911 SC rebuild - bottom end reassembly

I am rebuilding an 83 911SC motor. I plan to keep this car forever (it’s a European model Cabriolet) so my goal is to do it right, take my time, and not cut corners. I have never rebuilt an engine and am relying on the Factory Manuals (overrated from what I can see), the Haynes manual (almost as complete as the Factory manuals for less than a tenth the price), Bruce Anderson's: 911 Performance Handbook (great supplemental source), the Parts and Technical Reference Catalog for 911 (invaluable), and any other advice I can get from my machinist and on the net. I am putting the engine together in stages so I thought I would pass on the trials and tribulations. I would appreciate anyone who could point out the error in my ways if there are any.

Setting the stage: The case is split and clean. I have a very good machinist working with me. I had him recondition all six rods. The case, crankshaft, oil pump, and intermediate shaft are all in good condition (per my machinist… I don't have a trained eye). I purchased a "rebuild kit" that includes for the bottom end: rod bolts and nuts, rod bearings, crankshaft main bearings, intermediate shaft bearings, front and rear main seals, oil pump seals, timing chains, #8 bearing insert O'ring, oil pump lock tabs (3), case o'rings (24), intermediate shaft gasket, set of lock nuts and steel washers for the outer edges of the case, and an oil breather gasket. I have an engine stand and a good torque wrench. I have done everything except apply the compound and bolt the case together.

Some of the issues I have dealt with are as follows:
- Should I replace the dilavar head studs. This was a real point of confusion for me. The bottom head studs that hold on the heads and pistons are made of a shiny alloy called dilavar. The top row are made out of stainless steel. I was confused because I had heard and read very contradictory things about these head studs. I think I have straitened it out. On the pre SC 911s with the magnesium case the dilavar head studs are preferable to the stainless steel because the latter tend to pull from the case. The 911 SCs have an aluminum case and the stainless steel studs are preferred because the dilavar studs are more likely to snap. Anyway, my machinist thought it would be a good idea to replace the dilavar studs with stainless steel. The dilavar studs all looked fine so I opted to leave them in. Am I wrong?

- Bruce Anderson's book talks about two compounds to use in the engine assembly. Dow Corning 111 for coating O'rings for better seal, and Molybdenum disulfide compound to mix with motor oil for an assembly lubricant to use on the rocker arms and other high friction parts. The Dow 111 I found at a distributor called Grainger. For the moly compound I ran all over the place and wasted a lot of time. It turns out that you can now buy something called Assembly Lube at a place like Napa that has the Moly in it (i.e., no need to mix it with motor oil).

- For the rods make sure that you put the rod cap on the correct side. Only one side of the rod and cap have numbers on them (there is a photo in the Haynes manual). I put three on backwards and they would not turn easily. Also, I read that once a rod bolt has been torqued it should not be reused. To be safe I replaced the rod bolts (but not the nuts) on these three rods.

- Be careful when putting on the front and rear main seals. There is a metal elastic-like ring that goes on the inside. It comes off very easily. So easily that I have some fear that it could pop off while in use and cause some damage somewhere. Any danger of that?

- I was also confused as to whether to put anything on the main seals. I read some recommendations to put motor oil on the inside of the seals that come in contact with the crankshaft which sounded like a good idea. The front main seal (pulley end) has an O'ring. Bruce's book recommends coating it with Dow 111 which I did. I got conflicting advice on what to do about the outer edges of the rear seal (flywheel end - where it touches the case). One person said to leave it dry while I read somewhere else to use the Dow 111 compound. I left it dry but may go back and put a light coat of the Dow 111 on it.

- The factory washers for the case are called aluminum crush washers. I noticed my replacement washers are stainless steel. I talked to a shop on this and was told to go with the steel because the aluminum crush washers flatten out over time and make the nuts looser leading to oil leaks. That sounded reasonable to me.

- There are three lock tabs that go between the oil pump and the nuts. After tightening the nuts you are supposed to bend the lock tabs up to keep the nuts from moving. One thing that struck me as odd is there is nothing securing the lock tabs in place. Couldn't they just spin along with the nut or did I miss something?

- The manuals don't point this out explicitly, but when putting on Loctite 574 around the mating areas of the case, do not put any on the inside mating surfaces (e.g., where the through bolts go through). Only put it on the mating surfaces along the outer circumference.

- One question on applying the Loctite. Should it be applied to both case halves or just to the right or just to the left case half?
Everything else looks like it is explained well in the manuals. Thanks for the great site.
Steve

You might do a search on head studs to read some of the past discussions. I found this one were according to Warren, Bruce Anderson now recommends the use of steel for all 24 head studs instead of dilavar:
http://www.pelicanparts.com/ultimate/Forum3/HTML/001010.html

I assume you won't have to worry about time-serting the case. Anybody know for sure?

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Greg
72 911S

Steve,
The Oil pump lock tabs should have two tabs, one tab bends up towards a flat on the nut and the other bends down on the case thus securing the nut.

Applying locktite to the case half that holds the crank and layshaft (left) works out good. The right halft can them be placed over the left. Do not worry too much about getting locktite around the 'inside' of the case bolt holes, infact, I would go around each hole completely. There will always be some locktite that squeezes out on the 'inside' of the case when you make the cases up. For the (pulley) #8 nose bearing I would coat the o ring area with sealant, however I would only use oil on the rear main to case area. The front and rear oil seals have a spring arounf the lip to keep the lip in contact with the crank at the right contact pressure, I would not mess with this spring and as far as I know, they do not cause any problems in service (or at least I have never heard of any).

Definiately replace the rod bolts and be carefull not to use anything too slippery on them such as engine assembly lube. If you do you will risk yeilding them when you put factory spec torque on them (I know cos' I did!). I just used a drop of locktite with the factory torque. Use a lube on the small o rings that go one each end of the case through bolts.


I rebuilt my 3.2 at home and have put 6,000 trouble free miles on it so far with negligible oil consumption. It runs like a real gem all the way up to 6800rpm (regularly!)

Good luck.

Steve,
I don't believe your top row of studs are stainles steel. They are probably the 'plain' steel studs from the factory.

Could you look up the part number in your parts catalog and post it here? The reason I ask is those are the exact studs Bruce Anderson recommended to replace the Dilivar studs in your engine in a case just like yours with broken studs in the April 2000 issue of Excellence, on p. 46. There are a lot of regulars here that would like to know the correct part number for those studs!

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Warren Hall
1973 911S Targa

Beetos, thanks for the tips. I spent $2 and redid the oil pump lock tabs.
Warren, I think you are correct, the top row of head studs are probably just plain steel. The part numbers for the stock Porsche steel head studs is 911 101 172 00.
The Pelican Parts online catalog has a listing for head studs http://www.pelicanparts.com/catalog/shopcart/911/Med_911/por_911M_cylhds_main.htm. They mention the Raceware aftermarket replacements ($578 for set of 24) as well as a factory replacement for the Dilavar studs, which are micro-encapsulated steel studs that inhibit corrosion. They are listed at $550 for a set of 24 with the PN 992-101-170-51.
Best Regards,
Steve