[Mjp83]

Just finished my 420 rebuild and as I was reading over another forum members posts I noticed that a piston has an IN mark on it.

So I looked at mine, and sure enough, my IN word is facing the exhaust side.

I only started it to see if it shifted, have not ran it. Has not warmed up or revved.

Can I pull head off and rotate and reuse the metal gasket?

Do I need to rotate it?

 

[Mjp83]

Well it’s already flipped the right way. Now for cleaning and reassembly...

 

[alloutdoors]

Have you tried it yet?

 

[Mjp83]

No, head is back on. About to put valve cover on.

 

[Macarena Man]

Looking at the photo . . . just guessing that the intake lift is different than the exhaust lift.
Different sized valve reliefs on the piston. Could also be an expansion issue as the exhaust valve runs hotter ?
Again, just guessing . . .

 

[Camchate]

Looking at the photo . . . just guessing that the intake lift is different than the exhaust lift.
Different sized valve reliefs on the piston. Could also be an expansion issue as the exhaust valve runs hotter ?
Again, just guessing . . .

Good catch. Looking carefully I could see marking on the relief, it might be worth ones time to have a look at the valve.

 

[Mjp83]

Piston back in correct, with the IN facing the intake side. Now the engine is making a loud clacking as if the piston is hitting. I replaced the tapped screws and adjusted the valves per specs but it sure sounds like valve noise. I will readjust the valves, I had to loosen the screws after re-assembly, as they were too tight. I hope I didn’t over torque the head....

 

[SlammedRanger]

Piston back in correct, with the IN facing the intake side. Now the engine is making a loud clacking as if the piston is hitting. I replaced the tapped screws and adjusted the valves per specs but it sure sounds like valve noise. I will readjust the valves, I had to loosen the screws after re-assembly, as they were too tight. I hope I didn’t over torque the head....

Yikes. Piston installed backwards followed by that type of noise is scary. I would have to bet the piston being backwards bent a valve more than likely. They cut the reliefs in the piston for the exact depth and diameter of valve. And inside engines is a game of thousanths of an inch. Im keeping my fingers crossed im wrong and you got it flipped before the damage.

 

[Mjp83]

Good news!

When I initially put the motor together I was able to verify TRUE Top Dead Center on the compression stroke by the cam gear. After I pulled the head to rotate the piston, I assumed it was on the compression stroke, as both push rods looked to be about same height. Well, NO, it was on the exhaust stroke!

Slowly turned motor using wrench through back access plate and clearly saw the intake valve open and close as the piston was going up, check valves and I had waaayyy to much play- adjusted them and now it is as quiet as ..well, it’s just dang quiet. Now on to my next issue, clutch.

 

[SlammedRanger]

Phew! Dodged a bullet there. Sadly i cant help with the clutch on a utility quad. Havent the slightest of a clue as how they work. But my fingers are un crossed and glad all is well with the motor internals!