Just wondering if anyone rebuilds or maintains ther own motors? We run VLR and there are not many local builders. If you do do you hone your own cylinder? Or just change the ring…and/or piston? Just trying to gauge if its something I could do on my own.
Thanks
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I’ll do one top end (and/or change the main bearings - I don’t touch the crank, as I don’t have the tools or the knowledge) on an engine that was last put together by a builder/factory and is still in excellent condition, minus just being due for a refresh based on hours.
I’ve been doing this for several years with a few different type of engines, by just replacing with the same size piston/ring (do not recommend get into measuring a new size, unless you REALLY know what you’re doing), just being clean, careful, and kissing the cylinder with the a flex hone and I’ve been more than happy with the results.
However, if an engine is well used all-around, or there aren’t still nice clear hone marks in the cylinder I would send it out.
Also, unless you’re talking really low hours (like 1-2) always do a piston and ring together, imho.
Your approach should depend on your application. If you’re running laps recreationally then you’re needs may be different than someone competing for national wins. Don’t expect to compete up front with an engine bore not properly sized to the piston, verified round/true, and with the proper surface finish. That said, there are engine shops that will hone your cylinder and ship back to you if you send them the cylinder and new piston.
Servicing on our own here .
First of all we measure to see if the cylinders is in good shape and with in the limits of the repair manual says .
If its good news then we chose a piston with size according to the manual for the cylinders current size.
If its not a good cylinder we hone it and check again its dimmension before we chose piston size .
We almost never change the ring only , maybe in some occasions that we have opened the top end to check something else and just change also the ring to give a touch of freshness.
The point is . We always start with good measurements and the engine will tell us what it needs
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I consider myself to be pretty darn technical and VERY hands on, and I’m probably building up the big engine guys too much with this statement but the bore / piston fitting process is one of the few arts / intellectual property that the big engine builders have with the rule sets the way they are these days.
Getting the bore straight, using or not using torque plates in the process, choosing the right stones, finding the right cylinder wall clearance and ring end gap is the only real art that they have that the regular guy like me can’t pick apart and certainly can’t just jump into without a significant learning curve…and without a dyno to tell me if my ideas are great or crap.
Like Evan said…if you are just lapping and want to run a dingle ball hone through the thing a few times, throw the same size piston in it with a new ring and set ring end gap it’s absolutely going to work if you have mechanical knowledge, but in the world of spec racing i don’t feel it’s adequate to run at the front of a competitive field.
Better yet if you’re just lapping buy a new piston and send the cylinder off to a dirt bike shop and have the thing Nakisil lined and piston fit then you can run it just about forever by just swapping out the same piston and ring time and time again and having a good running piece…I’ve thought heavily about doing this for practice motors that I just want to bang out laps with.
I had a builder that would just fit pistons for me in the Yamaha days and it was great but I think you’d be hard pressed to find a big kart engine builder to do that these days. Woltjer did it for me once on the KA and then decided he didn’t want to do it again.
The labor / process on the bottom end isn’t even THAT hard if you get the right tools and a press and some v-blocks for balancing the crank and measuring run-out…but man I hold the piston fitting process as black magic I’m not even going to attempt for myself with the tools that I know are easily at my disposal.
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That describes what I’m doing, and I don’t disagree with most of what you say otherwise, at least for what I feel comfortable getting into or have the tools for. I would be very interested to know how a (for example) 10 hour KA100 that has been well cared for, still has its hone marks from the shop/factory and had this level of service done to it would dyno compared to when it was brand new. Seat of the pants that situation which I’ve replicated with other engines feels pretty whole to me, but that’s not worth much.
For sure, few who are already spending a ton of time, money, and effort on racing are understandably not going to want to engage in what could be viewed as ‘bean counting’ in that context.
Dingleberry hones will DESTROY 2 stroke ports… I’d never even put one within 10’ of my 2 stroke. Briggs tater diggers are another story… IMO, of course. YMMV.
The flex hones won’t destroy ports if you’re only using them for a few strokes to break any glaze that exists (we’re talking like 7-9 well oiled strokes in an out, that’s all). It’s when someone grabs one and starts to use it for establishing a new/actual honed surface, or even worse, a pseudo-bore bar that the problems occur. (which is why I’m only doing top ends on cylinders which still have strongly establish hone marks from the builder/factory)
I disagree. The knife-edge of the ports instantly suffers. If it’s hard enough to “break a glaze,” then it’s hard enough to cut aluminum and the balls spring into the port and whack that edge first… To what level? Time and pressure dependant. Still not getting near my motors. But if it’s working for you, I’m glad.
Well, I’ve done it plenty of times and inspected the ports. I’m sure if you got an electron microscope and took a look there would be some evidence but in terms of performance or passing tech, it’s not a problem.
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All great info! Thanks
The bristle/brush hones are better for two strokes as they are more gentle on ports.
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