Primary question w/pic

[Doc Harley]

Putting my clutches back in today. Thought I'd take a pic (back of primary.) Anything to be concerned about?
Other than that, no cracks anywhere. Pretty straight.

 

[Turboflash]

What does taper look like?

 

[Doc Harley]

Clean smooth surface.

 

[Turboflash]

Crank stub smooth without galling or scratch lines?
If so, then clutch did not spin on stub.
You're good to go.

 

[Turboflash]

Good idea to lap it while you're at it.

 

[Doc Harley]

Good idea to lap it while you're at it.

Lap it? Please explain....

 

[Turboflash]

Search "lap" here in this forum.
Basically it's using lapping compound (valve grinding compound) to make the clutch taper and PTO taper match exactly.
Apply lapping compound to crank stub and clutch taper, then put clutch onto stub and begin turning it (counter-clockwise ONLY - remember NEVER turn this 998 engine backwards!). Continue turning clutch while applying pressure inward. Remove clutch and observe pattern on stub. It should be smooth and uniform with no obvious high or low areas. If it's smooth, uniform with no areas that look different, you're done. Clean both PTO stub and clutch taper with acetone (or some use brake clean). Install clutch and torque bolt to spec. I always apply anti-seize to bolt threads. If after lapping 1st round you still have high or low spots, clean clutch and stub, repeat lapping until it's smooth and uniform.
This lapping ensures there is maximum contact between the mating tapers. When bolt is torqued properly, lapping ensures clutch will not slip on stub, even on big tunes with lots of traction.

 

[Doc Harley]

I understood the term with valves & seats. But I had no idea you guys are performing this to shaft & Primary?!?! Ty for explaining.....

 

[Fleecer]

I just take steelwool and clean both clutch and stubshaft. Remove all the rust and clean it up, then re-assemble.

 

[KnappAttack]

I understood the term with valves & seats. But I had no idea you guys are performing this to shaft & Primary?!?! Ty for explaining.....

Yep, Been doing it for thirty years starting on the hi powered race sleds.

I probably shouldn't even say this, as some won't think it safe at all, but if you live on the edge and don't mind shaking hands with danger, you can apply lapping compound to the clutch taper, start the engine and hold the clutch. I make sure to hold pressure on the center shaft as not to wear it unevenly, even rotating it some so as the engine idles so it wears in evenly. If your not the shaking hands with danger kid of guy, then one can just lap it manually, it just takes longer.

 

[Turboflash]

I made a drive tool that engages the clutch cover and fits into my cordless drill driver that rotates the clutch without engine running. I'm not quite as much on the danger-edge as I used to be.