Rear Muffler

[Dave Rutkowski]

But I think Triflow came out with a "quiet" version in the last couple of years, so they may be better now. I think the best bet might be running a cat, straightpipes instead of the resonator, and then a stock muffler. That's the setup I have on my '81 635 and it sounds great - more snarl and less drone than the Triflow.

Dave Rutkowski
'90 535iM
'81 635CSi (euro)

[Martin in Bellevue]

Sounded like rod knock to me.

Am I hearing a lot of piston slap in that first audio clip?

[Martin in Bellevue]

After listening a couple times, I'm more concerned with lower bearing noise.

Maybe the valve cover could be pulled to check the rockers; they do fail above repeated 6k rpm use. The lower bearng noise might be accompanied by slow oil pressure light at cold startup, or possibly oil pressure light at idle.

Hmm.

Sounded like rod knock to me.

[Scott H]

Oil pumps can wear out as well...Mine was putting out 7psi at idle which, although is in spec, was too low to supply proper oil to the far reaches of the valvetrain.

I would say low oil pressure at start up and at idle is contributing to such things. Tim C is replacing his oil pump soon as well on a seasoned M30

Hmmm..

After listening a couple times, I'm more concerned with lower bearing noise.

Maybe the valve cover could be pulled to check the rockers; they do fail above repeated 6k rpm use. The lower bearng noise might be accompanied by slow oil pressure light at cold startup, or possibly oil pressure light at idle.

Hmm.

[Martin in Bellevue]

Oil pumps can wear out as well...Mine was putting out 7psi at idle which, although is in spec, was too low to supply proper oil to the far reaches of the valvetrain.

I would say low oil pressure at start up and at idle is contributing to such things. Tim C is replacing his oil pump soon as well on a seasoned M30

Hmmm..

Is the issue a weak oil pump, or crap clearances on the main bearings?

I guess that ominous noise could be just about anywhere in the bottom end.

[Martin in Bellevue]

Maybe an oil analysis from blackstone labs would help identify the type of lower end damage done here?
The bearings would leech off nickel. Fragments would indicate other issues, as well.

[Scott H]

The bearings would also give off lead as well. The synthetic oils have so many additives that it is hard to read those oil analysis anymore!! The last one from my M30 left me believing the whole engine was breaking apart!!!

When I took my engine apart I found a nice four-corner score on the cylinder walls and scuffed up pistons skirts. It was the result of piston slap and it will be interesting to see if I can keep the cylinders and pistons without boring the block out and replacing pistons as that is $$$$$.

Maybe an oil analysis from blackstone labs would help identify the type of lower end damage done here?
The bearings would leech off nickel. Fragments would indicate other issues, as well.

[Martin in Bellevue]

The bearings would also give off lead as well. The synthetic oils have so many additives that it is hard to read those oil analysis anymore!! The last one from my M30 left me believing the whole engine was breaking apart!!!

When I took my engine apart I found a nice four-corner score on the cylinder walls and scuffed up pistons skirts. It was the result of piston slap and it will be interesting to see if I can keep the cylinders and pistons without boring the block out and replacing pistons as that is $$$$$.

Yep, it may be the time to investigate cylinder wear & possibly step up to 3.7l pistons.

Are new lower bearings & caps available directly from the dealer?

[Scott H]

I have a crank set and a rod set for my rebuild...Unfortunately the dealer sells them individually and they add up FAST!

The caps have to come from germany and cause quite the wait.

Yep, it may be the time to investigate cylinder wear & possibly step up to 3.7l pistons.

Are new lower bearings & caps available directly from the dealer?

[Martin in Bellevue]

BMW really bends ya over the fender with those metric prices on motor parts.

I have a crank set and a rod set for my rebuild...Unfortunately the dealer sells them individually and they add up FAST!

The caps have to come from germany and cause quite the wait.