Member postings for Dick Ganderton 1

It's a bit too late now, but you don't need to remove the spindle to change the belts on a Myford S7. The best way is to just cut off the old belt and fit a Nu T Link belt. My S7B is fitted with this and find that it runs quieter than than the conventional belt. You can buy it from your local Fenner drive stockist. The motor to countershaft belt is a 'Z' and the countershaft to headstock is 'A'. I did have problems with changing the belt due to lack of clearance between the headstock casting and the pulley, but a few minutes with the Dremel soon cured this.

I can also recommend the taper roller bearing mod to the back end of the spindle.

DickG

Neil, still haven't received it. Can you please send it again. What e-mail address have you got for me?

DickG

Just got back to continuing with the engine. I am making the crankshaft and have got to the point where I need to shape the crank end. Should the radius at the root of the cut away portions be 0.125" radius rather than 0.25" rad? O.25" rad implies a 0.5" dia cutter. It also makes the end of the 0.5" 'arm' completely rounded off getting very close to the crank pin hole.

I have made another cylinder jacket and have managed to get the fixing screws in by making them as short as I dare and machining the head diameters so that they clear the wall. 6BA would definitely be better than M3 but having already drilled and tapped the crankcase for M3 there is no going to 6BA.

I haven't managed to find a source of small hex metric screws. Any suggestions?

DickG

Definitely well worth doing. However, there are a few problems with the drawings and part numbers in the article.

I have since found that the useless oil nipple on the rear bearing housing wasn't letting any oil through. I have replaced this with a brass oil cup that really does let the oil get through to the bearings.

Here is what I found. (I think it was later published in MEW.)

I have just completed the mods to my Myford S7 Headstock as described in Ken

Wilson's Article in the April 2011 Model Engineers Workshop.

I have never been able to get this machine to run on the top speed range or to

get the rear bearings to properly adjust to take end thrust when drilling with large

drills. This is in complete contrast to my previous, earlier S7, which spent most of

its life running at top speed with no trouble. Now I can run at top speed - I have

even tried it at twice top speed as I have a 3-phase motor fitted driven from an

invertor to give speed control.

However, I think that there are problems with the dimensions given for the

modifications to the two locking rings and the new spacer. The recess depth,

given as 3.4 - 3.5 mm (0.134" - 0.138" in understandable units) is not deep

enough to clear the inner race of the new bearings. I had to increase the depth to

0.140" to just clear the inner race - 0.144" would be better. It's very frustrating to

discover this when you have got the headstock in bits and no way to remachine

the rings! Fortunately, I had opted to buy new rings from Myford - the part

number is G2340 not G2430 as quoted in the article, order that part number and

you will get a driver plate - so I was able to put the headstock back together and

take the extra few thousandths off.

Having gone to the trouble to make a new spacer to the dimensions given in the

article, I found that with it fitted the front locking ring protruded too far into the

headstock while the rear one was so far into the housing that the C-spanner

could not get hold of the slots. So I put the old spacer back and everything was

OK.

It's definitely worth doing the mods as it now runs faster and quieter and is much

easier to adjust than with the standard ball races.

Dick G

Chris. 6BA screws are smaller than M3 - which probably explains why you were able to get them in. I had to reduce the head diameter of all the screws I tried by around 0.03" to miss the wall of the jacket. 5BA would be a better equivalent to M3. I decided to use cap head M3 stainless screws throughout.

I prefer the bottom of the fins as shown in the GA - it just looks 'more correct'. Anyway, I have made it now and don't intend to make another one. At least my exhaust ports will line up!

I tried the trick of fitting the screws in the holes first but that didn't work either. The liner cannot be used to locate the jacket for two reasons - it doesn't reach down as far as the crankcase and it's a smaller diameter than both the bore of the jacket and the hole in the top of the crankcase. I turned up a locating plug from an odd bit of steel bar with the two diameters and just drop this in place.

The transfer ports are 0.140" diameter so the centre of the cutter will need to be 0.049" below the bottom of the flange.

Transfer Ports: The height and position in the bore is critical as this affects the timing on a two-stroke engine. They are straight slots radially disposed around the bore of the liner. They are angled upwards at 45 degrees and this gives a problem in determining where to start the cut if the ports are to end up in the right position. To make the slots the liner needs to be rotated. The photos of the set-up shows no means of doing this - there is no rotary table or three-jaw chuck. A 3.5mm cutter is just a few thou under the size of the ports - 9/64" is just over. Moving the mill's table across will result in a crescent shaped slot with the ends of the slots upwards towards the top of the cylinder bore. Perhaps this won't matter, perhaps it will, perhaps I'm worrying too much.

Cylinder Jacket: You are correct - a look at Photo 27 is the clearest. However, I tried every type of screw except hex headed - I haven't got any M3 ones - and found it almost impossible to get them in and start to turn them. I used ball ended hex keys but they have to be used at too shallow an angle to work and I do have keys with short ends to get into places with low headroom. Cutting the four scollops allows the screws to be easily inserted and whatever driver is needed to be used almost vertically.

Materials List: I always buy screws and the longest length I can and in large quantities. They are easily cut down - just screw a steel nut on, saw to length, tidy up sawn end on the linisher, remove nut to clear thread at end - but not easily made longer! Having a materials list would have made it easier to determine if my materials store at home had the required chunks of aluminium or the right grade and lengths of steel so that whatever I might need could be sourced at Ally Pally at the end of January.

Part 1: No dimension is given for the width of the top face. Somehow I ended up at 1.688, (11/16". But, it's not too critical.

Part 2 is more involved and has a lot of errors I'll try to explain them. They are only for those components that I have tried to make, so there could be others!

Liner.

The 0.075 dimension for the top of the exhaust port from the underside of the flange is smaller than the dimension of the exhaust port! I think it should be the thickness of the flange.

Transfer Port: No dimension is given for the top of the port where it enters the bore. Or do we have to guess that it's level with the bottom of the exhaust port? Also do we guess where to start cutting - at an angle - so as to get the cutter to just hit the corner of the flange and enter the bore just level with the exhaust port? What size cutter would I use? The photos show the set up the author used. It's a simple set-up with the liner clamped to a vee block. How did he rotate it to cut the three ports as slots?

Cylinder Fins: The bottom of this component is not like the GA! If it's made to drawing then the exhaust port bottom edge is 0.08 above the bottom edge of the exhaust port in the Liner. That's half the height of the port! I have made mine to match the GA

Cylinder Jacket: Having made this to drawing I found that it was well nigh impossible to get the four M3 screws holding it to the crankcase in place and then tighten them. The photos show cap head screws. I have tried all types of screws but, in the end, gave up. My solution was to machine four scallops in the top flange to allow the screws to be inserted and the hex key - with a 'ball' end' - to be used to tighten them. Of course, this means that the four long screws used to fasten the head and fins in place will need to be placed 'fore and aft' and 'across' the engine, but I don't think that will be a problem.

It would have been very useful to have had a Materials List in Part 1. This should have included the sizes and lengths of the screws.

I will probably try for the Crankshaft next.

DickG

Is anyone else trying to build one of these engines? The mistakes in the drawings for the crankcase in Part 1 are obvious, but the components in Part 2 are a bit more problematical.

Dick Ganderton