Awesome. Thanks guys. Brian
On 1/27/07, Tom Hargrave <[EMAIL PROTECTED]> wrote:
The life span difference between an engine used for highway miles & an engine used for in town miles has nothing to do with RPM variation. The issue is that 80% of an engine's cylinder wall wear occurs during the first 15 minutes of operation and if you think about in city driving, you'll realize that most of us reach our destinations in 15 minutes or less. During this time, the engine has not reached operating temperature & some of the fuel dilutes the oil that is protecting the cylinder walls. This causes excessive wear. Some call this "gasoline wash down" because it's much worse with a gasoline engine than a diesel engine. Gasoline wash down was a very serious problem before fuel injection & this one issue was the real reason most American V-8's would not go 100,000 miles. American car manufactures tuned their cars on the rich side for performance and drive ability & the result was even more gasoline wash down. Even in the 70's, you could put an American "land cruiser" on the road for 200,000 or 300,000 miles. Most don't realize that even at operating temperature, you have a thin layer of oil on your cylinder walls. And without this thin layer of oil, your top ring would be scraping directly on your cylinder walls. The oil layer is refreshed every time the piston makes a full stroke. The oil does not burn off because the heat it's exposed to is drawn off into the cylinder walls. Engine break-in is accomplished by honing a cross hatch pattern into the cylinder walls. The cross hatch pattern acts like sand paper against the outside edge of the rings, truing them to the contours of the cylinder walls. And just like sand paper, the surface wears smooth as the rings are honed. Some will tell you not to use synthetic oil during break-in but this is a bunch of BS. Synthetic lubricates no better than quality Dino oil. The real benefit of synthetic oil is its stability which allows for less frequent oil changes. It is true that you need to keep load & RPM down during engine break-in. The rings have a lot of blow by & you don't want to create enough pressure in the crank case to blow a seal. Also, the bearings need to break in. They don't really wear in together. The journals are very hard compared to the bearings and it's more like any high spots are worn off the bearing surfaces. Thanks, Tom Hargrave www.kegkits.com 256-656-1924 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Curt Raymond Sent: Saturday, January 27, 2007 9:51 AM To: Diesel List Subject: Re: [MBZ] RPM consistency and longevity of engine As we've heard in the past BZZZZTTT WRONG! Haven't heard that in awhile though... So actually whats happening when you're varying RPM on an engine thats breaking in is that you're trying to INCREASE wear. Specifically you want the rings to seat, that happens by wearing away a bit of the rings and a bit of the cylinder wall (these are very small bits btw) so they fit closer together. On big diesel engines, like tractors, problems have been reported where the engine is baby'd during the break in period and the rings never seat allowing excessive oil consumption. You'll find ESPECIALLY on diesel engines that stationary power units which sit and run at a constant speed will have less to much less wear than a comparable engine used at varying RPM ranges. The smoothest way to change RPM is to not change... -Curt Date: Fri, 26 Jan 2007 22:06:18 -0600 From: "Zoltan Finks" <[EMAIL PROTECTED]> Subject: [MBZ] RPM consistency and longevity of engine To: mercedes@okiebenz.com Message-ID: <[EMAIL PROTECTED]> Content-Type: text/plain; charset=ISO-8859-1; format=flowed The question I have thought about for some time is this: When someone puts a lot of highway miles on a car, their engine spends many hours at approximately the same RPM. Could this cause any inordinate wear (as opposed to varying engine speed more, gradually and smoothly of course)? I know that when a newly-rebuilt engine is being broken in, they tell you to vary your RPMs and not to cruise at the same speed on the highway for an extended period. Any correleation? An benefit from driving at varying speeds over the days of your weekly commute for example? (Not that I'd have the dedication to do it). I read that article on million-mile cars and one of the interviewees mentioned that he likes to keep his speed down on the freeway. He had read something about freight train research that revealed something like 80% of engine wear ocurred in the top 20% of the engine's RPM range. This is what reminded me of the question that I occasionally think about. Brian 83 240D 84 Saab 900 00 Honda CRV 68 Dodge Coronet 500 --------------------------------- Finding fabulous fares is fun. Let Yahoo! 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