Hard to Pull Fuel Primer (Primer rebuild or overhaul)

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Hard to Pull Fuel Primer (Primer rebuild or overhaul)

Postby Abe » Thu Dec 08, 2005 12:27 am

This may have been a past topic, but if it was I couldn't find it. It's winter here in NE Oregon and and we're finally beginning to have a "normal" winter with temps in and around zero (I know that's a warming trend for you all up in AK). The last few flights in this colder weather I have had a heck of time getting the primer pulled out for the first time (the subsequent pulls are a bit easier). I was going to work it over with WD 40, but thought you folks up north may have a better "fix" to help make the primer pull a bit easier in cold weather.
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Postby gahorn » Thu Dec 08, 2005 1:43 am

It probably could use a disassembly and rebuild. Parker fuel-lube is a good fuel-proof lubricant, but it's expensive, and you'll only need a "dab". Check with your local mechanic and see if he'll let you swipe your finger thru his can of fuel lube.
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Postby JJH55 » Thu Dec 08, 2005 2:00 am

Remove the plunger assembly and put a drop of motor oil on the o-ring and reassemble. While your at it, put a drop on your fuel cap gaskets too. They'll go off and on much easier.
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Postby Bruce Fenstermacher » Thu Dec 08, 2005 3:18 pm

I've been battling this problem for a few months now even in warm weather.

It all started when I replaced the shot O rings with new. Worked great for a week then I couldn't get primer out. Thought I might have put the wrong kind of o rings in and they swelled so I replaced them. And this time I put some fuel lube on them, because what the heck, it couldn't hurt. About month later I could get the primer open.

At this point I gave up and I didn't need the primer as the engine started without it. About a month ago I decided it was getting cold and I'd need that primer so I went to a different A&P with stock of o-rings. I told him my story and when I mentioned fuel lube he said that was probably the problem as it was to thick in his opinion.

I cleaned out the primer tube and replaced the o-rings and just used a small dab of DC-4. It's been fine for the last 2 months.
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Thanks for your Responses

Postby Abe » Thu Dec 08, 2005 4:14 pm

Thanks for the information gentlemen, I'll get the hanger heated up the next few days and I'll let you know how things go with the primer...One other thing that I've noticed this winter is that my tack jumps 100-150 RPMs the first 10-15 minutes after I start it up, but settles down after that time....I'm thinking that it to is cold and warms up after abit (like the pilot). The last two winters I've had this airplane were not this cold and I did not see this jumping in the RPMs...does anyone else see this....
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Postby HA » Thu Dec 08, 2005 4:19 pm

yup, Fuel Lube + cold = peanut butter glue

use DC-4 (Dow Corning 4 dielectric grease) on the orings and you'll be fine, your mechanic should have some since that's what you use on oil filter gaskets to prevent seizing

you could maybe use some light lube, like LPS-1, but it will shortly wash off in the fuel and you're back to square uno
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Postby gahorn » Thu Dec 08, 2005 10:28 pm

Well, I'll be jiggered! Fuel lube on mine for the last 4 years and it works just fine, hot or cold.
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An originality nut (mostly) for the right reasons. ;)
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Postby HA » Fri Dec 09, 2005 4:11 pm

come up and visit me in sunny Fargo sometime in the 9 winter months and you would be jiggered :D
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Postby webmaster » Fri Dec 09, 2005 9:09 pm

I think mine could use a little of that DC-4. How about a short primer on dissassembly of the primer? Do I need to disconnect the fuel lines and remove the assemble from the panel?

Thanks!
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Postby Bruce Fenstermacher » Fri Dec 09, 2005 10:01 pm

No Dale it is very simple.

1. Turn off the main fuel valve.

2. At the base of the primer there is a knurled round nut. This is the part that has the slot that you have to line up in order to pull out the primer.
Turn this nut counter clock wise until it is loose. pulling out the primer will assist this operation.

3. With a rag handy under the primer, pull the nut and the primer all the way out. The rag is to catch the small amount of fuel in the primer.
Caution. If you didn't shut of the fuel or your main fuel valve doesn't work, fuel may start to flow through the primer into your aircraft cabin. If this is the case quickly reinsert the primer.

4. Replace the o-rings if you want then lube with the desired substance.

5. Look inside the primer tube. If there is gunk in there clean it out with a rolled up rag.

6. Reinsert the primer.

7. Tighten the knurled nut finger tight.

8. Turn your main fuel back on.

Total time assuming your knurled nut spins off easily and you don't replace the 0-rings should be about a minute.

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Postby webmaster » Sat Dec 10, 2005 1:43 am

Thanks, Bruce! I'm glad I asked.

Great description!!

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Postby lowNslow » Sat Dec 10, 2005 2:06 am

Any body know which O-rings to use. Not mentioned in the parts catalog.
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Postby Bruce Fenstermacher » Sat Dec 10, 2005 3:08 am

In the 170B IPC figure 37 item 11. Looking under Item 11 which is the primer there is an o-ring listed.

It is a AN6227-7 which is also an MS28775-012.

You will need 2 of them and they should cost a little over a half dollar a piece.
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Postby lowNslow » Sat Dec 10, 2005 3:32 am

Bruce, thanks! For my serial number, 25400, fig.41 doesn't show the O-ring part number and has the primer PN as 0413215-1 vs. PN 0413215 for the earlier serial numbers. My guess is they use the O-ring.
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Postby Bruce Fenstermacher » Sat Dec 10, 2005 1:49 pm

While it could be a different o-ring but I'd bet not. One reason only one was listed is they may all be the same.

I have 3 different primers on hand, the one in the picture which I think by the knob is from a later 170B, the one in my 170 which has an aluminum knob with Koelher stamped and another Koelher I bought and installed in my Cub.

These all use the same o-ring.
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