QuestionI've got a 2007 Saab 9-5 2.4 manual which suddenly presented with a pronounced rod knock after only 63K miles. I had just purchased the vehicle 5 months before and it ran perfectly, till now.
Dropped the pan and found it quite clean - checked the big end bearings and they looked just fine! Having been so certain of the presumptive diagnosis, I had already purchased the new bearings so I threw them in anyway and checked with plasti-gauge.
Exact noise persisted.
Pulled the valve cover off and created a makeshift oil containment dam and ran the engine while listening to every area of the valve train with a stethoscope - all sounded fine 'up top' - not a valve train noise.
Pulled plugs and inspected pistons with a borescope - looked perfect.
Cranking engine with NO plugs installed results in NO NOISE.
Installing 1 plug at a time and cranking yields no noise until we get to the left most cylinder. With just that plug installed we have the exact noise with just cranking the engine.
At this point, I'm leaning toward it being a bad wrist pin creating the noise. Considered options for replacement include pulling the head and pan and yanking the piston out from the top, or pulling the engine & transmission and breaking them apart to allow removal of the crank to pull the piston out the bottom.
Questions for you:
1. Do you agree the noise is probably wrist pin ?
2. If you agree its the wrist pin, would you pull out the top by removing the head or out the bottom after removing the engine / trans?
3. My thought would be to replace piston / wristpin / rod together - would you agree or just do the pin?
4. With the recent bankruptcy of Saab, parts availability may be a big issue - your thoughts on aftermarket availability and on used parts? #seems like a lot of labor to find out if the used part is a good one#.
5. What's your estimate on labor hours, and or overall price?
This is a great car in immaculate condition but sounds terrible! Still driving it but only short distances till I decide what direction to take or to just run it till it stops or I can't stand it any longer.
AnswerBill:
What a pleasure to read your diagnosis and questions. Sometimes SAABS cause 'sobs', but with the pluck and skills you've demonstrated, that should be no problem.
Specifically, since you've eliminated #very analytically# everything BUT the wrist pin, I conclude that as you did, that THAT it must be it.
I would remove the head and pull out the piston from above..much less work than an engine pull in general. [However, as my profile states, my personal hands on experience is limited to the older 900s only..so its your judgement call]
Of the wrist pin assembly, the pin itself is made of a hardened steel, whereas the piston is aluminum and the con rod has a 'soft' bearing metal insert. In all likelihood, therefore, the problem is either with the piston or bearing insert, not the pin itself.
Aftermarket parts should be available for a long time to come. Good sources I know of are: <www.rockauto.com>, or <www.fcpgroton.com>. I would consider used internal engine parts ONLY as a last resort!
Labor Hours: In my day I could do it is 4-5 hours...if you have a trusted shop do it, figure $700-$800 complete.
PLEASE do not drive it anymore before the fix...the piston could break anytime and make the entire engine into spaghetti!!
