OK, a followup after more research. It seems I measured the rear crankshaft float incorrectly, and the front was artificially high because the bush itself was loose in the case, free to move back and forth. It looks as though the float is actually zero to slightly negative without shims, and thus ...

Hello all,

I measured the crankshaft end float on my 1952 Square Four Mk1: .016" rear and .033" front. According to Drags, correct float is .003” to .004” on the front crank and .005” to .006” on the rear.

But also according to Drags, "Ariels only ever listed shims to increase the end float, not ...

Alan,
Thanks for the Ben Longman suggestion. The Iron Horse website has no mention of con rods, but in any case I'm leaning towards retaining the MkII ones now in place. They're stronger than the MkI version, and it seems the main cause of rod failure is oil deprivation from a blocked slinger. As ...

Thanks for all the informed input!

It seems uncertainty remains on whether small end bushes were original fitment; on the one hand they're shown in the factory spares list and many people have observed them, on the other hand many have observed likely original rods without them. Perhaps some of ...

Nev,

Thanks, I can see that working. But it requires locating an oversize pin (where?), machining both the small end and piston bosses to fit, then possibly lightening the (hardened steel?) pin. It would be simpler to just enlarge the small end and install a bush, as Ariel apparently did on some ...

Hello all,

I'm tearing down my 1952 Mark I Square Four, taking arms against a sea of troubles, and have noticed the small ends have no bushes. The gudgeon pins, of standard diameter, run directly in the rod alloy. This seems odd, and I've never before seen such an arrangement. Also, I see a small ...

To follow up on this question,

Chris is graciously sending me a used Mark I style blade, so all is well (thanks Chris!)

I posed this question to Draganfly, and received the following very useful information:

"I've been down to our workshop to investigate the possibility of using the Mark II ...

Chris,

PM sent, thanks.

Dave

Hello all,

It seems my Mark I timing chain tensioner blade (2110-31) is broken, and new ones are out of stock at Drags.

In some earlier posts, it was suggested that the later Mark II design for a duplex chain (2110-56) might be used instead, even with the Mark I single-row chain. This is ...

Another bit of data: I queried Draganfly, who make their 4G pipes with the small one to the rockers, but Mark I pipes with the large one to the rockers.
They replied "we are confident the parts are correct to OEM specifications"