A

apatti

Well Known Member
All,
I was installing the carb and throttle/mixture bracket tonight on my Lyco O-360. I tightened the nuts that hold everything to the engine as much as I dare and there are still no threads coming all the way through. They are about even with the bottom of the nut.

There is a washer and a lock washer between the nut and the bracket. Should I remove the washer and just go with the lock washer? I am not sure that will even give me enough thread showing.

Comments/suggestions appreciated.
 
That's a tough one. Obviously you should have at least two threads showing. The only thing I can think of....short of backing the studs out a bit....is to try using an AN960L (thin) washer with a (thin) AN316 nut. For safety, you'd still have to use a lock washer though. Maybe someone else can offer a better idea....like how to easily back a stud out.
 
combo?

how about thin nut, thin washer, hi temp loctite and frequent (initial) inspections? or NAS509 (?) corner drilled, & safety wire?
 
Carb mount

apatti said:
All,
I was installing the carb and throttle/mixture bracket tonight on my Lyco O-360. I tightened the nuts that hold everything to the engine as much as I dare and there are still no threads coming all the way through. They are about even with the bottom of the nut.

There is a washer and a lock washer between the nut and the bracket. Should I remove the washer and just go with the lock washer? I am not sure that will even give me enough thread showing.

Comments/suggestions appreciated.
Click to expand...
My carb to sump studs are drilled and safety wired. I assume that yours' are not? If holes in bracket close around studs 5/16 studs-5/16 holes in bracket, forget the washer/split washer and just use an internal tooth lock washer. Or use the low profile metal lock nut.http://www.aircraftspruce.com/catalog/hapages/an363.php
Still think that sump studs should be drilled to be safety wired. Maybe Mel will chime in on that topic. Don't forget that gaskets fit on both sides of the carb/throttle bracket, ie sump-gasket-bracket-gasket-carb.
Hope that helps,
Mike H 9A/8A
 
Pictures please

apatti said:
All,
I was installing the carb and throttle/mixture bracket tonight on my Lyco O-360. I tightened the nuts that hold everything to the engine as much as I dare and there are still no threads coming all the way through. They are about even with the bottom of the nut.

There is a washer and a lock washer between the nut and the bracket. Should I remove the washer and just go with the lock washer? I am not sure that will even give me enough thread showing.

Comments/suggestions appreciated.
Click to expand...

Can you post some pictures please?
 
Fine vs. Coarse thread

mike109g6 said:
My carb to sump studs are drilled and safety wired. I assume that yours' are not? If holes in bracket close around studs 5/16 studs-5/16 holes in bracket, forget the washer/split washer and just use an internal tooth lock washer. Or use the low profile metal lock nut.http://www.aircraftspruce.com/catalog/hapages/an363.php
Still think that sump studs should be drilled to be safety wired. Maybe Mel will chime in on that topic. Don't forget that gaskets fit on both sides of the carb/throttle bracket, ie sump-gasket-bracket-gasket-carb.
Hope that helps,
Mike H 9A/8A
Click to expand...

I don't have my Lycoming catalog handy, but most Lycoming engine nut/stud threads are coarse, which in this case would be 5/16-18, not the 5/16-24 of the AN363 nuts...

Perhaps replacing the studs with longer ones might be the best (and safest) answer.

ADDED

ECI's official hardware for this location is a plain nut, internal serrated lock washer, and a plain washer - no safety wire involved.
 
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Thanks for the responses so far.

I called Penn Yan Aero (the folks who built my engine) and their response was to get a thinner nut. I asked and was told that Lyco does not call for Loctite on the threads. There are no provisions for safe tying, either. This makes me nervous. It seems like everything else on this engine is safe tied, why not this?? I guess the internal tooth lock washer holds everything together. The guy at PYA said he had never heard of a carb coming loose. I can't win the lottery. But, this contest I probably could win! :) Also, PYA told me NOT to remove the regular washer or trade it out for a thinner one. I also asked about backing out the studs and got a definite "NO" on that.

This is one of those strange cases where the "best practices" (at least the way I understand them) don't match with logic. I could replace the nut with a thinner one and probably have a thread or two showing. On the other hand I could stay with the full size nut and not have any threads showing. However, since the stud does come all the way flush with the bottom of the full size nut, I would have more threads captured by a full size nut. Isn't that what is most important? Is the requirement to have a full thread showing only for lock nuts and not for standard nuts that use a lock washer?

I am a bit surprised that I am the only one that has had this problem (that I know of, of course). I am not doing anything non-standard. The only variable here is the amount of gasket sealant used. I didn't think I put it on too thick. However, there are four surfaces that get some sealant.

Thanks again for the replies so far.
 
I also am faced with this same problem. Van's carb box install instructions only indicate to "wait for awhile" and re-tighten as the two layers of gasket material might compress somewhat. Well, I checked every weekend for several months, and nothing changed from my original torquing of the nuts. I am not comfortable with what I have (no threads showing, no lock washer, and a thin flat washer).

But, I will drill the two nuts that are installed on the forward side of the carb and safety wire them. I have not figured out how to safety the nuts on the aft side of the carb...just nothing to really attach the wire to or snake the wire around the carb to get the ends secured. I still do not have a final complete solution, so I am also looking forward to the replies on this posting...
 
Does this part....

apatti said:
.....
I am a bit surprised that I am the only one that has had this problem (that I know of, of course). I am not doing anything non-standard. The only variable here is the amount of gasket sealant used. I didn't think I put it on too thick. However, there are four surfaces that get some sealant.

Thanks again for the replies so far.
Click to expand...

...get any gasket sealer?

The Superior Assembly Manual seems to say no... and I can't get to my Lycoming one, but I thought most gaskets go on dry on the engine....

If your sealer is a mere 0.015 inch thick per layer, that is equal to one thread not exposed...:(

UPDATE

Specific text from Superior Engine Overhaul Manual

NOTE: Unless otherwise specified, all gaskets are installed dry.
 
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Maybe think of it this way.

If you had 5 threads showing, and the lock washer didn't do it's job, that nut is coming off!!!

6 planes, 5 carbs, no extra threads just like yours, no loose nuts(except in my head).;)
 
Any updates on this topic?

I just installed the MA5 carb on my ECi O-360 and I have no threads showing.

ECi recommnds the use of a "Nut, Hex, Lock, 5/16-18 UNC" where as Lycoming recommends the use of a "Nut, 5/16-18 plain" and a palnut on top of that.

When using the lock nut as called for by ECi, the thread doesn't reach the top of the nut. When using a plain 5/16-18 nut, the stud does come to the top of the nut but with no threads showing and there is no room to install a pal nut.

IMHO, this is an accident waiting to happen.

Do any of you have a suggestion?
 
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