Author Topic: 30cc Flat Four (Puma)  (Read 5484 times)

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #105 on: August 14, 2019, 09:56:56 AM »
I’ve 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 wasn’t that good. It was going to take ages and no doubt several rejects. I decided to go the fabricated route. I wasn’t 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

Online 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 I’d worked out the grinder configuration the grinding didn’t take much longer.
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #109 on: August 21, 2019, 09:36:09 AM »
It’s been a while since my last post and a bit of a challenge. I saw doing the remaining parts for the valves as a series of relatively simple parts that could be knocked out in quick succession.

How wrong I was. I think I started with the wrong mindset and consequently simple it wasn’t. There was also a degree of cockiness and “I’ve done these before”. For example, after I’d done the valve supports, I was checking Malcolm’s notes about something else and realised they should have been done in steel, not aluminium. So, they had to be done again. I recall wondering why they weren’t bushed when I was doing them in aluminium but just pressed on. I later found that the rockers should also be steel. Malcolm had originally planned to use aluminium but changed to steel as he thought aluminium wouldn’t be up to it. I’ve done mine on 7075 tool plate so I’m not doing them again.

One ‘problem’ I have had is getting things to fit. It all goes together but everything has been tight so it has taken time to get things to a working fit. Yesterday it was the cam followers getting them down by 0.0004” to get them to fit into the guides which I had reamed with a D bit made from the same material. They had swelled slightly on hardening 0.2491” was OK but 0.2495” was tight, 02497” was just about a press fit.

Anyway, some pictures of where I’m at
















And a brief video


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

Online Bluechip

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Re: 30cc Flat Four (Puma)
« Reply #110 on: August 21, 2019, 09:48:17 AM »
Private video here, no can see  .....  :noidea:

Dave

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #111 on: August 21, 2019, 10:05:40 AM »
Private video here, no can see  .....  :noidea:

Dave

Dave

Please try again

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

Online Bluechip

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Re: 30cc Flat Four (Puma)
« Reply #112 on: August 21, 2019, 10:39:04 AM »
Private video here, no can see  .....  :noidea:

Dave

Dave

Please try again

Pete


Yep!   That works fine now.  Very interesting build, been following discretely ..  :)

Dave


Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #113 on: August 23, 2019, 08:50:37 AM »
I’ve had the usual problem of getting the valves lapped and being able to test them. Lapping and reassembling on the cylinder and using the piston to check it they had sealed was getting a bit tedious. Taking them on and off coupled with knowing what properly lapped should look like.

I then had a bit of a brainwave. I already had a jig for holding the head in the rotary table to machine the curved heads. That was Malcolm recommended approach.



A bit more machining to accommodate the valves and a port to attach the airline.



Mounting the head and applying pressure from the airline allowed me to lapp the valves under pressure so it was pretty obvious which one was leaking and when the leak was resolved. The brass plug seals the spark plug hole.



When they went back on the heads and the piston pushed against the closed valves it was clearly a marked improvement.

Question – what degree of sealing am I to expect with these valves? Should they seal completely, say similar to a ball bearing clack valve? I'd guess that is ideal but is it really achiveable? Do they bed themselves in once the engine is running?

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 #114 on: August 23, 2019, 09:58:57 AM »
You should aim for a complete seal. It will make the first starts easier and also the valves may not bed in and the sealng can become worse due to carbon build up.
Best regards

Roger

Offline Admiral_dk

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Re: 30cc Flat Four (Puma)
« Reply #115 on: August 23, 2019, 11:29:55 AM »
I can tell you that any valve leak on a full size engine will destroy the valves and seats - and the more leakage the faster the destruction  :zap:

Considering how much compression preasure will be lost that smaller the engine is, the more difficult it will be to start the engine / get it to run continuesly ....

Offline Jasonb

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Re: 30cc Flat Four (Puma)
« Reply #116 on: August 23, 2019, 11:38:50 AM »
I tend to just give my engines a quick suck on the exhaust or carb holes and if there is reasonable resistance that's OK, never done a pressure test but expect it may leak away over a minute or so. All my engines seem to run OK.

With the soft bronze seats you will get then settling in and a better seal

Online Vixen

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Re: 30cc Flat Four (Puma)
« Reply #117 on: August 23, 2019, 11:41:07 AM »
I’ve had the usual problem of getting the valves lapped and being able to test them. Lapping and reassembling on the cylinder and using the piston to check it they had sealed was getting a bit tedious. Taking them on and off coupled with knowing what properly lapped should look like.

When they went back on the heads and the piston pushed against the closed valves it was clearly a marked improvement.

Question – what degree of sealing am I to expect with these valves? Should they seal completely, say similar to a ball bearing clack valve? I'd guess that is ideal but is it really achiveable? Do they bed themselves in once the engine is running?

Pete

Hello Pete,

Yes you should always aim to achieve perfectly sealed valves. It is difficult and time consuming but it can be achieved. Your test rig is an excellent way to identify any leaky valve seats.

I had 36 valves to lap on the Bristol Jupiter, which gave me plenty of opportunity to experiment and find a good quick way to seal each of the valves. Each of the 36 valves was lapped in and tested with a vacuum leak tester. The fine valve grinding paste supplied for auto restorers was simply too course for a small model engine. So,  I started by using Autosolv metal polish, This proved to be excessively time consuming. I next tried 600 grit silicon carbide, which was much quicker but did not give the best leak test results, the valve seats were a dull matt finish. Finally, I obtained some 1200 grit green silicon carbide powder from a gem stone polisher. The ultra fine powder was made into a paste with mineral oil and a little white spirit. The ultra fine abrasive powder worked well, each of the valves was lapped reasonably quickly and all were able to pass my full 30 second leak down test.

You can read the full story of my valve lapping adventures if you go to Reply #104 of http://www.modelenginemaker.com/index.php/topic,7559.100.html

Hope this helps

Mike
It is the journey that matters, not the destination

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #118 on: August 23, 2019, 12:48:14 PM »
Thanks for the feedback.

I'll admit that the Holts stuff is too course and because of that it has been parked at the back of the shelf for 6 years or so. It is  the 'fine' paste and I only used only the dust and fluid as the heavy particles had settled. I'll give  it another go tomorrow.  I have tried in the past 'Brasso' but that is too fine but, like Vixen, I do have Solvol Autosol so that may be the way to go for now. Finding some 1200 grit from a gemstone polisher may be a problem in the short term. (I'll check the link)

On the plus side the 1mm section Vition O rings replacing the 1mm CI rings do seem to seal OK so that's one variable dealt with for now.

(EDIT: just has a look at Mikes link to his Jupiter. I do have a seat cutter, I think to a George Britnell design (I could be wrong) that I made last time. I should give that a go but it does shave a lot off the seats and I'll admit I was reluctant to take a step to far)


Pete
« Last Edit: August 23, 2019, 12:57:21 PM by doubletop »
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Online Vixen

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Re: 30cc Flat Four (Puma)
« Reply #119 on: August 23, 2019, 01:06:22 PM »
Hello Pete

If you do an e-bay search for '1200 grit powder', you will get hits from all over the wold. UK, USA, China, Ukraine etc. It's often used by gem stone polishers.

It may be better to wait for the good stuff to arrive by post than to carry one with the wrong stuff.

If the valves are almost sealing, it may be better not to use the seat cutter again, just use the 1200 grit made into a paste with a little oil.

Mike
« Last Edit: August 23, 2019, 01:09:56 PM by Vixen »
It is the journey that matters, not the destination