It's been a while...

About a month actually. Ariel time in the last 4 weeks has been spent on a number of fronts: 

• welding cable guides inside the rear mudguard 
• finishing the wiring 
• messing about with the valve timing 

the latter item has been the most frustrating. I have a good set of guidance notes from Draganfly, written by Bruce Longman which I have followed religiously.

I assembled the head using only cylinder number 1, as I thought I would make it easy on myself and avoid having to turn the cam against four sets of valve springs.

Initially I tried the Waller-style method of aligning timing marks.

Having done this I turned the engine over to see the exhaust valve opening half way down the power stroke. Bruce says that sometimes the factory timing marks don't give the correct timing, so I tried again... and again... and again... eventually getting the timing discs and dial test indicator out to do the job the long way, all the while getting more and more proficient at releasing tension on the cam chain, removing the nuts, drawing off the crankshaft pinion before I could remove the cam shaft pinion... Always the same result.

Eventually I started doing this more scientifically, drawing the valve event charts and calculating overlaps & durations. This is what it is supposed to look like:

Frustrated with Cylinder #1, and confused by the fact that #1 runs backwards, I changed to #3 and drew another diagram:



This revealed that #3 was about 180 degrees out; while #1 inlet valve was correct and #1 exhaust valve was about 180 degrees out too. Confused, I thought about looking at #2, which was doubly frustrating because one of the pushrods would not go in the tunnel.

I set and reset valve timings for about a week, and then one day, looking at the rockers, pushrods and convincing myself that #1 inlet must somehow be on the wrong cam, I started looking at the #2 inlet pushrod problem when I happened to glance down the #1 inlet pushrod tunnel - to see the pushrod going off at a weird angle.

I now know it is possible to get a SQ4 pushrod in it's neighbour's tappet. #1 inlet was in #2 inlet's tappet, so it was operating from #2 inlet's cam! Now that I realise what I am looking at, it's obvious.

Ho hum. we live and learn. At least I found it before I pulled the head off again!

The head is on!

So we are all set. The sun is shining, I have a day free (after cutting the grass and making the family dinner) and I have all the parts, plus a very nice text from Bruce Longman via Draganfly with explicit instructions. Max is in bed, so he will be happy for a bit:

A Chocolate Sprocker, feeling very 'Sunday Morningish'

I have some high temperature silicone gasket as recommended by Bruce. Loctite say this is suitable for operating temperatures up to 275 degrees C (sustained) with excursions to 300 C:

So as recommended by Bruce, we start by laying a band of sealant around the pushrod tunnels, on both sides of the gasket. Actually easier to lay one bead on the gasket, and one bead on the block, making sure you have the handed gaskets the right way around:

No picture, but next I placed all the head nuts in position between the cylinder block fins, under their holes, with the flanges upward. Next, manoeuvre the head under the frame tube and drop it into place over the studs, making sure the extended, rounded ends of the studs drop into the nuts. Add the sleeve nuts inside the rocker boxes, and the 5/16" CEI reduced hex nuts outside the rocker boxes. You hand screw these down finger tight.

And as Kees Knegt pointed out in a comment to an earlier post, this would have been easier without the rockers! You cannot fit the pushrods with the rockers in place either (they don't slide sideways far enough) so I may as well have left them off... although I do like to trial fit everything at least once.

Next, with your thinnest 5/16" CEI open spanner, engage all the nuts on the downward facing head studs and turn them as far as they will go without using and force. You will realise now that if you leave one undone, and tighten the others, you will crack a fin by virtue of the loose nut pushing downward onto the fin below.

Once you have all the nuts finger tight you will see the head finally come down onto the gaskets. continue going around all the nuts inside & outside the rocker boxes until they are all snugged down finger tight.

You will need a variety of spanners to achieve this. The reduced hex nuts in the middle of the head, under the inlet tract are particularly inaccessible.

So, when everything is snugged down, use Bruce's torque figures and sequence to tighten down the head.

Job done.

Cylinder Head Assembly

So, I have most of the parts to replace the head, apart from the high temperature sealant recommended by Bruce Longman. Over the past couple of days I have fitted the new head studs:

The thread into the head on later engines is 3/8" BSW, and there is a parallel section on the stud which has to engage with a counterbore in the head. You can see these here:

As the head had been skimmed, much of the counterbore had been machined away. To deal with this, I recut all the head stud threads and remachined the counterbore. Hours later, I have all the head studs in place. After I'd done all this work I ran the 5/16" CEI die down the eight studs in the block, just to make sure there would be no trouble when the head went on.

Next up was the polishing. It's fairly clear from the state of the casting that the fin edges, the 'V' along the top of the exhaust ports, and possibly the sides of the rocker box were polished - maybe also the carburetter flange. Personally I'm not sure that Ariel would have done this, since the rocker box sides would be quite difficult to polish without resorting to small buffs and hand work - there is no access for a polishing wheel, so this would have been time consuming & expensive. I've polished the fins for now; I also like the contrast between the polished rocker covers and the unpolished rocker boxes.

Final thing is the assembly of the rockers themselves. These are all back in, with a couple of replacement shafts (thread damage). One of these went in and out several times - and turned out to be too large on the OD, and with the two grooves for the 'U' washer in the wrong place. The best of the old ones went back in and the replacement will go back to the supplier.

So, now I am waiting for the high temperature sealant and the head can go on!