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75 911s engine and transmission

Hi
My 75 911s engine and transmission removed from car. What are the important things that I must check/inpect?
Old 08-13-2019, 05:37 PM
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There isn't a whole lot you can check/inspect with the engine and transmission out of the car that you couldn't do with it in the car.

Why did you take it out?
Old 08-13-2019, 06:43 PM
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Out of the car you could check tightness of the head studs. (carefully). Adjust the valves and replace all the rubber fuel stuff.

You could also do a leakdown test.

Otherwise running and driving will tell you most everything you want to know, unless you are ready to do a COMPLETE TEAR DOWN and evaluate all the components that way.
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Old 08-14-2019, 08:45 AM
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If ever was a time to upgrade the exhaust, now would be easiest. Especially if your car was a cali 75 that had thermal reactors. The exhaust studs have a thin point to allow rocking the thermals into place. That makes them extra easy to snap when trying to pull the exhaust. If you want to keep the exhaust, fine.

If not, still a good time to throw SSI on or headers. Also attack the triangle of death areas, inspect the hydrualic tensioners and or upgrade to oil fed carrera tensioners. I would also change the clutch. If original, it's ready to give up the ghost. It's got a rubber center likely. inspect the trans, fork etc. New rear main seal.

a lot you could do to prevent headaches and leaks once it goes back in.
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Old 08-14-2019, 03:55 PM
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Quote:
Originally Posted by Walt Fricke View Post
There isn't a whole lot you can check/inspect with the engine and transmission out of the car that you couldn't do with it in the car.

Why did you take it out?
Trans leaks at nose cone seal
Old 08-15-2019, 12:25 PM
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Quote:
Originally Posted by Trackrash View Post
Out of the car you could check tightness of the head studs. (carefully). Adjust the valves and replace all the rubber fuel stuff.

You could also do a leakdown test.

Otherwise running and driving will tell you most everything you want to know, unless you are ready to do a COMPLETE TEAR DOWN and evaluate all the components that way.
What tools required for leak down test?
Old 08-15-2019, 12:27 PM
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Originally Posted by 75 911s View Post
If ever was a time to upgrade the exhaust, now would be easiest. Especially if your car was a cali 75 that had thermal reactors. The exhaust studs have a thin point to allow rocking the thermals into place. That makes them extra easy to snap when trying to pull the exhaust. If you want to keep the exhaust, fine.

If not, still a good time to throw SSI on or headers. Also attack the triangle of death areas, inspect the hydrualic tensioners and or upgrade to oil fed carrera tensioners. I would also change the clutch. If original, it's ready to give up the ghost. It's got a rubber center likely. inspect the trans, fork etc. New rear main seal.

a lot you could do to prevent headaches and leaks once it goes back in.
Thanks
Old 08-15-2019, 12:29 PM
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Originally Posted by hienz View Post
What tools required for leak down test?
https://www.harborfreight.com/cylinder-leak-down-tester-62595.html
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Old 08-15-2019, 01:29 PM
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Heinz - If the seal that leaks is the one on the shift rod, where it enters the nose cone: that seal can be replaced with the transmission still in the car - calls for drilling a couple of small holes in the steel of the seal housing, screwing some self tapping screws in, and wedging the seal out using the screw heads for purchase. It is a bit tricky, but can be done. With the transmission out, replacing the seal is pretty straight forward, as you can just pry what is there out.

If it is the joint between the nose cone and the next housing of the transmission, well that's different. Slathering the joint externally with epoxy isn't a good long term plan, though it might work. I don't think this joint is a likely source of leakage due to age, though.

But if this joint's seal is bad, as transmission repairs go it is duck soup, and you can do it yourself. No special tools or even really any special knowledge or understanding needed (at least until you start thinking of doing more than look).

On the advice of my local transmission repair shop, I don't use the gasket there. Instead I put a thin coat of Honda/Yama bond on the sealing surface. These surfaces are nicely machined and mate tightly, and a sealant works as well as the paper thin gasket. But you can buy the gasket and use it if you want.

If you have the nose cone off, you can inspect the 5th gear synchros, and the 5th gear engagement teeth. They shouldn't be worn - 1st may be the least used gear, but 5th has to be the next in terms of how many times you shift into it. If it is bad, then you might wonder what 2d and especially 3d inside the rest of the case look like. There is a way to get a peek at these. You can find out what they should and should not look like by some searching right on this forum.

If you have time on your hands, you could pull the left side cover of the transmission after removing the output flange, and inspect the ring and pinion. No reason to suspect anything amiss, but with the transmission on its right side, or on the engine stand, pretty easy to do. You could replace the large diameter skinny O ring seal for the cover, or just reuse your old one.

About everything is easier with the engine out (especially if up on a rotatable engine stand). The leakdown will give you an idea of how well the valves are sealing. Neither the intake nor the exhaust should leak. The rings always leak some, and some percentage of leakage there is not really a problem - many thousands of miles left (opinions vary on where the cut-off is, but maybe 12-15% would be a reasonable dividing line, plus how much variation is there from cylinder to cylinder). How do you know where the leaks are which lead to these more than 0 leakage? By listening - exhaust leak out there, intakes there, and rings leak into the innards of the engine case. Get a piece of plastic or rubber tube you can stick into your ear, and listen at the intake, exhaust, and through the engine breather cover, having removed the breather hose.

