Dilivar Disappointment Inside - shopping parts list?

[Lapkritis]

My guess: The middle cylinders will be hottest sandwiched between the other two... more heat=more thermal expansion and stress on the fastener. The cams on these engines must have bearing wear like crazy with this design.

[Packet82]

If it were just a matter of heat, I'd expect cyl 2 to be the one that cracks the most as it's also near the cat. Although, perhaps the passenger side bank cools down faster and thus gets heat cycled more quickly. Who knows. Either way, at least one of the lower studs will eventually break.

[chris_seven]

Originally Posted by Lapkritis

My guess: The middle cylinders will be hottest sandwiched between the other two... more heat=more thermal expansion and stress on the fastener. The cams on these engines must have bearing wear like crazy with this design.

If the studs are Dilavar then the increase in stress caused by expansion will be small and unlikley to be the cause of failure.

The stress in a Dilavar stud is about 45ksi even when peak cylinder pressure is taken into account.

The standard steel studs and the Martensitic Stainless Steel studs will develop higher stresses - which is due to differences in expansion- but only to around 75ksi.

None of these stresses are likely to cause stud failure unless macroscopic defects are present and the failures don't indicate this type of problem.

It is much more likely that failure is due to Stress Corrosion Cracking and precipitation hardening Austenitic Stainless Steels such as Dilavar can be prone to this mechanism, particulalry in the presence of Chlorides, when strengthened to levels greater than 160ksi.

The addition of high levels of Molybdenum used in Dilavar should be helpful in eliminating this problem but avoiding certain temperature ranges in the heat treatment schedule is likely to be more important, and perhaps not well controlled.

I am aware that this expanation is not widely accepted but the levels of stress developed in head studs is just too low without an additional failure mechanism being present.

[Lapkritis]

It's likely a combination of things like you say... you do have to wonder on a stud such as mine that has the epoxy coating intact how large the role of corrosion played. All available literature describes the primary purpose of the epoxy to be for thermal insulation yet it also creates a seal that would prevent contaminants or corrosives from being introduced to the surface of the stud unless physically compromised such as a sloppy assembly ... which even then would be unlikely as the coating is quite durable. The embrittlement and/or risers must have occurred during the manufacturing... I do think the flat 6 air cooled design is partially at cause here due to the incredibly high, relative frequency of fastener failure. Either that or a manufacturer pumped out a huge run of compromised fasteners and a few different labelers continued to push them out after knowing (or not) the goods were tainted. I'd like to believe retailers would pull such product from the market place but who's to say inventory is thoroughly managed after it has been through a few wholesalers... they might not even know their stock delivered last week is 20yrs old.

[chris_seven]

I would agree that if the coating is intact then SCC does seem unlikely but to create tensile failures of the type being shown would need stress concentration factors in the region of 3-4 and the small surface defects that seem to present under the coating wouldn't generate this level of stress concentration.

Alloys that are similar to Dilavar seem to have a tensile elongation that is typically between 15and 20%. This would indicate that the material is relatively tough and reasonably notch insensitive.

Looking at the failures this doesn't seem to be the case and it is clear that the material is quite notch sensitive. This seems to hint that the material may have been poorly heat treated and that it is more brittle than it should be for this application.

The operating temperatures involved in the 911 engine is unlikley to affect the material properties of the stud and it is unlikely that the ductility has changed with time and the next time I have a spare stud I will carry out a simple tensile test and see what happens.

[timmy2]

Originally Posted by Packet82

Someone else posted this list when my engine broke a stud:

Head studs X 12 $144
crankcase gasket Kit $57.75
Cylinder Head Gasket Kit $215
Cylinder to case gasket (.25mm) $36
574 Locktite case sealant $22.75
chain ramp brown $6.5
chain ramp black X5 $32.5
solid oil tube lines X 6 $53
Piston ring set $142.5

You may not need new oil return tubes or chain ramps since the engine was done 50k ago, but I'd replace them while I'm in there. They're cheap enough and you might as well.

Gee that list looks familiar...

[Lapkritis]

Taking my time breaking this thing down in the evenings after work... nice break from the desk after a more than full day. Popped the carbs off tonight as well as the alternator and some of the vents to make it a bit easier to slide from beneath later. Fresh alternator:




Removing the alternator/fan allowed me to take a look at the top of the engine where I could see some of the cylinder gaskets pooped out between the jug and the case on 2 of the cyls:





Appears the case was outfitted with Time-serts (timecerts?) already.



Popped the starter out as well and then called it a night. I need to read up on the clutch release bearing activity that awaits me before I can drop the engine.

[Packet82]

Originally Posted by timmy2

Gee that list looks familiar...

Yeah, I wonder where I got it from

[timmy2]

The leaks at the head cylinder gaskets to the case are not a good sign of a quality rebuild. I hope you've caught it just in time.
You could damage the machining and never get a good seal again if left too long bouncing around on loose or broken head studs.
Hopefully the last rebuilder didn't ignore old damage. It can be machined again if it's not extreme. Just a light trimming using up some more $ for your credit card!

Do some serious cleaning and measuring. Find any other broken studs?

[Lapkritis]

I did not see any more broken yet but I imagine they're in there. I can't view the bottom studs with the oil return tubes and air deflectors in the way. I do have an accomplished engine building machine shop close to the family so probably won't have to call visa for a limit increase. ;-)

[Lapkritis]

In regard to the base gaskets failing - what is usually the cause here? Crankcase pressure or vibration? It seems odd they would come out like that as they aren't under cylinder pressure like the cylinder head gasket up top is. I wonder if they were damaged during installation or re-used during the previous build. Any insight on common causes here?

