Ripping my arm off

[Learning2kart]

Why is it when I go to pull cord to start it catches and dang near rips arm and fingers off and breaks my wrist? Compression? Timing? I did just put a new billet flywheel on. Put original timing key back in,but have advanced timing keys--#5, #8, #10.

 

[anickode]

Flywheel is all you did? You didn't open the case at all? It sounds like something else got changed... Valve clearance, compression ratio, cam position, etc.

What type of engine? A flywheel's job is to add rotational inertia to the crankshaft to carry it through the compression stroke. If you went from say, a big heavy cast iron flywheel to a lightweight aluminum one, that would contribute to your problem. If it's a little engine though, that wouldn't make that much of a difference.

 

[Flyinhillbilly]

I agree. I’d check valve lash first since it has to be right to make the compression release work like it should. Maybe it was off before and the heavy flywheel overcame it.

 

[Nosandwich]

Yep, new flywheels are lighter than stock, and kick-back can be a problem.

At the same time, it could very well be a timing problem .

 

[qtband]

Since I've gotten older, I use these.

 

[BigWes]

Yea, the timing sounds a little high to me as well, you could always run higher octane fuel to help a little bit but best thing is the above checks on the valves, and make sure you have the right spark plug for your set-up as well. And those handles above are nice too.

 

[Flyinhillbilly]

I use an electric starter box, but mine are stupid high compression with no compression release, lightweight everything, and a whole lot of ignition advance.

 

[Hellion]

What's the engine? And where's the pic of the engine?
For a lot of small, high compression engines, kickback is about the norm. . . before the advent of the compression release.

I tell ya, I love these excruciatingly vague questions.

 

[Learning2kart]

Predator 212. Yes went from heavy to light in weight. How much is the lash gap and how is it measured? As far as timing should i advance it?

 

[Flyinhillbilly]

Advancing the timing will make the kickback worse. For me, step 1 would be to pull the valve cover and check the lash. I run everything at zero lash cold because it grows to the correct clearance when the engine warms up. A little bit can go a long way with valve adjustment, and if that don’t help I’d start retarding the timing. I have had some pretty wicked motors with lightweight flywheels and 38 degrees of timing that I pull started, but they would hurt you if the lash wasn’t spot on.

 

[Randy H]

What these guys said.

I world check the flywheel key too. One good kickback could shear it.

 

[Flyinhillbilly]

What these guys said.

I world check the flywheel key too. One good kickback could shear it.

This is true also, I didn’t even think about that.

 

[anickode]

What these guys said.

I world check the flywheel key too. One good kickback could shear it.

Especially if the flywheel wasn't properly torqued to spec after installation.

 

[Hellion]

Especially if the flywheel wasn't properly torqued to spec after installation.

All this from a fellow who's username is Learning2kart.
All kinds of things could be wrong.

I make dumb assumptions all the time, as in I assume things were put back together properly and to spec. Whoops.

 

[snowjob]

I have the same issue on my stage 4. I assumed it was the cam. Got a nice welt when I first started it. Now I will only pull the starter out a foot or so. Runs great though.


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[Hellion]

Well, truth be told--there's a right way to start small engines that have a manual or kick starter that most people may not be aware of.

In this case, you lightly pull (several times if needed) on the cord until you feel resistance or it stops coming out. That should be the piston coming up on the compression stroke.

Then, you ease the cord back into the recoil housing. Take a deep breath...

And pull with authority! Give 'er a good yank until she starts. Repeat as necessary.

This prevents or minimizes kick-back since you're pulling it through the compression stroke and not allowing the piston and crank to rebound. The rebound is what hurts you--when it tries to yank the cord out of your grip.

The same method is recommended on motorcycles, even if the compression release is set up properly, otherwise it will hurt you when that nasty lever smacks your leg.

 

[Kentucky Boy]

Same thing happens to my motors with mods. The aluminum flywheels have built in timing advance. Use Hellion’s starting technique.

 

[snowjob]

Makes perfect sense to me. I used this technique to start my YZ450f and it was a real pain in the ***. I eventually fixed it by switching to a KDX200 2-stroke that doesn't care how it gets kicked, just starts easy every time. This reminds me one reason I hate 4-strokes. No reason these engines should be any different. Thanks Hellion.

 

[wenee9w]

I missed how much lighter is the new flywheel.?

 

[snowjob]

The billet flywheel is 3.5lbs. Inter webs is guessing stock is 5lb+. I could go weigh it if you need an accurate number.

Oh, I completely forgot this technique last night and have a nice new welt. Starts nice and easy when warm though, just like my other 4 stokes did. I totally see electric motors or at least starters in my future


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