Pre Ignition

[BOATCH]

Could someone give me some advice on a 503 d ign . When been traviling long distance and you switch the mags of the motor tends to pre ignite and it takes 10 or so seconds to stop. Could it be that the idling is to high. Some times the motor switches of first time. :

[Morph]

When was the last time the motor was de-coked? A build up of too much carbon can cause pre-ignition, especially after a long extended flight. The Carbon deposits can get hot spots. When you cut the mags the motor still rotates a few cycles to stop, each rotation pumps fuel into the pistons (mechanical fuel pump). The carbon hot spots ignite the fuel and the motor continues to run.

Take your exhaust manifold off and have a look at the pistons. You will see black build up on top of the pistons. If there is black streaking down the sides of the piston, and especially if the streaking extends past the rings then your rings are stuck with carbon as well. Open up and decoke.

[BOATCH]

Hi MORPH Thanks for the info ,I think you are spot on . When a motor gets a decoke what needs to be replaced and what are the procedure do i need to remove the pistons and do the ring grooves also need to be cleand. Is this a procedure that kan be performed with the motor in place ie motor is instaled with the plugs to the top.I wish i had sutch freely advice in my current trade .

[Morph]

yes it can be done in the plane but if your motor is upright you have to be very careful when you remove the pistons, the roller bearings can easily fall out and end up inside the motor. Close all the holes etc with rags


Check these links out
viewtopic.php?t=1851
viewtopic.php?t=2057viewtopic.php?t=2029

[aeroden]

Hi Boatch,
I had the same problem. I do training on a 503 and thought with all the
hammering a school plane takes its just overheating. check your fanbelt
after i had tensioned it no more problems
Hope it works for you
Aeroden Flight Training Centre
Basie

[BOATCH]

Hi Aeroden I wil take time to check the belt ,becuase the motor was decarbed about 14 hours back by Clinton but would check all the info that you and Morph gave me thanks.