Rusty Manifold. Should I bother replacing

Bluebird911 · 15 Apr 2018

wasz said:
Yes pure titanium is more reactive than stainless.

However both stainless steel and titanium form a passive oxide layer when freshly cut, it is this that protects the metal and resists corrosion.

Titanium's oxide layer is more protective than the layer that forms on stainless. This oxide layer also insulated the titanium from other metals in contact.

This is why medical implants use titanium, it is least prone to corroding because the inert oxide layer protects the rest of the metal.

Hi Wasz,

You are correct about the oxidation layers and they form a protection to environment conditions, but these layers are not an electrical insulator, so will not prevent bi-metal corrosion when the joint between the metals contains an electrolyte. Remember, bi-metal corrosion is an electrical process.

If oxidation layers prevented galvanic corrosion, there wouldn't be the sophisticated inhibitors or sacrificial annodes that have been developed to manage this type of corrosion.

Because of its good oxidation corrosion properties, titanium is a really good material for use in the body such as the application you suggest. Ti is not used in bodies because its oxide layer prevents galvanic corrosion, this is not true. When in the body, Ti will not come into contact with another metal via an electrolyte; unless you are Iron Man!!!

Cue Black Sabbath!! :grin:

Alex, I recall studying this stuff at Uni many years ago, but it appears you have practical experience of the principles!! However, I have seen and worked on some ropey early Land Rovers (Aluminium body panels on Steel chassis constructed using steel fastners) before the motor industry took bi metal corrosion seriously!!

X51 996 · 15 Apr 2018

It seems that no matter what type of fasteners are used there's a downside!

Isn't stainless lower in strength than the regular steel bolts used? And what about the repeated heat cycling?

Always a hassle with steel/alloy fixings on these cars - which is pretty much everywhere, and as they're getting older there's more and more trouble waiting for the future.

Have to say the quality of the factory fasteners can't be all that. I've worked on loads of cars over the years - many much older than 996s and have never seen such badly rusted exhaust fixings as you see on these.

What are the typical exhaust studs used on most alloy heads made of? Black steel or coated steel with the copper/copper coated nuts - never had any trouble with removing either the nuts or the studs even on cars twice the age and mileage of most 996s.

I think going back to the OP's question - personally I'd leave alone. There's a good chance you'll never need to remove the manifolds in situ, and if you do it now you're still going to have hassles anyway. Save the cash towards other contingency work or something 8)

If you need to remove them in future just use a proper jig and take your time or let a specialist do it if required.

Alex · 15 Apr 2018

The problem with a 911 is the engine's almost scraping along the floor hanging out the back end and subject to everything off the road unlike most other cars.

eabeukes · 16 Apr 2018

I have a pair of old manifolds that were blowing that I have cut the pipes off - they make a perfect drilling jig. Feel free to PM me is you (or anyone) wants to use them for such!

Gooey36 · 16 Apr 2018

I've bitten the bullet as the cars a keeper for me and it's booked in with my local Porsche specialist tomorrow for drilling/helicoiling worse case. It does have a slight blow on it though...The rest of the exhaust is new so the old rusty manifold just looks 'orrible as well.

I had/have opted for Ti fixings over SS given the threads in the head should be 'dry" and a galvanic cell will not be created. Any residual moisture in the heads should disappear with heat from the head I would've thought. I do have some tef-gel which we use at work to prevent galvanic corrosion - not sure I need it though

I've used Ti fixings in many road and track sports bike engine applications in the past and some car applications and never had any galvanic corrosion issues in the past. Have had a few stainless fasteners sheer though!

What I am sure of, not putting mild steel in again!

P911X50 · 16 Apr 2018

Hi Gooey36,

Mine a keeper too and I am also considering getting it done. Has your specialist indicated likely costs??

Thanks

elwyn · 17 Apr 2018

manifold

i have been thinking of stripping mine also, at the moment no leaks, just know from prior experience they will be a bas.'#d, has anybody the jig for hire, they are expensive for one time use, regards to all

rdodger · 17 Apr 2018

alex yates said:
:thumb: Kool.

