Grinding valve stem to increase lash?
 

I'm making an assumption here so please don't kill me if I'm a little off.

I need to grind a few thousandths off of a valve stem on a small 8HP engine (Techumseh HMSK80) and I'm assuming it's similar to what gets done to an "A" in stock configuration.


If this is done on the "A" what is the common procedure to shorten a valve stem? I recall someone clamping a valve in a drill press with some modified blocks of wood and carefully grinding some off of the end of the stem. I've heard some guys just hit it with a file but that sounds a little too barbaric for my taste.

Re: Grinding valve stem to increase lash?
 

Before you do any grinding, be sure the cam lobe doesn't have a flyweight that holds the valve slightly off the seat for easy starting, then moves out of the way for regular valve timing. I found this out after the fact many years ago when I was working on an 8 H.P. grain elevator engine.

Re: Grinding valve stem to increase lash?
 

That is a new one on me. Thanks Tom for the heads up on that.

Re: Grinding valve stem to increase lash?
 

Hi Tom,

Yep, good point as it does have a compression release. I haven't checked the valve lash yet, but want to prepare ahead of time so I can just finish everything in one shot. Basically, the machine runs fantastic until it has a heavy load on it for a while, then it turns into a missing sputtering mess until it cools back down. I originally thought I was having carb issues and blew money on a genuine new Tecumseh carb. :mad:

Re: Grinding valve stem to increase lash?
 

Once you check the lash you'll have a bit more info. My recommendation is to find someone with a valve grinder and knows how to use it. Many old shops have one collecting dust in a corner, or, most aviation repair shops have one that is still in use.

That the lash measurement to the shop with you.

Re: Grinding valve stem to increase lash?
 

To do it correctly it should be held in a "V" Block that's been squared up to the SIDE of the fine grinding wheel. Only takes a second to grind.
Many of the modern small engine cams no longer have the weights to act as a compression release. Most newer engines have a small bump opposite the lobe on the cam. When checking the valve clearance/lash rotate the crank a quarter turn both ways to be sure your not on the bump. If you see the Clearance changes a lot you are hitting the bump (Compression release).

Re: Grinding valve stem to increase lash?
 

Would something like McMaster-Carr 4919A531 or 4919A561 work for this?

Re: Grinding valve stem to increase lash?
 

On Briggs & Stratton, I usually just buy a new valve & many times, the clearance comes out close enough for FARM EQUIPTMENT & ALL PRACTICAL PURPOSES, (Whatever that means???)
Bill W.

Re: Grinding valve stem to increase lash?
 

Hi Bill,
The issue in this case would be the seat wore more than the lifter/valve stem so a new valve isn't going to help. :D

Re: Grinding valve stem to increase lash?
 

All it takes is a lathe and a high speed tool bit.
Turn the compound parallel to the bed and use the calibrated dial for feed.

Re: Grinding valve stem to increase lash?
 

I still use a vintage hand crank, very fine, grinding wheel from the 1920's - 1930's used by my Dad years ago; and I can very accurately grind and very quickly adjust lengths of Model A valves or any other valves for original non-adjustable tappets.

Similarly to the Gentleman's Reply #6:

A. Make a wood, double "vee" box valve holder to accurately hold valve(s) "parallel" to the top of the horizontal work bench.

B. Vees can be easily cut out of pieces 3/16" Luan plywood & securely attached front and rear to a wood block below.

C. Vee box is securely clamped to workbench while accurately aligning valve(s) at 90 degrees to the side surface of the grinding wheel.

D. Remove very little valve metal until one gets experience as to how much metal is actually being removed.

Hope this helps.

Re: Grinding valve stem to increase lash?
 

Is lash measured between the valve stem and lifter or ........?

Re: Grinding valve stem to increase lash?
 

Yep.

Only annoying part is they aren't very specific at what it should be.
The manual says 8 thousandths and below that is 12 thousandths. Not sure if that's a range, or if one is intake and one is exhaust and seems like no one online really knows either.

My dad's opinion was since it only does it hot, see what it is now and it seems low just add a few thousandths to it.

Re: Grinding valve stem to increase lash?
 

Bill Stipe says with his cams to use .012 for both intake and exhaust

Re: Grinding valve stem to increase lash?
 

When dealing with thousandths of an inch differences, it is sometimes interesting to think about one's feeler gauge in considering:

A. Did your NAPA, Sears, J.C. Whitney or Harbor Freight feeler gauge come from Taiwan, Mexico, the U.S., or some place else?

B. Was your handy micrometer used for measuring your feeler gauge thickness made in the same country as your feeler gauge?

C. After stamping out feeler gauges, did the manufacturer remove the thicker stamping burrs on the outer perimeters of the feeler gauge?

D. Accuracy is important ..... but, best not to loose too much sleep ....... thank goodness for "Safety Factors" incorporated in recommended engineering measurements.

Re: Grinding valve stem to increase lash?
 

Good point, before I start I'll check the feeler gauge with my Starrett Micrometer (with clutch function). ;)

Re: Grinding valve stem to increase lash?
 

I do have Sioux Valve Grinding and Valve Facing machines. I can do it for you if you know how much you need ground. My Valve Stem Tip Grinder has a Micrometer feed on it.
I doubt you want to go through all this as I'm in California but I will do it for you for free other than the shipping.

Re: Grinding valve stem to increase lash?
 

Looks like my 12 thousandths feeler is actually 12.5. Close enough? :D It's hard to see in the picture but it was pretty much centered between 12 and 13. I made sure everything was clean and used the clutch to tighten it and checked several spots.

10 was dead on so I may go with that depending on what I find.


Fullraceflathead, Thank you for the offer but part of this is I want to figure out how to do it. It's a snowblower engine so I doubt it needs to be perfect. If I somehow fail at this, or, find the valve lash is fine I have a near perfect Honda GX-200 that will get bolted on in place of the Tecumseh.

Re: Grinding valve stem to increase lash?
 

mics can be calibrated and do not store them closed up

Re: Grinding valve stem to increase lash?
 

I always store it with a good 1/8" gap or so to be safe.

Can it be assumed that this mic zeros perfectly every time using the clutch that it is accurate?