Flatsixer

Since my C4 is parked for the winter, I have started the delightful task of trying to replace all the rusted nuts, bolts and screws throughout my 1990 C4. Everywhere I look there is more rusted bolts. ( mostly the undercarriage ) This will probably take years to complete !! I have also found that some of the pieces I ordered through my dealer to be the wrong size when they arrived, even though their computer specifies it is the right part ?? I have found the local hardware store to be a better source. I have found that some of the trim screws in the interior even have rust on the heads. Would this be due to the fact the car previously lived in a city with very high humidity in the summer months ? I have never seen this before on any car. I know the car has previously seen rain during the summer months, the car is in excellent condition and has been properly maintained, why so many rusty bolts ? Why would Porsche not use more weather tolerant pieces ( galvanized ) ?? Anyone else have similiar findings ? Regards, Brady

Matt Romanowski

Porsche uses zinc (or cad) plated bolts throughout. They do last a long time, but some may just rust. Depending on your amount of time, you can actually remove the bolts, bead blast them and have them all replated (pretty cheap - I replated everything on my 914 for ~$75). Two places to check out are www.mcmaster-carr.com and your local CAT dealer (so I've heard). Either way, make sure you are getting grade 8 bolts.

Matt

newmoe

I bit the bullet and went with Stainless.. A very time consuming process but well worth the results.. I have the light Grey interior and the Black oxide coating on the interior screws and nuts failed leaving little rusty circles on the interior carpet.

Flatsixer

I have replaced 99% of my interior screws already. I was able to find some black replacements at a hardware store. Porsche wants ridiculous money for these pieces and I found some to be the wrong size when they arrived. I am going to use all stainless replacements for the undercarriage (This will be a daunting task). My car is a driver, so I could care less if the screws and such are not OEM. Thanks for the input. Regards, Brady

914und993

Be careful where you use stainless hardware. A stainless steel bolt is generally not as strong as an automotive grade 8 carbon steel bolt, so don't substitute on stressed parts like the suspension.

Chip

Flatsixer

Thanks for the advice. I am simply replacing the screws that keep the front spoiler in place, fender liners, etc. etc. ( cosmetic stuff that no one will ever see ) I would only use the proper OEM pieces for any structural components. Regards, Brady

newmoe

Nuts and bolt's have a stress rating, be sure to get the proper nut/bolt for the application. I was a Gun Smith for years and found that with the proper foresight Stainless held many advantages in high stress situations. Always use antisieze with stainless regardless of the installation. Stainless can Gall.. In other words, the fastner may fail to tighten or loosen. Here's the quote from www.nutty.com;

Galling (also called Seizing) is a condition that exists when two metals or fasteners stick together and cannot be easily loosened. In tightening fasteners, for example, pressure builds on threads as metals rub against each other, and the passive film preventing corrosion on stainless may not form due to lack of oxygen. The Stainless Nylon Insert Lock Nut may freeze on the bolt preventing further tightening or loosening of the nut

springer3

Good topic, but there are some misconceptions. "Grade 8" is an SAE classification, and applies only to the "unified' thread system (sizes in fractions of inch). Porsche has always used metric bolts. Most are manfactured in Germany by Ribe or Karl Marx. You will see "RIBE" or "KX" on the bolt head. Metric bolts have strength designations as follows:

Property class 5.8: 75,400 psi carbon steel, similar strength to SAE Grade 2

Property class 8.8: 120,350 psi carbon steel, heat treated, similar strength to SAE Grade 5

Property class 9.8: 130,500 psi alloy steel, heat treated, no similar SAE grade

Property class 10.9: 150,800 psi alloy steel, heat treated, similar strength to SAE Grade 8

Property class 12.9: 176,900 psi alloy steel, heat treated, no similar SAE Grade

The important thing to remember when replacing bolts is to ensure you have both the correct size and strength grade. It is usually not a problem to substitute a higher grade, but consider failure mode. Sometimes it is better for the bolt to break before something more expensive bends or breaks. In that case, you should strictly observe the factory specifications.

I don't necessarily agree with the comments about replacement of coated steel fasteners with stainless. Strength is certainly an issue. 300 series stainless typically has 100,000 strength, and therefore should be used only for Property Class 5.8. There are heat-treated (400-series) stainless bolts, but those are not hardware store items, and are expensive.

Corrosion is still an issue with stainless bolts. The bolts don't corrode, but what about the surrounding metal parts? The protective chromate or zinc coating on a steel bolt also protects the surrounding steel parts. The chemistry is a little complicated, but metals corrode much faster when different metals are in close contact. If the parts get wet, your stainless bolt will be holding a package of rust. You can prevent this with protective coatings, but why use stainless if that is needed? It is better to have a bolt with a good chromate or electro-galvanized coating, because the coating will protect both the bolt and any nearby steel parts. This is especially critical in seacoast and contaminated industrial areas, and is most critical in regions where salt is used to de-ice roads in the winter. The protective coatings are designed to corrode before the steel. Over time, the coatings corrode away, and that is when you start to see red rust from the steel.

All the original fasteners in my 92 are still bright and clean, but the car has been in Atlanta and stored indoors when not driven. Environment makes a big difference in corrosion rates. I maintained a 1970 for many years, and I well understand the heart ache of corrosion.

A remedy I used on the early 911 for rusted parts, including fasteners, was cold galvanizing compound, available in both brush and spray-on formulations. You can wire brush (power brush preferred) to a clean condition, and then apply the coating. A cold galvanized spray coating will have the silver look of zinc galvanizing, and will provide the same corrosion protection as the electroplated factory coatings. Even new bolts seldom have very much zinc or chromate, because the materials are expensive. Therefore it will extend the life of even new fasteners if you add a cold galvanized coat. Do not use straight organic paint, and expect much corrosion benefit. The coating must contain zinc, chromate, or phosphate if you expect to slow corrosion rates significantly. This applies to both bolts and sheet metal protection (an also explains why most resprays do not last as long as the factory paint).

Flatsixer

Wow !! You know your bolts. Thanks for the useful information. The only non OEM bolts I have used thus far, are for my front spoiler as I had difficulty getting the right ones from my Porsche dealer. Porsche must have had a bunch of Kindergarten kids write their parts placard. It can be very confusing at times trying to decipher the right part. Regards, Brady

springer3

I agree the dealer is a bad place to buy bolts. The counter help seldom has a clue about bolts, and what you want is "out of stock". I had a Mercedes dealer send me to the hardware store when I needed clutch bolts. I have no clue what they used when their mechanics replaced clutches. I found that ACE carries most sizes of metric bolts, and has three different grades including Property Class 12.9.

German auto companies were under heavy cost pressure in the late 1980s Mercedes approached both RIBE and Karl Marx, and demanded steep reductions in prices, phased in over a number of years. They threatened to shop around in Japan and elsewhere if the suppliers did not meet their price targets (15% first year, 10% each of the next two years is the story I heard). Coatings cost more than steel in most bolts, so guess where most of the savings came? Of course we pay the price when the bolts rust sooner than they should. Porsche was not the instigator of the forced cost reductions, but they buy from the same suppliers as Mercedes, and I am sure they got the same bolts.

Sorry to hear about you corrosion problems. Stainless is a great solution for the plastic parts both outside and inside. Any bolts that hold steel parts should be kept steel, and fresh coatings will retard corrosion.

Flatsixer

Thanks again for the great info. Very much appreciated. Regards, Brady