Wednesday, 1 May 2019

Pre-Fitting Assembly

With the long block rebuild completed we’ve been getting on with engine re-assembly prior to refitting into the car.  

Progress has been made with all of the ancillaries, vacuum pipes, sensors, inlet manifolds, fuel rails and wiring loom bolted and connected back onto the engine.  

We’ve been replacing bolts and cleaning parts along the way. Vacuum pipes in particular caused us a problem with trying to refer back to our notes and photos of where the many different connections go.  Porsche make some things so complicated you couldn’t make it up, with different configurations for year, engine and gearbox types all being unique in some way. 

In parallel we have ordered a full set of clutch replacements parts as per the pelican parts guide and will switch to a sport clutch from the standard one.

The gearbox bellhousing was cleaned up and the old clutch release arm and release bearing removed.  A later style 997 arm was fitted with new fittings all round.  

The new flywheel was fitted following the torque procedure for the bolts. We then used a clutch fitting tool to centre the clutch plate before fitting the reconditioned clutch pressure plate.  

Re-install day should only be a matter of weeks away.  

Monday, 18 March 2019

Long block rebuild

It’s taken a couple of months to decide on a course of action and source the parts to rebuild the engine block.

9-Apart Porsche dismantlers had a good crankshaft of the right type (5 chain rather than the later 3 chain design). Without this there would have been no choice but to go with a second hand engine.   With two of the cylinders scored the option of iron cylinder liners was considered, but in the end we managed to obtain a used crankcase which we preferred.  

With these key parts sorted we were able to send the cylinder heads away to be skimmed, valve seats re-ground and valves stem seals replaced.   

Two of the pistons in cylinders 5 & 6 were scored so we had to replace these with used ones.  The no. 6 conrod was also beyond repair. 

Whilst doing this we balanced all of the pistons and the conrods.  This is fairly simple as they are designed with specific areas where minimal material for balancing can be removed. 

Then with the help and expert guidance of Archer Motorsport Services the engine was re-assembled with a standard engine rebuild kit of parts.  This included;
  • Bearing shells
  • Piston rings
  • Conrod bolts
  • Timing chains 
  • Chain tensioners and guides
  • Head gaskets
  • Cylinder head bolts 
  • Gaskets and oil seals 
  • IMS bearing 
  • Sealant and assembly paste 

Under hard cornering g-forces the oil can have a tendency to either stay in the cylinder head and not return to the sump or pool in the side of sump away from the oil pickup tube.  

To help prevent oil starvation we have fitted the Porsche x51 motorsport sump.  This isn’t a deeper sump but does have larger and improved baffles to ensure that oil returns and stays in the centre of the engine. 

The long block assembled with our lower temp thermostat and metal impeller water pump re-fitted.  

Inside the engine bay we have de-greased and cleaned everywhere, plus repainted the chassis cross member which was starting to rust. 

Before reinstalling into the car the engine block needs the intake manifolds, fuel rails and ancillaries refitting.  

The final area which will also needs attention is the clutch and flywheel. Both need replacing (as you would expect after 80,000+ miles) along with several parts of the clutch mechanism which wear out.    

So still plenty of work to be done before the engine can be run in!

Sunday, 6 January 2019

Engine Strip Down

Having got the engine out of the car the remaining ancillaries and intake manifolds etc were removed from the top of the engine, leaving us with what is known as a long block.  It was pretty dirty with oil residue from various leaks over time and a nice coating of Castle Coomb grass! for good measure.

We borrowed an engine crane and loaded the engine into the car, taking it over to Archer Motorsport Services in Hertfordshire.  With some much appreciated help we were able to  dismantle the engine in just under three hours.   The aim was to identify the root cause of the failure, determine if the engine is even rebuild-able or just scrap and form a plan on what to do next.  

Working on cylinders 1-3 first the cam covers and camshaft assembly came out pretty easily.  Next the cylinder head bolts are removed and binned.  These are single use so have to be replaced regardless. 

Inlet and Exhaust camshafts above connected by timing chain.

Pistons exposed - some carbon build up as expected

Cylinders 1-3 pretty clean and unmarked

The valves and pistons on this side of the engine looked pretty good.   Also there is no sign of bore scoring in the cylinders and only light carbon build up on the pistons. 

Moving to the sump we found evidence of a destroyed bearing shell. A lot of fine particles in the oil residue and some larger pieces of metal on the magnetic oil pickup - which isn’t good.  

On the cylinder 4-6 side, again the valves and camshafts were the same as 1-3, but removing the cylinder head we could immediately see the piston no.6 was loose with no big end bearing left.  This was the cause of the knocking when the engine ran.  

Crankcase split exposing the crankshaft box and pistons 4-6

The lack of a bearing shell has caused the conrod to damage the crankshaft surface. This is beyond the amount that can be ground so its scrap.  

Crankshaft removed - spot the damage!

No.6 con-rod damaged the crankshaft surface after the bearing shell disintegrated

It has also caused some scoring of the piston in the cylinder bore as there was too much play going up and down in the cylinder.  

Cylinders 4 (least) to 6 (most) marked/scored

Cylinder 6 is renowned for oil starvation issues in these engines.  It is the furthest from the oil pump.  This cylinder was showing low compression when we tested the engine a year ago.

It’s a marginal call as to whether to rebuild the engine or replace it with a used engine.  With a used engine likely to have at least 70-80,000 miles there are two considerations.

  • The engine will be starting ti suffer from wear such as our engine
  • There is a higher risk of a catastrophic problem since the engine history is likely to be unknown

We think therefore it is worthwhile trying to rebuild our engine.  To do this we need to source a good crankshaft first.   Then we can get cylinders 6 (and possibly 5) re-lined using either steel or Porsche Nikasil liners.  The head will need to be skimmed and the valves lapped, then it can be re-assembled with new consumables, bolts, gaskets and bearings.  Re-assembly should take a day.  

Through careful sourcing of the parts we need this should be only marginally more expensive than a used engine - but giving up the piece of mind and greater assurance over the condition of the engine at the end of the process.