Author Topic: Len Mason's "Mastiff" - chewed from the solid  (Read 10217 times)

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #105 on: August 26, 2017, 03:22:05 AM »
Progress on Mastiff has slowed down lately, winter viral infections and an unheated workshop don't go well together.

When I first re-drew Mastiff I'd decided to have the valves seating directly in the heads but after further thought I've gone back to Len Mason's original design with inserted, one piece, valve guides and seats. Doing it that way makes getting good alignment between the seats and valve stem guides much more likely. In addition the seats are then easily replaceable if the material (2011 called "machine rod" by the supplier) proves unsuitable.

The mounting holes in the cylinder blocks were reamed 8 mm so 10 mm rod was turned to a "Loctite" fit in the heads using the collet chuck:



then drilled 6.4 mm for the port then 2.9 and reamed 3.0 mm for the valve guide hole:



The seating is at 45 so the top slide was set over:



and a small boring tool ground up from a broken end-mill to machine the seating:



I had much finer control over clamping forces in the 3-jaw chuck than in ER32 collets so, after parting off the pieces were turned around and held carefully to machine the seating for the valve spring:



The products (including three of what Roger would call "test pieces") look like:



The reason for the rejections was mostly poor surface finish on the valve seatings.

I've managed to make one "test piece" for the valves leaving the top slide set up, holding the valve by the stem in a collet and taking very small cuts - pictures when I have the 8 valves finished.

DT

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #106 on: September 14, 2017, 09:15:15 AM »
The valves are made from free cutting stainless and the angle and finish on the seating surface, and the size and finish on the stems, need to be good. After turning the seats in the inserted guides I left the topslide set over and hoped that it would be possible to get a tool to reach the seats on the valves from the "inside" rather than trying to reset the topslide angle. The stems need to be 31 mm long, 3 mm diameter.  The length was set with gauge blocks and the saddle stop:



The tangential tool took 1 mm cuts to start with:



followed by a very sharp tipped tool intended for Al alloy to give a fine finish and form a radius under the head. The edge doesn't last very long but two were enough to finish all eight valves. After some fiddling with the angle of the tool holder, and holding the valve stem in an ER16 collet these tips (DCGT11T304 it says on the box) were also used to form the seating:



and this end of the valves now looked like:



With the large overhang of the work I expected to have to turn out some "spring" and this worked fine, however, the valve stems were still not quite parallel which was puzzling and a portent of a nasty discovery later. I'll try these valves when the time comes to run the engine, if they are no good then that will be the time to remake them.

A bit of good fortune allowed the valves to be reversed in the collet:



and project just far enough to turn in the groove for the cotters:



The cotters were turned and parted off and the slots cut by hand. The recess for the spring was formed using a slot drill then the collar parted off and Superglue'd to a stub so the cotter recess could be formed the same way:



With the seatings now Loctite'd into the blocks the bits could be assembled and tested for "feel" which seems OK right now:



I then moved on to making the cylinder liners and it quickly became clear that the lathe doesn't bore parallel holes. Everything came out beautifully concentric and the poor abused DCGT11T304 tips gave a very fine finish to the CI but when I measured the bore at each end of the 85 mm blank (two liners back-to-back) the chuck end was nearly 0.2 bigger, which matches the differences I found in the valve stems. A length of ground bar in the GripTru chuck showed a similar angularity and I'll now buy in a proper 4MT test bar before doing anything more drastic to the machine. It looks like the headstock may be out of line with the bed and the lathe did spend around 25 years in a Tech School so accidental abuse is quite possible.

I now have a month to relax a bit with a visit to the UK including the Forncett day out to look forward to from Sunday on.

Regards, DT

Offline Roger B

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #107 on: September 22, 2017, 06:58:26 PM »
Still following along  :ThumbsUp:  :ThumbsUp:  :wine1: I have made my valves from stainless steel screws and bolts which are already forged to something near the right shape.
Best regards

Roger

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #108 on: Today at 09:46:06 AM »
Thanks Roger,
I've thought of using bolts as a source of materials, never thought as far as finding parts near the right size to use as forgings. Great idea!
DT