Plastic cylinder head cover-fixings

[scm2004red]

The plastic cover to the cylinder head appears to have 2 different types of fixings,2  dome nuts at the front of the engine and 2 of some sort of plastic fixings at the rear ( one of which is missing on mine).

How is the plastic fixing removed, it seems to have a locating notch which prevents it rotating if it is to be unscrewed.

[Ardent]

I Believe they just prize out.
 Thin screwdriver to pop them it out.

[MRSwede]

Instead of the flimsy plastic clip you can use a standard M6x16 flangebolt

[scm2004red]

Thanks guys, didn't want to break the remaining plastic fixing. If using the flange bolt suggestion, is the hole tapped to receive it?

[Carolyn]

Thanks guys, didn't want to break the remaining plastic fixing. If using the flange bolt suggestion, is the hole tapped to receive it?

Yes it is. There's a tiny little plastic tab in the recess.  I remove those with a sharp blade to help the bolt seat properly.

[scm2004red]

Thanks, better solution than nasty plastic.

[Beachbum957]

Another option if you want to look "factory" is to use the OEM short cover stud and regular acorn nuts.  You still need to cut off the little plastic tab

Studs 92122-80612
Acorn Nut 90176-06023

[JohnGee]

Silly question(s), but I guess bolts connect directly into the cylinder head, is the cylinder head not made of aluminium, will a stainless bolt be OK here or will this accelerate corrosion of the cylinder head around the contact points? Would galvanised be a better option, or am I worrying over nothing?

[Joesson]

Silly question(s), but I guess bolts connect directly into the cylinder head, is the cylinder head not made of aluminium, will a stainless bolt be OK here or will this accelerate corrosion of the cylinder head around the contact points? Would galvanised be a better option, or am I worrying over nothing?

My thought was that stainless steel would be better than galvanised as the screw that is galvanised has a higher iron content.
This article is quite explanatory:

https://www.solaracks.com/galvanic-corrosion-between-stainless-steel-304-and-aluminum-alloy/

Probably why Mr T used plastic fixings.

But he could not be sure how long these fixings would be unused. Yours/ ours have likely been fixed fo no less than 14 years so plenty of time for dissimilar metal reactions.
We are now into a second life and the fixings will not likely be in place for so long. Either way, a reason why I typically lubricate most fixings when replacing unless torque value is critical, and then the argument for replacement fixings likely applies.

[scm2004red]

Ended up using stainless bolts and large washers, after removing the "pip" from the plastic cover, looks fine to me. Could have used ZP as have both in store It's a common size on the Porsche 924 and am constantly replacing the rusty OE ones with better quality.

[JohnGee]

My thought was that stainless steel would be better than galvanised as the screw that is galvanised has a higher iron content.
This article is quite explanatory:

https://www.solaracks.com/galvanic-corrosion-between-stainless-steel-304-and-aluminum-alloy/

Interesting article, excerpts below,

"When the stainless steel will generate a large corrosion current which will be concentrated on a small area of sacrificial metal. The aluminum will corrode quickly, and so aluminum fasteners in stainless steel are not acceptable. However, a stainless screw in aluminum is frequently used although corrosion of the aluminum immediately around the stainless is quite possible."

I can see why aluminium fasteners in large stainless components are undesirable, fastener failure leading to component loss of support and stability, but wouldn't a galvanised outer layer offer some (better?) protection to the cylinder head?

"An example of the safe use of stainless steel and aluminum together is where stainless steel fasteners and hold down bolts are used to secure aluminum roadway or bridge parapet guards."

It's been some time since I looked at bridge parapet design, but my recollection is that you had to do everything possible to avoid bi-metallic contact. On bridges over the motorway, posts, rails, baseplates, bolts etc were always aluminium. The mesh that was attached to the rails (to make climbing up the parapet much harder) was always stainless, but there was unreactive medium placed between contact points of the 2 metals. I think it was an aluminium bolt that held the stainless in place against the rails and thus didn't need separating from the rails, but it had an 'insulated' head to prevent reaction with the mesh infill.

There seem to be plenty of M6x16 stainless bolts available, options such as galvanised much less common.

I thought this was interesting,

https://www.hunker.com/12502151/screws-compatible-with-aluminum

This seems to suggest plated stainless is the way to go.

[JohnGee]

Ended up using stainless bolts and large washers, after removing the "pip" from the plastic cover, looks fine to me. Could have used ZP as have both in store It's a common size on the Porsche 924 and am constantly replacing the rusty OE ones with better quality.

Could it be that the rusty OE ones were fitted such that they degraded rather than the components they were attached to?

[Carolyn]

The whole engine is crammed with steel bolted into ally.

A bit of lube on the threads and you're fine.

[Joesson]

Ended up using stainless bolts and large washers, after removing the "pip" from the plastic cover, looks fine to me. Could have used ZP as have both in store It's a common size on the Porsche 924 and am constantly replacing the rusty OE ones with better quality.

Could it be that the rusty OE ones were fitted such that they degraded rather than the components they were attached to?

I have long believed that all car (and other factory assembled product) fixings are specified for the design purpose and also/ particularly for ease/ speed of assembly. I also believe that diy maintenance is not considered/ perhaps designed out.

[scm2004red]

Could it be that the rusty OE ones were fitted such that they degraded rather than the components they were attached to?

We are talking abut fittings on cars 30/40 years old. They were possibly ZP in their day, but this doesn't last for ever in that environment.

Have to say the underside of my Porsche 924 is a darn sight better than the MR2, everything on that seems rusty!

[1979scotte]

Could it be that the rusty OE ones were fitted such that they degraded rather than the components they were attached to?

We are talking abut fittings on cars 30/40 years old. They were possibly ZP in their day, but this doesn't last for ever in that environment.

Have to say the underside of my Porsche 924 is a darn sight better than the MR2, everything on that seems rusty!

Built to a different price point id imagine and less likely to be a garage queen.