Stuart 10V Build Log - Complete Beginner...

Coming together nicely, this is where the DRO comes into it's own and spotting through a thing of the past.

Thanks. Yes, slow, but - sort of sure.

My lathe work is noticeably worse than the milled stuff in terms of accuracy. I really need to get some DRO’s for the ML7, but all the methods I’ve seen for attaching them look a bit naff and fragile.

The last casting to be machined is the flywheel. There are several methods suggested in books or online. The simplest seems to be drill and ream the hole and mount on a mandrel.

Im wondering if it would be better to bore the hole to be a tight fit on the supplied shaft (rather than ream and get a running fit), and then drill the grub screw hole and mount to some spare crankshaft rod using the screw?

my thinking is that this is how the wheel will be fitted, so why not machine it as such and account for any slight deflection caused by the screw?

would boring the hole possibly not give a good enough fit in terms of possible taper?

suggestions welcome as always. Thanks.

The other thing is - is it best to drill the cylinder drain tap holes before lapping?

And what is the suggested size for the hole for these that breaks through into the cylinder? Presumably the threaded part doesn’t go all the way through the wall?

Personally I never machine flywheels on an arbor and it is just asking for chatter and a poor finish. If possible hold by the inside of the rim in either 3 or 4 jaw chuck. Stuarts are usually fairly true once cleaned up with files so 3 jaw will do. This way you can machine the face, 1 side, hub face and then finally bore all at one setting ( I don't ream) then just flip it over to do the other side of rim and hub which don't need any concentricity.

Drill drains first, 1/16" or 1.5mm hole will do, threaded hole about 1/16 to 3/32 short of cylinder

Edited By JasonB on 28/06/2020 10:08:58

Thanks Jason, that should keep me busy for a few days.

Got a bit sidetracked with this, but made a start on the flywheel this afternoon.

Expanded the 3-jaw Chuck to clamp the inside of the rim, and turned true:



Drilled the bore:



I do have a small boring bar, but unfortunately it was just too large for the job. I pondered buying one, but instead opted to ream it to suit the crankshaft:



And machined the inside rim and boss, then reversed in the chuck and did the other side, as suggested:





Fit on the shaft is fine, and thankfully, the features turned on the initial setup are true (at least visually, when spun on the shaft). However, the features on the reverse setup are noticeably off. I suppose a result of the casting not being perfectly uniform. So, I might set it up again in the 4-jaw (clocked to the o/d) and re-do the bits that are off. I don't suppose it matters from a function point of view, it'll just look a bit wrong when running.

So I've done the corrections just in the 4-jaw chuck, all the machined bits seem pretty much spot-on true now, so just needs the screw hole drilling and tapping, then on to the standard and main bearing fitting.

Quick bit of turning to get back into it: The valve rod packing nut. It’s turned from some hexagonal bar:



Then drilled and reamed to 1/8” to suit the valve rod.

Turned to 1/4” and chamfered to give a lead for the die:





Then chamfered the flats and parted off:



Seems to fit ok:

The piston rod seal packing nut is a bit different from the valve rod nut; it’s larger, and has screwdriver cut-outs for tightening instead of flats due to it fitting within the standard. It’s turned from the same brass stock suppled for the piston:



Drilled, reamed, threaded, then turned down to size before parting off:



There are six undimensioned cut-outs in the O/D. I don’t have a rotary table, so I made a simple fixture out of the remaining hexaganol stock from the valve nut:



It’s just sits in the milling vice on a parallel, and the slots milled to 2mm and 0.85mm deep from touching on the diameter. Then move around one flat at a time:



Worked OK:







The threads are a bit sloppy in their holes, not sure why. I suppose I could use thread lock if they loosen.

You are making good progress. A bit of slack in the gland nut threads won't hurt as it will allow them to self align with the rod should there be any slight misalignment. The compressed gland material should stop then from wanting to unwind.

Thanks Jason. Unfortunately (and somewhat inevitably) this is where it all goes wrong...

The valve rod is stepped, and threaded. First of all I made a split bush to fit the 3-jaw chuck (4-jaw won’t close enough). I got it to within 0.0015” of true, centre drilled and turned the end to be a good fit in the valve chest top as per the image:



Not sure if this was the best method, but I didn’t get a particularly good finish on the end. Still, it fitted smoothly enough.

