I'm ripping stuff off the bike left and right for the 351 switcheroo. When I got the cover off, I checked the valves. All were in spec but the exhaust valve clearance is towards the low end. I think the tolerance is .15mm to .25mm, and mine are at about 16mm. My question is, as things wear does that gap get bigger or smaller? I'm guessing as things wear, the gap gets larger.
Dan

 

Dan
I belive the gap gets smaller becuase the valves wear into the valve seats. But I would wait for confirmation from the more experanced guys.

 

They get smaller, especially the intakes. The valves cup where they close on the seats.

Ride on
Brewster

 

things get more & more tight next thing you know valves don't close completly

reminds me I need to do/check the clearances on the RR its only got 40K miles

 

Thanks fellers, I didn't know what wore. Valve seats wearing makes sense. I will have to keep an eye on the exhaust clearances then I guess.
Thanks Dan

 

While we are on the subject is the a good rule of thumb as to when to get new valves or a valve grind? Like if you have adjusted your valves a few times and the cumulative adjustment is Xmm or Xthousanths.
Cheers Jim

 

usually wear tighter, but sometime on the exhaust valve you may find them looser due to ash deposits

Personally I subscribe to the " if they have any clearance they are fine" school. Damn the spec. I'm not lifting a cam to shim a valve just because it a thou or two under spec.

 

When you can't get a shim that is thin enough to bring the valve into spec, it's time to replace the valve.

Ride on
Brewster

 

Thats sounds like a good way to make the decision. Should have thought of that. I guess I have a while to go then.
Thanks
Cheers Jim

 

So the cam valve gap shrinks? Makes sense with the valve still seating in the head. Guess maybe I should check mine at the 10k mile mark. Haven't checked them since when I did the cam chain at 5k miles, and I got 8k miles now.