FH - bottom end complete

A little bit later than expected I am back in the workshop. My generator decided to burn out it's alternator winding, and took the battery charger with it which meant buying a new generator, building a trolley for it (it doesn't fit where the old one was) and building a trolley for the welders - because their spot is now taken up by the generator...

Having got most of that out of the way, I can strip the cases again to fit the replacement connector rod nuts, BSA part number 37-1691. These are genuine new old stock from Vale-Onslow. Looking at the picture below, from left to right we have the modified Draganfly nut, an unmodified nut, and on the right the new lower profile nut:

This, by the way, is the mark left by the Draganfly nuts before I modified them:

Here are the Draganfly big end bolt washers. These are laser cut stainless and whilst some suggested they were rather small, they are much the same size as the bearing surface of the nut so I am leaving them in place.

Stupidly, I forgot to picture the new nuts in place on the big end caps. Mrs H phoned to see where I had got to (I'll just be 10 minutes dear!), and that's always a distraction. Suffice to say that they were torqued up to 22 lbf. ft in accordance with the BSA data sheet and I oiled up the various bearings before closing the cases. I made sure to remove all traces of Threebond and was very sparing with it when reassembling.

The case bolts are all stainless, from Acme as usual and they fit beautifully. I made this chart from the diagram in the Draganfly catalogue to show me where the different bolts go:

Lovely and easy putting them in; I used my frame spreader to make it a bit easier.

Now that the bottom end is in, we've got a number of workfaces to tackle:

• the barrel and pistons
• the primary case
• the timing gear

We can look at any of these really but before we do there are some components around the engine that will become less accessible as we progress. The first of these is the engine breather shown here in the form in which it arrived:

This isn't how Ariel designed it. It's supposed to bend around and appear behind the FERC, above the gearbox sprocket somewhere.

Another item is the magneto. It's fitted here temporarily with the long bottom nut, which is on the job list for zinc plating. With the primary case loosely bolted in place you can see that it's quite restricted in there:

Something that surprised me, and thanks to Daniel Rix on the FH Facebook page for this, is that you cannot get the brake bell crank on with the primary case in place. That's a pain, because I want to get on with the mechanical build and I hadn't planned on doing any plating just yet... and the bell crank needs plating.

The other thing I must remember is to fit the oil lines before I fit the primary cases! Access will be a trifle difficult if I forget, so let's not get ahead of ourselves and we will get on with sorting out some of the details.

FH - more shims & trimming nuts

 Following Thursday’s abortive first attempt, I pulled the cases apart again for a look at the big end nuts and to fit another shim to the drive side main bearing.

Roger Gwynn, all round guru, Ariel Hero and founder of Draganfly Motorcycles (without whom us Arielisti would be lost at sea) told me on the AOMCC Forum that the big end nut/crankcase clearance is close in these engines but you don't need to remove much material to avoid a clash. Roger recommended grinding some material from the cases.

What I've done today is make a 1 mm chamfer on the offending edges of the two timing side nuts, so now I know what clearance I need to provide. If I can provide that clearance without modifying components I will be a happy bunny.

Club member Mick suggested that the fact that no bolt thread protruded beyond the nut wasn’t satisfactory, since the locking part of the nut was probably bearing on a reduced (tapered) part of the thread:

I've ordered a new set of nuts, still self locking but to a slightly shallower pattern (still big end nuts, not something nasty) and I'll use these with larger but thinner washers I think. That will guarantee the self locking bit of the nut is on the full diameter of the bolt thread. I’ll probably have to make the washers myself on the lathe.

Meanwhile, adding a 0.1 mm shim to the 0.25 mm shim already there has given me 0.07 mm end float, or about 0.0027”.

That will do nicely.

FH - Assembling the bottom end

 With the crankshaft together and the few internal components of the crankcase assembled, it's time to put them together. First step is to thinly coat the mating faces with Threebond 1215:

With the cases bolted together, we can measure the end float again. This time we have 0.18 mm - last time we had 0.34 mm, and I added one 0.25 mm shim under the bearing. Something has changed, or I have made an error because 0.34 - 0.25 = 0.09, not 0.19...

That's 0.0075" - we are aiming at 0.005". I'll see what shims I have in stock.

The next challenge comes when we check crankshaft rotation - it doesn't. There are two clashes one on the rear of the case, one on the front; the rear is a scrape that allows the crankshaft to move, but the clash at the front is more serious and prevents movement altogether. You can see the witness marks in the picture - this is probably the big end nuts fouling the crankcase:

That's coming apart again.

FH - Plastiguage and the big ends

 Next step is to check the big end clearances. I've measured the journals, but I wanted to get some evidence of the clearance that I had ended up with after fitting new -0.030" shells. There isn't much detail on what the acceptable clearance is  before you must regrind, other than the data describing the sizes you regrind to and the recommendation that there should be minimal clearance after regrinding.

Waller indicates 0.003"- 0.004" for the big end shells used on 1948-1955 Square Fours (Fifth edition page 37); Phil Irving quotes 0.001-0.0015" clearance per inch of diameter (Tuning for Speed 3rd Edition), which equates to 0.00165 - 0.0025" for my 1.65" big end. Mr. Irving, otherwise known as 'Slide Rule' using those delightful pseudonyms beloved of motoring writers in the '40's, also notes that the clearance can be much larger as long as oil pressure is maintained.

So, let's introduce Plastiguage. This is a paste, extruded into rods a bit like Plasticene. You trap a bit in the bearing and squash it, so that the known Plastiguage rod diameter is squashed to take up the clearance of the bearing - you then use the card provided to determine the clearance from the width of the squashed Plastiguage. Plastiguage comes in different sizes to measure different clearance ranges.

So, you cut a length to suite the bearing like this, and then you make up the bearing. You make sure the bearing is clean first.

When you open the bearing again you can see the squashed Plastiguage and you can compare it to the card. This suggests something like 0.002 - 0.0025" clearance for the drive side. I'm happy with that.

This is the timing side, and it's about the same:

All good there then. Next job is to make sure the oil flows into the big ends. I'll inject it into the timing side oilway:

And it comes out the drive side big end!

During this process, I removed (with a little heat) one of the gudgeon pins from the new IMD 7.25:1 pistons I got from the AOMCC so I could check the fit in the connecting rod little end bearings. This proved to be perfect once I had cleared a small burr from one side of both bearings; not sure how that came to be there.

Happy days.

FH - no progress except for COVID

 Well, there's not much happening at the moment. After a few fun packed days babysitting the grandchildren, I have finally caught COVID - fortunately in it's latest rather benign variant.

In other news, the missing big end bolts have arrived from Draganfly. 

With some detailed advice on some crankcase questions, I'll start building the engine when I'm back on my feet.