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Re: Lighter pistons and oil problems, etc
Posted by BobS (more from BobS) on Sat, 7 May 2005 12:44:01
In Reply to: heat transfer implications (+), Dean, Fri, 6 May 2005 08:09:56
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Prime reasons for lighter pistons with higher rings are reduced emmisions from smaller dead space between top ring and top of the piston, and fuel efficency. The less weight to throw around the less work consumed.
The problem with lighter pistons is there is more deflection in the piston under load. This doesn't help the ring fit in the piston and bore, and the piston to bore clearance. Also the shorter piston is more subject to rocking in the cylinder. All of this causes more blowby.
Apparently Saab did not test this very well, management made decisions regardless of design considerations, or they have had continueing manufacturing issues. What you design and what you get out the door can be 2 different things.
Blowby primarily consists of water and other combustion gases, water in oil can lead directly to sludge. It would be nice to know if the oil squirters are the same size as in the 234 engine.
In light of the recent Nines article about the oil pump issues, it would not be a stretch to realize the squirters would end up short of oil for piston cooling. Hot pistons lead to sludge and stuck rings. The new pump design sure looks like it would be very subject to tolerance stackup problems and the resultant leakage. Any leakage at the pump would not only compromise oil flow and pressure, but also any leakage goes directly to heating the oil. It appears anyone with a 235 engine should take a close look at their oil pressure.
posted by 169.207.20...
Posts in this Thread:
- Piston comparison, BrianS, Thu, 5 May 2005 20:49:27
- Surprised no one has mentioned genuinesaab...., MI-Roger
, Sun, 8 May 2005 17:38:25 - Interesting to see as I just melted a 235R piston..., Andy E, Sun, 8 May 2005 16:28:32
- The B234 pistons were used in B234E, L and R, AdamB
, Sat, 7 May 2005 13:32:05 - heat transfer implications (+), Dean, Fri, 6 May 2005 08:09:56
- Re: Piston comparison, MTAERO
, Thu, 5 May 2005 22:45:12 - Pic 2, BrianS, Thu, 5 May 2005 20:52:23
- Pic 3, BrianS, Thu, 5 May 2005 20:51:13
- Re: Pic 3, Eric van Spelde, Fri, 6 May 2005 01:00:41
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