines and I understand that some of the learning process is just running them and learning from the mistakes. Hopefully, with the knowledge gained from this thread, I can prevent some unnecessary failures on my engine. If I can get a good grasp on these I think it could be cool to make some sort of comprehensive guide / complete beginners guide to these engines to help newcomers. Thank you for reading and thanks in advance for the help.
1)Believe NOTHING they told you about the engine. Unless it comes from a reputable shop or person you know and trust, assume worst case scenario and do a full rebuild. Look at it this way: you pay upfront and amortize the cost over a long time, gaining reliability and peace of mind as you are 100% sure you are resetting the clock and control it from there on. Alternative is to bring it to a good shop, an experienced eye can spot some subtle clues and figure it out but even then there are things you see only when you take it apart
2) Anything after the 10B is essentially running the same setup so you can stick with the info in that thread
3)Nothing to worry about. Put water in the cooling system (suggest distilled with a racing additive). If in super cold weather (below freezing), then drain it at the end of the day. Mix oil in the fuel (and drain at the end of the day), oil in the gearbox, don’t go overly lean with jetting (watch spark plug), keep the chain lubed, make sure clutch has some play (at rest, the clutch pushrod should spin freely=no pressure to the pack). That’s pretty much all you need to know. Maintenance-wise, stay on top of the intervals (that’s why #1 above is important). Driving-wise, try not to engine-brake or downshift like a madman. They are fairly resistant to over-revving if you make a mistake here and there, if you make it a habit it will shorten the engine lifespan
4)I don’t think you mentioned the fuel/oil. 4% is the ratio mandated by racing rules, I know for a fact you can go much lower than that, but run 4% and you’ll be safe happy. Leaded racing fuel (MS98L, Sunoco Supreme et or better) is very healthy for the engine…less for your own health, but it’s my go-to. ELF HTX 976 or 909)
5)Maxxima gearbox oil or motul
I would ask the seller who completed the last rebuild, as well as what was replaced (as specific as possible, but could just be “top end” or “top and bottom end”. It should be obvious when inspecting the piston whether it is new or not. Assessing the condition of rod and needle bearings is a little bit more vague unless you’re disassembling. If piston is new, you could assume the rest needs a break-in period and do so for 10 minutes on track as opposed to just 5. All depend on the info you get from the seller and how much you trust it.
Italian Motors has THIS DOCUMENT that gives a good starting point for most of your questions. They also outline some torque specs on the site HERE.
@Andy_DiGiusto has some good info on operation and maintenance in his other thread. TL:DR- jet conservatively, and document the time on the engine. These engines are generally pretty good if you’re on top of regular maintenance.
What Andy said about fuel and oil. I raced a series that mandated 5.3% oil mix (with Elf oil) and the engine always looked pristine when taken apart.
If you’re doing autocross you may want to look into an electric water pump so you can idle longer without overheating. Kart rules require axle driven water pumps, which work fine but are no good if the axle isn’t spinning. You’ll probably want to use a jetting app to help you get getting close each day.
The tm is a good engine it will serve you well the above info is all good. The kz10c has a 22 mm lower end bearing that holds up well. One thing not mentioned is when learning to drive do not downshift an use the engine as a brake it hurts the bottom end. If you keep the revs under 14000 it will last forever. Welcome to the most fun you can have.
- If one of you more experienced guys were to get a claimed “freshly rebuilt” engine, what would you check on it before you run it?
Take the cylinder off and have a look for discolouration. Not much can be looked at after that. It’s a gamble from a private seller.
- Are there any resources for knowing the recommended ring gap, squish, torque specs, nominal cylinder bore, etc.? Are these generally applicable to all modern KZs or are the model-specific ie. KZ10C?
Goodlook finding anything, I set my ring gap to .4 on a TMR1 on a 53.93. I was recommended to try anywhere from .3 to .4. But more recommendations for .4, hence what I use.
As for the rest I don’t know. I let my engine builder work on the bottom end.
- Best way to get comfortable with operating and maintaining these engines? Currently concerned about missing or forgetting one thing that leads to failure.
There actual easy enough if you play it safe on jetting. Keep it under 600c on your egt and you should be reliable enough in terms of seizing.
If you know any local teams that run kz , it may be worth paying someone to help you for a day and go through everything with them.
- Should I run the same oil and fuel that the previous owner ran or any recommendations for those? Also recommendations for mix ratios?
I was told by ex british kz champ to run 20:1, its what I have been running so far and no issues.
AFR recommended 25:1 on a social media post I seen, I have not tried this ratio yet.
- Recommendations for gearbox oil?
Thank you for the suggestion! This has just popped onto my radar of things to consider. In your experience has anyone made the axle-driven one work in autocross without concerns of overheating their motor? I am pushing to have my kart setup by the first event in early March and if I can safely operate without the electric one I will probably upgrade to it later.
Any experience/knowledge around running VP C12 instead of MS98L? My engine was ran with MS98L by the previous owner. I was planning on sticking with MS98L but my local race shop does not carry it but does carry VP C12.
You can make it work, but you’ll have to warm it up on a stand while you wait in line for your turn or at minimum a block under the rear so the rear wheels can spin. Definitely want it warm before you make a run.