so just completed this. all cylinders reading between 90 - 100 psi (throttle closed) apart from number 4 which was way down at 60 psi. when i pulled the plugs number 4 was wet, so suspected that to be the dodgy one. i poured some oil in and tested again and it was up to 100 psi so suspect piston ring failure. checking the car's file i have receipts for new pistons and barrels dated 1988 so should be plenty of life left in them. i didn't drive the car after discovering a problem, so hopefully not too much damage / wear has occurred.
so what could have caused it? don't think it's an oil supply problem as had all lines cleaned and uprated pump installed when it was rebuilt in 2004. some of you who've followed my car will know its been over-fueling so i wonder if unburnt fuel washing over the pistons might be the cause? any thoughts on that? i have been meaning to get to bob watson's to have it sorted for ages, could have been an expensive mistake not to get down there sooner.
so it's engine out over the winter and some 'whilst i'm there' detailing of the throttle bodies, engine bay, ignition etc.
must thank Paulyb for the loan of the compression tester - cheers Paul and omg your lightweight RS is to die for - sounded fantastic too
Last edited by willbrown on Sat Sep 13, 2008 2:02 pm, edited 1 time in total.
Will - no problem with lending you the kit. Thanks for the compliment on the car!
Does sound like the oil control ring on no. 4 is the most likely culprit, but might be worth getting a leakdown test before taking things apart?
Could be bore wash if it has been running really rich for a long time, otherwise what work was done when the engine re-build was carried out? Who did the work?
Does the car smoke much / burn much oil?
Thanks, Paul. Leakdown test a good idea and logical next step. One thing that is bugging me is that the clacking noise i've been hearing didn't occur when i turned the car over to do the compression test so wonder if a broken valve might be an issue? Car doesn't really smoke or burn much oil. Used to get black smoke on application of full throttle in first instance and then no smoke after that. Didn't ever see blue smoke.
Nick Moss (Early 911) did a full re-build in 2004 which included pretty much everything but pistons and barrells as they were deemed to be fine. See breakdown below:
1972 Porsche 911 2.4 S engine #6320051 re-build
FAULT 1:
Broken tappet adjuster on #6 cylinder
INSPECTION:
• Take off the right side rocker covers and removed the no. 6 inlet rocker. The adjuster was broken and the missing part was sitting in the lower cover, so no parts were missing
• On further inspection it was noticed that the surface that bears on the camshaft was worn badly. The camshaft was also badly worn
• On removing the right cam shaft it became evident that the problem was not confined to #6 inlet valve, all the inlet lobes and rockers had the same damage; matching wear on the rockers and lobes. Because of this it was wise to inspect the left side and that also showed similar damage
SOLUTION:
• Remove motor
• Remove both camshafts & rockers
• Regrind cam
• Install new rockers
• Install new rocker shafts
• Install new adjustment screw
• Install new lock nut
FAULT 2:
Small deposits of solid black material in oil lines
INSPECTION:
• The black material turns out to be the sealer used between the crankcase halves. The crankshaft itself was on the point of becoming a serious problem
• The last time the engine was rebuilt (1987) the crank was reground to -25 thou. The main bearing shells are located in the case by a small depression and on one bearing the edge of this depression had broken off and the shell had moved sideways into the crank web
• In a short period of time this would have meant that the crank would have been unsupported on one side, leading to a possible catastrophic failure
• The case needed repairing to allow the shell to locate properly and the crank needed regrinding as the small particles of the offending shell had got into the other shells, scouring the crank.
SOLUTION:
• Regrind crankshaft to +.50mm and install
• Crankshaft crack tested and main and big ends reground to +.50 mm
• Bores, pistons & rings all within spec
• Flywheel within spec and plenty of material remains on clutch plate
• Remove all oilway plugs and have professionally cleared
• Strip oil tank and lines, clean and replace
• Install new main bearings, big end bearing, gaskets, clutch and flywheel bolts, conrod nuts and bolts
FAULT 3:
Defective oil scavenging pump and oil pressure pump
INSPECTION:
• Oil pump gears and housing badly scored and excessive clearance between gears
SOLUTION:
• New OEM oil scavenging pump and oil pressure pump
FINAL ASSEMBLY:
• Check all components against factory specs
• Rebuild motor with new gaskets and parts as outlined above
• Replace motor, change oil and filter
• Road test
Clacking noise does sound strange. Assuming you've had the rocker covers off and checked all seems well there?
Does the noise change with revs?
The compression test certainly points to the rings rather than valves. Otherwise I had a mate who had a strange cluncking / clacking noise and found a few small bits of metal sitting on the top of the piston, and the bowl of the compression chamber was pitted. He assumed it would be a disintegrated valve seat or similar. Turned out a small screw holding an air filter backplate had come loose and sucked into the trumpet. We removed, cleaned everything up, re-lapped the valve seats, re-assembled and all was well
yup - had rocker covers off and everything seemed fine. although this is to the untrained eye...noise doesn't change with revs as far as i can tell, but difficult as anything above 4,000RPM is so loud that it drowns clacking noise out. not sure there's a lot more i can do to self-diagnose. it's now proabably at the stage where it needs a specialist to look at it.
if it helps the clacking noise started off as a sqweeking noise. at first i thought it was coming from a muffler skirt i just had fitted as it was exactly that metal on metal kind of noise. odd. i will check to see if there's anyway anything got into the trumpet.
James, thanks. I did wonder that. I did consider taking them off in France, but with no axle stands access looked v tricky. I will take covers off this weekend and have a look.
Sorry to hear of the mechanical probs Will. Hope it's not something too serious, although the piston ring theory must be a main suspect...
As suggested above, ditto leakdown test and checking inside the timing chain covers.
Rather selfishly, I was kinda looking forward to a few winter blasts with the targa in my mirrors, so fingers crossed that you are able to sort the problem fairly quickly
BTW, give me a shout if you want a hand dropping the engine.
Hi Will sorry to here of your wow's, you will need to remove the rear tin work, I think that this is better done with the exhaust removed, then you can just remove the chain cover. If you jack the rear of the car up it will limit the amount of oil that falls out. Also the cover will be tight you can prise the cover off using screw driver between the crankcase and the side of the cover do not be tempted to force a screwdriver between the mating faces. Good luck.
John
1970 2.2E Coupe.
2004 996 GT3 mkII
2015 Skoda Octavia VRS TSI DSG.
2021 Toyota GR Yaris Circuit Pack
So whilst you lot were blasting round the back roads of Wales (looks like the weather's good too )....I was getting to grips with getting the chain housing covers off. Know where I'd rather have been
Anyway, here's the evidence (sorry for poor quality images, but not much room to get the camera in a good position). Again to the untrained eye, it looks OK to me, but then I don't really know what I'm looking for. Chain seemed nice and tight and guides + tensioner look OK. You'll notice that it has the pressure-fed tensioner upgrade.
and omg your lightweight RS is to die for - sounded fantastic too 
