Putting on used head. Should I lap the valves in?

[cheburashka]

I just received a used Ebay head for my 3.0 Mercruiser 140. The head came off of a running motor and the combustion chambers all look good. The seats and valve faces are in pretty good shape, but show some discoloration in places. I have the keepers and springs off so I can replace the stem seals and I'm thinking about lapping the valves in slightly with a fine compound just to ensure that they'll seal well. Are there disadvantages to doing this on a used head? Would it be better to just put it back together and call it good?

 

[Gary H NC]

Re: Putting on used head. Should I lap the valves in?

its already apart,may as well do it.that way you know they seal good..

 

[cheburashka]

Re: Putting on used head. Should I lap the valves in?

its already apart,may as well do it.that way you know they seal good..

That's what I figured, but I'm surprised at how often something that sounds like a great idea ends up biting me in the outdrive.

 

[Coors]

Re: Putting on used head. Should I lap the valves in?

After putting it back together, turn it upside down and fill the combustion chambers with rubbing alcohol. that will check the valve seating.

 

[Don S]

Re: Putting on used head. Should I lap the valves in?

Since you have it apart already, you might as well get the valves and seats ground or every one will leak.
Once the valve is turned and is not sitting in exactly the same position on the seat, they will leak 90% of the time.

 

[cheburashka]

Re: Putting on used head. Should I lap the valves in?

Since you have it apart already, you might as well get the valves and seats ground or every one will leak.
Once the valve is turned and is not sitting in exactly the same position on the seat, they will leak 90% of the time.

Ouch! You mean they don't rotate? I always assumed that they turned in their guides.


Like I said--things that sound like good ideas frequently come back and bite me in the outdrive.

I'll lap them and try the rubbing alcohol test first, but I'm open open to the possibility that a full valve job may be necessary.

 

[Limited-Time]

Re: Putting on used head. Should I lap the valves in?

Have them ground. You're this far now, and if you don't Dons tag line will be the next thing munching on yer ''out drive"

 

[Don S]

Re: Putting on used head. Should I lap the valves in?

Ouch! You mean they don't rotate? I always assumed that they turned in their guides.

They don't rotate unless they have a rotator cap with a bearing on them, and 3.0L motors don't have them.

 

[Windykid]

Re: Putting on used head. Should I lap the valves in?

Since it is a used head, you should have it magna-fluxed before anything else. Why spend more money if there is an unseen problem.