Yep another Engine Rebuild I think?

[jaymatwhit]

Hello, I need a little help I think.
I have a US spec 1972 911 T/E mfi, I had the engine rebuilt at Bob Watson's in 2009 (9000miles ago) with E cams, barrels etc.
Last spring it went in for an MOT and the mechanic called me up as there were serious oil leaks and a strange mechanical tick every now and again (not every revolution) that puffed smoke and oil out of 2 cylinders - I have to be honest I dont understand this and have searched but can not find anything similar so inconsistent.
It was not leaking oil or making the strange noise the previous year and all I did over the winter was to change the oil to what Opie recommended - Titan Race Pro R 15/50 but can not imagine it could be this could it?
Anyway I think I will have to bite the bullet and plan for an engine rebuild that I will have to do myself this time unless anybody here can say no its such and such and easy to fix and cheap lol .
I have been reading up on the Dempsey book and need help on the best places to source parts and either rent or buy the special tools such as the valve timing, cam locking C spanner & dial gauge holder for now

Any help would be greatly appreciated as its my 1st rebuild
Jason

[Cortina]

I would be looking a bit further before I lept to an engine rebuild.
a) if Bob Watson has built it - then chances are it was done right (correctly)
b) 9000 miles is nothing - in terms of things "wearing out" so to speak.

Yes , something is not right ... but better to measure twice .... or three times .... before cutting !

(would not agree with choice of oil ... but that's another story .............)

Needs looked at by someone who knows these things , hard to say more "remotely" ... if you get my drift.

[hot66]

Check a rocker arm shaft hasn't started to move and the rocker come loose ... If they do you'll get a lot of oil coming from the head area and you might have a valve sticking open

Oil...can't see that having any detrimental effect. I always use valvolene VR1 20/40

Sent from my iPad using Tapatalk

[911SE]

I had an intermittent ticking noise together with a load of smoke, would come and go but when present it would stay for a couple of km's. A lose inletvalve guide was found at the rebuild...

[911hillclimber]

Do all the basics before even taking it out.

Pull the plugs. Are they even in colour and if any cylinders are burning oil, it will show on the soiled plug(s). Obviously focus you attention on those cylinders first.

Compression and leak-down tests. You can buy the test gauges etc from Halfords!
If all that checks out, check the valve clearances very care fully as Hot66 says though after 9k they should be as Bob set them. Adjust them using the correct 4 thou shim gauge for 911 engines, buy from Type911 for a few £.
total spend is about £40 so far, engine still in the car, and you have a lot of info.
I think this procedure is detailed in the excellent Dempsey book.

Rebuilding the early 911 engine is straight forward IF you have the correct cam timing tools (holder, crow foot spanners etc.) You almost need these tools to take it apart too, but not that expensive, OR do all the work and take the engine to someone who will set the cam timing for you.
You can get all the top-end parts from Type911, Design911 etc. Take it all apart before ordering parts!

When I did my first 911 engine rebuild (2.4 E/S) in 1992 I took the long engine down to Bob's for the cam timing to be set, I finished the build off and popped it back into the car.
You are in the Midlands? Try calling Zuffenhaus in South Birmingham, good Porsche Indie with an engine room, seem a flexible group of people.

Everyone has their own opinion on the Best Oil, inc me! (Bob told me what to use in 1990 and I've used it since)

[jaymatwhit]

many thanks guys, will keep you posted.
911hillclimb, what oil do you use btw?

[911hillclimber]

Shell Semi Synthetic Helix HS7 10W40.

Bob told me to use it in my road/hill climb 911 (73T with a 180 bhp 2.4/mech injection), changed it every 12 months.
He said the same for when I installed my 3.2 into the same car.

Those engines were USED, many runs to the rev limiter, lots of WOT on a hill climb. The 3.2 is now 130K miles in, I had it @ 60K miles in.
Uses no oil, runs a dream, never been apart ever. Fresh oil/ filter every 12 months no matter what the miles from 1996 to present.

