Brass eating at worm gear

[Vesa Helske]

On the way home from Finnish Ariel Rally a week ago I noticed that the Smiths Chronometric stopped adding kilometres. First I thought of cable breakage, but as the needle was still moving, I knew some clockwork is foreseeable. Fortunately I had a spare Smiths probably from an NH -56, so I hoped it would have the same gearing ratios. On the spare one , though, needle was not moving. Soon enough I discovered that a leaf spring was on the wrong side of the lever pushing the rocking spindle against the recorder wheel. Fixing that and after cleaning and lubricating a bit, I was able to test it with a Makita. Upon installation I had one issue more: the square end ferrule of the driving cable was 3mm a/f but the cavity on the spare Smiths was 2,5mm a/f. After some grinding/filing everything was fine. On the road it shows exactly same little error (as the original) due to primary drive gearing change. After opening the original Smiths, I was surprised how much brass debris the worm gear had produced, see photo.
A fellow member had, however, quite more serious incident on his 1930 A: he just reached the rally site when the drive end of crankshaft spat all parts outside the crankcase into the primary drive sheet metal casing, the drive chain locking transmission completely. Photo attached shows clearly the condition of thread at the end of shaft.
Vesa

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[Paul_Linden]

An interesting story, and it is good you could repair the speedo. Unfortunately the pictures don’t show on the forum.

[Vesa Helske]

New try with photos!

[nevhunter]

The breather pipe is much longer than original. There should be a grease nipple in the end of the engine driveshaft and the speedo gear is certainly scraping a bit of brass off. Brass is not much of a metal for worm gears. Make sure there's no stiffness in the mileage recording bits and I'd put a bit of light tacky grease sparingly about those gears and pivots. It's NICE to have a working speedo (and trip meter). . Nev

[Vesa Helske]

Thanks for comments! The spare speedo really works fine and accurately! Returning from a test trip to nearby Country Fair on Saturday , I found that the magdyno was rocking on the engine plate. One of four bolts (I added one when restoring the NH) had disappeared and the rest were loose. Also rocker spindle lubrication union was leaking at the soldering. Thus yesterday was spent in the carage, with success at the end!
Vesa

[nevhunter]

Your exhaust pipe is showing a bit of colour. Is the ignition advanced enough or perhaps not enough exhaust valve clearance? Nev

[Vesa Helske]

Nev,
you were right about insufficient exhaust tappet clearance, it was .004 only! Thanks for valuable advise! I guess it's the valve seat (or valve head) wearing out rapidly.
Vesa

[nevhunter]

It could be a pretty ordinary exhaust valve material. Give it a bit of extra clearance and keep an eye on it. If it keeps losing clearance off with the head. The insert might be impacting into the alloy head also. Are the Valve springs the really strong ones?. Nev

[Vesa Helske]

I believe the valve springs are standard, at least I haven't installed anything else and I've had this Ariel for 52 years now. Bought it from first owner in 1971. Obviously it's been unused during most of the last thirty years, so I'm going to check the head internals anyways, next winter.
Vesa

[nevhunter]

Check the valve guides are a tight fit in the Alloy. These heads while they cool better, are much more trouble than the Iron Ones. They are also pretty scarce too so look after it. Don't let it get monstered by someone who doesn't do good work. Nev