Hi all
My contribution here havent been the best - sorry.
I hope you might still want to join thread anyway.
Old story of my sprint that has been standing still a lot due to this issue (luckily inside my moms big garage).
Short recap:
first I had engine halt after overheating (bad temp switch?) - which gave a blown head gasket (& head slightly bent).
Head was replaced (used) with new head gasket.
Issue:
Running ok w good power but the issue is a (metallic) clacking noise (Audio files above).
Observations:
Frequency of noise is corresponding to half engine RPM (determined from PC audio analysis).
Clacking is not present when warm and running above 1500rpm - Reappearing 2-3sec after returning to idle.
Audible but vauge when accelerating modestly.
Noise gets vague if cyl 3 ignition coil is disconnected.
Seems to come mostly from center (around cyl #3) at top end - but can be heard from below.
Oil pressure 1.9-2.0bar hot idle acc to dash gauge - 3bar at 1500rpm+.
...
Actions done:
Oil system cleaning - rechanging oil a couple of times afterwards (and filter).
All 20 valve tappets were disassembled, cleaned and oiled - all are hard now.
Compression test showed its fairly equal on all cyls (within ~5% variation).
Latest:
I removed the sump (d*** what a bitch - not least because of A/C piping :-/ )
And then removed rod caps & bearings - carefully noting position and orientation.
BTW: (plastic) bushing for oil dipstick was damaged - seems hard to get a new one...
...
Theories:
a) Bent rod (cyl#3) -> piston slap
. I guess there would be bad compression on the relevant cyl?
b) loose pin (cyl#3) -> piston slap
. I can NOT feel any vertical play when pushing/pulling (any) rod from below...
. but I can tilt the piston(s) sideways ('quite a bit') perpendicular to pin axis...
(they move nicely along pin axis as they should)
. I can see a bit of scoring in cyl#3:
. but I would have expected this was a 'broader area' at lowest end of cyl?
c) Exhaust leak - eg from poorly assembled ex-manifold?
. I guess this wont change with temp? (nor dissappear with higher rpm?)
d) Bad (con) rod bearings?
. I dont think they look totally bad:
although there are signs of dirt in oil + one withoil starvation? + one with strange 'middle wear'.
. Maybe one of them (eg cyl#3) could be smashed from water in chamber?
but I forgot to check vertical play of pistons before removing all rod bearings :-/
e) Bad main (crank) bearings
. ? - I have not taken these off yet...
f) Loose valvepin (cyl#3)? (lazy?) -> knocked by tappets (cam)
. maybe - I did not disassemble the head before mounting :-/
. but I guess this would NOT change with RPM/oil pressure?
g) Bad sparkplug (cyl#3) - giving unwanted detonation
. I guess this would NOT change with RPM/oil pressure?
. I do have carbon build up in cyl#3 - quite a bit compared to when head was changed
h) bad injector? giving unwanted detonation
. this would also affect power, idle etc?
. I guess this would NOT change with RPM/oil pressure?
i) a tappet that can tilt slightly in 'housing'-> clacking on sidewall when hit by cam
. I could try to exhange tappets btw cylinders...
Comments / suggestions welcome:-)
Thx M