Grinding valve stem to adjust lash?

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Walt

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I already wrecked one valve for my Briggs and Stratton engine, so I'll probably pay to have the job done. But it really bugs me how I let this job defeat me!

The smaller B&S engines have no adjustment to the tappet, so when the valves are re-ground, they fit deeper into the head than before, causing the lash to shrink. B&S says to grind or file them square.

I don't have a good feel for how critical the squareness of the result is, but I'm pretty sure that hand filing the end of a valve stem wouldn't result in a very good job in my hands. So I tried grinding the end of a piece of stainless rod on my bench grinder. Rotating the rod as it was ground resulted in something that appeared flat, but the surface had some pretty ugly scratches in it. Would going to a finer wheel result in an acceptable valve?

Would someone with experience tell me if I'm on the right track? On line searches for valves and grinding pull up little besides fitting the heads.

Walt
 
Vince O can tell you exactly how to do this. He does this stuff for a living. Just PM him or wait for him to answer.

"Billy G"
 
I had to do this on my mower. I used my bench grinder that has an extra wide table I bolted to it. I set it so the table was as perpendicular to the wheel as I could get it. I used a 80 grit wheel because that's what I had. Rolled the valve left to right only taking a little as I went. I smoothed the surface after by drilling a tight fitting hole in a piece of flat bar with my drill press and using the block as an alignment tool I used a diamond hone I use for my hss steel bits to smooth the surface and refine the fit. Worked we'll and the mower is running like a champ.
 
When we raced go karts, We build our own engines and for customer.....hundreds of Briggs and scrap iron race motors over the years. Even a brand new valve has to be ground to get the proper lash... And on the race motors you have to grind the stem and or the tappet to get the valve to open at the proper degree....

I still have a few valve grinding fixture blocks laying around.... Its just a block of steel with a hole in it that holds the valve perfectly 90 degrees. We always knocked the bulk of the material off on the bench grinder and then did the fine grinding in the block with a file. finishing with the file keeps you from getting the stem hot and loosing its hardness. When taking the bulk of material off keep it cool with water :)
 
If Vince O is the expert, I'd wait for his response. If I had to make the decision for myself, I think some kind of fixture would be a minimum requirement to do the job properly. In my case, I would probably do it on a surface grinder using a vise and small v-blocks to hold it. If you make a holding fixture and do this on a bench grinder, you'll want to use the flat side of the wheel and not the round circumference.


Ray
 
So this BS must be an L or flat head without rockers or hydraulic lifters, right. As a kid with no knowledge or tools I used to "centerless" grind valve stems freehand on a bench grinder. Can't remember all the details but I would hold the valve tip in a holder which allowed it to rotate through the radius contact. Little (1600) English race engines used "top hat" shims to set lash. To grind for "select" height (lash) they were set on the tip of the valve stem and centerless ground. Brown temper color came up fast. The valve tips sometimes were ground so the hardness was in doubt. At that time it was fashionable to set the valves in water so just the tip protruded to be heated cherry red and then tipped over for quench. What did we know??:))
 
Last edited:
jamie76x said:
When we raced go karts, We build our own engines and for customer.....hundreds of Briggs and scrap iron race motors over the years. Even a brand new valve has to be ground to get the proper lash... And on the race motors you have to grind the stem and or the tappet to get the valve to open at the proper degree....

I still have a few valve grinding fixture blocks laying around.... Its just a block of steel with a hole in it that holds the valve perfectly 90 degrees. We always knocked the bulk of the material off on the bench grinder and then did the fine grinding in the block with a file. finishing with the file keeps you from getting the stem hot and loosing its hardness. When taking the bulk of material off keep it cool with water :)
Click to expand...

Ray: I'm waiting on a replacement valve. To replace the one that inconveniently became too short. So I have over the weekend to think about it.

Jamie: I tried working on the "waste" valve this afternoon. A fixture block helps a lot, even one made out of a chunk of 2x4 allowed me to hand file closer to square and with a *much* better finish.

Thanks for the ideas. This one was really getting under my skin. Shouldn't take it personally, but I know there has to be a way to do something pretty good without a multi-thousand dollar machine!

Walt
 
Walt said:
Ray: I'm waiting on a replacement valve. To replace the one that inconveniently became too short. So I have over the weekend to think about it.

Jamie: I tried working on the "waste" valve this afternoon. A fixture block helps a lot, even one made out of a chunk of 2x4 allowed me to hand file closer to square and with a *much* better finish.

Thanks for the ideas. This one was really getting under my skin. Shouldn't take it personally, but I know there has to be a way to do something pretty good without a multi-thousand dollar machine!

Walt
Click to expand...

Is this the kind of valve stem where the end is rounded or is it flat? If it's flat, use the flat side of the grinding wheel with some kind of holding fixture. Maybe just a block of wood or aluminum with a V notched-out. Just as long as the fixture is mounted firmly in place, you should be OK...


Ray
 
Ray got it right.On my Sioux Valve Grinder theres a jig on the left side of the machine that is just a v-block with a clamp to hold the valve and you dress it on the flat side of the wheel.
How much deeper did you grind the seat ? You still need some clearance between the top of the valve and the valve keepers. You can always shim the spring to get the right seat pressure. Or just replace the seat.
**********Just Saying *****************Gator**************
 
The old valve grinding machines used a clamp which rotated the clamped valve across the side of the stone. My bench grinder has round bars that hold the rests in front of the grind wheel. It would be easy to fashion a fixture that clamped to this round bar and allowed the clamped valve to be rotated down the side of the stone.
 
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