Valve Grinding

[Billy the kid]

I have my 51 8n block at the shop getting cleaned and the valve seats ground.
I am putting all new valves, gides and springs in.
do i need to lap the valves?

 

[Anonymous-0]

Billy,

Most likely...not. That said, when faced with the same decision, I always do! ;=)

Check them with some Prussian blue.

Tim

 

[Billy the kid]

Thanks Tim, think I will!!

 

[Hobo,NC]

You can check for leakage and should,,, if you have a leaker take care of it...

 

[Billy the kid]

Thanks Hobo

 

[Matt L]

Id grind the new valves. Had a lincoln v12 recently that we bought all new valves for. Did the valve job stuck em in and it barely ran. Yep it was the valves. Ground em and it ran fine.

So now I grind everything except some of the high dollar new stuff. And theres alot of new valves that arent all that.

 

[weaveman01]

I did an inframe rebuild, and found an old boy to regrind my valve seats back to the 3 angles it was supposed to have. Then an all new valve set.

I wondered at the time though if instead of grinding the valve seats to get the 3 angles, if it wouldn't be wiser to just take the original valves and put a 3 angle cut on the valves and leave the seats alone?

As far as lapping though, if the guy does a good job cutting you're valve seats, lapping at minimum is useless and more damaging than helpful at worst. The seats and valves are pretty hard, and you would have to do alot of lapping to make any difference anyways.

 

[Billy the kid]

Yah I was kinda thinking the same thing, but I like Hobo's thoughts about checking for a good seal. So I think I will just lap them in lightly to check things out.

 

[Ken(Ark)]

(quoted from post at 12:56:47 01/07/11) I did an inframe rebuild, and found an old boy to regrind my valve seats back to the 3 angles it was supposed to have. Then an all new valve set.

I wondered at the time though if instead of grinding the valve seats to get the 3 angles, if it wouldn't be wiser to just take the original valves and put a 3 angle cut on the valves and leave the seats alone?

As far as lapping though, if the guy does a good job cutting you're valve seats, lapping at minimum is useless and more damaging than helpful at worst. The seats and valves are pretty hard, and you would have to do alot of lapping to make any difference anyways.

I don't know how others do it but the guys I know cut a 45 on the valve , dye it and lap it in so they know where to cut the 30 & 60 degree cuts .

Most engines have 3 angles on the seats and one on the valve . I like to leave the seats alone as much as possible and fit the easily replaceable valve to it .

I don't see lapping as much more than a measuring tool . Might be OK for cleaning carbon and rust off of a seat to help it seal .

 

[Bob]

Valve seats NEED a 3-angle job to make the valve contact area NARROW enough to seal reliably and to keep the contact area back from the "lip" of the valve.

If the valve contact area is too wide it's more likely for debris/carbon to hold the valve from seating and cause it to burn.

A really NARROW contact area will wear faster so the tradeoff is between too wide (poor seating) and too narrow (rapid wear).

 

[Bob]

If the valves and seats have been professionally ground with good equipment do them a favor and leave the lapping compound on the shelf.

Use Prussian Blue or even a series of pencil marks across the valve face to see how it's seating and where the contact area is.

Less you think the pencil marks are a loony idea, Cummins Diesel has suggested that method in some of their shop manuals over the years.

 

[Tool man Tim]

Dont forget the valves need abit of margin to loose their heat against the seat that is cooled with the head or they will burn..

 

[LarryT]

With this many replies I don't normally say anything, but as I read I notice that in my opinion, most of the advice and ideas are right on the money. I ran an aircraft engine overhaul shop for five years. I would like to just add a couple of things to the previous posts. Yes I agree with checking your valve face area with Prussian blue but I also believe in checking the seat and face interface by lapping. As we all know the valves rotate and if you use just the blue and pop the valve up you can get a false reading when you spin the valve. Granted it gives a damn good indication but I have had it cover slight inconsistencies in the fit. On the other hand when you lap them in you get a good idea of the fit but when you remove the valve and inspect both the seat and face you can see exactly where everything is hitting. So I believe you need to use both to be sure. Secondly many spoke about leak checking but no one really told or advised Billy on the ways to do it. So if I may, without seeming overbearing, I would like to expound on the process of leak checking the valves. In the piston aircraft engines we were allowed 0 ZERO leakage of the valve over a 30 minute time period. We used neutral Stoddard solvent which is a lot like mineral spirits.
Make sure the seat and valve areas are thoroughly cleaned of any grinding or lapping debris. Set the valve in place and carefully with your lapping tool apply pressure and rotate the valve back and forth about 1/2 turn to clear any remaining contaminants. Make sure that the area around the valve is dry and install the Valve springs and keepers. Position the valve and seat where it is below the level of the port and fill the port with solvent taking care not to splash or spill the solvent outside the port area. Look to make sure that the valve/port area is totally submerged below the level of the solvent. Now watch from the valve side for any wetness to indicate valve leakage past the face or between the seat and block. Now how tight you want it is up to you but as I said we had to pass a 30 minute check on the aircraft engines. Now if you do have some seepage of the solvent through the valve, then pour out the solvent and with a dead blow or soft faced mallet, strike the top of the valve causing it to open and sharply close again. Then repeat the process. If you cant get it to stop leaking you may have to re lap the seat. If there is leakage between the seat and the block then the seat needs to be removed and redone as this is an indication of the seat being loose in the block. I hope this helps because that's all I am trying to do is share 60+ years of knowledge with those that may need it and don't have a way to learn it otherwise. I think that it's the reason any of us are here, To help other by sharing what we have learned in your lives. LarryT

 

[Hobo,NC]

Are add the solvent on top of the valve and look in the port, 5 min rule for me,,, you will know quick if its a leaker. If in a hurry (are in doubt) blow air into the port and look for bubbles around the valve. It does not take much air pressure maybe 10 to 20PSI,,, Remember you can force the valve to leak if you go overboard with the air. I do lap I don't like to chance it. If Doing this after the pistons have been installed tape up all openings. Its best to take care of this before the final cleaning of the engine block.

I like water base compound, those with experience can tell right off the bat by the feel and sound as soon as they spin the stick if its good to go.
The only time I use the blue chit is if I want to see the pattern better are if its going to be awhile before I assy. I thought I was good one time and a leaker bit me,,, it was hard to chew and don't want another...

I will take my chance with the compound, never had a issue with it. I always thin it down some with a few drops of water. I like to see it like runny grits with a gravy texture. Not were it globs up and falls off the valve and seat in chunks....

 

[rnorum]

The way I would like to check valve seat consentricity or to seal good, is to grind the new valves on a valve machine that has an accurate chuck, or in good shape. Then put the valve in the guide and raise the valve about a 1/4" off the seat, use 2 fingers and rap the valve in to the seat. Lift the valve straight out and look at the face of the valve for marks all the way around. If it leaves a mark all around it is very accurate. Also the exhaust seat should be about 50* wide for good heat disapation and the int about 40*wide