[durtkillon]

After removing the head, my mechanic informed me that there was a concerning amount of pitting around the fire ring area of the head. I can be machined off, but I think I will be forced with a decision on Monday of whether I get the head machined way down and use a thicker gasket or machine off as little as possible and go with an OEM thickness gasket.

I have a few questions. First, is the pitting caused by galvanic oxidation or detonation?

Second, any experience with the head gasket sets out there? I see that the Wide Fire gasket from Victor Reinz is highly recommended, but it only comes in standard thicknesses from what I can find on the web. Are there any success/catastrophe stories out there that I should be aware of.

Third, what is a safe amount to machine off before the change in compression becomes a concern?

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[flash]

pitting should not require a lot of machining - you should be able to take it down the standard amount- unless you had extreme carbon build up, or ran super cheap low octane gas, i seriously doubt it was due to detonation

the wide fire is the gasket of choice - i could have sworn it also came in the 1.4mm thickness

call pete - he'll have that info, as well as the milling spec

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[durtkillon]

Thanks Bob. I'll give him a ring on Monday.

How does cheap/low octane gas cause pitting?

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[flash]

low octane could create detonation - that could cause pitting

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[Cloud9...68]

I did a search on several sites, and many of the main parts houses carry the Victor Reinz head gasket, either by itself, or in a total head rebuild kit. But none of them mention the term "wide fire." Are all of Victor Reinz's 968 head gaskets automatically wide fire? Or is this a special version of the Reinz gasket? And what exactly does "wide fire" mean? I've used Victor Reinz gaskets on my daughter's BMW 325i, and have been pleased with their quality.

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[durtkillon]

It has a wider metal ring on the gasket. They are available at several parts houses.

Victor Reinz is the OEM manufacturer for a ton of Euro cars, including our 968.

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[flash]

so, apparently the wide fire is not available in the 1.4 thickness - bummer

as for the pitting, i guess you will have to have that checked to see how deep it is, and if it is repairable by shaving or not - also bummer

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[durtkillon]

I'll seek input from the pro's on the pitting/shaving. It will be educational for me. I'm not sure if shims are commonly used in this application. Some pepople contend that pitting is not the end all, but it doesn't instill confidence in me. if the head is re-intstalled with pits. I read that it may be caused by carbon build up and localized hot spots.

Another option is to shave the head 0.3mm and use the 1.4mm standard gasket. It's not the end of the world if I go that route. I will use the Wide Fire gasket, however, if it's within the reccomended tolerances. I should have an answer by the end of the day.

Rebuilt heads are available from RS Barn, but they may not take a pitted head as a core.

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[Fox944]

most shops will send your head out to a machine shop to get milled when replacing the head gasket. This is standard practice and i would not be concerned. My head was milled to 11.6:1 Compression Ratio and i'm running RS Barn Spec Cams (Version II). I have zero issues.

The head gasket i used was a Powerhaus triple Layer Stainless Steel gasket. OE Thickness.

I just had the Head gasket replaced on another vehicle as well and had the head milled prior to putting everything back together.

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[Cloud9...68]

So does Victor Reinz make both the standard and the wide fire gasket? I haven't seen any reference to a wide fire gasket at Paragon, Pelican, or Autohausaz, all of whom see Victor Reinz head gaskets. Thanks.

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[flash]

the problem with durtkillon going the shaved route is that he is planning on installing the supercharger, and is concerned about having less than what he could in the way of a perfect head and gasket - if it were me, i'd have the same concern - it's probably paranoia, but would i want to find out the hard way?

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[Cloud9...68]

Durtkillon,

So, what kind of shape was your old head gasket it? Was it thin as paper mache as others have reported, or was it in relatively decent shape? Thanks.

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[durtkillon]

Cloud9, RS Barn Sells them. It sounds like most 944 mechanics are aware of them. Apparently, they are common for folks seeking more boost and my local guy installs them on applications up to 1.5 bar (~20PSI). Yikes! They are both made by Victor Reinz.

