Author Topic: 30cc Flat Four (Puma)  (Read 5018 times)

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #105 on: August 14, 2019, 09:56:56 AM »
Iíve been doing the valves; I need 8 so it was going to be a longish job. I started by making them from 10mm stainless bar stock. A lot of machining and wasted material to get it down to the 8mm for the head and 3mm for the shank. Even when using a centre in the tailstock the 3mm was eluding me, either 2.98mm and too loose in the valve guides, or 3.02mm and oversize. Even with a new carbide tip when it got close to size the finish wasnít that good. It was going to take ages and no doubt several rejects. I decided to go the fabricated route. I wasnít sure if it was an accepted approach but a check of a few posts on here and found it was.

At the top 3 failed attempts from solid, below 9 heads and 10 shanks. It was 10 heads but one decided to eat my 3mm bottom tap. So only one spare rather than 2.



Silver soldered the heads to the shanks. Good penetration of the solder so I was happy with that.



The heads were oversize (10mm) so they could be machined down to size after the soldering to ensure concentricity.  Piston and piston rod style



I used my Deckel-alike tool grinder, which was contorted into service using the side of the diamond disc to grind the 45deg bevel



A bit of a final polish with some well-worn 600 grit paper and job done.




Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline Roger B

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Re: 30cc Flat Four (Puma)
« Reply #106 on: August 14, 2019, 11:32:57 AM »
I make my valves from stainless steel screws/bolts. This reduces waste and time. The valves shouldn't be too tight in the guides, especially for the exhaust valve, as the valve will tend to run hotter than the guide.
Best regards

Roger

Offline Brian Rupnow

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Re: 30cc Flat Four (Puma)
« Reply #107 on: August 14, 2019, 12:38:11 PM »
Nice job on the valves. A bit more complicated than making them from a single piece, but you do whatever it takes. I envy your ability to grind the valve faces. I have to turn mine, and it always leaves micro ridges I have to lap out.---Brian

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #108 on: August 14, 2019, 09:37:22 PM »

I make my valves from stainless steel screws/bolts. This reduces waste and time. The valves shouldn't be too tight in the guides, especially for the exhaust valve, as the valve will tend to run hotter than the guide


Roger

Point taken about the exhaust but concern was the inlets leaking too much when the cylinder doing the inlet stroke is trying to draw fuel/air mux through the carb and additional air is coming in through the valve stems. If you look at the drawing the length of pipe run between the carb and the 4 inlets ports is relatively long. I'm just expecting problems in that area so doing what I can to mitigate.


Nice job on the valves. A bit more complicated than making them from a single piece, but you do whatever it takes. I envy your ability to grind the valve faces. I have to turn mine, and it always leaves micro ridges I have to lap out.---Brian


Brian

Thanks

On balance the fabricated valves were quicker, or at least had a better yield, so proved quicker. As I've said before I'm not happy with the prospect of repetitive work and having to make more if one failed would only result in quality and yield falling away as I got more downhearted. With fabrication the shanks were relatively easy and quickly produced. The heads were a bit of a problem with tapping. I broke a tap, which slowed the job down as caution crept in. The soldering took less than 20 mins and once Iíd worked out the grinder configuration the grinding didnít take much longer.
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss