|
928 GT Engine Rebuild April 2009 By Paul Lacey |
|
The Story: I am an absolute fan of the Porsche 928. My uncle Alan is the guilty party for this. When I was a young lad he had a brand new 928, a white S4. I guess it would have been around 1987. It was the most beautiful thing I had seen on four wheels and I fell in love with the 928. But I never thought I could own one myself. Nine years ago, by complete chance, I came across a 928S2 that was so cheap I had to buy it. It had blown head gaskets and who knows what else but mechanical things have never scared me. The first engine rebuild I tackled was at 14 years old, an NSU Quickly moped. Since those days I guess engines, gearboxes, overdrives that I’ve rebuilt must be into the hundreds. So, how hard can it be I thought, an engine is an engine! So I bought it, phoned the AA to say my head gasket had gone, and got transported home. There followed three months of very heavy duty learning. I bought a full Porsche workshop manual, several volumes and read it all. Fixed the car and all the little things which didn’t work properly. This is now my wife’s very rare Turquoise 928 S2 |
|
Joined the 928 org community http://www.928.org.uk and continued the learning process. Then I spotted a dream 928, a 1989 928GT with very low mileage and a blown up engine. Baltic blue with cream interior and I had to have it! The most complex of the Porsche V8 engines this one with 32 valves, quite different to the S2 with it’s 16. But in the main it’s the same engine. So this time it was a complete engine rebuilt. The crankshaft, two conrods, two pistons were scrap. I took my time and seven months later the car was on the road (and track). What a great car! |
|
However, I had always fancied a Guards Red S4 and in 2008 came across my next 928. Sold the GT and bought it. This time only minor electrical work required, bit of tidying, and rebuild of power steering rack |
|
The Supercharged Engine Project |
|
During my parts search for the GT engine rebuild I came across a complete GT engine and bought it as I had decided to build a supercharged 32v engine. This would have around 450 horsepower at the wheels, a standard 928 GT is around 330 at the engine. However, a supercharged engine needs to be built for that purpose, lower compression, special head gaskets etc. etc. So slowly I started a complete rebuild of my spare GT engine. It would be destined for my Red S4 which I would also convert to manual transmission. But then came the economic disaster at the end of 2008! The supercharger and kit has to come from the US, 928 Motorsports. But now instead of £3700 for the parts I needed it is £5500+ No longer could I remotely justify this expense, after all the 928 is not a slow car anyway. I just really fancied the project, actually more than the results. Next disaster — after 30 years of driving with no accidents, convictions, or claims, I put my beloved 928 under the back of a Range Rover at 30 mph. The entire front of a 928 is aluminium, the rear of a Range Rover is made of steel girders. Result is my 928 is a write off |
|
So depressing ! I have to fix her. The insurance is going to offer some miserable amount I just know it. So funds are required to get TTA928 back on the road. My spare GT engine has now been completed and must be sold. I have taken great care of this engine rebuild, as I never had intentions of selling it. This is now the 5th 928 engine I have built. None of the planned modifications for supercharging have been implemented so it is a standard 928 GT engine. But it’s a beauty ! I took extra care on maybe stupid things, I spent ages for example finding a sump that had not a single scrape or scratch on it. You cannot even see this unless you crawl under a car but for me everything had to be as close to factory fresh as I could make it |
|
The GT Engine Rebuild |
|
Please click on any picture to see the full size version |
|
Assembly of cylinder block and “ladder”. This is the lower part of the block and commonly called the ladder because it looks like one. All parts must be absolutely clean before a thin coat of oil is smeared over the whole crankshaft. It’s bare steel and will rust if it’s not protected. New main bearings are used of course together with new front and rear oil seals. This crankshaft is standard size. Special care must be taken that all oil paths, oil pump, and the oil pickup is totally clean too. A special Loctite gasket cement is used between the block and ladder, applied very thinly. This is available through Loctite stockists. Tip: Mark the torque setting / sequence / steps with indelible felt pen. |
|
Central Main Bearing has the end float thrust faces on the bearing. Check everything turns freely and end float correct Tips: Do not rotate crankshaft until all bolts are at final torque except be sure nothing is trapped. The special Loctite does not set until there is no air, It then takes around 15 minutes so you have plenty of time. |
|
Here I have fitted the waterpump, new gasket of course, the oil pump drive sprocket (42 ft/lbs), the two new steel guide washers either side of the cambelt drive sprocket on the nose of the crankshaft. Tip: Buy one of these engine stands. Can hold a complete 928 engine and you can turn the engine when working on it. Fantastic value of £42 from Machine Mart ! |
|
All cylinder bores again spotlessly clean. No scores or ridges on the bores. This engine is standard bore and grade 1. When produced in the factory there were three grades 1 2 & 3. This is marked above each bore and also the matching pistons. Must never be mixed. Pistons must return to their original bores even with new rings. Pistons and bores are run in together. |
|
Here is the rear end of the block. You can see the new oil seal and also the clutch centre shaft bearing. Always replace this bearing it costs little ! |
|
Refit of pistons and rods. Again, immaculate pistons fitted with new rings correctly spaced around circumference. Use plenty of clean engine oil, preferably the oil that you will use when the engine is run. I am using full synthetic 5W/60 oil. Note the best type of piston ring compressor to use on the trolley below. Available from Halfords etc. Tip: Use rubber end of hammer to gently tap piston down through ring compressor which should be well oiled also |
|
From below all eight pistons and rods installed. New big end shell bearings are used and new conrod nuts. Note the thin fillet side of conrods face each other with the thick fillets facing out towards the crankshaft webs. Use plenty of oil ! Check everything turns freely after each rod is fitted. You will get used to how hard it is to turn after you add each rod. Don’t chop your fingers, there’s sharp bits in there !! |
