SQ4 - maintenance

 After a run to Norwich today, 55 miles at 27.4 mph average speed (according to my new Beeline sat-nav) the Square started making an odd noise on the way home, a bit of a squeak from the engine sounding perhaps like a leaky gasket. I stopped for coffee at the lovely Itteringham community shop:

After going on to reserve on the way home, I thought I would have a look at the plugs and do a compression test and the picture shows the result. All four plugs are the same colour, dark chocolate, all dry, numbers two, three and four all gapped to 18 thou but number one gaps to more like 25-28 which I corrected.  

Compression figures are good and consistent at 130-140 psi.

Restarting the engine after I had put the plugs back in revealed that the squeak had gone. Now I am worrying about the oil pressure on the last part of the trip home...

FH - oil from the drive side cylinder

 I might have mentioned a few times that the hunt master has been burning oil from the drive side cylinder, manifested as an oily exhaust pipe, and oily spark plug, and smoke when pulling away. It's always done this ever since rebuild. I had been hoping that this was just really bedding in but after 550 odd miles I think I have to admit there's something wrong. Since it's back in the workshop for its 500 mile service the rocker box has to come off anyway to retorque the head and we can do some investigation.

I had hoped that the rocker box drain might be blocked and excess oil being sucked down the exhaust valve guide with a poked down the drilling with a bicycle spoke reveals the hole is completely open - as I had expected since I cleared the hole out during rebuild.

Removing the head revealed this - a bit of an oily mess on the drive side (that's on the right of the picture) and a fairly normal looking though dark combustion chamber on the timing side.

And then this! That bear piston crown is the drive side, the one that is smoking. There is barely any carbon deposit there at all compared to the other side which looks quite normal to me. It should be noted that the mixture is quite rich at the moment as the mileage is not really high enough to do any proper plug chops.

This is the timing side exhaust valve.

And the drive side exhaust valve, looking a lot hotter.

Here is the upper side of the head gasket - that is the side that touches the head itself. The area within the red ring shows I think a leak from the cylinder into the head bolt drilling and possibly into the drive side exhaust valve drain. Perhaps this explains both the smoke and the oil coming from the cylinder head joint and dripping onto the primary drive case.

It pays to be careful when removing the cylinder. I released all the nuts and made sure that I collected them all with their washers and put them aside. Next we used the leather mallet to loosen the cylinder joint which was quite straightforward - not forgetting that the forward magneto pickup has to come out to remove the cylinder. 

It's wise to lift the cylinder with the pistons in their uppermost position so that you can lift the skirts above the crankcase mouth to get the couple of pieces of wood into the joint to support the weight of the cylinder. You can then introduce a suitable cloth into the gap to prevent any broken bits of ring or circlip falling into the crankcase. 

Once you have lifted off the cylinder the wooden battons can support the pistons.

Removing the cylinder very carefully reveals two pistons in very good shape - to be expected since they have only done 550 miles. The purpose of this exercise of course is to check that the rings are sound and indeed they are so we can take some comfort in the knowledge that the compression test we did months ago is supported by rings which appear to be in very good condition.

Investigating the head gasket sealing area and the bolt holes reveals a couple of interesting points. Well, one main point really and that is that most of the cylinder head bolts open into a gap between the fins, a few fins below the head joint and secondly that one of the front middle two bolts doesn't pull down properly as the thread appears to be very tight. This is in the area where we suspect the leak to have been.

We will leave this for now as I have a day on the railway tomorrow and some other bits to do. I've made a post on the FH Facebook group to make sure that I've selected the right tap to clean these threads out!

Model A - rear wheel

 It's over 35° C here today, and I don't feel like doing very much so I have been pottering about clearing up the workshop and listening to The Fellowship of the Ring on Audible, read by Andy Serkis.

When all the loose bits were put away I set to to remove the rear wheel rim by undoing all the spokes as I did at the front. Very therapeutic!

The rear brake drum for 1930 features this bolted in ring which is designed to retain any loose spoke heads and prevent them getting involved with the brake shoes - Ariel must have had some mishap to make them realise this would be a problem.

The ring is held in place by three square headed 2 BA bolts which come out easily.

Here is a close up:

The next step is to clean and scrape years of gunge and grease from the brake drum and hub.

The spindle is all present and correct, except that it is very slightly bent. We straighten this out with some heat in the vice.

When it's clean we can put a couple of coats of black gloss on the hub.

Model A - more painting

 This isn't very exciting post but it's important to make it to record when these items had their first coats of paint. This Tekaloid takes a long time to dry fully - about 5 weeks - and I want to know when I can assemble bits.

Today I have used the wheel to strip rust and old paint from the battery tray, the rear chain guard, the oil tank and the dynamo chain guard.

They have been degreased, had a coat of primer and their first top coat.

The second coat went on on the 9th of July.

Charlie's Shed - Concentric carburettor

 Since yesterday when I managed to accidentally drill out the pilot air screw thread on the 928, I've been thinking about how to approach carburetion on the FH. I fitted the Monobloc, which is a bit worn particularly around the mixing chamber cap screw and I realised that I would need to alter the cable lengths to use it. 

Some more thought had me realise that I could repair the damage to the 928 and have a better solution for my non-standard Huntmaster more quickly than messing about with a Monobloc. 

The first thing I did was to tap out the new pilot circuit access ports. The one in the inlet taps out to M5, but the one opposite the pilot air screw is a bit more tricky in that it's too big to tap to M6 and the wall thickness is too small to tap to M8 - but it is perfect for M7. Try buying an M7 grub screw! However, I do have M7 by 1.0 taps and dies by some streak of good fortune and I have tapped that hole M7. 

I drilled out the pilot air screw thread with I think a 4.5 mm drill. I tried tapping it M5 but I guess the whole was not clean enough for that and I had to go to M6. 

The next go/no-go job was to determine whether I could make a successful pilot air screw with a larger thread. I grabbed a bit of 10 mm brass rod:

That turned out ok. It seals most of the pilot air port (you can see the witness mark) but I suspect the thread is bottoming out somewhere. Blowing past it is quite difficult, so it will probably be ok. I replaced the tired O ring.

The next job is to seal the opposite port. I made a plug, but unfortunately the cheapo M7 die I have had for years just won't cut and is now in the bin.

A couple of days later, equipped with a new M7 die I made a new plug:

This seals the cleaning port nicely:

Now we can put it back on and road test it.