wear pattern
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Joined: Nov 2001
Posts: 1,377
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From: Vancouver Island, B.C. Canada
2005 smart cabrio; 2008 Mercedes-Benz B 200
wear
Well it usually refers to the pattern of wear that is established by the piston rings on the cylinder walls.
Here's one example:
Connecting rods and pistons stretch during high rpm operation. So for example, if you break the car in exclusively at super-low rpm and rarely rev it up afterwards, a ridge will develop over time at the top of the cylinder. Then, if you do rev the car up a lot afterwards, the piston rings will be very heavily stressed as they cope with riding a little ways up the wear ridge, possibly leading to problems, be it unwillingness to rev freely at the top end, or in extreme cases, ring/engine failure. Wear ridges take a long time to develop however...
Other examples include the other effects the rings have on the cylinder walls, such as during the over-run (deceleration), where the rings are forced into a somewhat different position, which benefits the engine....
I think it's good to not only rev a car up a little during "break in" but also to vary speed, avoid constant speeds and also to use strong deceleration on engine compression. It's also important to wind the car up regularly. Most European engines thrive on high rpm operation. My ~300,000 km (~190,000 mile) 1989 Peugeot 405 regularly sees 5500 rpm (300 above peak power) and it loves the treatment! The engine (and drivetrain) have never been apart and I expect to get at least another 100,000 km (260,000 miles total) before it starts to get old.
Anyway, I'm tired, the beer's gone to my head and maybe someone else can explain "wear pattern" in technical terms and more concisely...
Here's one example:
Connecting rods and pistons stretch during high rpm operation. So for example, if you break the car in exclusively at super-low rpm and rarely rev it up afterwards, a ridge will develop over time at the top of the cylinder. Then, if you do rev the car up a lot afterwards, the piston rings will be very heavily stressed as they cope with riding a little ways up the wear ridge, possibly leading to problems, be it unwillingness to rev freely at the top end, or in extreme cases, ring/engine failure. Wear ridges take a long time to develop however...
Other examples include the other effects the rings have on the cylinder walls, such as during the over-run (deceleration), where the rings are forced into a somewhat different position, which benefits the engine....
I think it's good to not only rev a car up a little during "break in" but also to vary speed, avoid constant speeds and also to use strong deceleration on engine compression. It's also important to wind the car up regularly. Most European engines thrive on high rpm operation. My ~300,000 km (~190,000 mile) 1989 Peugeot 405 regularly sees 5500 rpm (300 above peak power) and it loves the treatment! The engine (and drivetrain) have never been apart and I expect to get at least another 100,000 km (260,000 miles total) before it starts to get old.
Anyway, I'm tired, the beer's gone to my head and maybe someone else can explain "wear pattern" in technical terms and more concisely...