I know I also had a bone graft as a lot of the bone had rotted away. They used cow bone to do the graft then cover it in pig skin while it knits, stitching the flesh up over the top. Then 3 months later, open me up and remove the skin.

This deserves it's own thread!

I have 2 Ti implants. I also had a bone graft but from my hip. They did say at first they would use bone from my skull form the non dominant side. I thought the hip would be the safer option.

I too had mine done under sedation rather than GA. Not fun!

Gooey36 · 17 Apr 2018

P911X50 said:
Hi Gooey36,

Mine a keeper too and I am also considering getting it done. Has your specialist indicated likely costs??

Thanks

Yes - looking at £37 a bolt to remove and helicoil. Most I rang local to me (Notts) wanted between 350-700 worst case.

He said that he's never known all need drilling..so fingers crossed.

Paynewright · 17 Apr 2018

Another newbie here - owner of a 996 C2 3.6 manual since October 2017!

Already done the manifold to cat bolts. Fortunately they had been replaced with nuts and bolts previously rather than the press fit studs which are a challenge to remove. I've just used steel but purchased 3 sets so they will become a service item.

I plan to do the manifold bolts November time, when it will see a lot less use. I've already purchased poppopbangbang's TI stud set and picked up a Stomski jig from ebay. Thinking is if I have the kit to drill them out, they'll all come out easy!

Plan is heat the bolts up with a blow lamp and quench. Plusgas for a couple of days then use a hex socket (6 sided) to work backwards and forwards slowly.

I keep looking at the cheap stainless Chinese manifolds on ebay for around 150 a pair, as whilst its in bits??

Regards

Ian

Gooey36 · 17 Apr 2018

Paynewright said:
Another newbie here - owner of a 996 C2 3.6 manual since October 2017!

Already done the manifold to cat bolts. Fortunately they had been replaced with nuts and bolts previously rather than the press fit studs which are a challenge to remove. I've just used steel but purchased 3 sets so they will become a service item.

I plan to do the manifold bolts November time, when it will see a lot less use. I've already purchased poppopbangbang's TI stud set and picked up a Stomski jig from ebay. Thinking is if I have the kit to drill them out, they'll all come out easy!

Plan is heat the bolts up with a blow lamp and quench. Plusgas for a couple of days then use a hex socket (6 sided) to work backwards and forwards slowly.

I keep looking at the cheap stainless Chinese manifolds on ebay for around 150 a pair, as whilst its in bits??

Regards

Ian

Good luck with the extraction (and I mean that sincerely and not sarcastically! Sensible getting the jig in advance) I did the manifold to cat and started the manifold to head studs. Spent a week feeding it WD and using heat cycling - first one snapped like a piece of glass! I dare say the heating and cooling imparted more hardness and therefore brittleness/reduction in toughness making them easier to shear. Ideally, they should be tempered to resist he martensite phase (where carbon is trapped) - impossible to do this uniformly with a blow torch under a car! Hence getting a specialist who's done it as a regular task on 996's!

With regards to 'cheap manifolds" - there's tons of threads on here and an equal amount of opinions too. Some will say 'cheap Chinese rubbish" and 'you pay for what you get" others have run these on their cars for many years/miles with no issues.

Me personally I've bought 'cheap" manifolds from Toyosports and for the price, I'm happy with them in terms of build quality, materials, wall thickness and mass - all equivalent to much pricier manifolds. Best search the forum and go with what on balance is the most appealing to you.

Fastlane · 17 Apr 2018

TopGear manifolds are pretty cheap at under £400 with the discount and have a lifetime guarantee. Bearing in mind the amount of work involved in changing them, they would be my first choice over the eBay ones.

Rusty Manifold. Should I bother replacing

Should I replace my rusty manifolds?

Yes, the car is going to be much better with new

No, you won't really notice any difference

Bluebird911

Montreal

X51 996

Trainee

Alex

Nordschleife

eabeukes

Monza

Gooey36

Monza

P911X50

Nurburgring

elwyn

New member

rdodger

Spa-Francorchamps

Gooey36

Monza

Paynewright

Montreal

Gooey36

Monza

Fastlane

Spa-Francorchamps

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