MainePorsche

Guys,

Been a lot of good discussion recently about our water pumps.
Regardless of pump used, there seems to be a lot of bolt corrosion/breakage on removal which is a headache (I've been fortunate and never had this in my six belt/pump changeovers).
I bring for discussion here the thoughts on using a higher grade bolt such as a 12.9, and the use of the various platings available (i.e. zinc, galvanized, cadmium) for water pump installation application in order to mitigate bolt breakage.

Are there advantages, and/or disadvantages to be seen with this in the aluminum engine ?

Rob Edwards

Dunno about higher strength, but PET called out for M6x20 or M6x25, with the modifier Z2, depending on the year. I assume Z2 means zinc plated, not sure (?)

MainePorsche

Rob,
Thanks. Interesting re the modifier code.
I think it's elementary regarding going to a higher strength carbon steel bolt such as a 12.9. So long as the proper bolt size and pitch used, it wouldn't be a detriment. I'm just wondering about the platings available, and if they may be of help or harm. On some pilot forums they speak well of cadmium, but didn't give technical details. I've obtained, and used a 12.9 grade cadmium plated bolt for some caliper work. Greg and Colin gave the thumbs up on that. Bolt went from the freezer to the caliper years ago, and all has been good.

GregBBRD

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.

GlenL

No, it's not that clear.

Higher strength bolts don't mean less corrosion. They do mean stronger and that means harder to drill out. It's already miserable to drill the bolts out.

I'd focus on getting the right anti-seize on the bolts.

GlenL

+1

(I just need to be patient and "+1" what Greg says. Saves typing.)

MainePorsche

I was thinking a higher bolt grade may hold up better on the drill out, and not 'snap' as fast.

Mrmerlin

I have had good luck with removing bolts that have had Loctite PTFE non setting pipe sealant on them this prevents coolant from migrating into the bolt holes and corroding the bolts
I always use new carbon steel bolts usually found at ACE hardware.

SeanR

What does Kibort think about this? I'll go with that.

mark kibort

good advice. the mode of failure is normally the threads stripping out of the block. going stronger wont change the corrosive factor as was said.

Just use the stock stuff. be a little more careful on the torquing, and use a little dab of anti fungal on the threads.

James Bailey

that comment is too funny in so many ways

mark kibort

smart man!

jon928se

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.

MainePorsche

Thanks for the replies guys. Was educating.
Still wondering about the Z2 modifier for these bolts as Rob mentioned.

wpgshark

What about the effect on torque values? At recommended torque, the torque applied to a bolt actually elongates the bolt enough to help prevent it from loosening. If you use a stronger bolt the required torque to allow the bolt to maintain the same loosing resistance will go up. This higher torque may not be good for the threads in the head nor the gasket. Thread locker can be used to supplement.

Stronger is not always better. Personally can't say if the WP is a good candidate or not. I typically go with the factory recommended bolts when given a choice.