nasty knock for the ABC at Brooklands

The ABC engine is fully apart and it looks like a loose flywheel/clutch was the cause of our problems. This probable also was the cause of all the crankshaft bearings coming loose in the casing (hence the end play on the crank) and (via play in the gearbox mainshaft) some damage to the bevel gear. One the bright side, all the keyways and shafts look reasonable and everything else can be fixed. We are now in the process of cleaning up the parts and ordering some replacement bearings, in preperation for the rebuild.

A question for the group. The pistons/rings show little signs off wear, the bores are however 12 thou oval and are most likely already rebored to +20thou. The barrels are a work of art; however very thin - does the group know what is the max overbore size possible? I do not remember the ABC smoking when it was previously run, so we may leave the barrels as they are.
best regards
Ian

Here we go, on the Longest Day...
Prescribed Treatment for Nasty Knock:
(i) (Lucky that the crankshaft key and keyway are undamaged) Lap the flywheel onto the shaft and refit. Loctite the big nut, it seems that the extended grub-screw (for lack of a better name) that's meant to lock the nut, wasn't doing its job.
(ii) It's a reflection of poor design that thrust from the clutch disengagement mechanism could be resisted by the small outrigger nose bearing on the front of the 'shaft. I suppose that rhino-strength loctite on the rear main bearings should alleviate this. Worth a try, anyway.
(iii) Pistons, cylinders. (a) I've yet to see an oversize Sopwith piston, and even from new, the cylinder walls were far too thin to encourage reboring. (b) I believe that the Brooklands Sopwith has been fitted with Imp pistons, or similar. Anyway, if they work, and don't smoke, don't fix them!!! Be thankful!
(iv) What is the actual damage to the bevel gears? Are they chipped, or just worn? Either way, for this damage to have come from a worn front mainshaft bearing, the front of the mainshaft must have been waving around like a flag in a whirlwind. These components are not plentiful...ask Andrew! I recommend careful reassembly and adjustment (minimal clearance where play is just detectable) and perhaps a greater depth of oil in the gearbox to keep everything happy.
(v) Do not go for Jack Emerson's Outer Circuit record: it is not dignified for 95-year old metal to be thrashed in this way.
Good luck, Ian, please keep us posted of progress.
Paul.

Making Progress - The Brooklands Sopwith ABC gearbox is back together. We are awaiting some bearings and then will start rebuilding the crankcase, clutch and transfer shaft assembly.

We do have a problem, that the Taylor-Young rocker assembly is very worn and difficult to repair. If anybody in the ABC community has a spare set of rockers and mounts (any make) that would be available for use (to donate or nominal fee) on the Brooklands machine, it would be most appreicated. Please drop me an email if you may be able to help.

many thanks
Ian

Whilst awaiting delivery of the new bearings for the engine and transfer box, we kept ourselves busy by manufacturing and installing 2 new valve guides, also lapping heads to barrels and flywheel to crank. It had also been a long time since we took the ABC engine apart, so we also organised all the parts (like an exploded diagram) to remind ourselves of the order of assembly. Each time we look at the ABC parts we are impressed by the quality (e.g the crankcase castings) and also the small size of many of the parts (e.g. the cam shaft). We noticed some rather fine Sopwith stampings on each of the crank cases. Next week the bearings should have arrived and we can start assembly.

Please find attached the interesting casting stamps mentioned in the last post. There is certainly an S; however not sure about the other parts of the symbol? Also finally got the bearing spares we needed this week, so assembled the crank into the crankcase.

I think there was an army of inspectors in the Sopwith works, each with his own little hammer and set of stamps. Here and there, even nuts and washers have been inspected and passed! I suspect that the stamps identify the individual inspectors and perhaps the nature of the inspection (dimension: hardness: weight: roughness). My crankcase-halves also bore identification marks, to indicate joint-machining. "Lots and lots of stamps"!
Paul.