Lunch-hour progress today... removed the lower intake manifold/carb bases and then the main shroud so I could take a good look at the remaining top studs. All look fine. May drop tonight or tomorrow.

[Lapkritis]

All free... just need to coordinate some higher altitude jack stands to get it out the back without messing with the bumper/rear pan. S

[Lapkritis]

Popped the rear bumper off and wheeled the engine out. Started cleaning up the grime/debris so it's cleaner once I do have it opened up.

Boxes of parts for the gaskets kit, 930 engine mounts/hardware etc arrived from our host very well packaged. I shared the Jellie Bellie treats which helped smooth things over with the lady that I was buying yet more car parts.

[Flat6pac]

The studs run through inside the cylinders so you couldnt see a broken stud except removing the lower valve cover.
Bruce

[Lapkritis]

I searched for awhile to try to find instructions on how to do this and the manual I have doesn't specify exactly how to.

How to remove the rear bumper on a 1974 Porsche 911:

1) Unplug license plate lights so wires are loose... this takes about 2mins with a flathead screw driver.
2) 2x8MM bolts on the accordion bumper trims on each side are accessible from underneath/behind. Take the two on each side that are furthest to the back so the accordions stay on the car and not on the bumper. After you get the nuts off the back you must push the accordion away from the bumper so the studs release.
3) Remove small caps on the thin rubber trim on the back bumper... one on each side. Don't take the big one off... leave it alone. They will be about 6MM wide and blend in... there are phillips head screws underneath that have to be removed as well. Once the screws are backed out, peel the rubber strips carefully away from the bumper only until you see two nuts on each side... these do not come off entirely in this step. Clean up before reinstalling so you don't have damage to the paint from sand etc.
4) 2x13MM bolts on each side are the last step for the bumper to come free. Be careful to support the weight of the bumper as you get to the last so you don't drop it and wreck the paint.

Installation is the reverse of removal.

I haven't made as much progress as I would like to this point but I think it's more important to get everything clean and to be thorough in documenting as you break it all down. I've been through a roll of blue shop towels, 50 nitrile gloves, and 3 cans of cleaner to get to the point you see below. The amount of filth that has come off the engine thus far is incredible and there is a lot more to go. There was grime packed in everywhere...











My parts order from Pelican is in and the new headstuds are set to arrive on 10/3/2012. I removed the lower valve cover on the left bank and checked all the studs. Surprisingly there are no broken studs on the left side of the engine at all. I have more cleaning to do tomorrow before I may safely open the lower cover on the right bank to get the final count. I'm keeping my fingers crossed...

[Flat6pac]

Somewhere along the line I thought you were doing a 3.0. 3.0 you cant see the studs.
Bruce

[Lapkritis]

No 3.0L planned at this time unless I encounter something really nasty that is unexpected. The engine ran great prior to this exercise. Basically the oil leaks, plugwire popping off that one time from the broken stud and the infrequent cold start farts that I originally thought were carb related or this thing was top notch.


Lunchtime delivery... about 5 times as large as the original box that they sent that was mislabeled. I wasn't expecting these until 10/3 so now I'm feeling the pressure to locate a set of cam tools to get this thing done... I'm half way tempted to purchase the spring compressor tools myself to lap the valve and change the stem seals. If the other half of the engine does not have catastrophic failure evidence then I will probably pop for those.

[Lapkritis]

Finally had a chance to go through my folder of receipts. The engine was built by Stephen Rogers of Leverett, MA with some labor paid to Dutcher Automotive in 1988. Work & Parts at the time (would be nice to get these prices back):

2.7RS Pistons & Cylinders - $1298
Gaskets & Hardware - 150
Rod Bolts & Nuts - $146
SSI Exhaust - $750
Chains - $48
Tensioners - $116
Locks - $16
Oil return Tubes - $80
PMO Webers - $1118
Cams - $350
Rod Bearings - $75
Main Bearings - $60
Oil Radiator - $175
Valve Covers - $75
Paint/Cleaning Supplies - $42
Stress Bar - $110
Clutch Face Plate - $140
Cam tower oil lines - $19
Alternator - $140
Knee Pads - $17.40
Labor - $1190 (Remove & Deliver motor, port cylinder heads, modify sheet metal heat synks, install oil cooler, Clean & Paint sheet metal, assemble & install engine)
Total $6116.30

There's more pictures but I thought these were worth a share mind you they are from 1988:

[Lapkritis]

Took the right bank lower valve cover off tonight and no additional loose or broken studs found.

***I am now looking for cam tools if anyone has a set they aren't using ... otherwise I will purchase from the host on Saturday. ***

[Lapkritis]

Finally have a chunk of time off from work - hoping to have the heads all off to the machine shop by the end of this week for valve job and guides.

The studs on the left side of the engine all came off easily; appeared to be blue locktite around the base of the stud rather than red.

The intake studs where the carbs mount are about a half inch short and did not come through the bolt with the carb mounted up and the exhaust studs look whipped... I'm going to have the machine shop swap those all out as they're tooled and experienced for any breaks during extraction.

Ordered new rocker hardware and RS seals to assist with the incredible leaks from the rocker bores... any leak after all this work would be unacceptable. The cam housing rocker bores are all smooth, tight and un-scored. Hoping to start going towards assembly in the next couple weeks.

Sealant thread here for organization when the time comes: http://forums.pelicanparts.com/911-engine-rebuilding-forum/284737-complete-engine-sealant-thread-12.html