Should i replace the main bearings at 70 000mls

[David WDT]

Hi guys,


My names is David and i am fresh Bmw M3 owner (taking delivery of mt car tomorrow).
Since i have no experience with this engine what would you recommend to do?

I have to do the RB (never replaced) should i replace the main bearings as well?

The estimate from a reputable shop is around 4000 euro for the job it will include ACL RB with OEM rod bolts and OEM main bearings.

At the same time i will do also valve cover gaskets, spark plugs, water pump and engine mounts.

My car is a 2012 model year non-competition with the DCT gearbox

The car has 112 000 KM or 69 600 MLS


Thank you for your help and time.


David

[VtecforV8]

Not sure, though M539 Restorations' [youtube] video from yesterday suggests that the main should be a preventative maintenance item for higher mileage cars. I think (but am not sure) that most people here have just done RBs, but curious to hear from others. Feels like it would be most efficient to do them all at once if it really is a necessary item.

[spammysammich]

Pulling mains requires resealing the front and rear main seals plus the bed pan and if memory serves me correctly involves the use of an injectable sealant/special tooling. Not all shops are equipped with this or have experience doing work. Which is why we generally do rod bearings first.

[NiBe]

I was expecting such post after I saw the M539 video from yesterday With all respect to M539 I personally don't think that main bearings need to be changed preventatively as RBs on S65 engine.

[David WDT]

We need to take in consideration the milage of the car featured in Sreten’s video.

At the time when the engine went boom the car had 140 000 mls twice as much as mine.

That’s why I’m asking this quite difficult question.

[NiBe]

Originally Posted by David WDT

We need to take in consideration the milage of the car featured in Sreten’s video.

At the time when the engine went boom the car had 140 000 mls twice as much as mine.

That’s why I’m asking this quite difficult question.

What I mean is that even on a 200 000 miles S65 I would not change main bearings preventatively.

Concept of Sreten's videos is that he buys a broken car and then fixes it while filming it. So for him changing main bearings = extra content for YT so why not, he will have new bearings and money from YT at the same time, that's a good deal. But otherwise I don't see a reason why to do it preventatively.

That's my personal opinion. Keen to hear other opinions from more experienced forum members.

[VtecforV8]

Seems like none of us is sure! Hopefully the serious mechanics chime in soon. Trust me; I'm in no hurry to have my engine opened up again. Feels like I already spend a lot every year on maintenance as it is!

[NiBe]

I also think (guess) that in the Sreten's case there was a warning before the carnage - crank seals leaking.

[Scharbag]

Originally Posted by VtecforV8

Not sure, though M539 Restorations' [youtube] video from yesterday suggests that the main should be a preventative maintenance item for higher mileage cars. I think (but am not sure) that most people here have just done RBs, but curious to hear from others. Feels like it would be most efficient to do them all at once if it really is a necessary item.

Love M539 guy for sure - but he is NOT a professional mechanic... Great doode, but man alive he has some "out there" ideas (and has no clue how HVAC works in a car...).

I am NOT a professional mechanic either - but my buddy Jim is - and he has been wrenching for 40+ years professionally. He had a race engine fail like M539s and it was the crank that broke first, that then pooched the main, then pooched the rod bearings. Given the state of dis-repair of that donor car, it may be the case that it was "rode hard" if you know what I mean...

Anyway, as for the mains, it is a HUGE job. Engine out (unless you are nuts) and a buuuuunch of special tools and parts. And, we all know that "when you are in there" will make the job even more expensive. Absolutely not worth the money to do the mains preventatively. The other main shells on M539's S65 engine looked fine for 140K miles. He is a bit of a princess when he talks about wear Again, love the guy - but it is an engine, things will not look perfect after 140K miles.

deansbimmer posted about what is involved in changing the mains here. Again, it is a HUGE job.

