The International Cessna^® 170 Association

Hello All,
Hope everyone had a Merry Christmas!

I recently replaced the O-rings in my primer. All was well for about a month. Now, when I use the primer, it blows fuel out the back! I took it back apart, ORings look fine, used a very small amount of fuel lube, checked the bore and reassembled, same thing.
Any suggestions?

What do you mean by “blows fuel out the back”?

Do you mean the B-nuts on the connecting lines? Or do you mean the body of the primer?

Is it possible you cracked a B-nut when over-torquing it?l. Or perhaps the copper fuel-line has cracked at it’s flare (such as copper often does after long service and re-use due to hardening.)

Use Fuel lube(EZ Turn) on the O-rings. D

gahorn wrote:What do you mean by “blows fuel out the back”?

Do you mean the B-nuts on the connecting lines? Or do you mean the body of the primer?

Is it possible you cracked a B-nut when over-torquing it?l. Or perhaps the copper fuel-line has cracked at it’s flare (such as copper often does after long service and re-use due to hardening.)

The fuel is coming from the hole in the back of the barrel. Not sure, but I think it’s a vent. When the primer is pushed in, there is pressure then the fuel comes out the back.
The B nuts have not been disturbed and are not leaking.

I used a very small amount of Fuel Lube on the o Rings.

Sound like one of the o-rings has a cut in it that is difficult to see by inspection, or is “rolling” during re-insertion.

Thank you. I have some new O rings on the way. We will see what that does.

"O" ring gaskets from Harbor Freight (they carry an assortment box with multiple sizes) work well on our primers. I have had them on mine for 7+ yrs and no problem plus the assortment will fit many other things around the hangar and house.

I do not have one of these primers in front of me to examine.
But, I wonder if the "hole in the back of the barrel" is open because some check valve parts have fallen out of that hole.

170C wrote:"O" ring gaskets from Harbor Freight (they carry an assortment box with multiple sizes) work well on our primers. I have had them on mine for 7+ yrs and no problem plus the assortment will fit many other things around the hangar and house.

With full respect, Ol Pokey, I wouldn't use anything from HF on my airplane, or lawn tractor, or even my pitch fork.

I wouldn't use them either,you can buy the kit cheap from spruce. $6.50 with lube

Vern,
“Chestnuts roasting on an open fire” is a lovely scene ... unless they are your chestnuts and the open fire is under the panel. The primer is inches from electrical switches which have the potential to take on the role of a spark plug. I would ground the plane until you find and eliminate the source of the leak.

There is no vent on the primer. It simply has two one-way check valves, each made up of a spring and ball as shown here.If the primer isn’t leaking from one of the line fittings it must be that a screw cap holding the check valve in place is loose. I’d recommend your mechanic use Viton o-rings Cessna calls for in SE78-73. I’d also recommend your mechanic disconnect the AN4022-1 (or AN4002-1) primer nozzle from the intake manifold and confirm that it’s not clogged and has a good spray pattern.

bsdunek & mschlender, I have no argument with your statements. The only reason I used the HF gaskets was that an AP/IA gave them to me and they were HF items. I never expected them to last, but they have so far.

Gary,
That isn’t my primer but it probably works the same way. I’ll see if that’s a cap at the end of the barrel. Makes sense to me.
Thanks guys!!

170C wrote:bsdunek & mschlender, I have no argument with your statements. The only reason I used the HF gaskets was that an AP/IA gave them to me and they were HF items. I never expected them to last, but they have so far.

Most (black) HF O-rongs are Buna-N rubber and pretty fool-proof. I use them on agricultural equipment and have found them quite reliable. They also sell Viton and others in assortments. (Not disputing nor arguing with anyone who endorses genuine aircraft quality (AN or MS traceable ) O-rings for aircraft use... but for the average guy who simply wants an assortment on-hand for various uses they are easy and inexpensive.)