Specific Question - ARP Head Studs on 2.7 Magnesium case - Insane?

[Lapkritis]

Finally a break in the clouds and rain here... hot and humid.

[Lapkritis]

[Lapkritis]

Parked outdoors in the rain for a night and wondered why it started to feel and sound like it was down on grunt a few days later. Popped a carb cover off and had my brother hold the pedal wide open. Sure enough, the butterflies were only going to about 3/4 throttle. Confirmed linkage was snug and went after the pedals.

For shame Stuttgart, for shame... wood? C'mon now.



Will likely be ordering the Rennline aluminum floorboards to resolve the issue. Couple weeks until the dyno to figure it out and install.

[safe]

Wood is lighter and it held up for almost 40 years.

[Lapkritis]

For sure, but the car has been garaged daily since at least 1986. If they were made of a nonabsorbent/no-biodegradable material from the get-go there wouldn't be a problem. Pumping them out in aluminum would have been more costly $ wise.

[Lapkritis]

Catching up on a few items at a time. Intended fully to pace myself on this but hard to resist. The oil tank has been bothering me with random drops of oil and leaks when filled beyond half when hot. I suspect a spot weld on the tank mount tab to the rear has torn and dribbles oil out when tank level is high. There must have been 3-4 honest pounds of oil soaked dirt on the old tank. I did replace the level sender and gasket earlier this spring thinking that was the leak but that was not the case.



Cleaned up the old, pressure testing replacement and old before installing. If the original tests fine then it'll get a fresh coat of paint and reinstalled.

[Lapkritis]

Great part from Rennline. Perfect fit, this is what the factory should have done. All floppy/bendy action solved. Transferred throttle stop maintaining OEM pedals/application.

[Lapkritis]

Quick lunch:



Probably around 1k miles since the job. Might be excessive but on 4th oil change now. Next will be to synthetic.

[Lapkritis]

Stacked more miles on it this weekend for a local show which was the first for the car since I took over care-taking duties.

Some entertaining local news coverage showing the cosmopolitan nature of the event:

Video - WCAX.COM Local Vermont News, Weather and Sports-

[Lapkritis]

Great gallery of the event on AudiWorld if you didn't notice...

AudiWorld.Com Gallery :: 2013

[DWit]

Folks,

I'm sorry to beat a dead horse here, but this subject is near and dear to my heart. I am in the midst of building a 2.7 race motor with all the dreaded parts (7R mag case, factory 2.7RS Nikisil P&C, factory steel studs). The car is a vintage 73RS replica, so the parts that I have are what I have, and so I am going to go with them (not soliciting other parts options), however I would like the collective community's opinion on two matters.

1. Case Savers vs. Timeserts. Is there a significant difference between the two with regard to stud pull out with a mag case?

2. What is the best initial torque value for this combination? Would slightly under-torquing the factory spec be wise?

Dave

[Lapkritis]

Hi Dave,

Good luck with your 73RS replica - great car.

My opinion for your situation:

1) Go with Case Savers. They have a larger root into the case and will be less likely to pull.

2) I would torque to precisely factory spec using an assembly lube on the top threads and contact surfaces of washers/nuts.

Again, best of luck,

[Walt Fricke]

I have no opinion on the inserts.

But I'd torque to the specification of the stud manufacturer. If they are Porsche studs, use Porsche's recommended torque.

If aftermarket, use what the seller says to use.

Torque is a substitute for what is needed in a fastener - clamping force. Clamping force is created when the fastener is stretched, and turning a nut on screw threads is an Archimedean way of stretching the fastener. While it may be that the modulus of elasticity of all steels is pretty much the same, the engineers or shops experimenting with studs have worked out what works best for their product. Some will even give you several specs - one with this kind of thread (and washer to nut) lubrication, one with some other, and another higher one with no lubrication.

If the clamping force is inadequate, bad things happen. Nuts can rotate and loosen. And heads can lift momentarily, allowing hot exhaust gasses to escape in ways not up to withstanding that.

I'd rather stretch a fastener a little more than a little less than specified.

