Pain in the rear primer

flhrci

flhrci

Final Approach
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Jan 26, 2007
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David
Been flying since 1996 and never I have had a primer, Cessna 172M, in this case, not work.

Had my new student in the plane for his second lesson, prime the engine 3 times and I noticed I did not hear the noise it normally makes filling. Cranked the starter, and nothing. Try two more times, nothing. I primed it once more, and nothing. One more prime, two more start attempts, and nothing. Not wanting to run the battery down any more, walked over to the 172SP and went on about our lesson.

Plane is stored in a hangar overnight and had only sat outside in the 20 degree air for around an hour.

When I got back around 1:00pm, the plane was in the sun for several hours, 34 degrees out. Primed it 3 times, one crank with no start, 1 more prime and she started up. Each prime I could hear it filling.

I suspect it was ice blocking the fuel but I do not know. Let the plane run for 12 minutes to recharge the battery some for the renter half an hour later.

Odd and new problem to me. I hope this won't be an omen of tough winter flying this year. Unfortunately, the 172SP goes down mid-December for another engine and the 172M will be it for 4-8 weeks. The M has no preheater so probably will be preheating the plane manually from now on.

David
 
Primer jet(s) clogged. Have an A&P take off the primer lines and jets and clean them. Easy job, maybe 1.5-2 hours total.

Usually, the primer system gets one jet clogged, and no one notices, then two, then three, and finally it gets so hard to start that the last one is clogged and that's it.
 
Would there be any outward signs of a clogged primer jet? Or it just quits working one day?

David
 
flhrci said:
Would there be any outward signs of a clogged primer jet? Or it just quits working one day?

David
Click to expand...


If they're all clogged you won't be able to push the primer back in once you draw it full of fuel.
 
This post would work a lot better over on "Maintenance".

Just before I go, does "Challenger" or "Christie McAuliffe" and cold o-rings hit any sort of a bell?

Thanks,

Jim
 
docmirror said:
Primer jet(s) clogged. Have an A&P take off the primer lines and jets and clean them. Easy job, maybe 1.5-2 hours total.

Usually, the primer system gets one jet clogged, and no one notices, then two, then three, and finally it gets so hard to start that the last one is clogged and that's it.
Click to expand...


That theory doesn't work.. when the pump has no place to push the fuel out, you can't push it in.
 
Tom-D said:
That theory doesn't work.. when the pump has no place to push the fuel out, you can't push it in.
Click to expand...

Yes!


Sounds to me like the o-ring is so bad it just sucks air passed it.

There could be a cracked line from the fuel strainer too, (inlet side of the primer), but you should see a fuel leak somewhere if that was the case.

Pull the primer out and smear some engine oil on the thing for kicks and try again.
 
kgruber said:
Use the proper fuel proof grease.
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No! Don't grease it. That will make it worse over time. They get really sticky. Been there, done that, all with the MIL-spec fuel-proof grease. Had to take out all the primers that had been greased and clean them thoroughly, and put in new O-rings. MS29513-012. The fuel itself is all the lube they need. No more trouble after that.

Dan
 
Dan Thomas said:
No! Don't grease it. That will make it worse over time. They get really sticky. Been there, done that, all with the MIL-spec fuel-proof grease. Had to take out all the primers that had been greased and clean them thoroughly, and put in new O-rings. MS29513-012. The fuel itself is all the lube they need. No more trouble after that.

Dan
Click to expand...
When you apply fuel lube on new "O" rings they last for ever.
 
Dan Thomas said:
No! Don't grease it. That will make it worse over time. They get really sticky. Been there, done that, all with the MIL-spec fuel-proof grease. Had to take out all the primers that had been greased and clean them thoroughly, and put in new O-rings. MS29513-012. The fuel itself is all the lube they need. No more trouble after that.

Dan
Click to expand...

It makes sense to me. The strainer plunger o-rings aren't lubed and last for years.

That being said a drop of engine oil when it gets tight has worked real well for the last 24 months. It won't gum up check valves like fuel lube can. Plus you don't have to buy any.

What do they say? More than one way to skin a critter? :D
 
bnt83 said:
I'll try it next time. Don't recall if I had any when I had it apart last.
Click to expand...

A very tiny bit goes a long way. If you have more than what it takes to make the "O" ring shine you have too much.

use a 20 gauge shot gun bore swab and alcohol to clean the pump bore
 
flhrci said:
Would there be any outward signs of a clogged primer jet? Or it just quits working one day?

David
Click to expand...

Clogged output and you can't push the plunger, plugged input and you can't pull the plunger.
 
take the primer apart....clean, inspect, and replace parts as necessary.....then reassemble with a light-light coating of fuel-lube.

The stuff is wonder working....:wink2:
 
Norman said:
Fuel Lube plugs up primer nozzles. Still think he should use it? :dunno:
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It's a rental so not my call anyways but i already mentioned it today and got a typical wait and see if it does it again response.

David
 
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