Aggravating gasket

[Jim Hawkins]

A lot of you will know this gasket at first sight I bet. Yamaha 2 stroke 40-50hp. Aggervating thing. Seems whenever I get a motor where someone cleaned the carbs, if it's this gasket it wasn't put in right and got pinched and out of place.


Now I know you can hold a gasket in place using a little sticky grease but I'm wondering if there is anything stronger short of liquid silicone gasket that will not be a mess to remove?

 

[Jim Hawkins]

Dern! Another one.

 

[dingbat]

Trying to reuse gaskets?

This is what I use if grease doesn't work

 

[Sea Rider]

Don't ever resuse old shot carb gaskets, could have undetected fuel spills under the carb you won't ever be aware of. Before sitting new ones in groove usually finger rub a light coat of marine grease at both gasket's sides, never have had an issue with such type of rubber gaskets...

Happy Boating​

 

[99yam40]

I have reused them many times before as long as they are not swollen/ out of shape when removed.
e fuel does mess with them some times.
there should not fuel high enough in the bowl to be in contact with them under normal running conditions.
maybe when tilted up the fuel would come into contact, if the bowl was full when tilted

 

[Grub54891]

I have reused them many times before as long as they are not swollen/ out of shape when removed.
e fuel does mess with them some times.
there should not fuel high enough in the bowl to be in contact with them under normal running conditions.
maybe when tilted up the fuel would come into contact, if the bowl was full when tilted

Sorry to say: When underway, that fuel is rattling all over in there. yes, that gasket gets fuel on it running.

 

[Jim Hawkins]

Trying to reuse gaskets?

This is what I use if grease doesn't work
View attachment 354987

Thats what I'm talking about!!! Thanks Dingbat.

 

[Sea Rider]

The issue with E fuels is that will elongate any rubber or elastomer gasket the sooner or latter compared to non E fuels, been at both sides to know the huge difference.seen when pulling both out. Can't posibly sit well a new bowl gasket if their groove if not impeccable cleaned before install as seen in post 2 pic. A bowl gasket is only $ 12 max, all motor brands recommends changing them as a precaution when doing a carb restoration or full rebuilt.

Happy Boating​

 

[Jim Hawkins]

So, I think this is the 4th carb now (3 different motors) that I have seen the gasket misaligned like this. My first impression was just sloppy work but now I'm wondering if there could be something in the design of the carb that causes this to happen from some pressure. The red arrow shows the gasket curved where it should be straight. Seems odd it should always be the same spot. I repeatedly put the bowl on and took it back off looking to see if the gasket moved but I could never duplicate the misalignment.

 

[racerone]

Check float bowl and carburetor body for signs of warping.-----If it was the only motor I had I would install 3 or 4 wee pins on that surface.-----Just to trap the gasket , prevent it from moving.

 

[dingbat]

So, I think this is the 4th carb now (3 different motors) that I have seen the gasket misaligned like this. My first impression was just sloppy work but now I'm wondering if there could be something in the design of the carb that causes this to happen from some pressure. The red arrow shows the gasket curved where it should be straight. Seems odd it should always be the same spot. I repeatedly put the bowl on and took it back off looking to see if the gasket moved but I could never duplicate the misalignment.

Hard to tell from the picture of its a rubber or fiber gasket.. either way, you do not reuse compression fit gaskets, period.

In either scenario, the gasket is “crushed” between the mating surfaces to make a seal. The cross section of the gasket and the amount of crush (percentage of thickness) required to seal the joint is determined by the gasket material and the pressure which it must maintain. The torque on the fasteners is determined by the hardness of the gasket and the surface area in which the gasket has to be crushed.

Flatness of the sealing surfaces, torque sequence and tolerance of the retaining fasteners and the gasket’s thickness and or distortion all play into a gaskets ability to seal.

As noted above, a gasket is distorted when crushed. Paper gaskets become thinner in the area of contact and get thinner yet in areas of higher compression, ie over torqued fastener or distorted sealing surfaces.

Rubber gaskets typically flatten out and take a hard set (flat spot) where the gasket was in contact with the mating surfaces.

On top of the distortion, gaskets swell (change dimensions) when exposed either direct or indirectly to media. Rubber (oring) gaskets are the worst. Not only do they get larger in diameter they also expand in physical size. The 1” square gasket that fit perfectly when new is now 1.12” square after exposure. This seems to be the case with the gasket in question which is why you typically see paper gaskets in use with hydrocarbon media.

Bottom line…don’t reuse gaskets in critical applications.

 

[racerone]

If that was a paper type gasket I would simply cut a custom one.----With a series of holes instead of that long wide open part.

 

[Jim Hawkins]

What I didn't mention was on the bowl side the gasket lays in a groove which should make it impossible to move once the screws are tight.

I really was expecting someone who has rebuilt this model carb to chime in and say they have seen the same thing.

Otherwise, I suppose it's just coincidence that all these carbs were reassembled using old gaskets that had swelled.

 

[dingbat]

Otherwise, I suppose it's just coincidence that all these carbs were reassembled using old gaskets that had swelled.

The “not fitting” part is swelling. Going to happen over time.

If it’s an older motor could still be using Buna N instead of Viton (fluorocarbon) rubber which is a much better performer with E fuels.

 

[racerone]

So how does this gasket work it's way out of this groove ?----Lack of attention by those that pick on the carburetors ?----Often the first step in motor repair attempts.

 

[Sea Rider]

Many motor brands are using rubber (o'ring type) bowl gaskets, all my Tohatsul carb bowls uses them, have had 0 fuel spill issues with them. If well seated on well cleaned grooves and mating surfaces will last very long provided they are not removed while the carb (s) burns E fuels or won't fit to sit as used to if plan reusing them, which you shouldn't.

Question : is the rubber portion seen pointed with the red arrow an indication of having already a flattened surface ? When torquing carb's bowls must be done gradually in an X pattern. Can't possibly over seat those gaskets as both carb's mating surfaces once in touch will provide the correct amount of internal space needed for said gasket to sit well in place.

Happy Boating​

 

[Jim Hawkins]

The green arrows show where the gasket was crimped. The other picture shows the carb body and how it (should) line up with the gasket. And that brown residue may have been some sort of contact cement.

The thing is I just didn't want to believe people could be so sloppy even if they did re-use the gasket that had swelled. (I bought this motor from a local "Marine Mechanic") While waiting for new gaskets to be delivered I decided to experiment and see if I could get this exact gasket to fit, and with a little grease and patience I did. No leaks and the motor ran fine.

 

[Jim Hawkins]

So, the moral of this story is I gotta get me sumathis.

 

[boscoe99]

Some gaskets are known to swell up in the presence of gasoline. Which can make reassembly difficult if someone reuses the gasket. The gasket is simply too large or too distorted to fit properly. The gasket on a Racor filter assembly comes to mind.

This may be intentional insofar as the swollen gasket might help to make a better seal.

In many instances, allowing a used gasket to air dry for a period of time might allow it to return to its original configuration. In which case installation may turn out to be as easy as the installation of a new and used gasket.

 

[Sea Rider]

I find that most if not all shade tree mechanics does sloppy works while saving money on parts that needs to be changed, second hand motors must be fully inspected from lower leg to top cowl as could turn out you bought a Pandora Motor.

A carb is a mechanical component that must work flawlessly, that's with 0 fuel spills issues while the motor is running. Personally would never put my life and my boating mates lives in jeopardy reusing shot carb's o'rings that could ignite the spilled fuel to save $ 12.00 to buy cold beers. To each one their particular way of working...

Happy Boating​