Farmall Cub

I'm in the process of putting new valves in the Super C head. While the valves were rusted, and pitted with water damage, the seats looked relatively good, as the head was reworked prior to it's long outdoor sit. Once I stripped the head down, cleaned it up, it looked like new valves and guides were all it needed. I have installed the new guides, and am in the process of lapping the valves to insure a good seal, but wondered......how can I test the seal, or when do you know you're done lapping? The seats are about an inch recessed into the head to accomdate the stepped pistons. The valves looked seated correctly, but it's hard to see all the way around the valve due to the recess. I have held the valve closed with my finger and blown into the intake port. I get a lot of resistance.....but it isnt air tight. Should it be? I hate to put everything back together just to run a compression check. Is there anyway to do a leak test on the head? Maybe see it it will hold liquid for a while?

The experts will be here shortly but all the valve jobs I've done, I use prussion blue on the angle of the valve,insert it and spin a turn. if the valve seat shows blue all the way around you should be good to go. It will show if you have a spot that didn't clean up . If you have a good mark you should be good to go cause the valve will rotate anyway. just my .02 cents anyway. Grump

Take a magic marker and draw 4 lines accross the valves at 90 degrees. Lap them in. When the lines disappear you are golden.

Take a magic marker and draw 4 lines accross the valves at 90 degrees. Lap them in. When the lines disappear you are golden.

Ahhh, OK. That sounds like a good idea. Thanks.

If you see a hazy mark all around the valve and all around the seat you are good. If there is a skip on either you are still not done. The haze should be near the center for best heat disapation. Too near the large edge and you may burn the valve.

If you see a hazy mark all around the valve and all around the seat you are good. If there is a skip on either you are still not done. The haze should be near the center for best heat disapation. Too near the large edge and you may burn the valve.

This is the method I use for lapping valves.

Next suggestion is the have the valve seats touched up/ground. Fast, easy, accurate.

I used Cecils tip and it work perfectly. When I came back in and revisited the thread, I saw Beacons post about the haze mark. I went back out to the shop and put a light on the valves edges and there it was, a hazy ring, running fairly consistant in the middle. Thanks guys for sharing that knowledge.

Glad to be of help. I learned about valve and seat cutting and lapping long before many of the people on the forum were born. Way back when I was 14 years old 1946, same year I graduated 8th grade in PS 29.

Use brake clean to see if they leak is another good trick the techs taught me.I do this on my rebuilds.Seems to hold true.Kevin

There a "Youtube" video of a guy re-working a head off of an antique car....maybe an old chevy straight six, but anyhow he sounds like some of the sages on this forum......Probably forgot more than some of us will ever learn. If I can find it....I'll post a link.

http://www.youtube.com/watch?v=aCQIDTY2TeQ