Wednesday, February 5, 2014


Above is the data on Ford/Saab V4 engine PISTONS, for your information.

I am in the process of rebuilding a 1500cc Saab V4 engine, one that has been screwed with by some "wrench" who quite obviously had no concept of engine reconditioning in general nor of Ford/Saab V4 engines in particular. As a result, I've found some really "interesting" stuff...
To start off with, the balance shaft bearings were so worn there was about an eighth of an inch of side-to-side movement on the balance shaft [belt] pulley.  OY! The wear was so bad the balance shaft and the pulley BOTH had to be replaced. I expected to find really BAD connecting rod bearings due to the loss of oil pressure caused by the insanely loose balance shaft bearings.  But no...they weren't  too bad and the crankshaft wasn't damaged.  Obviously, the crankshaft bearings had been recently changed, and maybe the crankshaft as well....hmmm   BUT...neither the camshaft nor the balance shaft bearings had been replaced.  
Next clue: the pistons had almost no carbon on their crowns [see top arrow, below] and behind the rings [see side arrows, below].  I THINK the "wrench" did an overhaul--more or less--but didn't think to change the camshaft or balance shaft bearings.
The number three piston, however, had broken piston rings--both in the oil groove and the middle groove. The other three pistons were fine. I DID find a bashed place on the crown of the same [No. 3] piston where it looked as if the piston had been dropped. 
I cleaned up the pistons, then put them one by one into the engine and checked the clearances of the new bearings, using Plastigage--All OK. I installed new rod bolts and new rings, oiled up the pistons thoroughly, and installed pistons 1,2 and 4--all went into place just fine. But installing the new rings on No. 3...the center and bottom rings were not free in the ring grooves. I measured the grooves and found that in the area of the "bash" the grooves were almost 0.030" too narrow!  OY! Apparently the dumbass "wrench" filed open the TOP groove after he'd dropped the piston onto his concrete floor and let it go at that. I refuse to jury-rig something as important as a piston---I replaced the piston.
God save us from the non-professionals......

A couple of other notes: ALWAYS replace the connecting rod bolts and nuts with NEW parts during an overhaul, as they are torqued to a "yield" [stretch] condition at the Ford/Saab spec of 25 foot/pounds. [This is also true of the FLYWHEEL BOLTS don't want to true the NEW rod bolts !] Always check the clearance of the new connecting rod bolts with Plastigage. Use the OLD rod bolts for checking, THEN replace the old bolts with new for final fit-up in the engine. [You only want to torque the new bolts to stretch condition ONCE!] Use Loctite compound on the rod nuts for extra security.

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