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Cylinder Base and Head Joints...early models
Posted: Mon Feb 18, 2019 9:54 am
by Hugz
Inside cover of early original operating instructions
Re: Cylinder Base and Head Joints...early models
Posted: Mon Feb 18, 2019 11:47 am
by Collector Inspector
YEP!
BnC
Re: Cylinder Base and Head Joints...early models
Posted: Mon Feb 18, 2019 11:54 am
by Collector Inspector
Sorry Hugo
The "YEP" was in relation to the scan that you supplied.
Over many years many posts have been dealing with this very thing......"What to do" and "What to Use" in this case.
It is really cool that you have posted this pic as it just confirms past advice to others in need to know situations.
I think that this should be added to SOS site as a thing for John to allocate a place for it.
Well done in finding that book by the way.
Cheers
BnC
Re: Cylinder Base and Head Joints...early models
Posted: Fri Feb 22, 2019 3:53 pm
by Gannet
I have seen similar information previously, but not so highly specific and so very clear. So it is very interesting to see that.
My belief is that these Bostik sealants were chosen to prevent cooling water from coming into contact with the aluminium head and the aluminium crankcase. This was absolutely critical in order to prevent electrolytic corrosion.
The steel 'gaskets', which I prefer to call sealing plates also performed that critical task of preventing cooling water from coming into contact with the aluminium head and crankcase.
On some engines that I have stripped down, evidence of black go (presumably Bostik) has still been present on both faces of these sealing plates and the in places on the aluminium mating faces.
I believe that the function of these plates and the Bostik has not often been understood by subsequent rebuilders. They were not just to stop water from getting into the cylinder or into the crankcase. The plates and the specific grades of Bostik were there to seal cooling water away from the aluminium. When this was not understood by later rebuilders, electrolytic corrosion between the steel studs and the aluminium would have taken place. The aluminium is the anode and it would have corroded around the contact area of the stud. A lot of poorly re-assembled Early Series Forty exhibit this problem.
Corrosion was clearly a problem, especially on rebuilt engines. The next Forty model after the FV, FVP, LS and LM were the SJM/SJP. My suggestion has been that these letters stood for Sealed Jacket Minus and Sealed Jacket Plus, as the design was changed so that the cooling water jacket was basically sealed from the aluminium, and the risk of electrolytic corrosion was almost eliminated.
Jeremy
Re: Cylinder Base and Head Joints...early models
Posted: Fri Feb 22, 2019 5:18 pm
by Charles uk
Many years ago when CharlesP & I were researching the overview of Seagull practices, I vaguely remember CharlesP telling me about a conversation he had with Bostik technical to find out the properties of this gloop & whether there was anything that would perform the same function today.
If I remember right they had no details whatsoever & could tell him nothing about it.