Quote:
Originally Posted by Bmwdoubles_
I saw a post from 2018 kinda of around this issue but not as detailed as that video. Those guys show pretty good proof the the number 1 upper bearing is taking a heavy load explaining that the S85 doesn’t see that due to a single chain as opposed to the S65’s double.
I appreciate what you and your team do. Can you elaborate a little more as to why this wouldn’t be the culprit or why this not a preventative maintenance item?
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The S85 doesn't see the same kind of loading on the front bearing because the v10 has a longer crankshaft with a whole extra main journal for support. It's much more stable than the V8's shorter crank with one fewer supportive journals. It has little to do with a simplex vs duplex chain design or the strain the valvetrain places on the forward journal (all OHV engines have some degree of this strain applied to the front journal).
I can't fault a shop for their hunger to capture business, but a $3800 main bearing job will be rife with longevity concerns. I wouldn't touch that with a ten foot pole as an educated customer. As a shop owner, I wouldn't touch it from a liability standpoint either. I bill $2899 for a full service S65 rod bearing job. To add the further tasks for mains strikes me as insanity for anything less than double that. (assuming, academically speaking, in-car work).
Attempting mains in car, especially on a higher mileage is not a recipe for success. The cleanliness alone for such precision tasks is not conducive to such an environment.
Parts are not the main expense. The labor time and skill are the main cost. If a shop charges only $40 per hour then the low cost job explains a lot, but that leads to questions of the shop's establishment and qualifications.
Regarding parts costs and entertaining the notion of a down and dirty an in-car main bearing service, with rod bearing and rod bolt upgrades, seals, gaskets, cam timing consumables, engine mounts, etc., there should be roughly 30 part lines totaling roughly $3100 in parts alone (list prices). Given the wide range in quotes, this confirms that there is broad interpretation into what constitutes a main bearing job at an advertised price point.
Mains are not going to be a likely concern until the engine is near or past 100k miles. Off the top of my head I've only seen a couple of main failures on engines below 100k that weren't the result of poor maintenance.
For these reasons I recommend mains to only be considered among an engine-out rebuild where everything can be properly disassembled, cleaned, measured, etc.