Ohrndorf 5 Cylinder Radial

[petertha]

Then I use a 5C collet stop and a split holding fixture to hold the stem. The fixture is slightly larger diameter than the valve head. The stems were trimmed to finished consistent length.

[petertha]

The 45-deg valve face is cut with a parting tool corner in shallow passes. I pre-blued the stock with Sharpie. The valve seat profile is complete when there is 0.010" blue remaining relative to valve face. I just held a vernier with jaws opened 0.010" using a magnifier. And now seeing these closeup pictures, my carbide looks chipped which probably didn’t help matters.

[petertha]

To finish the valve face, I eventually decided its better to just get it off the lathe. Lathe power isn’t necessary, the cross slide or compound is not being employed, RPM is limited & usually comes with unwanted vibration. So I just held the valve stem in my Dremel (Milwaukee Cordless actually) with a collet & spin it whatever RPM its happy. I figure at this stage, its all about finish albeit controlled by hand, so I’m less concerned by collet or chuck running absolutely true. After doing vacuum pull tests trying different methods, my conclusion was leakage was typically related to the ‘record player’ micro machining ridges on the valve face coming off the lathe. If it vacuum happens to seal first time, I think its more luck than anything else. A polished finish seat stands a much better chance IMO & usually requires no seat lapping usually.

So to achieve that finish, I first blue the seat face with Sharpie & then carefully take the surface down in progressive stages with nice smooth motion, until the machining ridges are completely gone & no more blue appears. Hopefully the pictures provide a sense of this. I start at 1000# - 1200# (blocks with wet-o-dry paper). For final finishing I found these foam backed nail file boards work well, they have 3000# on one side & you can do a lot of valves. Initially I was paranoid of free-handing the faces like this, worrying about round over but its actually quite controlled. You can also re-blue & observe progress.

The vacuum seal success ratio improves dramatically & consistently. Now there may be something else going on & I’ll leave this as an opinion. Even though the polishing is using a backing board and probably only tenths are coming off, there may be some propensity to make the slightest of curvature on the face. This might not actually be a bad thing (within limits) if it means the valve profile can make a continuous seat line even if the stem is off by a teeny degree. Who knows.

[petertha]

more pics

[petertha]

Last operation is making the groove for the valve spring retainer. I used a Nikole system insert tools which are really nice. Then just chamfer the edge and give it a bit of dressing. I hardened the rockers but the valves are left stock.

[petertha]

Glory shot of valves and a few spares. All the soldiers ready for action.

[jcge]

This is a great thread and build to follow petertha - lovely work too !!
John

[Kim]

Wow!  Quite the update Peter!  Nice work on the heads, cages and valves!  A TON of work! 

I really appreciate the detail you give on how you did the polishing/honing work on the valves.  That's really interesting.

Kim

[petertha]

Not much to say about the valve spring retainers other that they are made from 303 stainless & rather fiddly. I have since what is probably a better machining sequence where it’s made in one setting with the cup side facing out vs 2-step flipping around like I did.

[petertha]

The intake & exhaust tubes are retained in the head ports with threaded hex nuts. The tubing end is flared & that is what the nut edge acts on. A Teflon seal washer will reside between the flared end & face of the head port.

The nuts were machined from 0.5" 303 stainless hex. Once the thread OD was brought to size, I made a thread relief groove with Nikcole radius insert of 1.5mm (0.059") diameter. There isn’t a lot of remaining wall thickness on the nut, so I thought this profile might be a bit better than using a square cornered parting type tool. The groove width doesn't offer much error in reaction time to disengage the lathe during threading. I also didn't consider until I got going that the thread point has to terminate in the middle of the circular groove, half the groove width. Not that I have a lot of threading experience but I am reasonably happy with these eBay / AliExpress threading inserts. I was concerned my lathe rpm might be too slow, violating most all guidelines for carbide, but they cut nicely and the insert did not chip.

[petertha]

While still set up in threading mode, I also made a solid port plug for sanity testing the actual valves. It’s not a definitive test but I figured if the valve stem is dry (no oil) air might find a way up the annulus & tell me if I had a problem. I installed an O-ring behind the plug to seal, then drew vacuum up the stem annulus. The valves passed at this stage. Later at some point I installed a vacuum line nipple on the plug, blocked off the top of the valve to test the valve seal more directly but not sure I took pictures.

[petertha]

The generous chamfer on the outboard side of hole is to accommodate the radius bend in the tubing. May as well toss in some more (preliminary) CAD images showing the general principle. In reality, flaring the tubing is not an exact science & I was fixated on having some kind of sealing element washer between the head face. Maybe not so much for exhaust, but for sure induction. All this takes up space in the port hole & robs precious few threads. So that’s why early on I decided to just increase the head diameter a bit & solve all these issues simultaneously.

[Roger B]

Fascinating work on the valves and cages         Keeping small bores true and concentric is a problem. On my SU style carb I drilled 2.5mm and then bored out to 3mm using a 2mm endmill as a boring bar.
 I made my own seat cutters, a bit like your lapping tool but out of hardened silver steel (drill rod), so they did not interfere with the head.
Loctited cages seem to work well from what I have seen on various builds. The critical area seems to be the section between the port and the seating which is the shortest leakage path.

[Admiral_dk]

Woa what an update - took quite some time to 'munch through' - very detailed and descriptive 

I couldn't help wonder - is it supposed to get Airborne later in life ...?

Per            

[petertha]

I made my own seat cutters, a bit like your lapping tool but out of hardened silver steel (drill rod), so they did not interfere with the head.

I'd like to see a picture if you haven't already posted somewhere.