Author Topic: Halfa, a DOHC inline Twin  (Read 1893 times)

Offline Dave Otto

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Re: Halfa, a DOHC inline Twin
« Reply #15 on: November 22, 2022, 04:30:52 PM »
Hi Ron

I somehow missed the beginning to your new project (just saw it this morning) looks like you are off to a good start.
I will be following along with your build and also agree that the picture size is much better.

Dave

Offline Roger B

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Re: Halfa, a DOHC inline Twin
« Reply #16 on: November 22, 2022, 06:50:37 PM »
Off to a good start  :ThumbsUp:  :ThumbsUp:

What sparking plug are you intending to use? It looks a bit tight between the valves and the plug. You will also need a special socket to fit and remove the plugs like on the Triumph Dolomite Sprint.
Best regards

Roger

Offline RReid

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Re: Halfa, a DOHC inline Twin
« Reply #17 on: November 22, 2022, 08:29:48 PM »
Happy to have you along, Dave!

Quote
What sparking plug are you intending to use? It looks a bit tight between the valves and the plug. You will also need a special socket to fit and remove the plugs like on the Triumph Dolomite Sprint.
Hi Roger. I currently plan to use the same 1/4-32 side fire plugs I used on the 2-Bits, sourced from Steve Huck. The well is sized so that a 5/16" deep well socket will fit down in there and that works fine in a similar, though less deep, set-up on the v-twin. As for the valve clearance, that x-section image is misleading in that shows a longer reach plug that I had inserted "just to see", and it is placed too far down. The plugs will actually sit more or less flush with the top of the combustion chamber.
Regards,
Ron

Offline RReid

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Re: Halfa, a DOHC inline Twin
« Reply #18 on: November 23, 2022, 12:29:31 AM »
Hi again, Roger. Following up on your comment regarding a special plug removal tool for the Dolomite Sprint, I found a service manual online with an illustration of the tool in use. It appears it not only removes the plug but also a shield around the plug, that I presume prevents sparking to the sides of the plug well. Is that right? If so, then I can see what you are getting at regarding my design. But I think that if such sparking does prove to be problem, a simple non-conductive sleeve could be easily made that would just slip over the plug. Since it won't be driving anywhere, there should be no need for it to be fixed securely in place. However, if you see reason to disagree don't hesitate to let me know. I'm still learning and am open minded!

By the way, is a Dolomite Sprint what you used in Rallying?
Regards,
Ron

Offline Roger B

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Re: Halfa, a DOHC inline Twin
« Reply #19 on: November 23, 2022, 06:39:04 PM »
Deeply recessed spark plugs can be a problem. The spark voltage will jump much further at atmospheric pressure than at compression pressure.

The Dolomite sprint was just a road car, there were a couple of design problems with the engine that made it fragile and hence expensive in competition use. My motor sport activities were carried out in a couple of Triumph Heralds. The first one was rallied until it started to crack up and had to be scrapped, the second one was sprinted and hill climbed and sold as a runner. The first picture is somewhere on Salisbury Plain and the second one is Gurston Down hill climb.

What fuel and ignition systems are you planning for Halfa? Yours I think would have had twin 45 DCOE Webers and a couple of years later they went to Spica mechanical fuel injection. Both could be a challenge  ::)
« Last Edit: November 23, 2022, 07:11:59 PM by Roger B »
Best regards

Roger

Offline RReid

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Re: Halfa, a DOHC inline Twin
« Reply #20 on: November 23, 2022, 09:11:47 PM »
Thanks for raising the issue of the deep plug wells, Roger. I hadn't considered the problem of rogue sparking before this. Now at least I know to watch for it when the time comes.

Looks like you had some good times with your Heralds. As a kid when I first read road tests of the Triumph Spitfire, they always talked about it being derived from the Herald. As Heralds are almost unknown here in the U.S., especially then, I didn't really know what they were talking about. But later  there was a guy, named Mike Rockett, who raced a Herald look-alike TR Vitesse around here in SCCA B-sedan and also in the Trans-Am 2.5 Series. He surprised and beat a number of quick Alfas and Datsun 510s. Until they banned 6 cylinder engines from that class.

Quote
What fuel and ignition systems are you planning for Halfa? Yours I think would have had twin 45 DCOE Webers and a couple of years later they went to Spica mechanical fuel injection. Both could be a challenge  ::)
To start with I'll keep it simple. The Upshur carb I've already made and used should serve to get the engine started. Then I can upgrade to a more sophisticated carb, either store bought or shop-made (maybe disguised as a Weber?). I do have the drawings for your CD Carb and fuel pump downloaded. And yes, My Alfa did have twin Webers, but 40DCOE, not 45. I think many people have found the SPICA injection to be challenging even at full size.

I'll likewise keep ignition simple, at least initially. A 360 crank will allow me to do a simple waste spark system with a single crank driven cam. Since the two cylinder Project 13-61 was meant as a bare bones economy car, that doesn't seem inappropriate. I have the idea that I could later make a second, 180 crank. With that, the kind of dual coil, dual breaker cam arrangement I use for the v-twin should work. It might be fun to see how the running (and sound) characteristics change with the different cranks.
Regards,
Ron

Offline Admiral_dk

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Re: Halfa, a DOHC inline Twin
« Reply #21 on: November 23, 2022, 09:40:08 PM »
Great project Ron - as many other, I will follow this one with great interest (perpetual Petrol Head)  :cheers:

Great pictures Roger - is that you behind the wheel in both ?

