924Board.org

[Peter]

Hi all,
Just like to share some pics of my 931 rebuild project. I bought this 1980 931 as a parts car for a 5 bolt conversion for my 924. However, I said to myself "Peter, you always wanted to learn how to rebuild an engine. Well, here is you chance." Okay, so I really don't talk to myself but you get the gist. I thought that even if I fail, I could resale some of the parts and what I loose in money I gain in knowledge. Anyway, I have attached three pics of the engine. The pics are self-explanatory.
I rebuilt this engine, and parts of the car too, with the intent of making it my dedicated track car. A car that would be reliable (no high boost numbers), still be street legal, and comfortable (for the 2- 3 hour drives to the track). I started with an engine rebuilt kit from EBS racing, then purchased parts from Hendrick Porsche in NC as needed, and purchased all miscellaneous, hoses, studs, gauges, etc from various industrial supply companies. This saved a lot of money. This is a very brief rundown so far:
HEAD: I ported & polished the head and replaced all intake & exhaust studs. The machine shop pressure tested the head, installed new valve guides, recut valves & seats, and milled head true.
BLOCK: Machine shop acid dipped, replaced all freeze plugs and bored cylinders. I blueprinted the oil pump & block and painted the block Aston Healey Green (POR -15 product)
PISTONS: I micropolished them. Machine shop balanced them.
RODS: I blueprinted the rods and the machine shop replaced bushings and balanced rods. Used new connecting rod bolts and nuts.
CRANK: Once again, I blueprinted the crank and micropolished the journals and the machine shop balanced the unit. New bearings.
CLUTCH: New friction disk and bearings (both in pressure plate, flywheel & bell housing w/ new guide tub).
FUEL LINES: Replaced all fuel line hoses and reused the fittings.
CV JOINTS: Repacked and alternated CV joints and used new 12.9 hex head bolts. I hate the triple star CV bolts!
SHIFT LINKAGE: Replaced bushings at shifter and at tranny.
You all get the general idea. There are other things I did but I won't bore you with all the details other than to say, I took my time, checked everything twice, and wanted to build a bulletproof engine. This is the first engine I built so I went slowly.
I will post more pics as the engine is put into the car, probably next week.
Things I learned as I went along:
Rule 1: If you can't afford to do it right the first time, where will you get the money to do it right the second time?
Rule 2: The car is 23 years old. Have a heart and treat it to new exhaust & turbo studs. You're a fool if you don't.
Rule 3: You are the best mechanic you know, because no one would put the time and love into your machine as you would.
-Peter

Here are the pics as promised:

[Smoothie]

Very nice. It's a beautiful thing.

[Rick MacLaren]

Rule 1: If you can't afford to do it right the first time, where will you get the money to do it right the second time?

Yes! Finally someone agrees with common sense.

Rule 2: The car is 23 years old. Have a heart and treat it to new exhaust & turbo studs. You're a fool if you don't.

Yeah, there's no point having to suck fumes. My exhaust was stainless so I kept it. Replaced the studs and exhaust manifold.

Rule 3: You are the best mechanic you know, because no one would put the time and love into your machine as you would.

Yeah, in principle that's right. I'd caution that if you're new to it, don't rebuild your turbocharged engine without spending $250 on new manuals and learning from books where the mistakes will get made. If it's a toy project, sure, go ahead and have fun but be ready to make mistakes. If (a) you've never used a plastigauge, or (b) know enough to clean your calipres before making your measures, or (c) you still think it's ok to buy your pistons and rings after you've bored your cylinder walls, or (d) you don't know how to detect lateral play in an installed piston or (e) how to find out if detonation is affecting the upper half of your rod bearings or (f) this is your first engine, then get help from someone knowledgeable.

[924RACR]

Very pretty, nice work!

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Peter]

Guys, thanks for the compliments. It was a lot of fun and a great learning experience to rebuild my first engine.
-Peter

[MRElliott]

Beautiful job. Someday I'll have to do what you have, and can only hope it turns out as well. Sounds like good advice from our more experienced listers.

