Use of Thread Locker

[Neil McDonald]

The Yanmar 3GMF on my H35 has been plagued by a fuel leak at the banjo joint on the discharge side of the engine mounted fuel filter (not the upstream Racor) due to the retaining bolt constantly loosening. When it gets too loose it also causes hard starting problems when air enters. Yesterday I managed to strip the threads on the casting when I was tightening it for the umpteenth time. :cussing:

A new assembly, banjo washer and bolts are now on order. Should I consider using some thread locker to prevent this cycle happening all over again?

 

[kloudie1]

Neil, I’ve heard talk of a new style washer from Yanmar that has a copper outside and a Viton elastomer inside.. I think I’d try that before going to the thread locker.. “usually” not always, the loosening is a result of a “not flat” (I mean microscopically flat) washer or seat on the fuel filter assy. When ya get the new assembly, check the flatness of the washer seats, inlet and outlet.. Make sure you use a new washer, and don’t try to re-use an old one once it starts leaking unless you grind it flat on a piece of glass with 400 grit paper.. Circular scratches in the gaskets or seats are ok, but radial ones are absolutely not ok

 

[Dan Johnson]

Neil...

since the filter housing is an aluminum casting, you may not be able to get sufficient grip in the stripped threads with a thread locker (assuming a Permatex type product). Future work might be an issue afterward.

Drilling out, retapping and using an insert may be one solution. A new housing might be the other (is this the "new assembly" referred to?).

 

[Don12364]

The fact that this banjo joint constantly comes loose is a worry in itself and you need to identify why this happens. It could be a resonant vibration of the pipe at certain engine revs. If so then some additional support for the pipe, or even putting an extra bend in it - or even adding some weight to it to lower its resonant frequency may help.

Do you have any vibrations which result from non-engine related causes such as transmission or prop?
I suggest you watch the engine very carefully through its rev range both out of gear and when driving the boat.
Are the AV mounts on the engine in good order and are they the correct stiffness for the engine?
Unless you find the cause and remedy it you are simply on a circular path and the new joint will go the same way.
As far as I am aware other owners do not continually suffer this problem so something is unique about your setup.
Can you get to look at another similar boat?

 

[Neil McDonald]

Kloudie - The leak starts after the bolt has loosened slightly and seems to substantially stop after I tighten it again, so I don't think that the face of the joint is the problem.

Dan J - I thought very briefly about trying to retap the threads or use a Helicoil or similar insert but rejected the idea and decided to buy everything new instead. Will get a little change out out of $100... which is a pretty good price by boating standards. What I am thinking about is using the blue thread locker on the threads when assembling it to limit the chance that it might start to slacken again once in service.

Donalex - Good points but I do not feel very confident in my ability to go down this path. I think that I will try the new assembly route first (probably with threadlocker) and see if this solves the problem.

Thanks everyone for you suggestions.

Neil

 

[Benny]

The threads on the casing of the secondary fuel filter on Yanmars have always been a weakness. The best solution is to get a new casing, washers and bolts and it seems you are doing just that. There should be no need for the use of a thread-lock but do not overtighten the bolts. It is easy to deform the threads and they will loose their holding power. Try hand tightening and when you reach the end just give it 1/8" turn with a small wrench.

 

[kloudie1]

Yip.. Neil, I think you are heading in the right direction.. A note on the banjo joint.. The copper deforms to mate with the aluminum faces.. It work hardens in the process.. The now-deformed faces of the washer are good bit harder than they were for the first seal.. They will seal when ya tighten them but the hardness makes them have a lot less friction .. so they will unscrew at the slightest provocation.. It is a surface thing.. and can be ground away on a flat.. The thread locker will probably work to keep it together so it doesn’t leak the first time.. Really careful application !! the close clearances in the HP injection pump are just downstream .. Good luck with it