Per

Offline RReid

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Re: Halfa, a DOHC inline Twin
« Reply #22 on: November 24, 2022, 12:44:47 AM »
Thanks Per! Always good to have you along.

A few more build photos before pausing for our Thanksgiving Day here in the U.S.

With the center of the oil pan/lower crankcase roughly scooped out, I then removed material between what will become the “legs”. I finished with a small router bit to leave a radius on the inside corners, a trick I've used before, and that I learned from one of Jo's posts.




Then I turned my attention to the upper crankcase. My little wood cutting bandsaw was used to cut a blank of a piece of 3/4” thick aluminum.


After squaring that up and bringing it close to the final outside dimensions, I clamped both it and the oil pan in the mill vise to drill for the 4-40 fixing screws, drilling through the pan and into the upper crankcase with the tap drill. A piece of paper, a bit of old credit card, and some thin brass were enough to shim out the dimensional differences between the two parts.


I went over to the drill press to clearance drill the holes through the upper crankcase. I used the shank of the tap drill to get lined up, clamped the vise to the table, then switched to the clearance drill and poked it through.




With the holes in the pan tapped, the two parts can now be fastened together for machining to the final outside dimensions, as well as later for drilling/boring for the crank bearings.




Happy Thanksgiving to all the American members and viewers!
Regards,
Ron

Offline Roger B

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Re: Halfa, a DOHC inline Twin
« Reply #23 on: November 24, 2022, 07:00:34 PM »
Thank you Per, yes that was me in my youth  :old:
Best regards

Roger

Offline RReid

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Re: Halfa, a DOHC inline Twin
« Reply #24 on: November 29, 2022, 12:22:55 AM »
With the holiday over, I've gone back to working on the two crankcase halves. Both are finished to outside dimensions, insides dimensions are close enough for the time being, and I got the (mostly cosmetic) fins cut into the lower part. Alfa oil pans do have fins on the bottom, and sometimes the sides as well, and anyway fins always add visual interest.


However, I have discovered that the local Troll thinks I've made a couple of bath tubs for his personal use. He likes to alternate between a hot and a cold bath, but being a Troll, he complains that the hot is not hot enough and the cold is not cold enough, while also proclaiming loudly that the Laws of Thermodynamics are just a hoax.



Regards,
Ron

Offline crueby

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Re: Halfa, a DOHC inline Twin
« Reply #25 on: November 29, 2022, 01:34:24 AM »
 :lolb:

Offline RReid

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Re: Halfa, a DOHC inline Twin
« Reply #26 on: December 01, 2022, 12:39:36 AM »
Next I want to start work on the cylinder block. The blank is essentially just a simple rectangle, but would need to be cut out of a much larger hunk of 1 1/2” thick aluminum. The blank for the cylinder head will also come out of this stock. My little bandsaw can cut aluminum, and has been quite a champ about some of the stuff thrown at it, but this would really be asking too much. So instead I decided to go the chain drilling route.

I first set it up on the mill, so I could get a good set of starter holes that were evenly spaced, straight, and parallel. Using a stubby #35 drill, I poked a set of approx. 1/2” deep holes around the outline and out to the edges so I could get in later with either the bandsaw or a hacksaw. This was more than a little tedious, but worked fine.


Then I went over to the drill press to extend those holes the rest of the way through. This was more of a problem than I anticipated, because of the habit of aluminum to load up the bit and grab in deep holes. At first I pecked, withdrew, stopped the spindle, and cleaned off the chips. This was ridiculously slow, so I tried being more aggressive and quickly broke a bit. Eventually though I found the mojo and things started moving along, still tedious, still slow, but not AS slow. I found the right “pecking” rhythm, and also found that I could use a gloved finger to clear the chips from the bit without stopping the spindle (most of the time). Eventually I got the lines completely drilled.


The bandsaw was happy to deal with this job, just cutting through the thin webs between holes, and I was left with a jaggedy but nearly square cornered rectangle, although well oversize (I wasn't taking any chances on being under!).


Back on the mill, I used a 1/2” end mill to finish each face and bring it to the proper dimensions. Still a bit more of that to do. In this last photo I'm side milling the end of the block to get a good squared off surface to stand it up on later.

Regards,
Ron

Online vtsteam

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Re: Halfa, a DOHC inline Twin
« Reply #27 on: December 01, 2022, 03:26:28 AM »
That's a very neat job of chain drilling such thick stock. I have some similar thick chunks to deal with, and I really like how you prepped it for your bandsaw.  :ThumbsUp:  :cheers:

Online Kim

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Re: Halfa, a DOHC inline Twin
« Reply #28 on: December 01, 2022, 05:39:51 AM »
Wow! Respect!  That does look quite tedious!  Congrats on getting it done, I'd have probably given up long ago.

Kim

Offline RReid

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Re: Halfa, a DOHC inline Twin
« Reply #29 on: December 01, 2022, 03:39:31 PM »
Thanks guys.

One trick I forgot to mention is that for the final deep drilling, I used a drill bit one or two # sizes smaller than the starter holes. That little bit of clearance around the upper end of the bit helped a lot to reduce (but not eliminate) the tendency to pack the hole full of chips and bind up.
Regards,
Ron