Fuel cap lost

I've had trouble with galling in the threads to the point of seizure and having to machine out the male thread. I remade the inner from brass to get away from the same metal galling and have found that they are much easier to tighten and , touch wood, have been very secure.
 
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It is very important to lubricate the coarse threads with fuel lune to prevent galling. I had one get stuck also.
 
Nev said:
Actually I've got 3 fuel caps sitting in front of me and all 3 are different. The smaller vent hole size has an inlet area of 1.75 ²/mm. The larger vent hole size has an inlet area of 9.0 ²/mm.
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I didn't see this addressed in the rest of the thread, what should the vent hole size be? Was there a reason for a bigger vent hole?
 
I didn't ever work out if there is a "correct" vent hole size. They all seem to work fine.
 
Untainted123 said:
I didn't see this addressed in the rest of the thread, what should the vent hole size be? Was there a reason for a bigger vent hole?
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I suggest consideration of your local insect population. I've heard a lot more stories of insects such spiders and as mason wasps blocking up small vent holes for VMC aircraft, compared to reports of other debris or icing. Having a vent hole smaller than a mason wasp is advantageous in our area, as they are prolific.
 
Virgil McKenzie of Bearhawk Aircraft is my authority, but the following text if from memory of a conversation he and I had a few weeks ago.

The vent hole size has increased over time.

The vent hole at the bottom of the cap where the venting air exits into the tank has a cotter pin obstruction. (The cotter prevents the bottom of the cap from falling into the fuel tank when your well meaning line boy unscrews your cap due to negligence rather than lifting (wrestle, prying) it out of the filler neck.)

A small vent hole (presumably from an older cap like my 2017 caps) with this cotter obstruction may have resulting in insufficient airflow for some higher fuel flow conditions. So, VIrgil had me drill out ONLY the bottom 1/4" of the cap ONLY where the cotter pin obstruction existed in order to facilitate proper venting.
 
I had a venting issue where my engine was not getting enough fuel. We (two buddies who are airplane builders and myself) were scratching our heads trying to figure out why my engine would not start., so we:
1) removed the fuel hose from the carburetor to find only a few drips of fuel
2) removed the fuel hose from the fuel flow transducer.. only a few drips of fuel

The above two eliminated an issue in the transducer to carb hose

3) removed the transducer (gold cube), and only a few drips of fuel

#3 elimated the idea of blockage in the transducer

So we were all scratching our heads trying to figure out the problem, and without saying a thing I stepped up on the tire and removed the fuel cap…. The fuel started flowing like a fire hose.

At that point we knew it was a venting issue. I called Virgil and discussed it with him, I was going on a work trip so sent my caps to Virgil and he drilled them out. I got back, put them on and my fuel flow was outstanding.

NOTE: Yes I did a fuel flow test prior to this episode, but I must have done it with the fuel caps removed and my flow test was well over 30 GPH

This venting problem was on engine start for a brake break in taxi run. Funny enough we had an issue on the initial engine run and thought maybe the fuel how was blocked, so we blew air up the fuel line from the carb connection backwards and the engine started.
 
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Utah-Jay said:
I had a venting issue where my engine was not getting enough fuel. We (two buddies who are airplane builders and myself) were scratching our heads trying to figure out why my engine would not start., so we:
1) removed the fuel hose from the carburetor to find only a few drips of fuel
2) removed the fuel hose from the fuel flow transducer.. only a few drips of fuel

The above two eliminated an issue in the transducer to carb hose

3) removed the transducer (gold cube), and only a few drips of fuel

#3 elimated the idea of blockage in the transducer

So we were all scratching our heads trying to figure out the problem, and without saying a thing I stepped up on the tire and removed the fuel cap…. The fuel started flowing like a fire hose.

At that point we knew it was a venting issue. I called Virgil and discussed it with him, I was going on a work trip so sent my caps to Virgil and he drilled them out. I got back, put them on and my fuel flow was outstanding.

NOTE: Yes I did a fuel flow test prior to this episode, but I must have done it with the fuel caps removed and my flow test was well over 30 GPH

This venting problem was on engine start for a brake break in taxi run. Funny enough we had an issue on the initial engine run and thought maybe the fuel how was blocked, so we blew air up the fuel line from the carb connection backwards and the engine started.
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Interesting, as I am now doing first engine starts, and I am having a problem that seems like fuel starvation. I initially thought it was something with the carb needle valve getting stuck closed (engine/carb had been sitting a long time), but now wonder if the problem is the venting ability. I too did a fuel flow test before first start, and was able to flow more than 30gph per side, but I did notice at time a "slurping" sound like air was having to go back up the line, but didn't think anything of it since I got the flow I needed over about a 10min timeframe. Now, I wonder if it was the vent not providing enough air, and a that's why I now can't seem to push the throttle in much without a stumble... Your scenario sounds almost exactly like mine.

I did the roll pin mod last night, and I don't see any harm in making the vent hole where the cotter pin goes through bigger and will try that next.
 
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