I then ran a hot Impreza, 360 bhp for hill climbs and road. Same oil, same process. Never missed a beat, thrashed to death, revved to 7900 and standing starts with 6500 rpm when the clutch got dropped etc. Changed oil every 12 months...

I have now the 911 and a 3.2 engined race car, all running the same oil, so same manufacturer spec oil used since 1990.

Many can tell much the same stories, long term use of a given product that gives confidence they are using the Right Stuff.

Do I use the best oil? Not sure, but for me I do. Should I need oil into a journey then I can get some at a Shell petrol station off the shelf.
Few know what the best oil is to use. Try defining 'Best'.
All depends on your use and miles covered which is why I've detailed the above to you.

I do know from experience Mobil 1 will run out of an old design 911 engine that would be oil tight with a semi synthetic, been there had it happen, got a bollocking off Bob as a result, and his advice which I've followed ever since.

I use Shell Vmax petrol as much as I can too.

[MikeyC]

Jason, if you are anywhere near the Banbury area and it's still in one piece and driveable, you are welcome to bring it into my workshop for some initial diagnosis: http://www.mceporsche.com. I have compression and leakdown test capability, a variety of borescopes, and a pretty good feel for what goes on inside a 911 engine. From your description though, it may not be advisable to run it any further until you understand what's happening, so I may be able to come to you if you're reasonably close.

Don't worry about the type of oil you're using. It's not that.

Feel free to get in touch if you need some help.

Regards,

Mike.

[911hillclimber]

Mike, I've sent you a message on your business system.

[jaymatwhit]

Thank you. Engine out now as compression figures all low, best was 100 worst 50!
I seem to recall reading that there was a bad batch of OEM head gaskets going around when I had it rebuilt - would this make sense?
O and gutted, honestly thought it would be loose studs

[911hillclimber]

Did you do a tdc leak down test?
Can be done if engine still in one piece.

[gridgway]

It's probably a really stupid question, but were you holding the throttle open on the compression test?
As Graham says, you should do a leakdown test before going any further to find out where the compression is going.
(the other) Graham

Thank you. Engine out now as compression figures all low, best was 100 worst 50!
I seem to recall reading that there was a bad batch of OEM head gaskets going around when I had it rebuilt - would this make sense?
O and gutted, honestly thought it would be loose studs

[MikeyC]

Jason,

How did the spark plugs look? Any clues there?

I would recommend not to attack that engine too much before doing some further fault finding. Compression tests alone are notoriously unreliable. As the Grahams have mentioned , cylinder-by-cylinder leakdown will be helpful, and with chambers under pressure at TDC with inlet and outlet valves fully closed (in theory), if you have any air escaping, you should be able to pinpoint where it's leaking through.

[fetuhoe]

I would be interested to know how your mechanic determined that 2 cylinders were 'puffing' out smoke and which are the affected cylinders, and what does he really mean by this description.

There are only a couple or reasons why a cylinder will smoke. One is oil passing the rings and the other is oil pumping down the guide.

If the smoke is due to external leaks then this could be due to a failure of the spigot seal or the CE ring.

A CE Ring failure may cause smoke on the compression stroke and can cause a noise which can sound like ticking.

It would be a good idea to start with a basic look at the outside of the engine for obvious leaks and has been suggested 'walking' rocker shafts.

Have you any idea of your oil consumption? I would also think about how often the engine is started and how long it takes before it stops smoking.

Mag engine may leak if they are left standing for a few weeks as the oil will drain into the case and the split line can weep as a result.

I would always start with a compression test and if this gives a positive result a leak down test just becomes a wasted effort.

Doing a compression test as a first step whenever there's an engine running fault can save a lot of time in the long run.

Run the engine until it reaches normal operating temperature. Tests done on a cold engine usually show lower readings.

I would allow a cold engine to idle for around 15minutes but if the car has been driven I would let it cool for around 45 minutes before doing this test.

