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The anti seize (or PTFE compound....I've never tried this, but Stan knows his stuff) is the solution to eliminate future problems.
Chase the old threads, in the block, to get rid of residual corrosion.
At that point, the grade or material of the bolt is moot.....virtually anything will work.....the only requirement is that the hardware be new and zinc coated (stainless should work, too.)
A year or three ago I asked if there's a justification for putting SS studs into the block, maybe with a spot of threadlocker on the tip and sealant (Hylomar or PTFE) on the upper threads), then just use SS nylocks on them and call it a day. If there's somehow a reaction between the studs and the block, no worry since you weren't disturbing that junction anyway.
I'm in the Greg camp on this otherwise. New bolts every time with anti-seize (or Hylomar or PTFE) on them and an adjustment to tightening torque for the thread lubrication. So far (knocks on alusil...) no issues at all with removal or seepage. Genuine Porsche gasket is always installed dry.
I'm not planning on changing the water pump more than one more time in my stewardship period. I put a pump in every other belt change, so it will get a new pump next time in another four or five years at the next T-belt. The bolts wee removed and replaced at the last belt change in early 2014 to inspect the pump and block; All the bolts came out quite easily for that. Cleaned up nicely, no corrosion on the CS bolts, so they went back in with a new coating of anti-seize.
Stronger also means that instead of snapping removing the bolt also removes the threads in the block.
I would use A4/70 stainless installed with Duralac Zinc Chromate paste liberally applied - If its good enough between aluminium and stainless in a marine environment it's more than good enough for a 928 waterpump.
Bolt strength is irrelevant in this instance - the multiple bolts are there to provide even clamping of the gasket - you would probably find that one or two at most, M6 grade 4.6 bolts would provide the total required clamping force.
if corrosion is a problem I would go with this advice. Stainless is a poor electrical conductor so galvanic process would be reduced.
I use 10.9 grade hex bolts in this location. 12.9 hex bolts are not very common...usually you have to get a cap screw to obtain the 12.9 rating.
I don't think I'd use a cap screw in that location.
The original bolts and most all of the bolts installed by any "flat rate" shop are dry.
A dab of factory never seize, chasing the threads, and new hardware makes this a non-problem.
Do you have a link to suitable thread chasing kit? I can only find them for M10 upwards or spark plug threads. Link would help me track down suitable set, thanks
Do you have a link to suitable thread chasing kit? I can only find them for M10 upwards or spark plug threads. Link would help me track down suitable set, thanks
I was recently talking to Turbo Todd about this and he suggested for fasteners this small, you want a 2 Flute chase (versus a 3 or 4 flute) and titanium coated for longer life.
I haven't found any like that in a set yet, only individual.
I was recently talking to Turbo Todd about this and he suggested for fasteners this small, you want a 2 Flute chase (versus a 3 or 4 flute) and titanium coated for longer life.
I haven't found any like that in a set yet, only individual.
Regarding the strength of a bolt and the relationship to torque settings: "Strength" of a material can have many meanings, like the proverbial story of Eskimos having 43 words for snow.
One meaning is stiffness, the "spring rate" of a material, also known as modulus; there are even several variations of that property, Young's modulus, bulk modulus, etc. The interesting thing about this property is that all carbon steels have the same stiffness, for all practical purposes. While acting only as a very stiff spring in the form of a bolt or other component, they all have the same level of this sort of "strength". Aluminum has one-third this sort of "strength". Stainless steel is a bit weaker than carbon steel. Carbon fiber composites are much stiffer. Many things turn out to be stiffness-limited, so this property is often more important than the sorts of strength that govern outright failures (such as ultimate tensile strength). Not bolts, usually, but stiffness is a factor - torquing a bolt is the same as applying a spring preload.
Apparently, I woke up this morning with the urge to lecture. I should go watch a Comedians in Cars Getting Coffee episode, or something.
Greg had it right based on my experience with fighting bolt / nut seizing in marine situations of aluminum and all kinds of bolts. Anti seize is the best and only real defense. No matter what type of plating or steel you use filling the threads with anti-seize is the only way to really prevent corrosion of threads where water is present. I love stainless hardware but it is not nearly as strong so I use SS bolts when I am sure the bolts are under low to moderate stress levels. Should be OK for this application but not necessary. Imagine dipping your motor into salt water each week and you can appreciate the corrosion experienced by boating enthusiasts that work on their own craft.
SS should work for this application as the pump bolts are only lightly torqued (7 ft lbs).
Thread protection is essential, especially the one(s) in the water jacket.
Full circle here.
I once worked in a research lab for a nickel company - our Canadian members know the one. Some very exotic alloys appeared in scrap barrels and the secret stashes of cooperative technicians, especially those in the Corrosion Lab. I once acquired some very expensive bolts for a small project for my parent's ocean-going sailboat. In a few thousand years, the only remains of that boat may be those bolts.
I'm surprised no one has suggested preserving a few oil leaks above the bolts in question. Very protective.
12-11-2015, 12:14 PM