If you remove the exhaust for whatever reason, you can check exhaust valves by inverting the engine, putting air pressure in the cylinder being checked, and spraying a little soapy water into the exhaust port and look for bubbles. You can use your shop air to blow the water out when you are done, and on to the next cylinder.

I've never had noise from my intakes or exhausts. That doesn't mean the engine might not perk up some if a valve job were done. But you don't have burnt valves. Once exhaust gasses are able to escape before their time, the fuse it lit. It is normal to keep rotating the engine as you test, and to be sure to come back to where you got any readings or sounds you didn't like, just in case a valve leak is due to a bit or carbon or something which might have fallen onto the sealing surface. Nowadays, borescopes are cheap ~$10.00 for something to hook up to a computer/laptop/tablet, various smart phones, and you can actually inspect the valve sealing surface to some extent (again, much easier with the engine out and you not needing to emulate a pretzel).

Since you report no other issues with how the engine runs and the transmission feels, I'd not go nuts with any of this. You've been given the obvious things to check - which can be part of periodic checking with the engine in the car, but are easier and less messy with it out.

The 3.2 Carreras have a problem with the original rubber fuel hoses back on the engine leaking as they age. Your 2.7 doesn't really have such an issue - my '77 has its original rubber fuel lines (now feeding a 3.0), which don't show signs of deterioration. But of course you can give them a visual inspection.

The long fuel lines inside the tunnel are some kind of plastic, and those look to last forever, absent something which cuts or drills into them in the tunnel.

The fun starts when you find something wrong, not just a valve or two a thousandth out of its proper 0.004" lash. A broken head stud pretty much requires a teardown. On these engines, you usually replace them all, and use Timecerts or Casesavers or Helicoils to beef up the magnesium case's threads. If you remove enough stuff so that you can insert case savers, you might as well crack the case and replace all the bearings. While you are at it, the heads go off for replacement of the valve guides as needed (likely if an unmolested '75 with lots of miles)and to freshen up the valves and seats (or have replaced, as needed). The rods probably should go off to a shop which can resize them, to go along with your new rod bearings. How are the rod journals on the crank? Cranks can be ground to first undersize, and those bearings (used to?) don't cost much more than standard. Some of the 12 rockers might need to be rebushed and reground. What do the rocker shafts look like? You will get advice about replacing the cam chains and gears, which you might or might not need to do. The labor for this any DIYer can do (buying or borrowing some tools), but the machining is not DIY (unless you are a machinist).

Oh, then there is line boring the crank journals (and IS shaft journals). The mag cases tend to wiggle around with age, so at a minimum a machinist level check of any disassembled mag case is a good idea. Happily, the shops in the know have a way of getting these journals back to their stock shape, so you won't have to use oversized OD main bearings.

In short, if the engine has been working well, and you don't find broken head studs, or studs which won't take torque (you might set your wrench a pound or two below spec for checking purposes), and leakdowns are good, maybe you leave well enough alone?

Checking the clutch disk is a good idea - with it in your hand you can measure its thickness and compare that to Porsche's "time to replace it" spec. The throw out bearing isn't all that expensive, so replacing it may make sense. Chances are good the pressure plate is OK - you can see if its surface has been greatly overheated - various blue splotches or deep gouges, or the clutch disc wore down to the metal maybe. Same with the flywheel.

If you don't have an engine main seal leak - where the crank emerges from the case and the flywheel attaches - I'd leave the flywheel alone, at least if it isn't in really bad shape. Replacing seals which aren't leaking (other than as part of a full rebuild of the whole engine)doesn't seem like all that good an idea. Getting a new seal in just right isn't all that easy, and you have to worry about which of the maybe four brands of new seal to get - some are reputed not to be as good as what Porsche put in back when. Same thing with the seal up by the pulley.

Oh - our host here (an engineer and car guy tinkerer) wrote a book on rebuilding 911 engines, and another on various DIY tasks short of engine rebuilds. You should have both in your library.
Old 08-17-2019, 01:06 PM
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Hi Walt
I did not know exactly where does the trans. licking from so to be very safe I dropped engine and trans just for that and I would like to learn how to drop engine and trans so I can do services for my Porsche. It is to easy and fun to drop engine and trans out of 75 911s. I have dropped engine and trans out of my 356c many years ago. I did not know I can get that nose cone seal out with the engine and trans still in place. Now I know.
In the process of having trans and engine out, I found two loose castle nuts which locating inside the oil cooler housing. I can take those castle nuts off with two finger without any effort.
Thank you for info. I will read and follow your suggestions.
Old 08-17-2019, 07:04 PM
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Castle nuts? That usually refers to nuts with a bunch of slots on the top, used with a bolt or stud with a hole drilled across it, so you can insert a cotter pin. There are none of those on a 911 engine.

The case through bolts, two of which end up behind the oil cooler where you can't get at them without taking the cooler off, are domed nuts - not open on one end. I don't know just why Porsche chose those for the case through bolts, but it did - maybe because oil that might leak through the threads can't as easily escape?

You don't hear of those being loose. Those two are what hold the case halves together at the #1 main crank bearing. Not a good sign, but to check the rest of those bolts you need to remove the engine tin.
Old 08-19-2019, 11:25 AM
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