Main Bearing Replacement Without Removing Engine - Best approach?

As the incidence of failed upper #1 mains increases, more shops are coming up with solutions for replacement that don't require a full engine out and total disassembly.
This got me thinking about the process by which they're doing this, and makes me keen to give it a try myself on my 100k mile E90.

I can only see two viable methods of doing it. The first would be to remove the transmission and flywheel, de-tension the timing chains and remove the vanos adjusters, then drop the bedplate and crank together, which allows full access to upper and lower mains. Given the work required to do this, it seems like you'd not be gaining much (if anything) in terms of hours of labour and that dropping the engine would probably be an easier approach.

The second approach, and one that interests me most, is simply dropping the bedplate and 'rolling in' the upper mains without removing the crank. This is commonly done on engines with main caps, but not so much on bed plate motors, at least that I've seen. Theoretically though, I can't see why it isn't possible.

I can't find any documented in-car main replacements online, so I'm also keen to do a video or forum post on this (if it can be done) that others can follow as this issue continues to become a more discussed topic.

Keen to hear people's thoughts on this and from anyone who has attempted it themselves.

Doing it in frame, is asking for catastrophe. Don’t believe anyone who says it is possible. It’s likely to turn your s65 into a paper weight or coffee table.

charliev68 wrote

Doing it in frame, is asking for catastrophe. Don’t believe anyone who says it is possible. It’s likely to turn your s65 into a paper weight or coffee table.

This is a pessimistic attitude, I think it can certainly be done properly if you take your time and are careful when doing it. There is one specific shop in Sydney, Australia that does it routinely.

Technically, there is nothing overly complex about it. Once you arrive at the point where the sump and oil pickup/pump are removed, you simply drop the bedplate which gives you access to the lower shells straight up. Rolling in the uppers is the challenging part, but in theory it should be no different to doing it on an engine with main caps.

The bedplate is sealed to the block by a loctite sealant. That means you have to clean the old stuff out of the grooves. You are also going to want to measure the main journals and inspect the journals for cracks.

Brandoch wrote

The bedplate is sealed to the block by a loctite sealant. That means you have to clean the old stuff out of the grooves. You are also going to want to measure the main journals and inspect the journals for cracks.

Cleaning out the sealant shouldn't be a worry, upside down or not.

Measuring the journals is the one thing that this method doesn't allow for, but if you replace it with like for like colour coded mains from BMW, or go with the slightly extra clearance offerings from a company like King or ACL, I would think you're fairly safe..?

Cracks in the journals shouldn't occur unless it's already spun a main, in which case a new motor is needed anyway.

Obviously if you want to be M539 level thorough, an engine out and full disassembly is a must, but if replacing mains can be done with marginally extra work than doing the RB's, I'm keen to give it a shot.

charliev68 wrote

Doing it in frame, is asking for catastrophe. Don’t believe anyone who says it is possible. It’s likely to turn your s65 into a paper weight or coffee table.

+1

Calling deansbimmer

I'm aware that people will want to poo poo the idea of a main replacement in car as it's not considered the right way to do it. Yes, it's more thorough and precise if you go the whole hog and drop it all out.

However given that it's now common practice from some highly reputable shops, there is clearly a way it can be done safely, and that is what I'm keen to understand.

Not poo poo…it just physically won’t be right. You are arguing against gravity in regards to the bed plate torque specs. The whole weight of the crankshaft is inverted throwing the whole sequence off correct torque.

Here's what it comes down to: The risk of a naturally occurring main failure will be much less than the risk that results from attempting the job half-assedly in car.

They way those shops do it in car is going to be by the way the OP proposes- dropping the bed-plate and rolling in new upper shells between the crank and block. There's very little room for the action and risks damaging the bearings, crank, or block if not careful. It might be possible by certain highly experienced and meticulous techs but the majority of 'mekaniks' are not qualified for that additional degree of skill and precision.

It doesn't matter if the assembly is upside down or right side up when applying torque to fasteners.

deansbimmer wrote

Here's what it comes down to: The risk of a naturally occurring main failure will be much less than the risk that results from attempting the job half-assedly in car.

