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Date: Friday, 3 February 2012

An Extraordinary Rally Blow up - The aftermath

Written by Lorraine Litster and Gordon Halliday.


Gordon Halliday at the Rally,  just before the engine seized

Gordon Halliday has been a regular VVC Rally attendee for many years, usually on his Velocette Venom. However this year, due to a gearbox fault on the Velo he brought his 2nd bike, a 1954 G80 Matchless 500cc. Unfortunately his bike seized up badly on the Saturday ride and he was given the "Hard Luck" award as a small consolation.

Gordon (with some assistance from me) has now removed and dismantled the engine. The result was a badly seized piston and a completely seized big end; In other word the worst of all possible scenarios, caused by a complete lubrication failure.

The crankshaft has now been split showing the most extraordinary failure, which you can see in the accompanying photo.

seized big end1

The big end has the rollers retained by an alloy cage. This cage has melted resulting in the rollers looking like the sausages in a dish of "toad in the hole".

I have never seen such a mess in my life.

seized big end2

What caused such a failure? You must be thinking. Well, there were no faults in the oil pump or the oil feeds. What had happened was that the Matchless big end appears very susceptible to sludge build up and this sludge starved the big end of oil which promptly melted!

The piston is lubricated from oil spraying from the big end, and with no oil from the big end piston seizure rapidly followed: goodbye engine. But why had sludge blocked the big end, you may ask?

It seems Gordon had never checked the oil tank for a filter, there was none. So the lesson I have learned is that if I owned an AJS/Matchless single I would be fitting a Commando MkIII oil filter quick smart! The alternative may be dire.

Written by Lorraine Litster and Gordon Halliday.






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