Hey guys I am curious of everyone’s thoughts on warming up the engine on the stand. I have a KA100 and usually just rev it up to 5-7K until the cylinder heads fins are warm. I have seen many times the top engine guys warming their motors up with full throttle and full brake for a few seconds over and over. Any insight?
With an air-cooled kart, it isn’t super necessary to get it piping hot on the stand. I always rev it a little just to get some heat in it and make sure it feels fine through the rev range. Then I drag the brakes and try and make the engine work a little to get a little heat in the clutch and get the brakes warmed up.
On my X30, I typically keep it below 6500 or 7k, until the engine is warm. I also wrap the radiator with a hoodie or a sheet during the first warm up, just to warm it up quickly without revving the nuts on it…
Warming on the stand is fine, but avoid rapid acceleration or decel. Putting it under load is acceptable, but be careful of this with a 4 stroke as you can over-clock the flywheel.
Some clutch assemblies are sensitive to this as well, so if your clutch assembly is held on with a woodruff key consider that when you load it up on the stand.
‘The hand on the head’ is a great way to judge when the engine is suitably hot.
I was told once that you shouldn’t really work the engine on the stand until it was over 30 degrees C (86F), that was water temp on a KZ engine.
And I now wait until 30 degrees C with my KA100 Cylinder Head Temp as well. The idea being to warm up the whole piston rather then just the top, before giving the engine a work out to clear the plug.
Does it help? No idea but it is a number to work with and that helps me.
Thanks for the good info guys.
I hate running them on the stand. It vibrates the bejeepers out of everything. When I do it, I usually brake load it, not doing so apparently can be hard on the rod bearings.
Haven’t heard of this term before… Can you explain what over-clocking the flywheel means? I’ve overeclocked a lot of computers… but I don’t think it’s the same thing.
I suppose I used a computer term, but the term seemed appropriate to me in this case.
Basically the Briggs flywheel is held in place by a woodruff key, and if you spin it up really rapidly under almost no load the key can get beaten up and you can shift the timing, or cock it slightly on the key.
I’ve never had the flywheel off a 206… So it’s just on a key and not a taper. Really the abuse in that regard on the stand is no worse than locking the rear wheels on the track. That’s not to say it’s a “good” thing, but I’ve never even had a rotor shift on a FA motor going from 19K down to zero, back up to 16, down to 8, back to 10 in quick succession on the track… but those rotors are on a taper, the key is just there to help make the location consistent.
Once decided clutches were too expensive and I would try a direct drive Honda gx160 and bump start it. Sheared the flywheel key repeatedly despite the taper and the automatic decompressor. Lot of inertia in those flywheels cf. a 100 2/. Some things just seem surprising . I would never have thought you could straighten a 50mm axle with a mallet. Anyone got any figures for deflection of an axle in normal use?
That’s odd, I did the same thing with GX’s when I was working with rental karts. I’d take a clutch that was totally shot and hammer the drum into the shoes.
Used it to practice push starts. But never sheared a crank or flywheel key .
That was almost 20 years ago though.
The great thing I am finding with this forum James is the number of people who have actually done things with their own hands and are reporting their results.
So I set up my direct drive GX and fully expected to be able to push start it, but to my surprise it just sheared the flywheel key. Replaced it taking particular care with key, taper ,tightening etc. Same again, so I assumed it was going to keep on shearing the key and gave up on the idea.
You did something very similar and it worked no problem. Must have been some reason but mine was 20 years ago too and I don’t feel any great urge to revisit. Cheers!
First time I’ve NOT broken something
With a water cooled engine, I think it is rather important to warm it up near operating temperature before hammering on it. I can’t see why a 2-stroke engine would be any different in this respect than a 4-stroke car engine, other than it will foul the plugs if run too slowly for too long.