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Diary of an Engine


This is the story of my Engine build, a cautionary tale perhaps, but one with a happy ending. Nothing in life worth doing is easy, and the looking after 30 odd year old cars is no exception. But, with patience, understanding and a little luck we can all have great cars that are a credit to ourselves and Porsche. We may need to spend a few quid along the way, but they are worth it, there are not many things able to put such a smile on ones face.

and so we begin…

Ever since I have known Andy Prill I have harboured a desire for him to one day rebuild my engine, I often thought I could attempt it myself, with the aid of the ‘Maestro’s videos, it didn’t seem too difficult. Yeah right! I might be able one day, but I sure can’t afford to experiment on my only engine

I have always be wary of the engine, not because it has performed badly or given me any problems, but because I do not know its provenance. There was always a nagging doubt in my mind that all was not as it should have been, no real reason, just gut instinct.

Mid 2002 I serviced the car before travelling up to Leeds for the PCGB event at Bramham Park, all was fine except I noticed a small amount of ‘grey oil’ as the last few drops dropped from the case… now I had never seen that before. Alarm bells started to ring in the back of my mind. I assumed this was something starting to wear, probably aluminium. Not good.

Contrary to my own advice I drove the car to Bramham, with no apparent ill effects. On the way home however there was a distinct smoke. Again not good.

At that point I decided the time had indeed come to get the engine looked at with a view to a rebuild. No more miles on that engine, I have seen total engine failures, and they ain’t pretty. So I put the car in the garage and rang Andy to hopefully jump the ever growing waiting list. Good things come to those who wait I say.

So, some many months later the time had come to take out the engine and get it to Andy, I also decided to have the gearbox overhauled too, I have always had bad syncro between first and second on the 5 speed (901 Gearbox), a common complaint with our cars. So another call to a gearbox expert to set those wheels in motion 🙂

With the help of Stuart Downward (yup its a two man job) we took out the sad lump. Those familiar with our cars from the outside only maybe shocked to see how ‘big’ the thing is when you eventually get it out. Many the time people have said to me ‘lets have a look at the engine’ only to be faintly disappointed when all they see is a couple of pulleys, fan and oil canister. ‘Is that it!’ Well no it isn’t, being a ‘flat four’ most is hidden. (and as we all know this helps our centre of gravity to remain very low, ergo ‘great handling’)

So now the engine is out, it’s into a van and off to Essex for the ‘strip down’. This is when you find out how well your engine has stood the tests of time and previous mechanics tinkerings.

It will take the best part of a day to take the engine apart and inspect each component, sorting parts for plating, powder coating, machine shop and dustbin.

Once the engine is down to the case, cylinders and heads we can start to really find out how this engine has been maintained. Porsche engines are precision made, every component built to exacting standards, anything not as it should be can have dire consequences, as I was to find out.

The rocker and valve assembly shows signs of bad assembly, not enough shims on the springs has lead to a very ‘tappety’ engine sound and bad valve action.

After removing the rocker assemblies we took off 3 and 4 head and we found number four piston (see pic)… ouch!

Andy deduced that this was a classic case of the previous engine builders mistake in not using the correct parts. The part that caused this damage is cheap i.e. pence, and it has caused thousands of pounds worth of damage.

So what happened? The culprit were the circlips.

The circlips that were used were the wrong size, being slightly too small they were able to move around in the slot. Over time they have ‘machined’ the slot larger and larger, until the worst one has totally disintegrated, trashing the area around the gudgeon pin hole and dropping a whole heap of metal into the circulating oil. (hence the silver deposits I noticed at the time of the oil change). You can see in the cylinder picture how the cylinder wall has also been ‘machined’ as the piston, equipped with its own 50p milling machine has travelled up and down the barrel. All of the pistons and barrels have this damage to a lesser degree. All of which need to be replaced. A lesson learned the hard way!

