Is it necessary after cleaning and changing springs (did not keep them in order:rolleyes:); can it be done with an elec drill attachment or does it need to be a back forth motion?

 

It's always a good idea to do it, but may not be necessary. You can install valves and springs and then pour water into the ports (put the head on end so you can fill up the ports). If water leaks past the valves you need to lap them.

Lapping should be done by hand. Smear a little dab of compound on the seat and then use one of the suction cup lapping handles to rotate the valve back and forth.




[Modified by zwede, 8:21 AM 9/16/2003]

 

Thanks for the water tip, I'll probably just do them all to be safe, shouldn't take to long.

:thumbs:

 

like zwede said ,lap them by hand with alittle compound till you a get a nice uniform grey circle on the valve and seat.

 

Lapping by hand is pretty quick and easy but it should be done WITHOUT the springs attached ! Just a few rotations per valve is all that should be needed unless you've got a major seat/valve problem. :cheers:

 

I am wondering which compound should I get?
None of the parts stores I've been to carry lapping compound anymore.

 

You must be able to get lapping compund in the US???? :confused:
To make the job easier I spray some WD40 on the seat, it makes it much easier to lap them in. Do it with a back & forth motion, as described, but occasionally lift the valve off the seat, turn it 90deg and carry on. Lifting the valve will pull some fresh compound onto the contact area & turning the valve will ensure an evenly ground seat.
What I aim for is a very fine, unbroken grey ring on the inlet valve & seat (the tinner the contact area, the higher the sealing pressure & the better the seal. On the exhaust valves & seats I aim for a slightly wider contact area for normal street use. There'll be less contact pressure but the greater contact surface area helps in removing heat from the exhaust valve (which is a lot hotter than the inlet valve). If that is duff info for a SB then somebody will hopefully chime in & put me straight!
I don't use water to check the seal as its not to good at showing up very small leaks. I prefer to use meths, white spirit or even fuel (no smoking!!!). All of these will show up very slight leaks.
Make sure that you clean every last bit of grinding compound off when you've finished. Just wiping it off with rags isn't good enough, I wash the entire head. Having seen a head that was run with a small amount of grinding compound left in it, it's a wise precaution :yesnod: The owner swore that he'd wiped all the compound off, but there must have been some left further back in the port. It got on the valve stem & rapidly trashed the new valve & guide :(
:cheers:
Oh yes, don't get any WD40 on the suction cup or valve head, or you'll be cursing me as you'll end up with the suction cup sliding all over the valve & not turning it!!!

Another edit: I've not done a SBC head (yet!) so this might not work. Rather than filling the combustion chambers with liquid I turn the head on it's side so that the ports are pointing up & I'm looking at the (clean) chambers. I then fill each port in turn with enough liquid to completely cover the back of the valve. Any leaks are easy to see as fluid will be seen dribbling out of the chamber (do just one valve/cylinder at a time so you'll know what one is leaking). Using fuel etc to do this also has the added advantage in helping to remove any grinding compound stuck in carbon or awkward areas. Suggest you hook up some music while you do the job - valve grinding can get terminally boring :)


[Modified by UKPaul, 6:27 AM 9/17/2003]


[Modified by UKPaul, 6:37 AM 9/17/2003]

 

Pep Boys, Autozone, O'Reily, all carry it. :cheers: