Valve Lash Setting Tips?

[SquidBonez]

I have a 420 Predator that tries to rip the pullcord out of my hand when starting it. The plastic handle actually just broke from the kickback. After asking around it seems the valve lash is the only possible issue after ruling out the keyway being sheared. Here's my question:

Should I set the valve lash slightly after TDC (at the beginning of the ignition stroke)? I heard some people do this to ensure they aren't setting there lash on the compression release on the cam. Or should I try adjusting the intake valve when the exhaust is fully open and vice versa? That's what Vegas Carts reccomends anyway. Any tips?

 

[Karttekk]

The settings are in this Owners Manual. Cold engine, Top Dead Center. Make sure you don't have the compression release applying.

https://manuals.harborfreight.com/manuals/69000-69999/69736.pdf

 

[Karttekk]

Take the plug out, put a long rod or screwdriver in the plug hole. Remove the valve cover. Turn the crank by hand and watch the screwdriver rise while watching the valves. One revolution opens the intake valve, next revolution opens the exhaust valve then there will be a slight bump with the exhaust valve next revolution. That is the compression release coming in. Once they have passed and the screwdriver is at its highest point, both valves should be closed. That should be Top Dead Center. Don't worry about the exact position of the crankshaft, once both valves are closed and there's no pressure on any cam lobe the clearance won't change. This is basic 4 cycle work, yours should be similar.

 

[madprofessor]

I'm pasting in a post that I always advise people to read about the "snatchback" of pullropes. It's titled "How much pullrope are you using?" Hasn't happened to me even once since I figured this out by accident last December, and my current Predator 212 hemi is running with 35.2 degrees of timing advance. "Snatchback" is your motor running backwards because you stopped pulling it forward before the piston reached TDC, and here's how to stop that from happening..................

I've read many posts and seen videos about people nearly getting fingers broken by the violent "snatchback" of pullropes. Experienced some of that myself on hotrodded Predator 212 @ 12 hp., and recently with my current 212 @ 15+ hp.
Many people have automatically thought about there being excessive timing advance when that happens. I myself went to the flywheel, looking for a broken advance key spinning the wheel, or anything else obvious. The 28 degree PVL flywheel got a #6 advance key, which was still okay. I put the OEM key (no advance) back in, so just 28 degrees total when trying again.
Still snatching back, but then I lost my balance yanking on it, stumbled backwards, and saw a bunch more rope come out. Had been pulling far enough to get through a full cycle, about 3'. The snatchback always was right at the end of that.
Measured my pullrope and found there's "51" of rope there to pull on! Purposely stepped back a bit from the motor to make room, yanked a full 4', and it hasn't snatched back on me since! As long as I don't allow the pull to stop at just 3', the motor fires forward instead of backward.
So when you're pulling, step back and force a nonstop longer pull.

 

[SquidBonez]

I'm pasting in a post that I always advise people to read about the "snatchback" of pullropes. It's titled "How much pullrope are you using?" Hasn't happened to me even once since I figured this out by accident last December, and my current Predator 212 hemi is running with 35.2 degrees of timing advance. "Snatchback" is your motor running backwards because you stopped pulling it forward before the piston reached TDC, and here's how to stop that from happening..................

I've read many posts and seen videos about people nearly getting fingers broken by the violent "snatchback" of pullropes. Experienced some of that myself on hotrodded Predator 212 @ 12 hp., and recently with my current 212 @ 15+ hp.
Many people have automatically thought about there being excessive timing advance when that happens. I myself went to the flywheel, looking for a broken advance key spinning the wheel, or anything else obvious. The 28 degree PVL flywheel got a #6 advance key, which was still okay. I put the OEM key (no advance) back in, so just 28 degrees total when trying again.
Still snatching back, but then I lost my balance yanking on it, stumbled backwards, and saw a bunch more rope come out. Had been pulling far enough to get through a full cycle, about 3'. The snatchback always was right at the end of that.
Measured my pullrope and found there's "51" of rope there to pull on! Purposely stepped back a bit from the motor to make room, yanked a full 4', and it hasn't snatched back on me since! As long as I don't allow the pull to stop at just 3', the motor fires forward instead of backward.
So when you're pulling, step back and force a nonstop longer pull.

I'll give that a try. This 420 is significantly larger than a 212 so it would make sense that it's naturally harder to pull. But I'll give it a shot. Although I still don't understand why its so hard to pull. I'm using the stock cam with stock timing, theoretically it should be just as easy to pull as it was stock.

 

[Flyinhillbilly]

35.2 degrees of ignition timing seems awful specific.
How did you measure the .2?

 

[Snaker]

Manual stating is part brute strength and part technique.
I've experienced kickstarts on various engines and learned to "prime" the kickstart to the perfect position before compression.
Pull starts are similar.
Larger cc snowmobile engines in freezing temps can tear up a shoulder as well.

Try pulling the rope slowly through the strokes.
You will find the position before compression, start the pull for real there.

Also keep in mind winds of rope in the recoil give different gear ratios.
Wraps at the outer edge of the pulley give better leverage than wraps down towards center.

 

[madprofessor]

All my performance parts come from Jerry Dover at diyperformance in N.C.. They cut their own advance keys, and the numbers on each one represent 1.2 degrees of advance. Running a #6 key gives you (6) x (1.2) = 7.2 degrees on top of the 28 degree PVL flywheel and hi-perf coil also from Jerry. The combination of PVL flywheel, #6 advance key, hi-perf (resistors disabled) coil, .022 low and .036 main jets, 22# valve springs, Superman .265 cam, and .012" head gasket was all put together by him as a performance package meant to wring the most out of a 212 I don't intend to oversize the valves on.
Note: He knew at that time I had already selected a .020" over-length ARC billet rod for the build.

 

[SquidBonez]

Manual stating is part brute strength and part technique.
I've experienced kickstarts on various engines and learned to "prime" the kickstart to the perfect position before compression.
Pull starts are similar.
Larger cc snowmobile engines in freezing temps can tear up a shoulder as well.

Try pulling the rope slowly through the strokes.
You will find the position before compression, start the pull for real there.

Also keep in mind winds of rope in the recoil give different gear ratios.
Wraps at the outer edge of the pulley give better leverage than wraps down towards center.

Yeah whenever I pull this engine I get it to the compression stroke before yanking it. Seems to help but it's still difficult. Just re-checked my lash. After my new handle comes in I will update this post.

 

[madprofessor]

Snaker, that's such a blatantly obvious factor of physics that I'm embarrassed to have never thought of it before.
Did you get what he said, Squid? The first part of the pull on the rope will be trying to roll over less revolutions than the last part, like a large axle sprocket getting smaller as you go. Low speed to start, shifting to high speed by the end.
I'm embarrassed.