Miller Overhead Wrap-Up

Hardened rollers and shafts

Hi All...if you recall my last post, I had to finish up a few things on the overhead.  Specifically, the rollers and their shafts.  I finished making them a couple weeks ago, just had to heat-treat.  I made them from A-2 tool steel, which requires an air quench instead of oil or water.  Nice stuff to work with and machine.  I wanted them about 56 Rockwell C, which required a heat soak at 1450 F, then 1725 F, followed by a tempering at 900 degrees.  I'm not completely sure this is the hardness I want, but I'll watch them and see how they, and the valve stems wear.  They are easy to make if I have to redo them sometime.

 In the following pictures, you can see everything installed with the intake and exhaust valves properly adjusted at .010".  You can also see the grease zerk, not found on the stock overhead, that allows the valve train to be lubed - except the roller, it still has to be manually oiled.

So now, I'm going to start closing up the gear end of the engine.  The water pump, carb, etc. can then be installed.

Got back on the airframe a little bit too.  I had fit up the fuel tank a couple months ago, and had some hope that I was going to be able to use it after a good cleaning.  Well, looking inside with a borescope revealed mice had made a home in there for many years.  I think everyone has a good idea what mouse pee does to metal - not good!  I guess it was wishful thinking anyway, that a nearly 90-year old tank would be useable!

The tank is galvanized steel with soldered seams.  My friend, Mark helped me unsolder the old tank and flatten the sheets for a pattern.  We then cut out new pieces from 22ga. galvanized steel.  The tank has a rolled seam around the perimeter that is soldered.  All the pieces are cut out, just have to run them thru the bead roller to form the seams, and solder it all together.  Sounds easy, but not really.  Manipulating this large, 40 gallon tank will definitely be a 2-man job!

Original fuel tank skins

So my next post should have a completed fuel tank...if all goes well.

Miller Overhead On The Curtiss OX-5

Many people operating the OX-5 opt for the Miller overhead instead of the stock setup.  Developed by Leslie Miller, they made valve train components and others like high-compression pistons for the OX-5.  I've heard some say that the Miller overhead offers little advantage over stock as far as valve guide wear.  While that may be true, it does offer another advantage - the components are much beefier.  

Rocker arm replacement version

Miller offered 2 versions:  This one shown to the right was a rocker arm replacement along with the "positive action" mechanism. This supposedly offered more positive opening and closing of the intake valve especially at high RPM.  The rest of the components were stock.

Complete Miller conversion

This version was the complete conversion.  All of the components were made more heavy-duty and a grease zerk allowed greasing instead of oiling most of the moving parts.

Rocker arm comparison

Stock vs. Miller comparison

Here you can see a comparison of the rocker arms of the different versions.  The top rocker arm is stock - it has a radiused tappet that rides on the exhaust valve.  

The middle arm is the Miller replacement for stock.  It adds the roller, but all components still have to be oiled. 

The last one is for the full Miller conversion.  It has a grease tube (soldered on top)  that allows the yoke for the exhaust push rod to be greased.  



This clearly shows the difference in the rest of the components.  The stock are on top, the Miller below - much more heavy-duty.













This being my first OX-5 I'll be operating, I can't make any comments at this time on whether the Miller is worth it, but it makes sense to me that the roller on the rocker arm should offer less friction and less side load on the valve.  I don't think you can argue either that the more heavy-duty components are also an advantage.  With my engine being so low time, my stock setup was fine, but when I came across a Miller setup, I thought it was worth the conversion.  The only components I will not be using is the "positive action" portion.  I didn't have those parts, and it's questionable that there is any advantage.

ASSEMBLY

Miller overhead components

Intake tappet on left after polishing out flat spot

These pictures pretty much tell the story, but I'll point out a few misc. items along the way.

Pre-assembly done

Safety for brass plugs

Prior to soldering

Soldered and safetied

Exhaust push rod tube yoke is safetied by soldering

Cleaning out threads on intake yoke

The intake tappet that mounts on the "H" tends to get a flat spot wore on it.  I found this easy to polish out.


