Then, the 5BA thread. The die wouldn’t go on the turned-down end. This is where my heart sank as I realised what I’d done. The hole in the top of the valve chest should be 3/32” (2.38mm), but for some reason I’d ended up with 2.75mm.

The root diameter of the 5BA tap is 2.49mm. so obviously it won’t go on.

M3 has a root diameter of 2.46mm (too small) and a slightly finer pitch Than 5BA. I had an old M3 die which did, for whatever reason, fit over the spigot, but the thread was all over the place. A new M3 die wouldn’t fit at all. The rod also got slightly bent during all this. It does fit, and it does slide in the chest, but it’s not right at all - too sloppy, and the end got damaged by the die:





So...I don’t want to re-make another valve chest because it fits everything else perfectly. The only option I can see is to drill the top chest hole out to 1/8” (same as the reamed gland hole at the bottom), Loctite a brass plug into it and re-drill to 3/32”. That would effectively leave me with a 0.4mm wall thickness sleeve in the top end.

And of course I'd re-make the rod from scratch.

I could do with some advice on turning small diameter rods in silver steel/stainless. I've never been able to do it properly. In this case, I had to leave enough protruding from the chuck so I could remove the tail centre and keep test fitting it in the valve block, which is relatively deep. I'll need to nail a technicque for doing them for other critical parts that are on the horizon.

If I do have to buy another valve chest casting and start again, I will do, but I'd really, really prefer not to.

Thanks!

As you won't get a full depth of thread on the reduced diameter guide more a flat rod with a spiral groove I doubt it will make any difference to the running of the engine so you can make it to fit the hole then run the die down the lot.

You did not say if you reduced the shaft to 3mm before cutting the M3 thread if not that could explain it being wonky and an old die will always struggle in stainless.

Your biggest issue at the moment is the wayward thread as it may twist the valve nut and cause it to lift off the port face but that will depend to some extent how tight the valve nut thread is. ideally make a new rod same size to fit the end hole and thread 5BA as it is easier to do that now rather than having to mount the piston onto a replacement rod.

Use one of your DCGT inserts on the stainless and in fact on any long slender work, your holding and tailstock support is fine.

Thanks Jason.

I will use the old rod to practice getting a good finish.

I appreciate that a partial depth thread on the spigot end would probably be fine, functionally, but I just don’t like the thought of it being like that. I’d rather make it to size, and get it right.

Apart from time and messing about, can you see any issue with plugging with brass and re-drilling? Apart from having to set-up the block in the 4-jaw again, I think I can get it true to a decent level. As you say, the gland seal seems to do most of the alignment, and the spigot just stops any major wobble.

Thanks.

Have you got a travelling steady? It helps with some jobs on long slender parts where only the end needs machining but it is not being done close to the chuck. Even a lashed up steady will help, it doesn't have to be pretty (I haven't got one but I think the Smart & Brown one is an ugly lump).

Martin C

I do have a Myford one yes. I've only used it once (came in a box when I bought the lathe). I could give it a go. Thanks.

As you have things lined up already with the existing hole you could just loctite a sleeve into the hole. Make it a bit smaller say 1.8mm ID so it has some strength and turn the end of the rod down to suit.

There's an idea.

I've got a load of brass tube for modelling. I wonder if some might happen to fit...

Anyway it looks like this evening's entertainment is arranged. I have *just* enough rod spare to try once more. No room for error though.

Hi Dr G, still following your progress.

Just a thought you might like to consider on the valve rod set up.

Instead of threading the rod and valve nut just have a nut that has a small grub screw set into lock the nut in position.

The big advantage of this is that when setting the valve you do not have to keep breaking the valve linkage apart in order to make adjustment by turning the valve rod.

I used this idea which was passed to me by 'KBC' over on MEM when rebuilding my ST twin. It works really well, does not slip and has simplified valve setting no end. I pass it on in the same spirit that George did

Regards - Ramon

Edited By Ramon Wilson on 22/07/2020 15:06:19

Thanks Ramon, that's a very neat idea. I wish I'd have heard of it before trying to thread the un-threadable.

I only just read your post, and have spent this evening trying to correct the valve chest hole (outlined below). If I have further issues with the thread, I'll use your grub screw method. Thanks very much.