OX-5 Valve Guides

Since my friend Mark and I like working on old engines, and we were getting a little stir crazy from the Holidays, we decided to see how the valve guides would go.  It went extremely well, but a little background first.

An early method of replacing valve guides

The OX-5 cylinder is one-piece (no separate head) and is made from a single cast iron casting.  The guides are also integral to this casting.  This makes guide replacement more involved than more conventional ones that are removed when worn out and replaced with new.  Early companies like the one shown to the right and others like Miller made replacement guides.  The old ones had to be machined out, the hole threaded and then new ones screwed in.  This required careful fixturing to ensure the new guide was somewhat concentric with the valve seat.

Fortunately, there are better methods available today and the one I chose was to use guide liners.  The challenge, though, with liners is again keeping the lined guide concentric with the seat.

In most automotive applications, the guide can be machined from the seat side to accept the liner.  There are centering tools available to keep everything concentric.  With the OX-5 and other aviation engines, the machining has to be done from the valve spring side.  This is because the head and cylinder are integral and the valves sit at an angle, so the machining can't be done from inside the barrel.

Modified reamer with pilot and centering cone

Here's a picture of what I made to ream the guides to fit the liners and keep them concentric with the seat.  I first obtained a reamer of the proper size to fit the liners.  I had the tip ground to fit a long pilot that was pressed over the end.  I then made a cone with a  bushing pressed in the center. The cone sits in the valve seat and keeps the reamer concentric with the seat as it is being reamed.  Some pictures farther down in this post will make this easier to see.

K-Line valve guide liners

Several companies make liners, and the ones I chose were from K-line.  These liners have a spiral groove machined on the inside for lubrication.  Since the OX-5 valves have to be manually lubricated, this feature is perfect.   The liners have a .015" wall, or in other words, fit in a .030" oversize hole.  The nominal OX-5 valve size is .375", so the holes are reamed to .405"

Tooling required for liner installation

There is some other special tooling required as seen in this picture - probably best to describe them as I go through each step.












Step 1:  Ream the guide

Guide reaming

Here you can see how the reamer is inserted in the guide from the valve spring side, with the pilot going thru the guide and into the centering cone.  

Liner insertion

Step 2:  Insert the liner

A short stroke rivet gun and a special insertion tool is used to press the liner in the reamed guide

Liners after insertion

The liners are longer than needed, so after insertion they have to be cut even with the guide at both ends.

Sizing the liner with a carbide sizing ball

Step 3:  Sizing

The liners then have to be sized.  This does a couple of things:  Allows for proper fit between the valve and liner, prevents the liner from getting loose in the reamed guide, and allows for heat transfer between the liner and guide.  The sizing is done with several sizes of carbide "sizing balls".  Balls of various sizes are pushed thru the liner with a special tool and rivet gun until the proper valve to liner fit is obtained.  The dimensions of my valves required a .375 and .376 carbide sizing ball.  The ball can be run thru multiple times and each time, up to a point, the ID of the liner gets slightly bigger.

The liner is then lightly honed with a honing brush and the valve can then be checked for fit and proper sealing at the seat.

Finished installation showing internal spiral grooves

Now to the valves... As you may recall from my previous posts, this is a very low time engine.  My hope was to use the original valves, but I was unsure until I could get them cleaned up.  Well, they cleaned up great.

Original valve prior to lapping

Hard to believe, but here's a picture of an 86-year old valve that has not even been lapped yet.  Amazing!

Checking valve fit with bluing

Intake and exhaust valves after lapping

Now the moment we've been waiting for - is the liner concentric with the seat???

YES!  This whole process couldn't have worked out any better.  The seats and valves required no grinding, only a light lapping was necessary!

This was a relief, because if you're familiar with stock OX-5 valves, or see in the pictures, there is very little margin to do any valve grinding.

Every once in a while something just seems to come together nicely, and this was one of those times.  Thanks to Mark for all his help on this too.

Cleaned studs

 In a different, but OX-5 related topic, I got the engine studs black-oxided.  I bought a kit to do this myself and it is very easy to do.

The studs first have to be very clean.  I used a wire wheel to remove any corrosion.

Chemicals used for the blackening process

The parts are then put thru a 4-step process.  

1.  A cleaner to remove any grease and contaminates.

2.  A prep to make for a deeper oxide finish.

3.  The blackening process.

4.  A protective coating to improve the corrosion resistance.

Finished studs with black-oxide coating

I made a little basket to put the studs in, and about a 2 minute dip in each solution is all that's required.  Parts come out very nice looking and protected against corrosion.

























Back on to the wings soon, but still waiting on capstrip material.  So, I'm not sure what my next post will be on, so stay tuned!