I've got a '79 Euro-spec 931 that does not have that tube/line connecting from above the turbo to the cylinger head between injectors #1 and #2. Is that an emission control line of some sort? I find it very interesting to see the differences in plumbing between model years and US vs. Euro-spec. It has always intrigued me how manufacturers "tweak" things for different markets.

[Peter]

The line you refer to is to allow excess oil that exits the turbo from backing up as it enters the oil pan. If you look at the turbo pic, you will see a blue hose (bulk silicon hose used in place of old Porsche hose). This hose exits the turbo and carries hot, and very foamy oil back to the oil pan. However, the foamy oil can back up into the turbo, which is not good. This was the set up on the early cars. So, Porsche put a secondary tube (hard to see in the pic because it runs behind the turbo mount, which runs to the top of the head. If you look at the frontal pic, you will see a black tube that runs in front of the timing belt. This is that tube that carries excess oil and foam to the head (and then back to the oil pan).
The head I used did not have this mount, so I drilled a hole in the head to accommodate the return line. (I did some planning before I started my rebuild ).
-Peter
P.S., don't be afraid to try a rebuild, you only need patience and common sense.

[Rick MacLaren]

What did you pay for your exhaust manifold Peter?

[Peter]

Rick,
The manifold came with the car. Yours didn't?
Seriously, I had (& still have) excess engine paint. So rather than having it waste away in the can (shelf life is short) I painted the manifold and turbo.
If you look closely, you will see "Porsche 931" painted on the manifold. I downloaded Porsche font from Pelican parts and made a stencil, which I painted over the manifold. Hopefully it will confuse the tech inspectors at the track.

[Rick MacLaren]

Yours came with the car?

Well! Some rotton bastard sold me one without it! Then I had to get a new one just to make it stop pharting!

lol

I had two hairline fractures that made exhaust smoke stink in the engine bay - they have such a reputation for cracking.

[Peter]

Just expanding on Rick's comments. Having and knowing how to use the proper tools for a rebuild is important. With the crank, for example, it's important that the journals are round to spec. To determine if the crank is to spec or needs to be reground, you can take it to a machine shop, who for a small fee, will check it. Around where I live, mechanics don't check cranks. They send out all the parts to a machine shop where they are cleaned, checked, and repaired if necessary. You can do the same and save the costs the mechanic would charge.
You can also buy a set of micrometers, learn to use them, and check the crank yourself. This is what I did. Very straight forward.
Lastly, and very easy, you can purchase plastiguage ($1.50 a strip) and use it to check the machine shop's work and to check your own earlier measurements. You can never check enough
This first pic is of the plastiguage on the crank journal.

You place the plastiguage on the crank journal, then torque the bearings down to spec. When you undo the bearings, you should have something similar to the second pic.
The second pic is of the "squeezed" plastiguage.

Here I am comparing the level the plastiguage expanded to the supplied chart to determine the gap between the bearings and the crank journals. You then compare this number to the factory specs, and if all went right it should be within range. If not, then the crank has to be reground and you have to use oversized bearings. You would tell the machine shop what the next available bearing size is and they will grind the crank down appropriately.
Know you know how to check a crank.

[Smoothie]

Interesting stuff, but I noticed you use the plastigage oriented 90 degrees from the way I've used it - though I guess it works just as well either way.

[Peter]

Actually, I've used it both ways. The pic is of one way only. At $1.50 a strip, you can afford to play around.

[Rick MacLaren]

Yes that's useful Peter. I can't quite make out some of the shots. It'd be great to have on this board a kind of 'task' description with good photos that would help folks with rebuilds.

One guy here wrote in that he'd sourced some of the work and basically accepted the shop opinion for some engine rebuild matter. Anyways, the car didn't function properly after the rebuild and work had to be done again. The idea was that he'd have saved some time and effort and money by having folks around that he could call upon for specific questions to help him help himself.

A colleague of mine at work decided not to do any of the work himself and had his local Toyota dealer rebuild an engine for him and reinstall it. The rebuild went perfectly, but then again, it should, he paid $8700 CDN for it. But hey, he's still not happy with the truck.

