Main bearing count
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Posted by: matin ® 10/20/2005, 10:02:50 Author Profile Mail author Edit

We have a 6 piston 1 MW diesel engine at our facility as per general rule of thumb it has 7 main bearings.I need to know why is the count of main bearings is 1+ then then number of cylinders. What is the function of thrust bearing mounted on the crankshaft of engines.Does small engines have them or only big one has.

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Re: Main bearing count
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Posted by: swearingen ® 10/21/2005, 07:40:21 Author Profile Mail author Edit

The simple answer to your first question is that assuming that there is one bearing between each cylinder and one at each end, you'd always have 1 more bearing than cylinders in an in-line engine. With one cylinder, you've got a bearing on each side - 1 cyl, 2 brgs. With two cylinders, you've got one between the cylinders and one on each end - 2 cyl, 3 brgs, etc.

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Posted by: tooleng ® 10/20/2005, 16:23:03 Author Profile Mail author Edit

All straight six cylinder blocks have seven main bearings. As far as thrust bearings . It depends on the application. If you are trying to repair this engine stop what you are doing and call a engine professional.

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Posted by: Dan Timberlake ® 11/06/2005, 10:23:12 Author Profile Mail author Edit

"All straight six cylinder blocks have seven main bearings." Heavy duty and modern passenger cars use 7 mains. A rule of thumb I read once upon a time suggested 7 mains provides greater bending stiffness and strength at the expense of torsional stiffness. https://metalworking.com/DropBox/_2000_retired_files/crankshaft.jpg https://www.ucmr.com/galerii/imagepages/image-cap64.html Older passenger cars and trucks inline-6s used 4 mains fairly successfully. https://www.vanpeltsales.com/FH_web/FH_images/FH_six/flathead_49-51crankandcam.jpg At least one semi-modern passenger car six has attained near legendary status for reliabilty with 4 main bearings. https://www.slantsix.org/articles/stroking/crank_kit_l.jpg

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Posted by: randykimball ® 10/26/2005, 01:21:32 Author Profile Mail author Edit

It is not unusual to get questions from sincere members which leave us scratching our heads. A rare few of these members continue to come back with questions that cause one to wonder how they ever became responsible for engineering or machincal equipment. It can be very fustrating wishing you could tell them how wise it would be to simply go do something else and let someone with more skills and experience with their equipment take care of it. I wonder how often these people don't realize that many of the problems they are having with their equipment are being induced by their own lack of knowledge. For example: Not knowing why an engine has thrust bearings suggest strongly that they have never considered testing the end play in the crank of these engines that run hour after hour for months. Knowing why thrust bearing are present would be common knowledge to a mechanically oriented person. If an engine has severely loose thrust bearings all sorts of things can happen, not to mention it would be very tough on the rods and oil presure. Also just as frustrating is the fact that some of the same people come back month after month with questions that suggest although they are trying the best they can they simply continue not to understand that they need a trained professional mechanic. In my case, although I'm well trained in math, I use a professional accountant to do my taxes, I know I'd mess them up because there are so many fine details I don't understand and never will. I bet my accountant doesn't work on his car engine, because he knows he not mentally equiped. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Wed, Oct 26, 2005, 01:34:14

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