So by now we are into a set of barrels and pistons, but as you may guess the prognosis at this stage is not good. As this wear has been taking place metal has been circulating in the oil to every nook, cranny and bearing in the engine, not good, in fact, a recipe for total disaster. Now to remove the barrels and pistons and get ready to remove the third piece and split the case. Let’s see what transpires…

Once the third piece is removed we can see another classic worn component. Not related to the metal in the oil directly, the oil pump drive slot and tang are often worn on old engines, this will hopefully be saved, thus negating the need for a new cam, unless the cam is junk from all that oil/metal lubrication.

So now to get into the case, lets hope the cam and crank are Ok.

The first problem Andy encounters is the Flywheel nut. This nut is often torqued to around 400ft/lbs and is a key component. The previous ‘mechanic’ had re-used an old nut. This is a major no-no as this is a major stressed component. The worst thing about this nut however was the fact it had rounded off faces. Andy had to customise a socket to manage to get enough grip on the nut to remove it at all.

So now the case is split and we can take out all the components for further inspection and dismantling.

The cam doesn’t look too bad… good news at last.

Next the crank, this is the prime contender for disaster. As the bearings are most likely contaminated with the oil/metal abrasive mixture the cranks life lies in the balance. If it has been reground previously then we may be in serious trouble. As the main bearings are removed Andy discovers they are undersize, meaning the crank has indeed been reground. Not in itself a bad thing. But, bearings are expensive and hard to find, and undersize bearing even more so. So the bad scoring of the journals means we will need another grind, that will take the crank ‘two under’. Bearings can still be found for this size crank, so no worries so far

The rods have been marked with lovely lines to denote the cylinder numbers when the previous rebuild was done. Seem like a good idea? No!! these lines have been scribed directly into the metal at a point in the rod where it is very likely to fail, there is no need to give physics a helping hand here.

Disaster!!! as Andy removes the rods he chucks me one of the bearings for closer inspection, not being a bearing expert it takes me a while to discover the disaster Andy has alerted me to. Not only are they badly worn they are marked .75, meaning they are already ‘two under’ size. So the crank is an expensive paper weight, due to the fact it cannot be re-ground three under as the bearings are unavailable.

So if you ever see this, you know what to do! The particles of metal attached to the magnet and the ‘grey’ oil were a sure sign of imminent trouble…

Everything will now be inspected and sorted… this is where the Engine builders art begins…

May 2003

I sent some bits n bobs off for Chrome plating, detailing this stuff is where the your engine will ‘look’ great, vanity maybe, but as they say ‘if it looks right, it often is’! It’s up to the owner if you want originality or not.

I have now got the Gearbox back from being re-built., this was not part of the original plan, but I have always had the usual syncro problems that are ever present with the 901. Don’t get me wrong, the 901 is a great gearbox, and it’s a testament to it’s strength it has withstood many years of hard shifting. So, I decided to get it sorted. I could think of nothing worse than a superb engine mated with a tired box 😉 So off it went.

Well it just wasn’t my lucky day, most of the components were well worn, replacing them isn’t such a hard job. The problem is the cost of replacements! But you get what you pay for I guess, however hard that might be.

I am also replacing the 912 gearbox mount with a 911 one. This should significantly improve shifting due to its firmer nature. The slight downside is supposed increased noise transmitted through the mount, we shall see.

Now, the next job was mine and mine alone. To restore the engine compartment to something befitting the incumbent engine. So after 4 days (yes four days) of scraping, sanding and degreasing, I was in a position to paint the engine bay. Here’s a hint… to remove spray glue which someone used to hold a firewall pad in place, it’s quicker (not quick, remember the 4 days) to use paint remover carefully to get a patch at a time cleaned up from this God forsaken gloop. So now that’s done! What a difference. I will replace all the boots and ground strap and engine compartment seals, as I get finished up.

Next to inspect the drive shafts. Now I am wondering if you can guess the state of them? Well done! They are also tired and in need of new CV joints. Instead of replacing them all I decided to get new complete units. Not cheap, but not that much more than the bits needed to repair the old ones, and these bolt straight on. It’s important to use snore washers when bolting them on, if you don’t know what they are better change them. Lot’s of CV grease too!

