Tuesday, March 11, 2008
Sometimes a problem on one of my bikes is far beyond my skill to repair, and I call on a Professional. In this case, the pushrod tips and rockers on my '28 Sunbeam had worn themselves away terribly, and I needed new ones, as spares simply aren't available - the rockers and side plates are unique to three years of ohv Sunbeam models 9 and 90 ('25-'28).
The original exhaust rocker had shattered about 5 years ago on an AMCA club run, while I was doing about 80mph down Stewarts Point Road, when I suddenly lost power. Ten people had searched the grass for my 'lost' pushrod, which I found wedged safely on the gearbox; when I attempted to replace the pushrod, the cup into which the pushrod tip fit, was simply gone, and a jagged rocker arm greeted me.
John Prideaux made a fine bodge of welding a new blob on the end of the rocker, and we did our best to form a tip and round cup for the pushrod tip - he used a welding rod which was used for repairing Caterpillar tractor treads, which was incredibly hard. The repair lasted 4 years (about 2000 miles I reckon), before the pushrod tips themselves began to wear away from the imperfect cup interior.
Amazingly, at the Banbury run autojumble last June, Brian Page had a pair of rockers waiting for me - problem solved! Or so I thought; when I got them home, it became clear that these rockers would soon meet the fate of my originals - 80 years had worn the cups extremely thin. The construction of the rockers is very delicate to begin with, as they are lightweight racing items, and we're decades beyond any 'service life' ever envisioned for them!
Jo Groeger was enlisted to rebuild the pushrod tips and rocker cups; Jo is has vast experience as a master machinist (he is turning 88 years old March 14th!), and a renowned Vintage BMW enthusiast/restorer/parts maker (see pic of BMW crankshaft in jig and /2 engine on a stand). Apparently he doesn't mind working on Sunbeam parts, though, and he made the replacement bits in a couple of weeks. Those are pics of Jo (Joachim actually), at work on the pushrods - the second photo shows him at work on the lathe, his hands a blur; yes he works very quickly, and the parts came out looking better than new. You can see the new parts compared to the old in the lower photo - the original cups are very delicate, but Jo says the new ones will outlast me! He remade the pushrod cups from a hard steel, welded them onto the rocker, then hardened the cups by heating them up with a torch and powder, then letting them cool slowly in oil over 24 hours. The new cups are a bit heavier than the originals, as can be seen in the photo (new rocker and pushrod tips on the right), but I'm not going to lighten them for performance; the bike is plenty quick, and I don't think squeezing every bit of rpm out of an 80-year-old machine is a good idea.
The bike was reassembled within a hour - exposed valvegear ohv engines are so very easy to work on; all the parts are out in the open, and four bolts hold it all together (see photo which shows the rocker shafts still screwed to one side plate, and the cam follower/rod pusher cups on the crankcase).
Bottom photo shows the completed engine, ready for a ride.