[Henry Schmidt]

Originally Posted by DWit

Folks,

I'm sorry to beat a dead horse here, but this subject is near and dear to my heart. I am in the midst of building a 2.7 race motor with all the dreaded parts (7R mag case, factory 2.7RS Nikisil P&C, factory steel studs). The car is a vintage 73RS replica, so the parts that I have are what I have, and so I am going to go with them (not soliciting other parts options), however I would like the collective community's opinion on two matters.

1. Case Savers vs. Timeserts. Is there a significant difference between the two with regard to stud pull out with a mag case?

2. What is the best initial torque value for this combination? Would slightly under-torquing the factory spec be wise?

Dave

Inserts first: CaseSavers should always be used in magnesium cases for head studs.
There are 4 8mm studs, one inside the case and three on the perimeter that should also be inserted and Timeserts work fine for this application.
The key to mag case survival is actually history. What has the previous life of the case been like. If it was case used in a thermal reactor engine (75-77 Cali), there is a good chance that it has been over heated and would make a poor choice for a performance engine. Knowing if the engine was used for racing is also paramount.

Torque specs: Like Walt says, fasteners should generally be torqued to the manufactures specifications. In the case of head studs, it will ensure proper preload during the critical warm up and running stages.

[DWit]

One more question. Would it be a good or bad idea to use the top-side air deflectors with a mag case? The long ones on either side which cover the case bolts and the bottoms of the cylinders (as used on the aluminum case motors). Again, this is going to be a race-only motor.

Thanks,
Dave

[Henry Schmidt]

Originally Posted by DWit

One more question. Would it be a good or bad idea to use the top-side air deflectors with a mag case? The long ones on either side which cover the case bolts and the bottoms of the cylinders (as used on the aluminum case motors). Again, this is going to be a race-only motor.

Thanks,
Dave

The top side tin is a design enhancement specifically intended to divert much needed cooling air from the cylinder base to the top fins and cylinder heads. As I stated earlier in the thread, heat in the cylinders is concentrated in the top fins of the cylinders as they try and pull heat from the heads. Diverting the air to the top is indeed a benefit worth pursuing.

[Lapkritis]

Dave,

Just adding on - I know you said you weren't looking for parts suggestions. I would recommend the thermal barrier coating for piston tops, combustion chambers, valves, exhaust ports and inside the headers. These coatings seemingly work well to limit heat transfer into the heads so you can make more power and also as we now know have less thermal expansion and stress on the case as a result.

[DWit]

Originally Posted by Henry Schmidt

The top side tin is a design enhancement specifically intended to divert much needed cooling air from the cylinder base to the top fins and cylinder heads. As I stated earlier in the thread, heat in the cylinders is concentrated in the top fins of the cylinders as they try and pull heat from the heads. Diverting the air to the top is indeed a benefit worth pursuing.

Henry,

I was specifically wondering if the top side tin would be exacerbate the head stud pulling issue with mag cases, since they block cooling air from the exact area of the case into which the head studs are fastened.

Dave

[Henry Schmidt]

Originally Posted by DWit

Henry,

I was specifically wondering if the top side tin would be exacerbate the head stud pulling issue with mag cases, since they block cooling air from the exact area of the case into which the head studs are fastened.

Dave

The case operates at the temperature of the oil and gets little or no cooling from the fan. Install proper CaseSavers and control the engine temp and head studs pulling is a non issue.
Cheers

[Lapkritis]

Originally Posted by Henry Schmidt

The case operates at the temperature of the oil and gets little or no cooling from the fan. Install proper CaseSavers and control the engine temp and head studs pulling is a non issue.
Cheers

I know what you're trying to convey here but a quick fact check ...

The oil temp and case temp are different. They're close at operating conditions but different. They tend towards an equilibrium due to the surface area they share in contact with each other. The case temperature is also very different depending on location of measurement. The temp of the case at the base of the cylinder is not the same as the bottom near the seam where it washes with the breeze. That has been my observation with the infrared thermometer.

I believe Chris posted the temperature/ fatigue data earlier in the thread for magnesium. It's fairly strong to a certain temp and then drops quickly.