The shafts on the intake yoke are kept in with a brass plug.  Miller had an unusual way of safetying this - a wire that looks like a staple is soldered on the plug and wraps over the edges of the yoke.  The original had a semi-round profile.  I found that a cotter pin had the same shape so I cut and used those.













































The exhaust push rod yoke is safetied in a similar manner - soldered but no "staple".










The intake valve pull-down tube screws into the bottom of the yoke.  Running an 11/16-24 tap to clean out the threads makes assembly easier as well as adjusting the intake valves.

Spanner wrench for adjusting intake valves

Installation complete

 Another helpful item when adjusting the intake valves is a spanner wrench to turn the pull-down tube.  Here's a picture of one I made, it fits in existing holes in the tube.













So here they are installed.  If you look carefully, though, the rollers on the exhaust end are not installed.  New ones had to be made, and I wanted to make sure what diameter to make them. 

If you look at other sets of Miller components, you'll see different diameter rollers and other things liked shortened push rods.  I believe these are all attempts to change the geometry of the rocker arm so the proper valve setting (.010") at the exhaust valve can be obtained.  With the Miller rocker arm, you loose one degree of adjustability:  the stock arm can be adjusted at both the push rod and at the tappet.  The Miller one can only be adjusted at the push rod.

Why does the geometry change?  The most common thing is eliminating the cylinder hold-down spider.  Many people eliminate this to get rid of the 4 long cylinder studs - I don't think my engine came from the factory with this installed.  The thickness of the gasket under the water outlet/rocker arm support can change the geometry.

You can make up some of this difference with the adjustment of the exhaust push rod, but as you keep threading it up (to increase the clearance of the roller at the exhaust valve) it eventually hits the rocker arm.  I think this is why sometimes you'll find shortened push rods.  Since I had to make new rollers anyway - I could just make them to the proper diameter.

Old and new rollers

Complete set of new rollers

Here you can see the new rollers I machined.  These were made at .720" diameter which gives the adjustability I need.  I made them, as well as the shaft they ride on, from A2 tool steel.  I still have to heat-treat both the rollers and shafts as they are hard.





















Once I heat-treat the rollers, I can start finishing up things on the gear end of the engine.  So I'll keep plugging away - check back soon!

January 9 Update

New galvanized steel firewall

Upper bend of firewall

Hi everyone!  

As mentioned in the last post, the firewall is done.  It was made from 22 ga. galvanized steel like the original.  A lot of bending, but not too difficult overall.  The final fit came out nice.

Cam gear

 Then it was back to the OX-5 for a while.  I wanted to find and mark TDC and confirm that the magneto timing marks were correct.  The magneto is timed to 32 degrees BTDC.

Timing indicator used to find TDC

I'm a big fan of the "flower pot" timing indicator.  A plug is screwed in the spark plug hole of cylinder #1.  The engine is then rotated in both directions until the piston contacts the plug which will accurately locate TDC of that cylinder. 

Timing marks

The black ink mark is just my reference for TDC, the 2 "MM" marks is the tooth location for the magneto drive gear.  Once these marks are moved to the proper location, they are 32 degrees BTDC - Good!

Intake pull-down tubes and straps installed

I then installed the intake valve pull-down tubes and straps as previously talked about.  This will allow me to install the rest of the overhead which I am preparing now.  I should be ready to go over that in the next post.

Water outlet hoses

Prior to installing the rest of the overhead, the rocker arm supports that are also the water outlet tubes had to be installed.

Original hose and clamps with new clamp

Having original hoses, I as able to determine they were red in color. I also had original clamps, although unusable - most were broke.  You can still purchase red radiator and heater hose which is what I did as seen in the upper photo.  Fortunately, I as able to find very similar looking clamps from Restoration Supply Co.  Although not a perfect match, they are very close.

