I've just managed to removed one head from my car and was expecting to see mangled valves and damaged pistons. However although there obviously has been contact all it appears to have done is dislodged 16 years worth of carbon deposits.

I know the only way to be sure is to do a leakdown test, but I don't have a compressor or a leakdown tester, and the left head is off the car now anyway. I'm really not sure now whether I should go ahead and purchase a pair of second hand heads.

In case you're wondering the reason the gasket is such a mess is because the air pump feed stuck after I undid it without me realising.

I'm tempted to buy a single head gasket and just try to put it back together, how foolish would that be?

http://www.928.org.uk/ukkid35/project/index

Pics 44 - 47 heads
Pics 48 - 51 pistons
Pic 53 oilway where tool disappeared
Pic 54 air pump line that stuck

The engine originally died at 4000rpm WOT, but I'm now wondering whether it slipped a few teeth and lost compression, and then the valve contact happened during one of my many attempts to restart the engine.

Look forward to hearing your advice, thanks

 

I see no evidence of piston to valve contact, so there is no need to replace the head. From what I've heard, even when there is piston to valve contact the head and pistons due to a cam belt breaking they usually are not damaged, all that is needed is to replace bent valves.

I suggest removing the other head and look for bent valves. Take them both to a machine shop for a refurbish (milling if needed and valve grind, new valve guides, valve spring tension check). If you just get another set of used heads you don't know the condition of the valves, springs and valve guides.

 

agreed there is no piston to valve collision there, however why dont you pull the head gasket off the head and tke a few more shots, and it looks like the car hasnt had the best treatment and could have used some coolant systme flushes abit more often

 

Oh, and before you put it back together. The head to block surfaces need to be totally clean for assembly. You need to be careful to vacuum out what crud there is already in the pistons and keep anything from the cleaning out of the pistons. Anything that falls in can potentially lodge between the piston and cylinder wall and cause scoring ... you don't want that.

While you're at it, I'd rub assembly oil in the cylinder boars that are exposed so there is some lubrication for the rings. However, there must be NO OIL on the top of the block when you lay down the head gasket.

Other "while you're in there" items, replace the cam chains and updating the oil pressure relief to the 944 turbo type, part numbers are:

Oil pressure check valve (2) 951.104.229.00
Oil Pressure Relief Spring (2) 928.104.129.00
Oil Pressure Relief Steel Ball (2) N.025.669.2

Clean out the thermostat housing, replace the thermostat if it hasn't been replaced in the past few years and check the gasket behind the thremostat (928 106 163 00), often that has never been changed and needs replacement.

The head bolts are torqued differently too. The bolts need to be very clean with just a dab of anti-seeze spread on them. You need to paint a line on the head of each bolt and watch how many degrees you crank after the initial setting of torque.



If you have to pull the oil pan to find the part that fell down, replace the rod bearings while you're down there. After this, you 928 will be good for another 200k miles from the engine.

 

Looks much better than I expected. Probably a good idea to take the heads both to a machine shop for a refurbish - maybe somebody in UK can suggest a good one.

Marton