Author Topic: Len Mason's "Mastiff" - chewed from the solid  (Read 33444 times)

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #60 on: January 25, 2017, 05:32:07 AM »
Thanks Art.
Re-bushing would be a bit hair raising  - there is a lot of work gone into the crankcase that I'm reluctant to put at risk. Also there is slightly less than 2 mm of metal between the top of the bore for the bush and the top deck of the crankcase. In a cast iron or steel block I might have tried silver soldering in a plug and expecting that the sliver of metal left from it after reboring would stay fixed, in Al I'm not sure glue would stay put, might be wrong.

I was lucky (and a bit surprised) that the method worked out first time - I was prepared to try again with another dummy brass bush if I'd had to.
DT

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #61 on: February 11, 2017, 01:09:08 AM »
With the camshaft bushes lined up properly I now had to get on and make the cams – I hadn’t done this before and it looked difficult. The method for making cams described by Len Mason in the mastiff book looked far too complicated and it’s no surprise that a few other ways have been published. After a lot of searching around on the web I found the work of Rod Jenkins, as modified by Ron Chernich, and this looked like the way to go considering the workshop gear that I have. The hassle of running Java code on Windows (and the usual desire to find out what’s inside anything) motivated me to re-write the software in Python 3; when I’m convinced that the cam-follower velocities and accelerations are OK I’ll let the program loose. The offsets needed for cutting cams look good and text files for the Mastiff inlet and exhaust cams are attached. These are tabulated at 1° steps but cutting at 3° intervals worked well for me.

The cams started as two lengths of ½” silver steel  which were necked down to leave four cam blanks in a row:



Transferred to the dividing head on the mill the blanks were (rather laboriously) cut to the base circle radius for 240° (inlet) and 230° (exhaust) in 3° steps. About now the urge towards CNC became even stronger.




The rest of the cam profiles were then stepped through (this is the second set where I added tailstock support to improve the surface finish a little):


 An outbreak of stupidity made this process much harder than it should have been – when going “over the top” of the cam I twice messed up by, completely without realising, changed the direction I was turning the dividing head handle. Must be something in my psychology?? Anyway, I’m not into analysis so I decided to fix the problem mechanically and burrowed in to 40+ years worth of “things that would come in handy sometime” (known to someone else as “all that junk down there”). What I found was a pair of gears (original use long forgotten) with a one-way clutch between them:


With a simple adaptor sleeve this fitted neatly on to the dividing head drive shaft:


Now it didn’t matter what happened inside my head, the shaft could only turn anticlockwise and the two sets of cams were ready for polishing and parting off. The cams were much easier to polish as a solid set than as individuals:



Each cam was then faced to length on a taper mandrel:


And the final results look like:


A bit of tweaking of lengths and “selective assembly” in the block made it important to keep track of which cam was which during hardening, cleaning and final assembly:


To assemble the cams on the shaft core I followed the method described by Mick Knights in his “The Mastiff Plus” series in Model Engineer (Parts 8 and 9 in #4521 and #4523). This needs a guide pin machined to fit the cam noses:


And centred over the core mounted in the dividing head:


Then slid along the core at the correct (I sincerely hope!) angular location with some Loctite 638 on the core:


With the bearing journals added the final product looked like:


In the block it looks good!


Phew! That took longer than I thought…
It is also going to be a long wait before I find out if the cam angles are correct but for now I’ll move on to finishing the timing end gearing, oil pump etc.
DT

Offline PJPickard

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #62 on: February 11, 2017, 02:22:14 AM »
Just want to say I'm following along here...I have it in my my to do the same build eventually. Nice work you are doing!

Offline Nick_G

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #63 on: February 11, 2017, 07:22:47 AM »
.
That was very informative and well presented documentation.

Many thanks for the time and effort you took demonstrating the above so that others can benefit.

Nick

Online Dave Otto

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #64 on: February 12, 2017, 12:57:41 AM »
Interesting way to assemble a cam from parts.

I always enjoy seeing progress on your engine DT.



Dave

Offline Flyboy Jim

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #65 on: February 12, 2017, 04:27:06 AM »
Great explanation of the process of the making of these cams, DT. But now, it begs the question: How the heck did you line all these pieces up to get them at the correct angle?

Jim
Sherline 4400 Lathe
Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #66 on: February 12, 2017, 04:45:36 AM »
PJP, Dave and Nick - thanks for the positive comments and the encouragement.

