View Full Version : 503 pot running cooler

keith_b - n/a
31-Jul-08, 04:11 PM

I have a standard, fan cooled 503. I have EGTs on both pistons, at idle and at flat out they are roughly the same - however at 3500 revs, the piston nearest the fan runs significantly cooler, at a similar temp as at idle.

There appears to be no other symptoms, just a cooler piston.

Any ideas?



Hornet - n/a
1-Aug-08, 02:29 AM
I had this problem with a Robin EC44 with the rear cyclinder running much cooler. The cause was the rear cyclinder getting more fuel than the front, thus running richer & cooler.

Do a plug reading after running the engine at a throttle opening at which both cylinders are running similar temps.

Then do a plug reading after running the engine at a the throttle opening at which one runs cool.

If the plug colours differ in that the cool cylinder is runnining richer then I suspect its a fuel issue.

Because both cyclinders are running the same temps at idle and full throttle it would appear that your pilot system and main jets are ok. It could be a problem with your jet needle and needle jet or your slide syncronisation.

Bob Beech - n/a
1-Aug-08, 08:02 AM
Hi Keith,

I notice this with My Scat/Cuyuna.

The rear plug is just the right colour but the front black and oily. I put it down to the front being cooled first by the fan.

After about ten hours the engine will start to be slower to respond from tickover when hot but otherwise runs sweetly. A clean/change of plug brings it back to full response.

Having done well over 150 hours with this setting I have no desire to change what seems to work ok.

keith_b - n/a
1-Aug-08, 09:17 AM
Cheers - richer mix sounds about right.

I bet it's carb synchronisation - I'll get some help next time I check it.

Will it do the engine any harm to run the temps differently like this (as in, if I see this reading out on the river/sea, is it time to get onshore quickly or just keep goiing)?


Hornet - n/a
1-Aug-08, 11:32 AM
As long as one cyclinder does'nt run so lean that it overheats and starts melting a piston it might be ok. But I would'nt like to risk it. Best option would be to check your carbs,test run the craft, do some plug readings and find out what and how critical the problem is first. The EGT's on both cylinders should be reasonably close, if they are vastly different then something is not right and so if you notice this condition while hovering then I would stop the engine ASAP.