KA100 rebuild times

I did a search on this topic but the responses were old an all over the board.

In typical club racing level about how long roughly for a top end on the motor and how long for a bottom end rebuild? How many bottom end rebuilds before the cases need replacing?

Just trying to get an idea on this motor as it is new to me having only ran the KT100 in karts.

There are a few topics in the forums on the subject of the KA and this topic has been hashed about. Generally, I think most are doing top end between seasons (12-16 hours), however, they can probably go further. I had mine done at 12 hours and it honestly could have gone longer but it was the end of the season. I believe the thinking is bottom end every other top end.

As for the case, I don’t think that subject has come up. I think these motors have been around for 4-5 years in the US, I would be surprised if that has been required at this point.

Compared to the KT100 these motors are very reliable, durable, and more powerful. Unlike the KT my experience has shown that if you are too lean it just doesn’t seem to run well whereas the yamaha would run good but overheat or worse.

Run 16:1 mix, even though the manual says 20:1


Thanks Robert! And I wondered about premix ratio…

Robert is right on. I sent in one of my motors at the end of last season for a top end, and it had about 15 hours on it, but probably could have been a few more hours. As Robert said, it was the end of the season and would give me a fresh motor to run our regional series with, and move my other motor to the club and testing motor. The end of the year I will probably send the one in and rotate their usage.

For the premix, since we run SKUSA sanctioned events, we run 1 Liter of oil (ELF) to 5 gallons of VP MS98L. Yeah, metric to SAE ratio, at least the oil has 10 markings on the side that makes it easy to mix per gallon. It’s roughly 19:1.


Does SKUSA require that mix ratio? I know they spec fuel and Elf oil. I asked the question to IAME east and they stated stick with 16:1 even though the manual states 20:1.

Per SKUSA Rules

Oil mixture: 1L of Elf-HTX 909 with 5G of VP MS98 (6.76oz per gallon)

Yes, as Matthew stated, 1L of Elf to 5 gallons of VP MS98L is spec from SKUSA. I’ve always ran my mixture at 20:1 (1qt per 5 gallons) or 18.9:1 (SKUSA ratio), but that is top of the line synthetic racing oils.

18 posts were merged into an existing topic: Castor, castor/syn blend, or synthetic

Disregard that deleted post. I can’t read apparently. :joy:

My brain literally only processed half of what I read and quoted. :man_facepalming:

I guess I’ll buck the trend in this thread, but in exposure to 3 major engine shops for the KA I’ve never seen one of them recommend over 10 hours on a top end for a senior KA motor. General consensus is 8-10 hours for a top end and 20-25 on a bottom end.

I don’t have exposure to junior motors so they may be able to go longer. Also if your engine is stock and not blueprinted and/or you stick to lower RPM ranges similar to the IAME guidance that would likely allow for longer rebuild intervals.

I’ve never heard of replacing the cases after a certain number of bottom ends and would only think that’s be necessary if they were somehow damaged.


I think that is another key to rebuild times, typical RPM range that the motor is ran. Higher RPM will require an earlier rebuild, and lower will last longer.

However, I hate to say it, but builders make their money by doing rebuilds, so they will want them to be rebuilt sooner.

One experience I have with extending the life of an IAME motor is with a Mini Swift, while I know it’s not a KA, it is an air-cooled IAME. We sent it in for a rebuild with 20 hours on the top end, and over 40 hours on the bottom end. When I talked to the builder regarding the condition, he said it was in great shape and didn’t look like it had that many hours on it. That motor was still setting track records at our local track the week before we sent it in for rebuild. Basically, proper oil mixture and the good oil will help extend the life of a motor.

This is about what we are seeing on regional and national level engines. I know of many engines that have gone much longer though. If peak performance isn’t your main concern, you can definitely get away with much longer intervals before rebuild. I know a few guys who got the engines in back in 2017 and pounded almost 50 hours on them to durability test them and there were no failures. Sure, small loss of performance after that much running, but no catastrophic failures.

I’ll add to this data point here. Chris and I have 3 KA’s from 3 “National” builders (comet / Woltjer / BBS). All recommend somewhere between 8-12 hours if you are competitive and run at the front. All recollect every 3rd-Ish top end to bottom end ratio.

We have BOTH had premature failures in the 8-10 hour range, we have also BOTH won races with motes with around 12 hours on them.

Personally I feel like 12 hours is about that happy spot on the top ends, but you can certainly go longer if you are just interested in racing and not in the mix for wins.

Any of these recommendations are just that. The thing starts to feel flat find 10 hours just send it for service.

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On the KT100 we would start seeing hairline fractures on the cases at the main bearing pockets around the 4-5th bottom rebuild. I wondered if the KA100 was the same. Given a KA100 is 4-5 times the money of a KT100 I could see individuals running the cases longer to save on buy a complete new motor.

I’d also add that reliability is important for their reputation too.

It’s interesting to see the difference in experiences here with longevity. Makes we wish we had a better way of measuring wear/load than simply time. I like fuel a little more as a measure, but even then that doesn’t quite tell the full story of what the engine has endured.

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While the retail price appears higher than a KT100 in reality when you factor in a clutch, header and pipe and the work required to make a KT competitive the KA is about the same money if not less. Also, and I am sure this will change in time, the KA holds value well.