Valve Lapping Tips?

[Merkava_4]

I'm rebuilding a little Briggs & Stratton engine and have never lapped valves before. I'm thinking if I lap the valve faces and get them to fit the valve seats better, I might get a little bit better compression and maybe a more efficient running engine.

I need to get one of those suction cup things right? And some valve lapping compound?

 

[vssjim]

alot of times if the valves and seats look ok just make the face with a shapie then twist it in place on the seat and look at the valve and seat if it has wiped a band on both. lapping the valves won't do anything but put grit in the metal, if not smooth bands they need to be resurfaced. ps that permatex lapping compound is like rocks in a tube, real lapping compound comes from Clover in different grits.

 

[ossaguy]

If the valves and seats are pitted or worn looking,the best fix is to have them refaced using the sets that Neway makes for these small engines.You can put a perfect 3 angle cut in the seat,and a perfect face on the valve.They use 3 precise cutting blades set at the different angles so they are more accurate than stones.If they need to be done,and if there is a good shop nearby that has both of those sets,it wouldn't cost much to do I'd think,if you just brought in the valves and block,since it doesn't take much time.These sets are expensive,but they are the best.
For a nice lapper tool,a dealer could order you a nice lapper that B&S sells,made by "Woods",that comes with 3 sizes of suction cups,and has a neat sucking-in feature to really holds the valve on the cup.Be sure to check the guides for slop,as they can be rebushed in needed,too.Remember to check the valve lash after doing it,too.
Hope these tips help.
Steve

 

[Major Ramifications]

Hey, look guys.
Who says Merkava doesn't use any of his tools.

Just make sure to polish them when you are done.

 

[autoace]

If the valves and seats are pitted or worn looking,the best fix is to have them refaced using the sets that Neway makes for these small engines.You can put a perfect 3 angle cut in the seat,and a perfect face on the valve.They use 3 precise cutting blades set at the different angles so they are more accurate than stones.If they need to be done,and if there is a good shop nearby that has both of those sets,it wouldn't cost much to do I'd think,if you just brought in the valves and block,since it doesn't take much time.These sets are expensive,but they are the best.
For a nice lapper tool,a dealer could order you a nice lapper that B&S sells,made by "Woods",that comes with 3 sizes of suction cups,and has a neat sucking-in feature to really holds the valve on the cup.Be sure to check the guides for slop,as they can be rebushed in needed,too.Remember to check the valve lash after doing it,too.
Hope these tips help.
Steve

All this is truebut, if the valve faces and seats look good, you could just give them a good polish. Lisle makes a good/cheap lapper, go easy on the lapping paste, and after cleaning you can check your results with blue dye(Permatex make both compounds)....If they are pitted, nasty looking, go with the above.

 

[Uncle Buck]

Or for the price of decent lapping compound you could just drop it with your local engine rebuild shop and pay tham a few bucks to take care of it and be done with it.

I am usually rather cheap about a lot of stuff, but I would rather let a machine shop grind the valves and seats for me.

Last time I had this done on a Kohler engine a year or so back I think I spent all of about 20-25 bucks total.

 

[toadjammer]

Hell it sounds like you are just making sure it ain't leaking. It isn't like this is a HP motor. Just get some compound lapping tool (suction cup) and make sure it hits all the way around. If I am wrong and you are doin HP rebuild cutting the 3 angle seat and such would help. Also to consider just as much is guide wear. And for compression cylinder and ring wear.

 

[Merkava_4]

Also to consider just as much is guide wear. And for compression cylinder and ring wear.

The guides seem to be in good shape; the valve stems don't wiggle at all. I am changing the piston rings and the crankshaft seals. There seems to be only .003" wear in the cylinder and I'm allowed .010" - so I may not have to use an oversize piston.

 

[ossaguy]

If they are still available, B&S used to sell a "chrome ring "set that I remember worked well if it's an aluminum cool bore cylinder,that's got some wear,but not enough for the need to go oversized.

 

[Merkava_4]

That's right!! Thanks for reminding me.

 

[ossaguy]

I forgot to add that when using the chrome rings,the B&S book says to not hone or deglaze the cylinder.They don't require it to seat.
I remember we would always run it about an hour or 2 and change oil before sending it out to remove the tiny disparities caused from them seating in.
In case you were not aware,on all B&S engines the piston has to be 1/4 inch down the bore past TDC,when you check the valve clearance to be accurate.This is because of the compressiion release feature,(be it the mechainical or the easy-spin system) need to be positioned away from the valve tappet face.

Steve

 

[tdkkart]

Just buy new valves, they're cheap, then lap them into the seats. A good cutting polishing compound will work, as does pearl drops toothpaste.
.003" taper or out of round in a Briggs is no big deal, they go that far out of whack the first time you start them. For that matter you'd be amazed at how far you can pull the bore out of shape just by bolting them engine down to a bent mounting plate.

When I started doing karting engines I played with a couple Briggs motors, thinking about building them along with my Yamahas, but found that they were such a piece of **** that anyone who claims to do precision work on them is fooling themselves. I could have made alot of money on them but decided to pass.

 

[rsanter]

valve lapping is out of date. lapping is for old engines before hard seats were introduced. all of the B&S valves and seats are hardened and lapping will only slightly polish them. not worth the time
you will need to grind them
I happen to have the stuff to grind B&S valves and seats

bob

 

[Bob Paulin]

valve lapping is out of date. lapping is for old engines before hard seats were introduced. all of the B&S valves and seats are hardened and lapping will only slightly polish them. not worth the time
you will need to grind them
I happen to have the stuff to grind B&S valves and seats

bob

AND......

....it has been shown that once an engine reaches operating temperature, the valve and the seat - being different materials and surrounded by different masses - have expanded at different rates, so the lapped areas on the valve and the seat do not contact each other in the same areas as when they are cold.

Lapping valves is a waste of time.

I haven't lapped a valve in 30 + years, although I still buy lapping compound for my engine turning activities.