172 Nosewheel Struts Leak Nitrogen

[jls]

I rebuilt one and the best A&P on the field rebuilt the other one, on 1966
and 1957 172's. Neither will hold nitrogen. What's the secret to getting
them not to leak.

I bought a complete O-ring kit from Trimcraft in Wisconsin. My personal
A&P told me that only one or two large O-rings were leak-prone and crucial
for replacement so I replaced those only, at his urging. Now I think I'll
install the complete kit, which includes at least 6 O-rings. How about it
A&P's who are Cessna savvy? What's the trick here to getting these struts
to stay up and not leak nitrogen? I know they are not leaking around the
Shrader valves. I have done too much testing with soap suds looking for a
bubble to emerge. Besides, both of the Shrader valves and the valve stems
have been replaced and are official Cessna parts.

The flight school A&P on the field says some of the struts just have to be
re-gassed with nitrogen occasionally, but that's not a satisfactory answer,
far as any owner would be concerned.

Thanks in advance for any good advice you can give on this frustrating
problem.

[MikeM]

jls wrote:

> I rebuilt one and the best A&P on the field rebuilt the other one, on 1966
> and 1957 172's. Neither will hold nitrogen. What's the secret to getting
> them not to leak.
>
> I bought a complete O-ring kit from Trimcraft in Wisconsin. My personal
> A&P told me that only one or two large O-rings were leak-prone and crucial
> for replacement so I replaced those only, at his urging. Now I think I'll
> install the complete kit, which includes at least 6 O-rings. How about it
> A&P's who are Cessna savvy? What's the trick here to getting these struts
> to stay up and not leak nitrogen? I know they are not leaking around the
> Shrader valves. I have done too much testing with soap suds looking for a
> bubble to emerge. Besides, both of the Shrader valves and the valve stems
> have been replaced and are official Cessna parts.
>
> The flight school A&P on the field says some of the struts just have to be
> re-gassed with nitrogen occasionally, but that's not a satisfactory answer,
> far as any owner would be concerned.
>
> Thanks in advance for any good advice you can give on this frustrating
> problem.
>
>

If its leaking around the lower O rings, then oil would be forced out.
As long as there is any oil in the strut, then it will be forced out
first (unless the airplane is laying on its back!) before nitrogen begins
to leak.

The only place nitrogen can leak is at the top, around the Schrader valve
or through it. Another possibility is a leak around the plug/metering
rod at the top (inside) of the strut tube. In this case, the nitrogen would
be leaking down the tube, and exiting through the hole in the fork.

MikeM

[Dan Thomas]

" jls" > wrote in message >...
> I rebuilt one and the best A&P on the field rebuilt the other one, on 1966
> and 1957 172's. Neither will hold nitrogen. What's the secret to getting
> them not to leak.
>
> I bought a complete O-ring kit from Trimcraft in Wisconsin. My personal
> A&P told me that only one or two large O-rings were leak-prone and crucial
> for replacement so I replaced those only, at his urging. Now I think I'll
> install the complete kit, which includes at least 6 O-rings. How about it
> A&P's who are Cessna savvy? What's the trick here to getting these struts
> to stay up and not leak nitrogen? I know they are not leaking around the
> Shrader valves. I have done too much testing with soap suds looking for a
> bubble to emerge. Besides, both of the Shrader valves and the valve stems
> have been replaced and are official Cessna parts.
>
> The flight school A&P on the field says some of the struts just have to be
> re-gassed with nitrogen occasionally, but that's not a satisfactory answer,
> far as any owner would be concerned.
>
> Thanks in advance for any good advice you can give on this frustrating
> problem.


The top of the oleo has a slug with an O-ring on it; the same piece
that has the valve screwed into it. The slug is retained by the
through-bolt that attaches the oleo to the firewall bracket. The
O-ring will deteriorate and leak, and when it's replaced it can get
cut on the edges of the bolt hole as the slug is reinserted. If only
nitrogen is escaping, it's this O-ring or the valve.

Dan

[JDupre5762]

>" jls" > wrote in message
>...
>> I rebuilt one and the best A&P on the field rebuilt the other one, on 1966
>> and 1957 172's. Neither will hold nitrogen. What's the secret to
>getting
>> them not to leak.
>>
>> I bought a complete O-ring kit from Trimcraft in Wisconsin. My personal
>> A&P told me that only one or two large O-rings were leak-prone and crucial
>> for replacement so I replaced those only, at his urging. Now I think I'll
>> install the complete kit, which includes at least 6 O-rings. How about
>it
>> A&P's who are Cessna savvy? What's the trick here to getting these struts
>> to stay up and not leak nitrogen? I know they are not leaking around the
>> Shrader valves. I have done too much testing with soap suds looking for a
>> bubble to emerge. Besides, both of the Shrader valves and the valve stems
>> have been replaced and are official Cessna parts.
>>
>> The flight school A&P on the field says some of the struts just have to be
>> re-gassed with nitrogen occasionally, but that's not a satisfactory answer,
>> far as any owner would be concerned.
>>
>> Thanks in advance for any good advice you can give on this frustrating
>> problem.
>
>
> The top of the oleo has a slug with an O-ring on it; the same piece
>that has the valve screwed into it. The slug is retained by the
>through-bolt that attaches the oleo to the firewall bracket. The
>O-ring will deteriorate and leak, and when it's replaced it can get
>cut on the edges of the bolt hole as the slug is reinserted. If only
>nitrogen is escaping, it's this O-ring or the valve.
>
> Dan

Dan is right. Lots of mechanics forget or don't know about the upper o ring on
the Cessna types. In most typical flight school operations it is the lower o
rings 9 times out of ten that fail. But on that tenth time it is the upper o
ring. I have found some that were original from the days when they used to
color code o rings with a dot of colored paint. Most often too that o ring has
worn to a square profile too. Somebody's A&P doesn't know all that he should,
but then who does?

John Dupre'

[Martin Kosina]

>
> Dan is right. Lots of mechanics forget or don't know about the upper o ring on
> the Cessna types.

Same experience here, turned out to be the upper, oft neglected
o-ring. Also inspect the inflation valve, those can slowly leak if
they have never been replaced.