Remove the HT leads and take out all the spark plugs. The ignition system should be disabled. If this isn't done it will continue to generate high tension voltages into the HT leads which will have nowhere to go with the plugs out. These high voltages will find another route to earth and can damage the ignition system Unplug the low tension connections to the coil.
It is also good practise to unplug the fuel injectors or disable the fuel pump during the test.

Screw the gauge into cylinder 1 and rest it somewhere you can see the dial while you crank the engine. Open the throttle fully either by pressing the accelerator or wedging the linkage open. If the throttle isn't open then air can't get into the cylinder and the readings will be far too low. Crank the engine until the gauge stops rising and count the revolutions while you do so. It should normally take no more than 10 engine revolutions (5 compression cycles) to get a full reading. You can count the cycles by watching the gauge too - each jump of the needle is one compression stroke. Write down the final reading and also make a mental note of how quickly the gauge rose on the first few cycles. Then just repeat for the other cylinders. Make sure that each cylinder reaches its highest reading after the same number of engine revolutions. If all readings are good then the test can end there. If any cylinders are low then a "wet" test can be done. This involves squirting a few ccs of oil into the cylinder and repeating the test. The oil will help seal bad rings and increase the reading but won't affect it if the problem lies in the valves or head gasket.

An engine in good condition should have readings within the specified range (preferably at the upper end of it) and with all cylinders within 10 % of each other. A perfect engine might have almost identical readings on all cylinders - it is certainly possible to achieve this on a really well blueprinted competition engine. A good cylinder will reach about 2/3 of its final reading on the first compression cycle and reach the full reading after only 2 or 3 cycles. If the rings are worn you often see a gauge rising in smaller jumps of 20 to 30 psi per cycle rather than one big initial jump and also taking more revolutions to reach a peak reading.

If all cylinders show similar psi but are below the minimum figure then this usually indicates excessive ring and bore wear due to high mileage. It is possible that a cam timing issue could cause similar results and very low readings can be caused by bent valves.

If One cylinder is low this means a bit more detective work is needed. If the wet test improved things back to a normal reading then the problem lies in the rings or bores. If not then its usually either valves or gasket not sealing properly. To an extent I fail to see the point in worrying overmuch about exactly where the problem lies. Most of the time the cylinder head is going to have to come off so you might as well do that first and see what shows up. It may of course not be just one problem though and there is no point in spotting the bent valve and refitting the head but failing to realise that there was a broken ring as well. A leak down test will help here.

One problem that might not lie inside the cylinder itself is a worn camshaft. If a lobe is badly enough rounded off then that valve won't open fully, or at all, and if no air can get into the cylinder then of course it's not going to generate much of a cranking pressure.

This involves pumping high pressure air into the cylinder and noting how quickly it leaks out on a gauge. The leakage rate should be very low if the rings etc are in good condition. During the leak down test you can also listen for where the air is escaping and this can pinpoint the problem to a valve, gasket or ring fault. If the leakdown test shows no fault but the cranking pressures are low then it must be a cam lobe or cam timing type of issue.

Guides are more likely to cause smoke on the overrun but even a leak down won't show this problem when the valve is seating correctly.

Wear in the guide normally occurs at the head end on the valve so it is difficult to make a sensible judgement without stripping the head.

The basic quality of Porsche replacement guides isn't particularly good in the first place and even if they have been replaced that don't always last very long.

If the problem is the guides then they can be replaced or you could use a K-Liner.

We never use 'thin' oils in 911's we use VR1 20W/50 on a routine basis.

[gridgway]

Great write up Chris!

It's the fact that all cylinders are so poor that strikes me as strange. Now I'm an amateur, but all cylinders having poor compression means they all have a problem and most likely the same problem.

So unless it's a mega miles engine, they've all suffered the same failure or there is a failure that is affecting all of them which I don't know what it could be.

Now the engine is out, your can't easily redo the compression tests, but can do the leak down.

When my 2.0 had poor compression on #1 I used a leakdown test to work out that the exhaust valve wasnt closing.

Graham