Halfa, a DOHC inline Twin

[Kim]

I certainly understand how drilling 6 holes can take all day!  I'm not a fast worker to start with, and I usually only have a couple of hours in the shop on any given day (2-4 probably), but I have to think through what I'm doing, then start to do it, then think through it again - and frequently this involves following up on some rabbit hole like "Where will that hole be used?  Is it really in the right place to mate up with whatever going there eventually?" Then after researching that, I finish my third think-through, finish getting things set up, check it again, and then finally actually do the operation.  And after checking that it's right, I'm off to the second operation of the day!  Or I've blown my concentration budget for the day and I'm ready to go in.

I clearly understand how drilling six holes can take all day!   

Kim

[RReid]

Yeah Kim, that's pretty much the way it is. Not a thing wrong with it either, especially when there is little margin for error and there is not a boss looking over your shoulder saying "Be more productive!". On top of all that, there's the fact that rushing deep holes in ali can lead to wandering or even broken drill bits. Those are bad.

[Art K]

Ron,
Good work on the head! I have been following along but can't often reply at that moment. It's good to follow a post that moves along, but not so fast I'm three or so pages behind when I get back to it.
Art

[RReid]

Thanks Art! Happy to have you along.

I treated myself to an easy and relaxing day today, just making a start on the camshaft bearing caps. Working in brass makes for a nice change of pace as well.

[RReid]

After getting the head drilled and tapped to mount those bearing caps, it was time to bore them and the head together to accept the camshaft bearings, which will be 3/8” OD x 1/4” ID, and turned from bearing bronze rod. With the head set-up vertically in the mill, I started with a 1/4” end mill, choked up as much as possible for the upper end. I used end mills for this mostly because of the step you can see there between the edge of the head and the bearing cap. For the lower part the end mill was extended just as far as I could get away with, which was almost but not quite enough to get all the way through.




I then switched to a 3/8” end mill and repeated the two steps above. Finally, to get the last ~1/8”, I had to finish off with a jobber length 3/8” drill bit.




When all was said and done they ended up nicely concentric. Now to make and fit the bearings themselves.

[Keith1500]

Nicely done.

Looks like you have your mill nicely trammed. In a case like this would you check the tramming before or do you know and trust your machine?

Just curious
Keith

[RReid]

Thank you, Keith.

I tram the mill from time to time, usually at the start of a new project, then after when either I have reason for concern, such as a "crash" or just a critical job, or else when I start to feel that "maybe I should". I checked it just a couple of weeks ago for the last reason, and it needed no adjustment. Generally this machine does hold tram pretty well. Also, I've been doing a lot of surfacing jobs lately, which tends to show the state of the tram, and I've been satisfied with those. So for this job, no, I didn't tram before hand.

[RReid]

I made up a set of camshaft bearings using a rod of oil filled sintered bronze. I've used Oilite bearings before, and wanted to try making my own from stock. I also made a set from regular 660 Bronze, but those lack a shoulder because I started with a smaller OD rod. Machining properties are similar for both, except the oil filled is oilier. So I have two sets, and can use either, but I'd like to use the oil filled ones because of the problem of getting oil to those bearings, and I prefer the shoulders. The other camshaft oiling scheme I have is this: the cam cover fixing screws will thread into the tops of the bearing caps, and will be SHCS (consistent with Alfa practice, by the way). So if I drill through the screws and the caps and the top of the bearings, then the screws can do double duty as oiling cups (not consistent with Alfa practice, by the way).

Here's the set of oilies, assembled with dummy camshafts.

[vtsteam]

Bearing caps and bearings look great, Ron!  Engine is getting prettier every day.

Speaking of Oilite bearings, I once cast some pillow blocks for my Gingery lathe's motor reduction with simple Oilite sleeves cast in place. I did it by first dissolving the oil out of the sintered bronze sleeve in a jar with some lacquer thinner in it, drying, and then packing sleeve with greensand.

I had already made a wooden pattern of the intended block with a sleeve shaped core print in it. After molding the pattern and lifting it out, I placed the sleeve with the packed sand into the core print impression, closed the mold, and poured aluminum. The aluminum flowed around the outside and bonded, but was blocked from filling the bore. It came out really well. I then put the new pillow block into another jar with oil in it to restore the lubrication, and it's been serving ever since -- about 20 years.

Looking forward to seeing how you make the cams! 

[stevehuckss396]

Speaking of Oilite bearings, I once cast some pillow blocks

As we type the building where Oilite was invented is being demolished. Another piece of history gone.

[RReid]

Thanks Steve. Clever solution on the Oilite pillow blocks. It never occurred to me that they could be "recharged" so easily, but it does make sense. The only thing I know for sure about making the cams is that it will either be done on the lathe or on the mill with the RT.  Just today I was re-reading Steve Huck's write-up on turning cams at the modelenginenews,org site. And lo and behold:

As we type the building where Oilite was invented is being demolished. Another piece of history gone.

That's a real shame, Steve. Apart from the history, that's a pretty cool building in it's own right.

[RReid]

Here we have a mix of easy, almost trivial jobs, and some pretty important ones.

The easiest of the easy jobs was giving the head it's first beginnings of shape, so it's no longer a plain blockhead. That meant cutting in the lower areas that will carry the intake manifold and exhaust headers. That was followed by drilling the respective intake and exaust ports. The side angles that show on the drawings were not done at this time though. They will be done last, after I'm sure I no longer need those flat planes for measuring and clamping. Also because the tilting table is still set-up at 40บ and I'll be needing that a little farther on.




Now for the more important jobs. First of these was making a set of valve guides. These are turned partway to an interference fit in the valve guide bores, and partway a little larger, which serves as a stop, but is still small enough for the valve springs to fit over. I think the drawing explains it better than I can.




The guides were then installed into the head, and the head was clamped onto the already set tilting table. A simple drill bushing was made to guide the drill for the hole the valve stems will pass through.


This was followed by a #2 drill to give a valve seat that's as concentric with and perpendicular to the valve guide as I can make it. The actual valve head will be 0.25”. The seats will be dressed by hand with my G. Britnell valve seat cutter.


Looks like two beady little eyes lookin' back at me.

[Kim]

Nice looking beady eyes, Ron! 

More good progress on the now non-block head. 

Kim

[Admiral_dk]

The Head is geting closer and closer to a fully functional Head - great build and progress 

Per       

[RReid]

Thank you, Kim and Per.