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UPDATED - Engine Swap - 335D Crankshaft Main Bearings and Bolts Question
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05-01-2018, 09:34 PM | #1 |
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UPDATED - Engine Swap - 335D Crankshaft Main Bearings and Bolts Question
EDIT - See post #22 for details of the engine swap.
Hello All, I'm a first time poster on this forum and have a serious question to ask: Are the crankshaft main bearing bolts one-time use? I ask because my mechanic and I recently noticed what can be described as a clunk when the engine was revved to about 3k rpm. We suspected the issue would be the connecting rod bearings, so we dropped the oil pan to replace them. What we found was that all the bearings had extremely minimal wear and that there was no way the sound was coming from the connecting rod bearings. After consulting with a few other tech's, we now suspect it might be the main bearings on the crankshaft. Before taking taking these apart, I wanted to know if the bolts that hold these bearings on are one-time use. If they are, then I want to order the bolts at the same time as the bearings. Any and all help would be greatly appreciated! Last edited by apexit4; 06-07-2018 at 10:12 AM.. |
05-02-2018, 01:20 PM | #2 |
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I did a little more digging around and called a few parts departments to see if I could get a good answer. From the responses I received, I was told that it "appears" that these bolts are not one-time use (also known as "stretch bolts"). Stretch bolts, at least in BMW's, tend to be made of aluminum and are marked as "ASA" in the parts catalog. The ASA note was not present when these bolts were looked up so it appears that they can be re-used.
Although my research points to the conclusion these bolts can be re-used, I havent found anything completely definitive on the topic. Hopefully this will help someone in the future. |
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montr157.00 |
05-08-2018, 10:35 AM | #3 |
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That would be the first time I heard that the main bearings of the M57T2 fail. Have you done the "easy stuff" like engine mounts already?
Anyway, the bolts do need to be replaced. Basically, any bolt that is tightened to a specific torque first and then rotated to a specific angle needs replacement. See attached documents. |
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05-08-2018, 07:13 PM | #6 |
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So kinda like a diesel sound?
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05-08-2018, 07:14 PM | #7 |
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Yea? What makes the knocking noise?
A failed rod bearing makes noise because the rod is going up and down and there is too much clearance between the rod bearing and crank/ Rod. The main bearings don’t knock. You’ll see a drop in oil pressure but you won’t hear a knock like you do with a rod or piston pin issue. |
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05-09-2018, 10:22 PM | #8 | |
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05-09-2018, 10:36 PM | #9 |
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With regards to the issue at hand, turns out the noise is the front main crankshaft bearing. The sound the car was making sounded like a connecting rod bearing was quite worn or spun. So we took the oil pan off to inspect the connecting rod bearings and.......they looked good as new. So the next step was to inspect the main bearings and that's where we found the issue. It looks like the previous owner might have ran the engine low on oil and spun the main bearing. They tried to remedy the issue by replacing all the connecting rod bearings and fitting what we think is an oversized main bearing to silence the issue and get rid of the car. Unfortunately the rod knock could only be heard when the engine was revved past 2.5k rpm so I never heard it when I bought the car. According to my mechanic they did such a shitty job of fixing the issue that the noise went away for a few thousand miles before coming back.
So, now I'm faced with the dilemma of how to fix the issue. We are having a BMW engine guy come and inspect the crankshaft for any scoring before proceeding. There are four options at this point: 1) if the crankshaft isn't badly damaged we might be able to carefully polish out the imperfections and fit new bearing and end caps. This will be tough to do with the engine still in the car. 2) if the crankshaft is damaged, it will need to be removed. I've been told that to do that the engine has to come out 3) buy a new engine and do a swap. I've already been on Copart looking for donor vehicles. My mechanic can source me a warranties engine for a bit under 4K and there are only two available in the US 4) slap on some oversized bearings, sell it to Carmax and let them deal with the issue I'm really hoping option 1 works out as I love the car. If it wasn't a true M Sport and all the maintenance I did on the top end of the engine this past year, I'd get another 335 and start over. |
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05-10-2018, 06:33 AM | #11 |
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Once you replace that, you noise will likely be present. You likely have oil starvation/ clearance issues in other areas of the engine now. Main bearing failures do not make noise. They cause noise due to the loss of oil pressure elsewhere in the engine.
If one main bearing looks like that, the rest of the bearings should be inspected. The mains are the first to receive oil, anything past that main could be damaged. I hope you decide to fix or replace the engine and not just dump it off to carmax. |
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05-10-2018, 02:23 PM | #12 |
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If the bearing didn't spin in the main bore, pull the motor, send the crank off to be polished or ground .5mm undersize and get new bearings from Idparts for $100. They have both std and .5mm. I worked with them closely to find the correct PN Mahle and Kolbenschmidt bearings for m57s. You'll also need to replace the rod bolts, main bolts, rear main, front main, timing cover gasket, and I'd also suggest the oil pump at the same time. These motors aren't that bad $$ wise at all to rebuild now that good quality aftermarket parts have been sourced.
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05-10-2018, 06:15 PM | #13 | |
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05-10-2018, 06:20 PM | #14 | |
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05-10-2018, 06:54 PM | #16 | |
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05-10-2018, 07:40 PM | #17 | |
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05-10-2018, 10:31 PM | #18 | |
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The outer tabs on the first bearing from the front (shown in the photos in my previous post) are missing, which I assume indicates a spun bearing (not to mention the scoring on bearing itself). |
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05-10-2018, 10:49 PM | #19 |
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Well crap, it spun. That block is done. Get a junkyard engine and swap it in with new gaskets. Only way to maybe fix that block is to laser weld the upper main saddle, new main cap, and line bore/hone. That's an easy $1k+ right there.
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05-10-2018, 11:02 PM | #20 | |
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How likely is laser welding to help? Sanding/polishing the upper saddle wouldnt work? |
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05-11-2018, 08:21 AM | #21 | |
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You can't just sand or polish the saddle unfortunately. The issue in now the main bearing bore diameter is larger than spec because the shells spun and machined it out. The bearing bore needs to be extremely precise because the main bearing shells are actually lightly crushed when you torque the main cap on. That crush is what keeps them from spinning, the tabs are for alignment only during assembly. Laser welding would actually build the material back up on the block so it can be remachined to the proper diameter. But if a main cap can't be purchased, then it just got much harder. The normal process is just to grind the mating surface of the main cap down a few thousandths to reduce the bore diameter, but with the ridges on the bmw caps you can't do that. |
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06-07-2018, 10:18 AM | #22 |
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After speaking with Megs335 and my mechanic friend, I decided to do an engine swap on my M-sport as its the only way to guarantee things wont break down the line in the current engine.
I've already ordered a new engine and started tear down on my car. If anyone is interested, I can post updates on this thread. |
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bearings, bolts, crankshaft, wear |
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