Automotive Plastics: Plastic radiator tank repair - BMW K1200S., tank, radiator

Question
Hi Octavio,

I'm currently rebuilding an '05 model-year BMW K1200S motorcycle. Unusually for a motorcycle, the radiator side tanks are plastic.

One of the mounting lugs (an integral moulding with the radiator tank) has been severely bent, creating cracks along the area where the lug joins the tank. Replacing these radiators outright is only a solution for those with money to burn (a replacement radiator costs the equivalent of US$650 in South Africa, depending on the prevailing exchange rate).

I'd like to ask your advice with regard to home repair of these cracks. The lug is still more-or-less solidly attached to the tank. It never broke off - the plastic used seems to be relatively flexible.

Luckily, all current BMW parts carry material identification codes for recycling. The materials code moulded on these plastic tanks is >PA6,6 GF30<. What is the best way of repairing this particular polymer? And what adhesives, if any, should be used?

Thanks man. :)


Nick Van den Berg

Answer
Hi Nick,
Thank you for providing such complete info. on the tank polymer identification.
Radiator tanks are normally made of a 6 carbon polyamides >PA 6.6< therefore that marking that stands for  plastics sold under  commercial names like Nylon and others.
As a general rule, polyamides for this application (pressure and hot water container)are not repairable. This is due to the fact that Nylon is a plastic that is processed under very high pressures and heat in injection moulds. There are no adhesives or sealant of any kind suitable for Nylon. then the alternative is welding. This polymer is prone to be and remain porous after welding without pressure and as you suppose, the tank will irremediably leak. All these is of course bad news. However as a stubborn repairman, I would suggest you to send me detailed and close up photos of the affected area, to see if we can devise some sort of rubber seal that upon mechanical expansion could seal the cracks.I am not 100 percent sure that this is a viable solution for you but after all, we have nothing to lose.Mi mail: manual@bumper2bumperplasticsrepair.com . Please mention the words "plastic repair" in the subject box.