Len Mason suggested the cam assembly method in his original Mastiff book but he used a complicated jig to get things in the right place.

I have a book by Arthur Rubbra on the development of Rolls-Royce aero engines with which he was involved. On one occasion they couldn't get a new prototype engine to run on the test-bed and found that the crankshaft had been designed for one firing order and the camshafts for another (even RR can make SNAFUs!). He writes: "However, the experimental shop night shift soon had us running properly by slicing up the hollow camshafts into six pieces and pinning them to a central shaft in the correct firing order." If its good enough for RR...

DT

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #67 on: February 12, 2017, 05:38:30 AM »
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

Offline Flyboy Jim

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #68 on: February 12, 2017, 02:27:09 PM »
Thanks for the explanation and drawings, Dt. That's amazing work you're doing!

Jim
Sherline 4400 Lathe
Sherline 5400 Mill
"You can do small things on big machines, but you can do small things on small machines".

Offline Doc

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #69 on: February 12, 2017, 03:02:44 PM »
Looking good that cam looks really nice!!

Offline Roger B

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #70 on: February 14, 2017, 11:34:16 AM »
Nice work on the cams  :praise2:  :praise2: I used 6° steps when cutting mine with a 60 tooth gear as the dividing plate. I would certainly be interested in you updated cam calculator when you feel it is ready to be released  :)  :wine1:
Best regards

Roger

Offline 90LX_Notch

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #71 on: February 14, 2017, 04:48:19 PM »
Nicely done and an informative write as well DT.

-Bob
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My Engine Videos on YouTube-
http://www.youtube.com/user/Notch90usa/videos

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #72 on: March 18, 2017, 06:44:22 AM »
With the camshaft and crankshaft completed the timing case and its contents can be completed. To make sure of getting the auxiliary drive gears spaced correctly the oil pump has to be available. In the original design this is a gunmetal casting, in the spirit of carving metal mine was made from part of a scrap dental flask clamp. My late father-in-law was a country dentist and kept his own dental lab gear for when there wasn't time to send work into the nearest town. The flasks and clamps were used as part of the kit for making acrylic dentures and are made from bronze. I scrounged these when we cleared out his practice and have used them ever since as a source of semi-precious metal. I first cut a slab for the pump cover (15/16" x 5/8" x 18"), finished it on one face and superglued it back on to the scrap to finish the other side:



Then trimmed the sides of the block with an end mill to create the blank pump body:



Which was then cut off and finished all round:



This looked so good that I felt like keeping it intact as a piece of jewellery but common sense prevailed and I drilled the mounting holes through both pieces; the superglue bond broke , for once, at just the right time. I then bored the 3/8" hole for one gear, plugged that with brass and drilled and D-bitted out the other:



The other bits needed for the fabrication were simple turning and threading tasks and the gears came from Hemingway Kits. The drive shaft is from FCMS and has a flat at the top to engage with a matching flat on the shaft that will drive the contact breaker:



In the Mastiff book Len Mason suggests leaving the shaping of the outline of the cover until the rest of the pump is finished. This is a good idea - shaping the two parts together, as I did, results in a lovely match between the two but then you have to locate the axle for the idler gear very, very accurately to maintain the match and the alignment of the mounting holes. Needless to say this didn't happen first time around and the hole for the axle pin had to be nudged around. I didn't take pictures - it wasn't pretty.

Assembled the insides of the pump look like:



and the outside:



Drilling the mounting holes into the timing case was the last act:



And I could move on to mounting and securing the timing case after making and fitting the camshaft drive gears.

DT

Offline steamer

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #73 on: March 18, 2017, 11:31:32 AM »
Little gear type pumps are challenging!    getting the centerlines right for mesh and then the mear wisp of clearance on the OD...is tough.

Looks like you nailed it!



Dave
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Damned ijjit!

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #74 on: March 20, 2017, 02:45:14 AM »
Thanks Dave,
Like the rest of the engine I won't know how well the oil pump works until I can test it for real. Len Mason suggests that it pumps far more oil than Mastiff needs so there should be a bit to spare.
The clearance between the gears and the casing is more than I would have liked, had to trim the gears to get them to run concentrically. The two helical gears that came from Hemingway are very well finished and run well, the rest of the gears supplied were not so good. See the next post...

David T