Dom - We run the outer most part of the track in a counterclockwise fashion. The hair pin is also the high point of the track.
Thanks, the hairpin seems like a challenge.
The manual says every 5 to 10 hours to open the engine head and clean. I basically take contact cleaner and spray the chamber and wipe it down. I also remove some of the carbon build up on the top of the piston. I’ve noticed an increase in performance after doing this.
The pistons really can go at least 10 to 15 easily without damaging the cylinder. If you are running 8oz to a gallon, the 15 hours is very easy to hit. The experience with this is not with a KA, but with a Mini Swift. Granted it’s 60cc versus 100cc, but both air cooled and turning same RPM. We had a Mini with over 20 hours on a piston before being replaced, and we were told it looked very good and no abnormal wear. It was also setting track records with that many hours on it.
Depending on your engine builder and how they build the tolerances into the piston and cylinder, it could take a few hours just to free up and spin easier. However, that is the other reason for taking the head off, is to check the piston and make sure it’s not too loose in the cylinder and that the locating pin (area on the piston that keeps the ring from turning) is still good.
The Vortex VLR seems to be the the most supported package in the Northeast.
When changing a piston the cylinder should be honed. Keeps the cylinder true and refreshes the cross hatching for better oil retention.
Bill, Help me understand. Your earlier post you mentioned the piston and in turn the cylinder will wear unevenly over time, which I assume is indicating the piston and cylinder become out of round by some measurement. However, doesn’t a hone tool follow the path of the cylinder? So yes, a hone will give the metal surface a new texture but will it also correct for wear?
An actual honing machine with proper mandrels and stones will get it round, true, and square to the deck. It’s not easy to do any of that with a drill hone, even a nice one. And, yes, it’s true if you go too long between top ends, your cylinder will get out of round. When that happens, you need to take off more material when you hone (in the process of evening things out), which in turn reduces the lifespan of your cylinder. If you do top ends every 10 hours or so, you barely need to remove any material when you hone.
Mostly true, but “square to the deck”, how does any hone do that? Sunnen hones are great, but the fixed stone handhelds are good too. That’s all I ever used on my McCullough’s. You may be thinking of the spring-loaded glaze breaking type hones.
What I meant was it will keep it square to the deck. With modern kart engines, other than honing, you aren’t allowed to machine anything, so however square your cylinder is to begin with, that’s what you get. Fortunately, modern engines are very well machined in the first place.
Thanks for the clarification.
In my day, the McCullough’s were fairly tightly controlled as far as there were rules on everything. That didn’t keep people from machining the blocks, just to make sure they were right at the rulebook specification. It’s not legal, but there’s no way to detect it if it’s done by a competent machinist. After all, the ports and all the machined surfaces were machine by somebody else, why not you?
By the way, keeping the deck 90° to the bore is not nearly (maybe not at all) as important as keeping the base 90° to the bore.
KA 100’s specifically have marks put on during manufacture that theoretically prevent illegal machining of surfaces.
@mtbikerbob, basically what @Christian_Fox said.
I use a drill hone with parallel stones for small errors and send bigger problems to an actual honing machine to correct bigger alignment and out of round issues. Every few sizes of pistons I think the cylinder should be put through a mandrel hone machine.
Cylinder will wear on the power stroke side of the cylinder, where the bulk of the force from the piston is transferred to the cylinder face. Which is a bit hard to explain with out a picture.
Thank you for clarifying. I was only familiar with the drill style hones. Just so I understand boring and honing I assume are not the same thing? I have been watching youtube videos on this. It looks like boring is actually cutting metal while honing is done with stones. Also, I assume anyone that does this kind of work would know what the cylinder needs based on measurements?
Boring is a rough process to remove material, only done on raw cylinder sleeves or very badly damaged cylinders. Honing is the finishing process to get precise sizing and to put the fine cross hatch finish on the cylinder. Honing only removes a tiny amount of material. Boring is typically done on a mill with a boring bar, honing is done on a honing machine with a mandrel with abrasive stones. A bored cylinder will always need to be honed. All that said, a modern kart engine will likely never see a boring bar once it leaves the factory.
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Good to know. Thanks for that information.
Sounds like a good idea!
I have been looking through the IAME information on this motor and found this information from the homologation details:
Bore 48.20 mm
Max. theoretical bore 48.53 mm
and the parts list show a variety of pistons starting at 48.20 up to 48.52
I guess this speaks to Christians point that a cylinder would most likely never be bored as that sounds a very small amount of material. Would an engine builder hone to a size or hone till completely round and fit the appropriate piston?
Someone was asking about costs. The list price of a piston is $120.65
Iame makes a huge array of piston sizes, so it’s very easy to hit your target piston clearance. If a cylinder is out of round, I will hone as little material as possible to get it round. And once it’s round, I may take off a little more material in order to fit the closest piston size given the clearance I’m looking for. And when I say “remove material” we’re talking tiny amounts, nothing like you’d do with a boring bar. So the answer to your question is both, hone to round, and if necessary, hone to fit the next piston size.
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I’ve been overly impressed with the KA platform. It’s been everything j had hoped this year.
Here’s my contribution to tips and tricks.
If it’s cold…go super rich on the jets. Common sense I know but I’d suggest like 8 minutes of adjustment for really cold air and back off if you find it’s too far.
I managed to stick a piston on the out lap of our morning warmup last weekend. It was literally 45 degrees cooler than the last race session the weekend before. I was thrashing to change a bent axle and just did a small twist but really didn’t put enough thought into How much of an adjustment really needed to be made to compensate for the air temp difference. Better safe than sorry, twist those knobs to the rich side as the weather gets colder!
Does anyone have feedback on which angle degree motor mount to use with KA on an OTK chassis? What degree is the factory OTK mount? I see 5 degree and 10 degree options. Elbow clearance will likely be an issue for me so I’d like the motor as low as possible without causing chain clearance issues.