Best Diaphragm Sealant found!

[Iron-butter]

The best sealant for repairing diaphragms is actually a black polyurethane sealant designed for roofs & flashing.
It's Loctite "PL S30" roof and flashing sealant. It’s available at Home Depot in 10 ounce caulk tubes for ~$6 per tube.
This stuff never gets stiff or brittle even after years of sun exposure on Arizona rooftops.
Some expensive polyurethane adhesives need to be used up shortly after opening because the product will cure in the container.
This sealant does not have that issue, but it does need to be capped well for use later.

Use in well ventilated area. There are warnings on the tube to users who have lung or breathing problems and sensitivity to isocyanates.
They are warned not to use this product.

PL_SEAL_RF_tds.pdf

The odd thing is that it smells like tootsie-rolls until it cures. Thin layers like what are needed on diaphragms take a few days to completely cure.
Make sure the diaphragm is cleaned well with isopropyl alcohol and completely dry prior to application.
I tested a cured patch of it in a 12 hour bath of gasoline. It did not discolor the gasoline, break down or soften and remained flexible, but it did swell about 20% in size.
After drying out for 2 days it went back to its pre-soak size and remained flexible. I spread ~1" square patch on a nitrile glove and let it cure for a week.
Was unable to peel the edge up from the glove, but was able to delaminate it by stretching the glove severely.
Diaphragms have reinforcement fibers that prevent stretching (or ballooning) so this should not be a problem.
The working time is about 5 minutes for thin coats and longer for thick coats.

I coated the high pressure side of a diaphragm that had several pinholes and a small vertical split (3-4mm).
Will be assembling carburetors soon and putting rebuilt engine back onto frame. Will update any significant progress as it occurs.

Diaphragm repair.JPG

[shardesty101]

So how did it work? Looking to seal mine as well.

Thanks,
Scott

[atotheroh]

This is amazing- looking forward to what you find.

[Iron-butter]

So how did it work? Looking to seal mine as well.

Thanks,
Scott

The diaphragm looks good and the sealant is completely cured. Carbs are back together except for brace between top covers.
Seem to have misplaced it. Have to search through the garage & man-cave to find.
Replaced one carb bowl that had a stuck drain screw and stripped head.
Need to find a replacement drain screw for "new" bowl.

Fuel tank has been welded back together and stripped down to bare metal. Will level out contours with epoxy, sand smooth, primer & paint.
Engine is rebuilt and ready to mount in frame.

It may be a while before I'm able to get everything back together and report any results. You may want to pick up some sealant and do some independent testing for your own curiosity before committing to use it on your diaphragms. A 10oz tube cost about $6. The sealant is almost as flexible as silicone sealant, but tougher.

My current plan is to break the engine in with the original carbs then convert to fuel injection after break-in. Have a friend that has successfully converted his XJ1100 to fuel injection. Have already invested in MegaSquirt computer, throttle bodies, injectors (& harness), fuel pump, regulator, and a fuel return port in fuel tank. Everything is doable, but contingent on successful break-in with carbs.

Iron-butter

[shardesty101]

I'm looking to do something similar. Can you update us on how this experiment went?

Thanks,
Scott

[shardesty101]

I'm looking to do something similar. Can you update us on how this experiment went?

Thanks,
Scott

Just FYI I ended up ordering new diaphragms replacements through this site:

http://jbmindustries.com/

Good prices and if installed correctly people seem to have success. I should be getting mine in the mail this week.


-scott

[Hellgate]

How evenly does the diaphragm move when slide moves? Does it bunch up?