Another friend at work rebuilt his 944 Turbo engine. He's rebuilt go kart engines all his life, and VW engines for fun. He has a 911, 944 Turbo, 5 other cars, an 8 car garage, all the tools he needs, and a hoist (new). He gets to torquing his head bolts. He reads the spec in the book, adjusts his wrench to the precise figure stated in the book, and torques the head bolts in PRECISE order. But it turns out his $99 wrench was set to ft/lbs rather than nM! So he has to retorque it, down to the right spec. Then he puts the rest of the engine back together. He turns it over by hand to make sure the valves don't hit the pistons. Then he started it. White smoke and coolant in the cylinder. Seems his overtorque of the head crushed the head gasket. Oh well, hours more work and another head gasket. One moment of inattention and an otherwise competent job is partly botched.

Even Frisky just broke a journal. And I busted my an oil feed line in the head during my project, and couldn't get the crank out (blush).

It can be irksome to read about most mechanical efforts on bulletin boards when they're painted as a simple matter, as if the work mechanics and automobile engineers do is either entirely 'doable' by the home mechanic (who, by the way, likely doesn't have half the tools he'll need, or half the math required to make an intelligent decision). Like, just looking at your engine I can see that you did a lot of work on it. Cleaning, prepping, sorting parts, keeping track of nuts and bolts you'd use, and those you'd have to order, budgeting costs for gaskets, rubber, seals. Ordering parts. Finding matches if bolts weren't readily available, checking torque specs, rechecking. It's not that any one particular task is earth-shatteringly difficult or complex, rather, it's that the SUM of all the tasks, done properly, and in the right sequence where sequence matters, is actually quite a feat.

The facts about rebuilds (and I'd extend this to adding body kits, messing with the aerodynamics, tire choices, even instrumentation choices) are: It does take precision in measurement. It takes attention to detail. It takes research, as often our manuals (i.e., Haynes) or our own shop manuals can be out of date or even wrong (i.e., the 944 Turbo manual, for example, had torque specs for head bolts actually revised in a later service bulletin). It takes money to get the parts and the tools to do it right. It takes time. It takes effort. And it takes patience to do the job over a period of time.

That's what you pay a good mechanic or engineer to do. And nothing is free. So if a mechanic or engineer is not doing the job, and you're doing it instead, plan on giving the job your full attentions. It's not necessarily a cake walk.

[ This Message was edited by: Rick MacLaren on 2002-10-15 12:52 ]

[Peter]

Going over my earlier posts and Rick's comments, I feel as if I may have over simplified rebuilding a 931. It is not my intention to instill a belief that "any monkey with a wrench & a screwdriver could rebuild a 931." It is far from that. Not only do you need the proper tools for a standard rebuild (metric sockets, wrenches, etc), but you also need the special tools to remove those parts that are fused on. Tools such as an air-body saw or die grinder to remove those "stubborn" CV bolts. Did I mention how I hate these bolts? You may also need cobalt drill bits to drill out broken turbo & wastegate studs. Not to mention a metric tap& die kit to clean threads in the block and head. An air compress is almost mandatory to remove the flywheel and crank bolts when the engine is on a hoist. The list goes on, but you get the gist.
Rick, you mentioned organizing parts. You do not know the half of it! I purchased a few boxes of resealable "sandwich type" plastic bags in various sizes and "bagged & tagged" every part that came off the car. Otherwise, there is no way I could remember which bolt went to what part. This is time consuming to say the least.
For example, I took pictures and notes as I took parts off. Here is a pic of the block after I took the water & oil pumps off. (It's so clean you could eat off it ).

The bolt pattern of each pump is marked in white, along with the passageways in the block that will NOT get a freeze plug. Months later when I totally forgot how to put it back together, I could refer to the pic and know how it all goes.
As for putting it all back together, some parts I put on then took off because paranoia set in & I believed that I forgot a step during the first install.
A 931 rebuild is doable. It's a lot harder than a 924 rebuild, but still doable. You need the time and the materials. My rebuild is going on over 1 year. It 's a hobby, so I don't have a deadline. However, if you want a car to drive now, I would suggest that the time you would spend rebuilding your 931 is better spent working overtime to pay the mechanic who could do the job a lot sooner than you could.