Cheers,

[NiBe]

Originally Posted by Scharbag

He is a bit of a princess when he talks about wear

True true

[Redd]

Originally Posted by Scharbag

deansbimmer posted about what is involved in changing the mains here. Again, it is a HUGE job.

Damn. I had intended to refresh all the bearings and seals - including the mains - at 170k kms. But not anymore after looking at this. Not because I can't afford the labor charges but because I doubt there's any mech here will go to the detail that is required to do a good job.

What about oil seals. Is it possible to do the oil seals without cracking open the block?

[Scharbag]

Originally Posted by Redd

Damn. I had intended to refresh all the bearings and seals - including the mains - at 170k kms. But not anymore after looking at this. Not because I can't afford the labor charges but because I doubt there's any mech here will go to the detail that is required to do a good job.

What about oil seals. Is it possible to do the oil seals without cracking open the block?

Bah. It is a BMW. It is designed to leak.

[spammysammich]

I seem to recall the front and rear main seals requiring injectable sealant but I would be happy to be wrong.

[amrazM]

Originally Posted by spammysammich

I seem to recall the front and rear main seals requiring injectable sealant but I would be happy to be wrong.

correct, it requres a sealing compound be applied on this type of bed plate engine.

[VtecforV8]

Woof; no thank you to any of that!

[rjsiciliano]

slightly off topic but still pertinent to the conversation. With the element of the main bearings being a potential problem, would it be wise to run a tune with an 8600 rpm raised limit? Alex at Alpine suggests against it and my guess is even if the rod bearings are done this raised limit could still put wear on the main bearings.

[MAE90M3]

Stupid question on my part, but as far as I can tell people are saying the main bearings should last the life of the engine. What does that really mean? Let's take my situation. My car has 130k miles on it. I plan to never sell this car. I drive about 5000 miles/yr. Let's say I live 40 more years and add 200k miles. Should I still expect the main bearings to be fine/not spin on a 330k mile engine? Or should I expect to do an engine rebuild some number of years/decades down the line to refresh everything including the main bearings?

[MP0W3RD]

Dude, you’re overthinking this big time.

Change your oil every 5000 miles and warm your car up properly.

Live and enjoy your life and don’t spend another second of thought on this non-issue.

[MaximusB]

Originally Posted by MAE90M3

Stupid question on my part, but as far as I can tell people are saying the main bearings should last the life of the engine. What does that really mean? Let's take my situation. My car has 130k miles on it. I plan to never sell this car. I drive about 5000 miles/yr. Let's say I live 40 more years and add 200k miles. Should I still expect the main bearings to be fine/not spin on a 330k mile engine? Or should I expect to do an engine rebuild some number of years/decades down the line to refresh everything including the main bearings?

In less than 40 years gas cars will be banned, climate change will melt the tires right off the car, and what if someone crash into you tomorrow? (knock on wood). Will there even be parts for this car in 10, 20 or 30 years?

My point is just enjoy the car for what it is. At end of the day it is just a car, no need to overthink on the what ifs. Cross that bridge on engine rebuilt if and when you get there.

[Redd]

Originally Posted by MAE90M3

Stupid question on my part, but as far as I can tell people are saying the main bearings should last the life of the engine. What does that really mean? Let's take my situation. My car has 130k miles on it. I plan to never sell this car. I drive about 5000 miles/yr. Let's say I live 40 more years and add 200k miles. Should I still expect the main bearings to be fine/not spin on a 330k mile engine? Or should I expect to do an engine rebuild some number of years/decades down the line to refresh everything including the main bearings?

I echo this. I don't think it's over thinking. I do a lot of preventive maintenance just so that I can enjoy the car without any fear. I drive the heck out of the car cos I trust it and know that any potential weak points that may ruin my enjoyment have been resolved before hand - eg. rod bearings, injectors, vanos covers etc.

But the way it's looking, mains are a lot of work that needs specific knowledge and tools. And there's many very high mileage cars running with factory mains. So I think I will skip it this round.