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Author Topic: Engine seiziure - an unlikely cause  (Read 690 times)

Bullet Whisperer

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Engine seiziure - an unlikely cause
« on: April 12, 2013, 08:05:52 am »
I want to share this, as it is the first time I have come across it and I will post it on some other forums, as it could save someone lots of trouble and money.
 One of the early 'Asbo' Bullet 500's, which has covered thousands of trouble free miles since the build was doing an 'end to end' run here in the U.K., going up to the extreme north of Scotland at John 'O Groats from South Wales, then heading for Land's End at the very south of England.
 Loaded quite heavily with rack, top box and camping gear etc, the machine made it to 'the top', but soon after setting off from there to travel south, the engine suddenly seized while travelling up a long, steady and shallow gradient.
 The owner contacted me and described what had happened, stating that the engine became free straight after suddenly tightening up and briefly locking the rear wheel just as he got the clutch in. After this, the engine turned, but with no compression, so he had it trailered here and we took a look at it.
 The piston had suffered a heat seiziure, depositing some thin streaks of alloy on the bore and trapping the piston rings in their grooves.
 Everything was cleaned up and freed off, no scoring or ring damage was noted and it was all reassembled.
 There was no obvious reason why the engine had seized, so as a matter of course the ignition timing, carb etc were checked over.
 The culprit was soon found - an almost completely blocked main jet caused by debris coming either from the fuel, fuel tank, or fuel pipe. Pulling at a steady rate, it had been ok, but Pete opened her up a bit because another Bullet on the same run was gaining a little behind him. This was when it suddenly tightened up and stopped and would have been caused by the sudden extra intake of air alone, with no extra fuel getting in with it, this sudden change to a very weak mixture with a pretty hot engine led to a sudden rise in temperature in the cylinder and caused the engine to seize in the blink of an eye.
 No new parts were needed [no head gasket is used] and it left here to carry on southbound running as well as ever before .....................
 BUT - with an inline FUEL FILTER now fitted !!!!!


  • phaneropter
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Re: Engine seiziure - an unlikely cause
« Reply #1 on: April 12, 2013, 03:36:59 pm »
Thanks for posting.
Would this still be possible on a EFI unit as it monitors mixture and temperature more closely?
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Re: Engine seiziure - an unlikely cause
« Reply #2 on: April 12, 2013, 07:52:20 pm »
With a EFI system there isn't anything to monitor the actual fuel/air ratio except the O2 sensor and if the fuel injector was badly plugged I doubt that the computer could increase the fuel/air ratio enough to avoid a similar situation.

I know the fuel pump has a screen in its inlet and hopefully it is a fine enough mesh to prevent the injector from becoming plugged.
Course, there's no way to monitor that pump screen except to remove the pump from the tank and so far I haven't heard of anyone doing that unless they were replacing the tank.
2011 G5 Deluxe
1999 Miata 10th Anniversary