Valves

[bob54 12]

When doing valves on a small engine, should they be refaced or is lapping good enough?  and if you reface the valves do you grind the seats?

thanks everyone, 

[JAinVA 4,619]

Odd as it might sound, since I have been messing with engines for many years. I too would like to hear from you folks on this question.

The insight from you guys is always worth the read.JAinVA

[lynnmor 6,762]

The valves should be ground, and the valve seat re-cut.  There is usually a one degree difference specified on the angles.  The seat width also has a specification and will always be way too wide on a worn engine.  Having too much contact will lessen the pounds per square inch pressure to seal the valve, and a seat too narrow will not allow enough heat to flow out of the valve to the block.  After the machine work, a very small amount of lapping is OK, but I don't even recommend that.

[ri702bill 7,274]

All:

Before I remove the valves, I check the clearance from the stems to the tappets. Then I remove the valves and check each valve face, the size of the margin - the flat portion of the major diameter, stem diameter where it goes thru the guide, the undercut for the keepers, and then chuck it in the lathe to check for wobble. If the face is resurfaceable, that's fine -  if any else is not acceptable then I replace the valve. The seats need to be inspected, as do the valve guide diameters.

Then I grind the valve faces and seats, removing as little material as possible, as this affects the tappet clearance. Then I put the valves back in the block with no springs and seating the valve by hand, check the tappet clearance. If it is too small, you have to grind the end of the stem accordingly. Once that is all set, I do lap the valve to the seat, as this leaves a visible ring on both the valve and the seat. If both rings are even all the way around, it's time one last cleaning and reassembly. Reassemble with the springs, check the tappet clearances for the last time, as it may have closed up a thousandth or so.

Bill

[bob54 12]

Thanks guys,,I knew it was done that way with bigger engines, guess it makes sense to do the same with smaller ones. Now I have an excuse to buy more equipment  

 

[oliver2-44 8,836]

For me, it depends what I'm doing to the engine and what I;m going to use it for!

if Im doing a complete overhaul (rebore, new piston, etc, or it going to be a weekly worker) I have the valves and seats ground as other members have described above. ( do'n have the equipment yet to do it myself) 

 

If I'm just doing a refresh maybe for a show tractor (honing the cylinder/new rings) I inspect the valves and seats as described above. If they checkout and if there is not any pitting I can see with the naked eye I inspect them with a magnifier and if there is only some tiny pitting I will try lapping them.  As I lap them i inspect them with a magnifier to insure that the lapped valve and seat seal area clean look good.  (I'm also a little biased to go ahead and try lapping them due to the fact that it's an 160 mile round trip to the only machine shop that will work on a small engine around here, and they have a $100 minimum charge)

 

If I pull the head to inspect an engine and the bore measures good and i decide a re-ring is not needed, I de-carbon and inspect the valves and seats with my magnifier. Since i usually would have the valve cover off to check the tappet clearance,  I almost always decide to pull the valves and relap them.  It just seems if I've gone to the effort to pull the head and valve cover i want to get all that areas as clean as possible and the lapping the valves is one more simple step.a simple step  

 

 

 

[Howie 882]

I always reface the valves and cut the seats. Have a Neway seat cutter with thze cutter to narrow seats also.Also helps to

have a valve grinder.