Bond of Brothers

Hermetite... Hylomar... Yamabond... Wellseal... Hondabond... B&Q Bathroom sealant????

So many choices - but which one?

In the old days, in these situations I used to use traditional Red Hermetite or more recently Wellseal. I've also use blue Hylomar in the past. Usually the selection is made on the grounds of availability - what I had in the toolbox at the time.

I've no real engineering information for any of these products, and have never made a proper assessment of them.

However, for the SQ4 I wanted to look at a modern sealant. I hope to avoid tearing the engine down again anytime soon and with the legendary folk tales of excessive engine temperature (300 F at the plugs) I wanted to make sure I had something which was:

• suitably rated for temperature 
• compatible with engine oil 
• compatible with aluminium 
• a suitable colour (i.e. not red & smeared all over the cases!)

Several books and web forums I have read, both bike & car related (& even stationary engines!) mentioned Threebond products, Yamabond & Hondabond. Now, a quick Google reveals that Yamabond & Hondabond are both rebranded Threebond products.

Threebond describes itself as a fine chemical technology company with its roots in the automotive industry. Apparently, more than 90% of the world's motorcycles are assembled using Threebond products. Probably worth a look then!

Threebond say:

1200 Series silicone-based liquid gasket fills gaps on a flange surface and thus completely prevent leaks. When cured, it forms an excellent rubber-like elastic body offering excellent resistance to vibration and shock. Also it has an excellent resistance to heat, and effectively seals joints that are subjected to high temperature.

Here's the specification for Threebond 1207B:

• Excellent chemical resistance against coolants and engine oil 
• Outstanding mechanical and thermal resistance 
• Excellent adhesion even to slightly contaminated surfaces 
• Extremely fast curing 
• Instantaneous impermeability for pressure- and fire test. 
• Acceleration of the curing process by heat and contact with the medium 
• No shrinkage and no generation of corrosive gases 
• No corrosion of metal and only very slight reaction on plastics 
• Normal disassembly

Here are the material properties:

 I now have a tube of this. It has a Honda label & part number!

Number Crunching

Lest we forget: Cylinder numbering for the four, according to Mr. C.W. Waller:

Next job is to lift the head. We remove the four sleeve nuts inside the rocker boxes; we loosen the twelve nuts around the outside of the head and, using a 1/4" BSW ring spanner especially reduced to fit in a confined space as shown in the picture on the left we remove the final four nuts.

A curiosity here. The front two studs were both fitted with two nuts - one with a regular 1/4" BSF nut, the other with a reduced hex 1/4" BSF nut. One is tempted to think that was to allow a bit more room to throw a wrench around, but I suspect it was more a question of convenience - whatever came to hand. The two nuts were I guess fitted to protect the threads.

In theory, according to the book the next job is to lift the head and place two 1/8" wooden strips between the head and the block, to allow us to raise the head and then to actually remove the nuts from the twelve studs.

The operation will be something like that shown in the picture from the Floyd Clymer Ariel Motorcycle Owners Handbook (3rd Edition) shown as Figure 11 below.

Well, I hope it will. It hasn't happened yet. The head is stuck fast with the adhesion of decades of setting time of a whole tube of Hermetite, by the look of it.

I have taken the hide mallet and waved it around near the engine in a vaguely threatening manner, but I don't plan to do anything else with out a bit more thought and a plea to the AOMCC forum members.