Outer Limits 4x4 Board

Actually some stainless is OK other is no good.

18-8 3% Mo stainless 316 (active) is ok
18-8 stainless 304 (active) is ok
13% chromium stainless stell 410 is ok


18-8 stainless steel type 304 (passive) Bad
18-3 3% stainless stell type 316 (passive) Bad


Bazzle

bj on roids wrote:

murcod wrote:What about using marine grade stainless bolts with the aluminium blocks? Stainless and aluminium don't react- that why they use stainless fittings on ally boats.

mate, thats the biggest load of crap ever, there is a really bad electrolysis and corrosion action between alloy and stainless!! DAMN!

OK thankyou we've established that! Was only going on what I was told by the place that sold us an ally boat years ago.

Most of the problems encountered with rusty bolts (as cheezy mentioned) would be from fitters using non coated black high tensile replacement bolts (commonly called licorice). These bolts have no form of rust prevention, but when painted with a high zinc paint and with careful assembly, some 'neversieze' on the threads and the ends of the bolts painted, there shouldn't be a problem.

Go the ally blocks, paint the contacting surfaces with some aerosol body deadener (or the Durlac mentioned), most of the product will squeeze out anyway, but will provide a reasonable seal on the outside if tooled properly.

murcod wrote:
Or just get nylon blocks and save all the hassle.

Nylon absorbs moisture (hygroscopic) so you will probably have the same problems as with Al. A few states only allow metal blocks. There are better platics than nylon that don't absorb moisture - UHDPE and others.

well, thanks for all the info, lift will be of ally, got some duralac 2day for the ends, and will be using grade 8 high tensile zinc plates bolts from CAT, which i will also coat in duralac, just to be sure.

Well heres my 2c, late i know, but just in case anyone wants to know, galvanic corrosion occurs when two dissimilar metals are in contact with each other, the more reactive metal becomes the anode and gets eaten away - it becomes a sacrificial anode, the closer the electronegativity of the two materials is, the less of a reaction you should get
e.g. if you bolt magnesium to titanium, the magnesium would become the sacrificial anode and slowly get eaten away,

Heres a list of em,

http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm

I've got plastic blocks in case you're wondering, but plenty of people do use alloy, upto u, if u wanna use them i'm sure you'll be right with duralac, as its for marine environment.