Primer?
 

Hi.

I was wondering if anybody knew why the primer on most 4 cyl. piston engine aircraft is attached only to three of the cylinders?

I posted the same question in maintenance a couple of weeks without any luck in responses.

Happy flying.

Could be wrong, its been a while,
but I believe the relevant hole is drilled in all the cylinder heads, but is used for something else on one cylinder, I think CHT probe. If I get time I'll try and look it up.
FlyVMO

This was one of those questions that got you thinking how little you know about the aircraft you fly so I got searching.

Found the following link which was of interest:-

http://www.lycoming.textron.com/main...ldWeather.html

Basically the article states that no two aircraft are necessarily the same and the number of cylinders that have priming lines is down to the manufacturer. I guess some of the old nags I have struggled to get started on a cold morning might have only had 1??

Was told years ago that it prevents flooding of all cylinders in case of
a little over enthousiastic priming.
Would still give you a chance to start...hopefully.
Don't know if it's the official reason, but it does make sense.