Next job is to drain the fuel tank and get rid of the gunk that has collected over the years, I don’t want to block my new Webers as soon as I drive off! Watch this space.

I have also decided to get my seat belts re-webbed. They look like the originals so are in desperate need of new web. It’s one of the best and cheapest safety upgrades you can do. It should cost about �70 per pair. Worth every penny. And look at the difference! Enough to make a ‘concours queen’ blush!

June 2003: The story continues…

So I had my Seat Belts re-webbed, wonderful!
So one sunny day with hopes a high and a spring in my step I got down to the Garage to do some more work in preparation for the Engine arrival. I think expectant Mothers call this ‘nesting’. The Engine Bay was now done and looking ok, I had tidied everything up, new underseal here and there, new clutch cable, new boots and earth strap too. The Bay itself had been the hardest job but I was pleased… well you know what comes before a fall! and here came that fall… I started to fit the drivers side seat belt, and the anchor bolt just kept turning and turning, with a nice sound like someone stamping on your cornflakes…. hmmm rusted out huh? *@&%!!! Guess the Porsche Gods had to teach me the lesson the hard way… I had kept the car outside for too long before I found my Garage. Then as I was inspecting further I found some more even worse! The front cross member had a rather ‘channel tunnel’ size opening in it underneath the flakey underseal. Oh well nothing a weeks welding can’t sort out! You have to be pragmatic about these things… no point thinking rust will never hit, it’s just ‘when’.

But some joy ahead… Andy emailed me some pictures of the bottom end coming together. There is always an ‘up’ for every down in the Porsche world!

So Andy sent me some more pictures of the engine coming together, so there it was, finally finished and sitting in all it’s glory at AJP. With the engine bay done, I fitted the gearbox and new drive shafts ready for the engine.

The install went without a hitch, we just had to remove a small piece of cross member metal to allow the left hand Weber shaft to spin freely, then it was fired up. I have to say it sounded superb. Gone was that ‘tappety’ rattle, and in it’s place a deep throaty growl. Obviously the engine is very tight still, and stops the moment you turn the ignition off, it will require gentle and thorough running in, Andy has provided detailed running in procedures, which need to be followed religiously.

The gearbox has also to be run in, at present it’s hard to shift, this should 
improve dramatically once I get the car on the road.

I have to say a heartfelt thank you to Andy who really put his heart and soul into this rebuild and helps you ‘Keep the Faith’

Final Specifications:

NOS Porsche Crank

New Weber 40IDF Carbs

AJP Full Flo kit

Shasta Barrels and Pistons

Power Pulley

Norris 337S Cam

New Carb Manifolds

Everything blueprinted and balanced,

refurbed and detailed.

A masterful job worth every penny!

Andy Prill:

Footnote: August 2004
The engine is now fully run-in and is a revelation. The power and the noise are something to behold! The gearbox too is now as smooth and precise as you could hope for and although I was initially worried about the clunky hard shift action I remembered Harry Pellows words that after about 1000 miles it would change overnight into a smooth shifter, and it did! I guess the ‘Porsche Gods’ smile on those who believe. Andy has now done some re-jetting and I am awaiting the Pertronix ignition. The car is now a real joy to drive, and makes you remember why they are so great, the feeling of driving down a Norfolk road recently with the sun setting and the engine at full song will stay with me forever.

A pictorial record…

1968 912 Engine, prior to rebuild, the engine had shown tell-tale signs of imminent failure. ignore signs from the Porsche Gods at your peril!

So Stuart and I removed the engine and gearbox ready for delivery to Mr Prill.

Andy starts to strip the engine to see where that grey gloop came from, much breath being held.

Now to remove the heads and barrels

Check out the state of number four piston

Piston was about to disintegrate

The barrel was scored by the pins occilations

What hope the crank?

Some not so handy scribing in the rod end

Crank and bearings are junk

Particles on the sump magnet

Gearbox back from the machine shop with 911 mount