Author Topic: engine bearings  (Read 4179 times)

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blykins

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Re: engine bearings
« Reply #30 on: April 10, 2021, 09:59:45 AM »
I can agree on the decline in quality control at F-M - - really irks me since that was my product line a decade or so ago and back then we took a lot of pride in those parts.

Without going into a full dissertation on bearing flow dynamics, I will say that I do not like full groove bearings at all.  You are better off with a half groove design.  The three quarter is a really good configuration as long as clearances come in well.
There’s the rub for us guys that don’t know all the lines well.
FM (Speed Pro) is down in quality but they have the better (qualified) design.
From my brothers dealings with Mahle I know they are picky about quality, so Clevite is appealing but they are full groove. Obviously there is a difference of opinion on the full groove vs 3/4 or 1/2.
I’m going to venture a guess that for regular hp builds (say 500) it doesn’t matter which quality bearing you choose as long as your target numbers are good. For higher hp builds the 3/4 half groove is a bigger deal.

I've used the full groove coated bearings on a lot higher horsepower engines than 500.   When you adjust the clearances to match, I personally see no issue with them. 
Brent Lykins
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Barry_R

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Re: engine bearings
« Reply #31 on: April 10, 2021, 07:46:51 PM »
The line I use is "good enough is good enough".  As long as your parts meet the needs of your application it won't matter if you have design headroom of 5% or 50%.  Means that those full groove bearings might well get the job done, but I can promise you that they are not the best design for any performance application.  Like cross drilled cranks - they work right up to the point where they don't, and then its often hard to decide where the issues lie if and when they do show up.  Some high end racing stuff is running a partial upper groove these days - under 180 - groove does not even extend to the parting line.

Think of oiling like electricity.  Oil under pressure follows the path of least resistance.  When you feed oil into the unloaded side of the bearing it does not "like" to go into the highly loaded lower shell surface.  It pursues lower resistance paths until they become saturated, where the flow area becomes a restriction that limits relief.  It bleeds out at the parting line chamfer, at the eccentricity area approaching the parting line, and around the periphery of the shell depending on clearances.  A full groove provides an additional circumference that doubles all these bleed areas into the unloaded area.  Not a full loss since its not into the sump - but a reduction none the less.  Coupled with a +/- 10-20% reduction in load bearing area for that lower shell.