m52 rattle from 2k to 3.5k ish

Post Wed Feb 15, 2012 12:51 pm

There was also some sludge around the exhaust side stud on the same cap..

Post Tue Mar 20, 2012 3:32 pm

Cylinder 6 spun bearing.

That's the cause of the noise once I'd managed to get the sump off and check. Thankfully the crank looks good, still feels very smooth under my fingernail.

I'm comfortable working on engines, however I've never worked on the bottom end of an engine before and I want to make sure I know what I'm doing before hand.

I don't plan on taking the engine out of the car to remove the crank and spend loads on having all the bearings changed. As I would much rather look for another good low mileage engine if I have to pull this one out. In the meantime all the other rods are tight and it was only no 6 that was loose and ultimately where the noise was coming from.

I would like to identify the cause but I also need the car back on the road asap. I do remember some slight pinking which when I did the vanos seals I found that the sprockets weren't aligned properly. Some of the lining of the bearing has flaked off and looking carefully you can see fine crazing on the lining material.

I have vernier calipers but it's tight and difficult to get them on and more importantly off there. From the first quick check I got consistent readings of 44.7mm and also 44.74mm this is due to my lack of access and micrometer. Am I looking at +0.25mm bearings, are there any markings on the crank to identify the size?

Glad I finally found the cause, now I hope I can get this sorted.

Post Tue Mar 20, 2012 4:08 pm

at least youve found it now mate,
hopefully it wont be too much of an issue to get you sorted again

Post Tue Mar 20, 2012 4:22 pm

It's taken me long enough! lol

I think (I'm hoping) I'll be good to go with a polish and new bearings. I need some help though in making sure I don't make a mess of it.

Anyone know what the clearance should be?

Post Tue Mar 20, 2012 6:48 pm

Sounds like you got it just in time, big ends should be 45mm, unless its been ground before? is the rod or cap damaged? They usually get some abuse from a spun shell.
I would be fitting a new set of stretch bolts and checking out the others while the sumps off

Post Tue Mar 20, 2012 7:49 pm

Seems as though it may have been ground at some point to 44.75. I'll be ordering new bolts but wanted to make sure I got the right shells and that the clearance is good.
Gonna try and pick up a micrometer tomorrow and triple check the journal.

The rod and cap both have some scoring where it has spun. The tabs on the bearings are pressed flat and haven't gouged anything.

Any ideas as to how this has happened? localised det or something more sinister?
I've taken the pick up pipe off and will be ordering a new gasket for that too as I've read that these can suck in air and aerate the oil which in turn fries bearings.

I'm having trouble getting exact specs on re-assembly. So far I've got 5nm application torque, 20nm jointing torque and then a torque angle of 70 degrees.

Thanks for reading and all help is very gratefully appreciated

Post Tue Mar 20, 2012 8:04 pm

That sounds right for the tightening, there is a torques sticky in Tech Help

Usually the rod bolts stretch which is how they end up spinning, maybe they were not renewed? Plastigauge is good for checking clearances

Post Tue Mar 20, 2012 8:22 pm

Thanks Dan. Do you know what the clearances should be, or where I can find them?
No point me sticking a plastigauge in there if I have no idea what the tolerances are.

The previous owner told me about the headgsaket change but never mentioned anything about touching the bottom end, and I have no reason to think that he did touch it.

It is a linered block with the stud near the starter, could the dealer who fitted the block put a ground crank in???