Valve lapping

Quick poll: lap 'em or don't? I have heard yes, and I have heard no, don't bother as thermal expansion
shifts the point of contact.

The existing seats are a bit pitted and i will touch them up with a valve seat grinder.

I have new valves.
 
William,

It's been at least 40 years since I last rebuilt a head (or a block on some old flat head engines I used to fix), but at that time, we always lapped the valves. I probably still have that old vacuum cup stick that we used to use to spin the valves somewhere around here.

Times change. Techniques change. Materials change. I don't know what the current procedure is.

Tom in TN
 
(quoted from post at 09:28:56 02/28/16) I never lap if using valve grinder.
xactly. The only reason to lap valves is I'm too cheap to send the heads out, or in the case of flatheads, too lazy to pull the engine and strip every last part and stud off the block so the machine shop will grind the seats.
That said, I haven't lapped a valve in 32 years. I kinda avoid buying flatheads for that reason.
 
thats an obsolete operation. there is an interferance angle done when grinding valves to make sure they seat. for example... valve seat ground to 45 dgrees, and the valve is ground to 44 degrees.
 
rustred- When I rebuilt engines for the ASTM Octane test, we still used the lapping of valves along with the interface angle.

It seems to make a sealing valve seat. IMHO
Poke here
 
The machine shop I use laps them after they grind them.
I have always lapped valves using a suction cup.
I have had this for many years, but have never used it.
Richard in NW SC
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I always lap mine. Found out some high end (5 valve yamaha & suzukis) valve are coated and lapping removes it. Plain steel / stellite and I lap em. $65+ a piece Ti valves and I leave em.
 

Depends on wither they seal are not.
If they seal NO
If they do not YES...

I normally do its what works best for me... Always leak check either way...
 
I have one almost identical to that one Richard.
Suction cup on the end that just oscillates back and forth when
the handle is cranked. I also have a few different stick types.

I use them mostly on lawn mower and golf cart engines, but I
have used them on a flat head 8N engine that leaked by the valve.

I pay a local machinist to do my valve-in-head heads/valves.
Great guy, does awesome work at a fair price and I've never had a leak.
Next time I'm up there I'll ask him if he laps them in any way.
 

I have done more than my fair share it should not even be questioned THIS IS A IMPORTANT STEP unless you have a good way of checking your work for leaks.

I thought I had got so good one time I was running them out the door with a quick leak check. I got bit by one so it became part of the process to check the fit in some form are fashion LIKE I ALWAYS did till my head got to big for my hat.

Unless its my own I send them out to a pro that has the correct equipment. I have sent out the last few of my own mainly because my grinder in in my old shop with no heat and I usually do my own engines in cold weather. I usually install new valves, seats, guides are over sized valves either way you go its expensive. The seats need to be resurfaced any ways...

Support your local machine shop....
 
My personal experience, when I was using a seat grinder (which I hate) I always ended up having to lap valves to get good contact.

Now when I got my neway valve seat cutters they did such a good job with the seats I had full contact from the start and valve lapping stopped right there. My local automotive machine shop uses the same cutters I use and he's the same way, no lapping anymore.

If you have good valve guides that aren't worn out you should be able to successfully touch up the seats and get a good valve seal.
 

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