The report I got was that my gasket was not in terrible shape and the pitting did not look bad initially, but it didn't shave off either. He also said the intake was pretty fouled with carbon. This is a little troubling. I think 5 thousands is typical for reconditioning a head, but I'm not sure what the limit is for ours. As Flash stated, shaving leads to higher compression, which is the wrong direction for forced induction. It's the reason many tuners run ethanol and race gas. They get themselves in to situations where they need insanely high octane to keep their engines from detonating early.

I wish I could be more engaged in the repair, but I am painfully swamped with work lately. I wanted to take photos and document it. I'm pretty sure all the parts will be saved. I love working on this kind of stuff and learning from the pros. I contemplated doing it myself, timing the cams and balance shafts seemed a little challenging and our local guy is walking distance from work. He's also a heck of a nice guy and a local PCA driving instructor.

It will all work out, I"m sure. I'll keep you guys posted.

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[durtkillon]

The latest feedback from the machine shop is that the pitting started at the water jacket holes and encroached the ring sealing area. Apparently, the concern is that the pitting is under the fire ring and the ring may not seal properly. My mechanic believes this could have been caused by using tap water in the coolant. He said it was clear the direction the corrosion came from. It was not coming from the cylinder inward, but rather from the water jacket. They started at 5 thousands shaving. They are going to cut another 5 tomorrow and report back.

The good news is that I should have pics tomorrow.

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[Cloud9...68]

Thanks for the info. It's interesting that not <i>every</i> 968 head gasket turns to paper mache. How many miles are on your engine?

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[flash]

that's where they start to fail from age - it's the holes between the cylinders, not the ring areas - they just deteriorate over time, varying in degree from engine to engine

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[durtkillon]

I'm at 98K miles.

I just read up a little on antifreeze and the use of Phosphates - very interesting. I don't think it's well understood, but according to a Chemist from BASF, Phosphates in antifreeze can actually lead to the corrosion of Aluminum. They are typically used as a buffer for corrosion inhibitors in coolants, but they tend to precipitate out when they react with Calcium in hard waters. As the Phosphates are consumed, the solution goes from acidic to basic and tends to accelerate the corrosion of Aluminum and render the corrosion inhibitor ineffective. In addition, phosphates apparently can react with Aluminum at very high temperatures and have been known to degrade heads near the exhaust ports (or fire ring perhaps?). The chemist reproduced the reaction in EG with heat in the presence of dissolved Phosphate. He could stop the reaction by removing either the heat or the Phosphate.

In Europe, the average hardness for water is higher than in the US or Japan, so they tend to use silicates in place of phosphates to avoid salts from precipitating and killing the water pumps.

I'd like to hear from Pete if he sees much pitting.

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[flash]

that's why porsche will void the warranty if phosphates are introduced - they were unusually stern about it when i called them years ago to find out what coolant to use

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[durtkillon]

Most people will tell you that the reason they recommend avoid Phosphate controlled coolants is because the precipitants plug up the water jacket. It would take a lot of really hard water to do that and I doubt Porsche would get on a soap box for that reason alone, since distilled/de-ionized water is readily available. That sounds like BS to me. Perhaps the Germans are keeping secrets or they paid attention in chemistry when they were in High School.

I remember my grandpa topping off the Chrysler with the garden hose 30+ years ago. I doubt that thing had any Aluminum in it, though and I think they used lead in rubber hoses. [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]

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[chudson]

It may be that I'm getting in this thread a bit late for my suggestion to help but over the years I've sent many a special or hard to replace head out to have the pitted areas blasted and welded. This allows the machinist to mill the head very little since the pitted areas are now built up by the welding process. With the right talent striking the arc it has yet to fail for me provided the antifreeze hasn't permeated the aluminum to the point of contaminating the weld. Only drawback is if the head is horribly pitted the labor can sometimes outweigh the cost of a used or rebuilt replacement head. If you insist on keeping your original head it's a possibility.

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