They way those shops do it in car is going to be by the way the OP proposes- dropping the bed-plate and rolling in new upper shells between the crank and block. There's very little room for the action and risks damaging the bearings, crank, or block if not careful. It might be possible by certain highly experienced and meticulous techs but the majority of 'mekaniks' are not qualified for that additional degree of skill and precision.

It doesn't matter if the assembly is upside down or right side up when applying torque to fasteners.

Thanks for the quick response and informative post as always

Upside down could increase the running torque until the surface touch. If this is the case then you’d have to add the running torque and preloading torque to ensure you get the full preloaded torque. This is typically done when assembling spacecraft; however, we have a max allowed running torque to determine whether you go or no go. I’m not familiar with what the expected running torque would be for an upside-down torquing configuration vs. a right-side up torquing configuration. It may be negligible and, therefore, have no impact on the preloading torque.

you have a higher risk of main failures after the replacements, than you do not worrying about them. lmao.

also we know you are talking about Brintech, just say their name man.

It’s so easy and fast to drop the engine out the bottom of the car. Why would any shop decide to do it in the car?

deansbimmer wrote

Here's what it comes down to: The risk of a naturally occurring main failure will be much less than the risk that results from attempting the job half-assedly in car.

They way those shops do it in car is going to be by the way the OP proposes- dropping the bed-plate and rolling in new upper shells between the crank and block. There's very little room for the action and risks damaging the bearings, crank, or block if not careful. It might be possible by certain highly experienced and meticulous techs but the majority of 'mekaniks' are not qualified for that additional degree of skill and precision.

It doesn't matter if the assembly is upside down or right side up when applying torque to fasteners.

Thanks for the honest response. Great to know that this is how said shops are doing it.

I appreciate the risks involved, but I'm optimistic that if done meticulously it could be successful.

charliev68 wrote

It’s so easy and fast to drop the engine out the bottom of the car. Why would any shop decide to do it in the car?

Because while it may be 'easy and fast' to drop the engine out of the car (tell me that while you're doing it ) , by dropping the bedplate and rolling in mains you'd add maybe 1-2 hours work at most.

If you do it the 'comprehensive' way you're then pulling the trans and flywheel, and dealing with the timing system to get the crank out of the block.

omgzirra_exe wrote

you have a higher risk of main failures after the replacements, than you do not worrying about them. lmao.

also we know you are talking about Brintech, just say their name man.

Given how bad most #1 upper mains that come out of disassembled engines are looking these days, I'd rather take my chances with replacement than wait for what seems to be the inevitable.

Yep, I was referring to Brintech, however they are not the only ones doing main replacements this way.

TassieBMW wrote

by dropping the bedplate and rolling in mains you'd add maybe 1-2 hours work at most.

1-2 hours for the extra work is wishful thinking. You forget there’s oil pumps and front/main seals to deal with. The rear main will never seal well afterwards if done with the trans in and not replaced.

deansbimmer wrote

1-2 hours for the extra work is wishful thinking. You forget there’s oil pumps and front/main seals to deal with. The rear main will never seal well afterwards if done with the trans in and not replaced.

True, it will be longer than that but still significantly less time than the alternative.

The oil pumps aren't a concern, but not replacing the seals is probably my least favourite part of doing it this way. I agree it is less than ideal to not replace them, but the guys who are using this method must be getting away with it...?

I suppose the alternative, which everyone seems to suggest is the best idea, is to leave it and just cross my fingers that it won't blow up. Having seen so many experience main failures not long after doing RB's though, I would only feel comfortable doing both at once, not one or the other individually.

What's the labor time delta on doing it this way compared to dropping the motor and doing it the "right" way?

Not taking the advice of one of the best S65 wizards in existence is crazy..

charliev68 wrote

It’s so easy and fast to drop the engine out the bottom of the car. Why would any shop decide to do it in the car?

literally or if you dont have a table you can pull the engine out the front in 3 hours

S65Hunter wrote

Not taking the advice of one of the best S65 wizards in existence is crazy..

I have an idea and I want people to tell me it's good...

I'm lucky that I'm within driving distance of Coulter and my M3 takes an annual trip there for some TLC.

greyspoke wrote

I have an idea and I want people to tell me it's good...

I'm lucky that I'm within driving distance of Coulter and my M3 takes an annual trip there for some TLC.

Yup, im in Dallas so its just about a 45min drive for me. They did my Vanos covers, great work over there.