Author Topic: Len Mason's "Mastiff" - chewed from the solid  (Read 30878 times)

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #255 on: December 11, 2018, 05:00:07 AM »
Hi Art,
Rambling is good! I wasn't intending to reduce the CR on Mastiff - it was just a suggestion to Michael that if he was concerned about the CR on the Bugatti being too high he could drop it temporarily with a thick head gasket.

Now rambling: I first learned of this idea from my Uncle Ted who had ridden a 500cc AJS single through WWII when petrol was very hard to find. He made up a thick copper head gasket and ran the bike on a mixture of kerosene and whatever else he could find, "smoked a bit" was his only comment. U Ted was a pressure vessel draughtsman and reserved from active service (I said he "made up" the gasket but maybe he just drew it and talked nicely to the shop floor). He also belonged to a Territorial Army regiment and manned a 3.75"  AA gun defending his factory at night, I'm not sure when those blokes ever got to sleep.

Regards, David

Offline michelko

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #256 on: December 11, 2018, 09:52:06 AM »
Hi Michael,
Thanks!

If you look back through the build log you will find a long list of the mistakes I had to correct before Mastiff would run well. These included leaking gaskets, over-size main jets, wrong timing and leaking home-made spark plugs. The compression ratio is about 3.8:1 and at first there wasn't much compression but this has developed as the engine has been run. With small cylinder volumes the thickness of the head gasket has quite an effect on the CR, could you try a thick gasket to reduce the CR?





David thanks for your Reply. Unfortunately i have to stay with my actual gasket with 0,5mm. The Timing housing didn´t allow much more because of the Overhead camshaft´s. The easiest way would be to reduce the height of the pistons, but then tere would be now way back without make them new.
I am nearly sure i will try this way.

Regards Michael

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #257 on: December 11, 2018, 10:53:00 AM »
Michael,
I should have thought about the camshaft drive. Its obvious (once you pointed it out) that with overhead camshafts there isn't much room for adjustment in height.

George,
Thanks for your interest and the info that "I don't think the throttle range is being limited by the single carb and longish intake runners", I'll stop worrying about that! I don't really know what a "vapor fuel supply" system is, please tell me more. With Mastiff I just did what Len Mason said to do:



Couldn't get the depth of field in one shot but the blue line across the carby marks the height of the top of the jet:


After blowing into the central bit of pipe to get the fuel flow started the engine will pull petrol until the little jar is close to empty. If the level is much past half way down then even a small bubble in the fuel line stops the engine. I guess that in this system the fuel flow varies with throttle opening and engine load, so far I haven't added any load to the engine. Right now Mastiff idles around 1200 RPM and spins up to 4500 (only very briefly, I chicken out very quickly) but isn't smooth at any speed, maybe a load would smooth things out?

Thanks again, David

Offline gbritnell

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #258 on: December 11, 2018, 12:40:12 PM »
Hi David,
I spoke in error. Now that I see a close up shot of the fuel reservoir I see that you are pulling fuel from the bottom of the jar. When I first looked at it I thought it was a vapor type set-up where one line feeds air to the tank and agitates the fuel while the other line just pulls the vapors from the air space above the fuel level. A lot of fellows use this type of set-up on their hit and miss engines.
I'll pay more attention next time.
If you're getting that throttle range from idle to high speed I would say it just about perfect.
One thing you could try the next time you run the engine is to loosen the distributor enough so you can just turn it and as you bring the rpm's up try advancing the timing just a little. Some engines will perform better with a little advance. Once my engines have "broken in" I set my timing this way. I give them the maximum advance then back them off just a little. Doing this will generally raise the idle speed a little so it all depends what you're trying to achieve.
gbritnell
Talent unshared is talent wasted.

Offline michelko

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #259 on: December 16, 2018, 01:30:43 PM »
Jim,
The short answer is that Len Mason provided a diagram of the angular positions in his book on "Building Mastiff" and I followed this very carefully:



The original diagram was about 2" by 2 1/2" and the reproduction not very good so I scanned it and printed it A4. The generally poor to very poor reproduction of the drawings in the book was one of the reasons I re-drew the whole engine in Geomagic Design. Having the 3D CAD meant I could produce my own drawings and pictures as checks (.pdf s attached).  Moving each cam to the correct angle in turn required the dividing head to be turned backwards or forwards by various angles and I worked out these angles and wrote a list of the moves needed. The last picture in the post looks enough like Fig 15 on p87 of the book to be reassuring.

The essential design info needed to work out the angles for yourself is that the camshaft turns anticlockwise looked at from the timing end, on each cylinder the cam nose centrelines are 110 degrees apart with the exhaust leading. The firing order is 1,2,4,3.

Thanks for the interest!

Dt

Hi David,
I am a Little confused about your camshaft layout.

From my knowledge the cams of cylinder 1 and cylinder 4 should have the same angle. The firing of the cylinders is divided by 180 degree, the space between  cyl 1 and 4 is 360 degree. Because of the1/2 reduction of the camshaft i makes then 180 degree. While cylinders are opposed and not inline the cam #1 should be in the same position as cam #4  In the cut at the left side of the drawing it lookslike they are a bit of. A typical 4 Zylinder boxer camschaft on vw Typ 1 or type 4 engines also have only 4 lobes.

Am i wrong?

Regards Michael

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #260 on: December 16, 2018, 09:26:19 PM »
Hi Michael,

Yes the camshaft is the trickiest bit of Mastiff to get right and is different from other boxers. The shaft is well above the cylinder horizontal centre line and the tappets and valves are in a straight line, unlike a VW motor there are no push-rods or rockers.

This all means that the tappets and valve stems slope down from the camshaft at an angle of 13 degrees below the horizontal. #1 and #4 cylinders are on opposite sides of the engine which accounts for the two 13 degree angles (easiest seen around 360 on the timing diagram). On cylinders that are on the same side of the engine the slope just moves the valve timing around by 13 Degrees, e.g. #1 exhaust fully open at 347 and #2 exhaust at 77, still 90 apart but rotated 13 degrees.

The other consequence is that you cannot combine cams for cylinders on opposite sides of the motor, and each cylinder must have its own pair of individual cams.

Hope this helps, David

Offline Art K

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #261 on: December 16, 2018, 11:16:50 PM »
David,
I had to reread that to wrap my head around that. But then It makes perfect sense.
Art
"The beautiful thing about learning is that no one can take it away from you" B.B. King