Restoration Project - Four digit Cub

[Slim140]

# 1 & 2 valve seats.

[Slim140]

Started with this.

[Stanton]

Looks to be a great improvement!

[Slim140]

Decided I may as well shave the head while it's off. Took .0075" off of it.

[Jim Becker]

Wow. Some of those valve seats looked nasty before you ground them. I'm sure you know this, but I'll mention it because they are easy to overlook. Check the specs for maximum width of the seats and the minimum thickness of the edge of the valves.

[Slim140]

Wow. Some of those valve seats looked nasty before you ground them. I'm sure you know this, but I'll mention it because they are easy to overlook. Check the specs for maximum width of the seats and the minimum thickness of the edge of the valves.

You wouldn't happen to have those numbers handy would you Jim? I have googled it and can't find it.

[BIGHOSS]

Click on PDF Manuals at top of this page. Find engine section under "Blue Ribbon Service Manual". You should find all that you need to know about specs.

[Slim140]

Click on PDF Manuals at top of this page. Find engine section under "Blue Ribbon Service Manual". You should find all that you need to know about specs.

Thank you BIGHOSS! Going to print that one out, 32 pages of Cub goodness!

[Jim Becker]

Some of the detailed valve specs aren't easy to find. Looking at the Blue Ribbon Service Manuals that you have found above, there are GSS-1007 Engine and GSS-1008 Specifications.

For the seat width, GSS-1007 says 3/16 in the text and (a more believable) 3/64 in the table. GSS-1008 gives a range .040 to .050 (which brackets 3/64). I notice GSS-1008 gives a slightly different seat angle too. I wouldn't worry about that for an early tractor. Look at the illustration (#31) that shows seat position relative to the valve. The OD of the seat needs to be smaller than the valve and the entire seat needs to hit the surface of the valve. If you need to reduce the OD of the seat, you grind a bit at another angle, typically using a 20 degree stone. A steeper stone can be used if needed to further reduce the seat width (increasing the ID) after the OD is set. These adjustments are the source of the name of the "three angle" valve job.

The edge of the valve is the really hard thing to pin down. By the way, the proper term for this is "margin". GSS-1007 says "carefully check each valve margin after refacing" and has an illustration showing two kinds of wrong and one correct with no specifications. GSS-1008 doesn't seem to address it at all. My general information from a valve grinding tool set just says to check for a "good margin". Other web sources, all I found was a small engine site that says new valves typically have a 1/32 margin and a reground valve is OK with at least 1/64. Those are probably reasonable numbers. A uniform margin on any individual valve is important and a variation indicates a warped valve.

[Cecil]

When you lap the valves take a permenant marker and put 4 marks on the face of the valve at 90 degrees to each other. When you wear the marks off the valves are lapped in.

[Slim140]

After looking at what you said Jim and also marking the valves with a permanent marker like you said Cecil this is the first one I lapped in. I made me a tool to put in the hand drill and turn it real slow with lapping compound on the valve/seat. I put 2 ~ 5/64" roll pins in a piece of 7/8" steel and welded a 1/4" bolt in the middle to chuck on. This is the first time I've ever done my own valves, I'm beginning to see why machine shops charge so much, lol.

[tst]

hard to see the lap line in the pic, it should be in the middle of the valve face, to close to the top of the valve and it will burn through in a short time

[Urbish]

This is the first time I've ever done my own valves, I'm beginning to see why machine shops charge so much, lol.

Be careful with that drill. Are you going slow with light pressure and in both directions? If you go one direction only, you can wear contours into the valve and seat not unlike how a badly worn brake pad and rotor will have matching concentric rings. Looking good as always!

[Jim Becker]

hard to see the lap line in the pic, it should be in the middle of the valve face, to close to the top of the valve and it will burn through in a short time

Yes, there needs to be good contact in the right place to maximize heat transfer from the valve to the block. Having the seat extend past the valve also encourages carbon deposits. Check illustration 31 in GSS-1007. The illustration is hard to see, but a close look helps.

The valve in the illustration is a "perfect" valve. After regrinding, the face may extend closer to the valve stem, which is harmless. As long as you have "some" of the marker lines showing at the outside of the valve seat you are good.

[Slim140]

Aright Jim and Tim, (thanks Tim for your info as well) I been reading the part Jim has been talking about and I just put another grinding wheel on and re ground the seat, not so much the seat where the valve meets but above where the valve meets the seat to make it look like the correct picture. It's hard to tell in my pictures but where the grey is that's from where I lapped them and haven't cleaned it well. The shiny part is where I just ground to give me less contact area on valve/seat. Thank everyone for their input on this!