|
From above, beautiful isn’t it, such a shame it’s all inside the engine and cannot be seen. Cylinder 5—8 Note here you can clearly see the number 1 on each piston, also the arrow on each piston that points to the front of the engine. Double check everything !! |
|
Here is the other side, cylinders 1—4 Double check everything !! |
|
Time to seal up the bottom with the immaculate sump. New gasket again is a must. Tip: Locktite the bolts in place they tend to undo over time. Very thin smear of high quality silicon gasket is also a good idea. Double check everything !! |
|
The complete “Short Engine” Tip: Make sure ALL places where things could drop into the engine are covered. You do not want to be taking the sump off again ! |
|
The GT Engine — Cylinder Heads |
|
New head gaskets and do not use anything other than genuine Porsche Cylinder head fitment is straight forward but there are lots of bolts and the Workshop Manual must be closely followed for the torque settings and order. You should use a degree gauge as I did but you can manage without if careful. 90 degrees is easy to measure ! Tip: Ensure the arrow on the gaskets points to the front of the engine. Be sure the TOP mark faces upwards. Be sure it says 5.0L on the head gaskets for GT S4 SE models (or whatever your engine size is 4.5L, 4.7L, 5.0L, 5.4L) |
|
The hydraulic tappets must return to their original locations. Again you can use a fine marker pen for this. When replacing make sure to liberally lubricate with oil, don’t forget when the engine is started there will be quite a few seconds before these get oil through the system. |
|
Now the camshafts — they must return to original locations, you can see I used blobs of yellow paint, also mark them Ex and In because they are very similar ! Camshaft caps are marked both with their position number and a unique number matching the cylinder head (in this case 71) Note: The engine must be positioned at 45 degrees before TDC Cylinder 1 when installing the cams. In this position no valve can hit a piston Find a position where no valves are much open so that you can very gradually tighten down the bearing caps. Do this very slowly and gradually. Each cam has a raised pointer or “nose” and these must point to the marked chain links. Always use new chains, they are not expensive. |
|
The cam chains have an hydraulic adjuster between them. On Cyl 1-4 this pushes up, on 5-8 down. They are different. Replace the yellow nylon sliders if worn (you can see the part number here) Replace the alloy washers that are on the oil supply pipes for these adjusters. |
|
This is cylinders 5-8 and you can clearly see the noses on the camshafts in relation to the cam chain. When you fit the oil supply pipe be very very careful not to drop anything — it will end up down in the engine ! |
|
This is cylinders 1-4 and again you can clearly see the noses on the camshafts in relation to the cam chain. Note the difference of the hydraulic adjuster to the other one When you fit the oil supply pipe be very very careful not to drop anything — it will end up down in the engine ! |
|
The rear bridges contain several rubber seal, use new and do not miss any out because they also seal the oil passages, you will have reduced supply to the valve gear if you miss them out ! The rear disk shaped seals have a tendency to leak so I smear a thin coat of silicon gasket round the outer edges of them. Tip: Be sparing with silicon gasket, do not get any inside the engine, wipe off excess with petrol or white spirit |
|
Camshaft sprockets can be put on after replacing the cover plates behind them. You need to use three small bolts / allens to temporarily hold the sprocket, do not tighten the central bolt, cam timing needs doing first. Camshaft sprockets need to be replaced if there is any sign of wear. They are toughened (anodised) on the outside and once this wears through they will deteriorate quickly. Examine them carefully. |
|
Engine still at 45 degrees BTDC and cam belt now roughly located in correct position. In this photo I have put one cam cover on but that is only temporary to stop dirt / dust getting in. Note the routing of the cambelt and always use a new belt ! |
|
Engine still at 45 degrees BTDC. The camshafts have a 27mm nut shape cast into them. Turn the driven camshaft in the correct direction (crankshaft turns clockwise viewed from front) until the timing marks on the camshaft sprocket align with the notch on the rear cover. When both bank of camshafts are correct turn the crankshaft to TDC number 1 and put the cambelt around the sprockets Note: The cams may try to spring back, be careful ! |
|
You should have rebuilt your cambelt tensioner. Use a new rubber boot on the front even if the old one appears OK. This gets brittle and splits, result is no oil in the tensioner and it’s performance is then incorrect. The tensioner is filled with engine oil but not before it’s fitted ! Always use a new gasket too. |
|
This is how to hold everything temporarily so the camshafts do not move and whilst you fit the tensioner. Note how everything goes. Use new rollers on the tensioner arm, the large one is especially important, the top one is just a guide roller. Note the rollers under the nose of the crankshaft. Some engines have one roller but GT’s seem to have two. |
|
Having fitted the tensioner and double checked the cam timing is roughly correct it is time to tension the belt. I have a Kempf tensioner which works well. Tip: Tension is checked at TDC number 1 cylinder. Then rotate engine two full rotations and check again. Turn the engine VERY slowly and stop if you feel any unexpected resistance. If you do then check the cam timing again ! |
|
Now it’s time to do the camshaft timing properly. You need a dial gauge to measure valve lift. A mounting for the dial gauge can be made from a thick piece of steel. I am not going into great detail here except to say it must be done methodically and according to the Workshop Manual. There is quite some scope for error here, triple check everything. Tip: The camshaft centre bolts (47 ft/lbs) must be done up while counter holding the camshaft or they will move spoiling the timing. |
|
Now all the front covers are replaced together with the crankshaft pulleys Tip do not forget to remove the temporary bolts from the camshaft sprockets otherwise you will never be able to fit distributor arms ! |