OX-5 Cylinders

Another chunk of work completed - the cylinders.  I took them to Mark's shop a couple of days ago to hone the barrels.  Mark made a nice honing tank that is set up with a Sunnen rigid hone.  This type of hone does the best job in keeping the bore round and even making it round if it is out.  

When I measured these prior to honing, I was amazed how consistent the barrel dimensions were.  The stock bore size is 4.000", and all cylinders measured within .001" of this anywhere they were measured.  Many, in fact, were within .0005".  I've had bored cylinders returned from a machine shop that were not this accurate and consistent.

So the honing was easy, all I had to do was take out a few minor imperfections - scratches, etc., and put in a nice cross-hatch.

Cylinder being honed with Marks very cool
Hudson project in background

Sunnen rigid hone

It's hard to tell in this picture, but the mounting base is not flat
due to being overtightened and not properly supported

I mentioned in the last post a little mod I made to the water outlet/rocker arm support on the top of the cylinders.

A poor design by Curtiss, along with many other things in this engine, but I just have to keep my head around the fact that this engine was designed over 100 years ago!  

The mounting base (shown at the bottom in this photo) is not supported at the ends where the studs go thru.  So as the nuts are tightened, the base bends.  As leaks occur and it is tightened down more, it leaks worse.  I've seen where some people flatten them back out by grinding or sanding, but I'm not a big fan of removing material that will actually weaken it even more.

So I came up with an idea (it's possible someone came up with this idea before me - forgive me if I'm not giving credit where it is due) to install an O-ring around the short tube protruding out the bottom, and chamfer the top of the cylinder to allow the O-ring to seal.  This has the advantage of eliminating the original gasket which will make for more rigid mounting since the rocker arm mounts here too.

The other problem to address are the support ears where the studs go thru so they don't bend down anymore.  I did this by machining thick washers that fit around the studs.  Now when bolted down, everything sits flat.  But first, I had to make sure the base was flat again. This was easier than expected by properly supporting it and using an arbor press.  

Here's the O-ring installed.  It's a Viton -018 size.  I chose Viton for its temperature range and chemical resistance properties.

I've used this modification before as a cylinder base gasket on engines that originally had no gasket.  Worked good in those applications, I see no reason it will not work here.







Here are the washers, the ones on top after being modified.  I bought extra thick, 1/4" washers even though the studs are 5/16". The O.D. of the 1/4" washer better matches the mounting base.  I had to machine them to about .092" thick and used a hole saw to notch them.  The I.D., of course, had to be enlarged to 5/16" too.

This picture shows the bore on the top of the cylinder after it was chamfered.  A chamfering depth of .095" gives the proper "crush" of the -018 O-ring.

It also shows the modified washers installed,  and you can see why the original design was prone to failure.  The area around the studs did not support the base of the rocker arm support, eventually causing it to warp and bend.  





It will be a while until I will actually know if this mod works, but I see no reason why it shouldn't.  I guess the one nice think about it - if it doesn't, I can keep the washers and install a regular gasket which will still be better than it originally was.

OK...for those of you bored with all this engine stuff, I'm bending capstrip and will soon be ready to start installing it on the wings.  Stay tuned for a wing update in the near future.