TOPIC:

I've got the KZ400H LTD engine back together, and it went very well, but for some reason I woke up this morning thinking of valve lapping vs grinding vs cutting. I lapped in the valves for the bike and it went pretty well - I put about an ounce of alcohol into the valve ports when I finished each one and only got a very slight bit of wetness spreading out of one, so I figure it'll run, but ideally there shouldn't be any escaping. The seats looked like the surface of the moon when I started, and I finished with a nice gray ring around the seats and valves. I was only pressing the valve into the seat with my fingers when I added the alcohol, so I figure the springs will hold them much more securely - but when it comes to refinishing the valves and seats, what are you guys doing/using? 

Fwiw, what I do when lapping is put some valve grinding paste at four points around the valve itself, stick the valve through its hole and attach a bit of fuel line to the valve stem, and attach that to a shank that I have in my battery powered drill. I then pull the trigger and rotate the valve with the dressing on it at moderate speed, gently pressing the valve into its seat with my fingers and periodically lifting the valve off the seat as it rotates in one direction, then reverse it doing the same. This way I get a nice even ring around the valve and seat, and it takes far less time than hand-rolling those suction-cupped wooden hand grinders - which tend to come off anyway - plus you can hear when the valve smooths out in the seat. Then I take a Sharpie, color in the seat and re-do it to make sure all the Sharpie is rubbed off by the valve, which shows me whether the valve is making even contact with the seat. If not, I do it again until I get the Gray Ring of Success.  

I haven't yet ground or cut any valve seats - I haven't really had to, lapping has worked just fine for me - but the thought is there; power is produced in the head, after all - but is anybody on here taking it to the Next Level and grinding and/or cutting valve seats? What benefit is there to grinding over lapping, and cutting over grinding?  I've heard about the Sioux grinders, and Mike Nixon goes on at length about how crappy that system actually is here:  valve seat tools www.motorcycleproject.com  - or is all this getting outside of the realm of most garage mechanics? 



 

Lapping valves should be done using an oscillating motion not spinning with a drill then reversing and spinning the other way !! also lapping is still required after cutting or grinding

I don't grind the seats, only cut and lap by hand.
Grinding risks taking too much off on these shim and bucket engines which will increase the stem height and can reduce shim sizes to the point where you have to tip the valves and even the collets and retainers to regain clearance.
You usually only need to cut after fitting guides, fitting new or larger valves or to reduce the 45's seat to the correct width with a 30 and 60 cutter if it's been over lapped and the seat is too wide.
I use Neway cutters .

To me, lapping is to clean valves/seats and verify contact pattern.  It should not be done for correction of problems, like pitting, unless very shallow.  
I also use Neway cutters.  A very light skim cut typically dresses the seat beautifully, unless the engine is high mileage.  The inside and outside cut then can be used to narrow, and position the seat on the valve.  Regarding valves, I take mine to a shop with a centerless grinder.  Used valves are brought back to new, or better than new, condition, after a nice cleanup.  

 

I can never get those wooden lapping sticks to work. the rubber suction cup always slides off the valve. Is there a better tool?

ckahleer wrote:

I can never get those wooden lapping sticks to work. the rubber suction cup always slides off the valve. Is there a better tool?

There are drill attachments like the below that give the alternating action required through the internal gears, however I have managed with a wooden stick for the last 40 years (cleanliness and having the tool central is the key) 
 

Cutting is what you (or your chosen engineer) has to do when necessary (e.g. when there's a fault or when you're installing new valves). The cutting angle should be precise to fit your valves. 
As I understand it, lapping is just breaking down the tiniest of surface irregularities on the valve seat. I have lapped many times on different bikes but never reground. I use the stick and suction cup, and lapping compound (rough then fine). It does get there quickly even though the suction cup frequently slips. The sound gives an indication when it's done, and then you change angle and go again. I've never had a problem by staying within my limits. If at some point I get a project bike that isn't too precious and has a valve issue, I may attempt to recut the valve seat myself using an improvised/garage method.

Just as you wake up in the morning you think one over exaggerated thing but after the first cup of coffee you think another, and more clearly. That’s my experience. 
If the engine is bolted together, run it. It’ll be fine.

Wookie58 wrote:

ckahleer wrote:

I can never get those wooden lapping sticks to work. the rubber suction cup always slides off the valve. Is there a better tool?

 I have managed with a wooden stick for the last 40 years (cleanliness and having the tool central is the key) 

 

Maybe I need a better lapping stick. I have a Craftman one from the 70's and a cheap one I got off E-Bay a few years ago. What brand should I get?

As long as the valve face is clean and the tool is centred with a rubber that is in good condition I wouldn't worry too much about brand - the ones I have used have been from a local auto parts store