With these parts installed, I'll be able to attach the rest of the overhead once finished.

Streamlined wires!

 And...all of my streamlined wires arrived from Bruntons.  I didn't want to open them all up yet, so this picture is not very exciting - sorry!

Here is one of the transverse wires, though.  These wires go diagonal between the cabane struts and adjust the wings so they are centered over the longitudinal axis - hence, why they are called transverse wires.  These wires have a round portion and streamlined portion as typical with most biplanes from that era.

Transverse wire

To be honest, I'm not sure what I'm doing on the airframe next.  On the OX-5, I'll be finishing up the overhead.  Until next time....

OX-5 Update - January 1, 2016

Happy New Year everyone!

I've been working on the firewall, it is just about done.  The next post will include details.  Mostly, though, I've been working on the OX-5.  It's been slow-going and taking a lot longer than most engines I've done, but extra care will be worth it in the end.

Installed lower crankcase half

Engine builders?? initials engraved into baffles

 One of the first things I did was finish up the lower end.  This involves installing the screen, oil pump, internal baffles and oil level indicators.














Here's a shot of the baffles.  These are original, made from galvanized steel with an interesting galvanizing pattern. If you look closely at the upper part of the baffle, you will see some initials engraved in the metal.  Maybe the original engine builder??

Oil level float components

New float modified with brass bushing

Completed float assembly

 The OX-5 uses a cork float to indicate the oil level in the engine, in other words - no dip stick.  The original cork float was broke, so I made a new one.  I modified it to hopefully make it last longer by adding a brass bushing  where it rides on the arm.

Float level indicator (left) and oil level fill plug (right)

New oil sump gaskets

And of course, like everything else, new gaskets had to be made.  A little bit of care here, though.  Too thick or too thin and the front thrust bearing will not be captured properly and the front plate will not bolt on.  .032" gasket paper was the proper thickness.

New intake gaskets

The intake manifolds were then permanently installed.  I had a new set of copper crush gaskets that you can see here in this picture.

Intake manifolds installed

Next will be installing the valve train, so I spent quite a bit of time getting the components ready like making sure push rods were straight, etc.  Also, modifying the intake pull rod hold down straps.  The intake valves are pulled open on the OX-5 by a tube that covers a conventional looking push rod that pushes open the exhaust valve.  One of the interesting oddities of the OX-5.  The modification involves making sure the pull down tube remains lubricated where it slides thru the hold down strap.  The importance of this is mentioned in old manuals like the Miller Rev's for OX's, where it talks about "lots of rev's are lost here from friction".

The metal-to-metal joint itself can simply be lubricated, but won't last long.  I've seen where felt has been safety-wired around the pull down tube then soaked with oil which seems to work pretty good.  I wanted something a little more "factory" looking without doing a whole lot of fabrication, so here's what I came up with...

This picture shows the intake pull down tube in the strap with felt washers installed that can be periodically oiled to keep the area lubricated.

Components used to make the "lubricator"

Holes drilled on top of strap

Brass cotter keys bent over to avoid interference with spring

 The components are inexpensive and can be purchased from numerous sources:  3/4" felt washers and a plastic washer as a backup.  1/16" brass cotter keys hold the parts in place.

Completed assemblies

I started by drilling 2 small holes on the top of the strap.

The plastic washer followed by the felt washers are slid down, and the 2 cotter keys slid thru the washers and into the holes in the strap.  It's important that the cotter keys are bent over flat and out toward the edges of the strap so they don't interfere with the intake pull down springs that go in the straps.

Here they are all ready.  The brass wire wrapped around the top is just to keep the felt washer against the tube so the lubrication works.  

We'll see how they work...

Also added the "crown jewel", the data tag.  Now it looks like a real Curtiss!

So now I can install the rest of the valve train.  It will take some time as there is a lot that has to come all together.  Plus, I need to make new rollers and shafts for the Miller roller rockers.  I'll also keep plugging away at airframe items too.  Check back soon!