There was dampness in the air when I left home at 09.30 for the Local VMCC New Year’s day run. My Scotts seem to like that dampness and the Clive Waye modified engine (Silk cranks, ported pistons and barrels, modified gallery and crankcase stuffers etc) that I fitted to my ’57 Brum some years and about 15,000 miles ago, was running sweetly. The run from our Copthorne club house to a pub in Newdigate was only about 30 miles, and is where we stopped for a beer and festive food.
I left the pub at about half past one and headed for home. Six and a half miles later and at a speed of exactly 42 mph (I carry a trip logger in my pocket so that I can down load trip data to my PC), there was a noise that I’d never heard before, nor want to again, from my Scott, and the engine stopped dead. My first thoughts were that the primary chain had broken and had jammed under the engine sprocket, but when I stopped, it was obvious that it was still in one piece and that the engine was locked solid. Maybe a broken crank – a first ever for me.
Nothing I could do but call out recovery.
The following day I put the bike on the bench and started taking the engine down. Dynamo and left hand c/c door off first – nothing wrong there. Oil pump, distributor and right hand c/c door off next. CARNAGE! A three inch by half inch front section of the crank chamber was missing but the crank was still in one piece. So off with the tank, radiator and barrels. More carnage. Two thirds of the right hand piston below the gudgeon pin missing, half the barrel skirt boken up, and a crankcase stuffer block rattling around.
What caused this disaster? I think that one of the two screws holding the stuffer block in place must have come loose and jammed between the piston and cylinder skirt causing them to break up and cause further damage to the crankcase.
The only useable bits left are the cranks, rods (maybe after checking), flywheel, cylinder head and transfer ports.
Hey Ho, Scotting can be such fun!!
Argh, not the first and probably not the last to have an engine munched by loose stuffer blocks. What kind of bolts had been used for them and was there any secondary locking in place such as peened over bolt ends, lockwire, dot punched bolt head etc?
Sorry to hear of it, I hope the bike is back running soon.
Each stuffer block had been counter-bored and held by two allen bolts for each block. Each bolt was then locked in place by three punch dots level with, or just above the top of the head. As I said earlier, the engine had been built up by Clive Waye of sprint and racing fame, so he did things properly. I’m only assuming that a stuffer bolt decided to go walk-abouts, which is the most likely cause, but who knows without forensic investigation. I will be looking at the wreckage in more detail later to see if anything can be salvaged.
Good luck with the rebuild Dave!
And remember, better to damage the bike than yourself!
The only positive thing that can come from such a misfortune, is if it sounds a warning to others. I have had two or three like this from customers, generally the outside stuffer where there is not so much depth of thread possible to anchor the cap screws. One security device is to tap out the counterbore for the cap screw with a course thread like Whitworth and deep enough that the top of the installed cap screw is at least half an inch under the top of the stuffer block. Degrease thoroughly then after assembly as normal, cast in the tapped counterbore with epoxy resin. To extract all the potential from a Scott engine, there are quite a few opportunities that can be exploited and stuffers are one of them. When I had the patterns made for my own crankcases, I had the stuffers cast in, so I could have the benefit without the risk. David Holder has a few unused late Birmingham cases with regroung cups. You will have to weigh up your options as given the damage, a weld repair would likely distort the case to a degree that would render it unuseable without extensive remachining, including reboring main bearing bores and fitting new cups. I am sure we all wish you well and hope you will be back on the road before long Roger
Thanks for your advice and commiserations. The bike was back out on the road today fitted with an engine that was destined to be fitted to a ’46 Scott that I was accumulating parts for.
I now have everything except an engine to put into it!!