w126 overboost whining? - PeachParts Mercedes-Benz Forum

lowriderdog37 · #1 04-14-2008, 01:39 AM

I am getting a real gut-wrenching whining sound coming from under the hood of my '86 300SDL. It seems to be when to turbo gets to full boost. What's the possibility that that sound is the overboost releasing pressure?

I am going to try and rig up the boost gauge from my '85 tomorrow and see what it says.

I rebuilt the turbo about 6 weeks ago (the sound started yesterday), but never messed with the wastegate, because it couldn't really be opened. The car has been breaking piece by piece since I bought it, so I wouldn't be surprised if it was exactly that.

PatricdeBoer · #2 04-14-2008, 01:46 AM

Loose manifold or a bad gasket perchance? I got a pretty bad squeal from my 300sd when the nuts that hold the manifolds on got loose.

sixto · #3 04-14-2008, 01:58 AM

I second something less than an airtight seal between the turbo and the intake manifold.

"I rebuilt the turbo" makes me nervous. The rotating assembly has to be precisely balanced because it spins something like 30-50K rpm at full tilt. If you moved the turbine wheel relative to the compressor wheel, it's possible the imbalance is causing one of the wheels, likely the compressor wheel, to scrape the compressor housing. Pull the crossover pipe and make sure there aren't aluminum shards getting to the engine. Pull the turbo air inlet hose and check that the turbine blades aren't shinier or sharper than you left them.

Sixto
87 300D

#4 04-14-2008, 02:40 AM

Quote:

Originally Posted by sixto

"I rebuilt the turbo" makes me nervous. The rotating assembly has to be precisely balanced because it spins something like 30-50K rpm at full tilt. If you moved the turbine wheel relative to the compressor wheel, it's possible the imbalance is causing one of the wheels, likely the compressor wheel, to scrape the compressor housing.

Two problems.

1, You are about 100,000rpm off.
2, The compressor wheel and turbine/shaft are balanced independently, you can put them on at any position without causing imbalance. If they needed to be put on at a specific orientation there would be a key on the shaft to align them.

Brian Carlton · #5 04-14-2008, 08:51 AM

Quote:

Originally Posted by ForcedInduction

Two problems.

2, The compressor wheel and turbine/shaft are balanced independently, you can put them on at any position without causing imbalance. If they needed to be put on at a specific orientation there would be a key on the shaft to align them.

The nature of balancing any component and then assembling that component to another component results in unbalance. While these components may be balanced independently, it's a far better result to balance them as a unit.

I'm quite sure that any rebuilder would do exactly that.

BTW, there is no such term as "Imbalance".

#6 04-14-2008, 08:55 AM

Quote:

Originally Posted by Brian Carlton

BTW, there is no such term as "Imbalance".

imbalance |imˈbaləns|
noun
lack of proportion or relation between corresponding things : tension is generated by the imbalance of power | the condition is caused by a hormonal imbalance.

http://www.thefreedictionary.com/imbalance

Most turbine and compressor wheels are not match balanced, they are balanced independently.

Brian Carlton · #7 04-14-2008, 08:58 AM

Quote:

Originally Posted by ForcedInduction

imbalance |imˈbaləns|
noun
lack of proportion or relation between corresponding things : tension is generated by the imbalance of power | the condition is caused by a hormonal imbalance.

http://www.thefreedictionary.com/imbalance

Turbine and compressor wheels are not match balanced, they are balanced independently.

The "free dictionary" is hardly the source to quote for an engineering term. The proper term is unbalance.

Turbine and compressor wheels are properly balanced as an assembly. The result is significantly better than the alternative.

You can do what you wish with your own vehicle.

lowriderdog37 · #8 04-14-2008, 11:28 PM

OK, well I did a little searching for anything out of the ordinary today. I took the crossover tube off, It didn't have any metal in it, but did have a pretty good bit of oil. I took off all of the air filter system up to the turbo...nothing blocking, and the air filter is immaculate. The teeth of the turbo are in good shape, the turbine spins well, but does move up and down a little. There was oil in every section of the intake after the air sensor. I did rebuild the turbo about 2 months ago...a friend at work was saying the center of the housing was probably too far gone before I ever rebuilt it.

Anyways, I made a new gasket for the crossover tube, tightened it, as well as the intake manifold. Like damn near everything else on this car, the bolts weren't tightened enough, each needed about 1/8 of a turn. I didn't see oil anywhere around the gasket of the intake (however I know there was some in it). I did see some oil around the first o-ring above the turbo compressor, but I am worried about a larger problem with the turbo now. Any thoughts?

PS. I don't really know the how it should be said, but if our current President has taught us anything, it's that we can make up words as we see fit. That given, it all works fine for me, as long as we all know what we are talking about.

When I talked to the guy at 'The Turbo Shop' locally where I got my parts, he did say that the parts of the compressor were balanced separately, so it didn't matter how I put them together. Again, I don't know these things...so that's why I am asking, that's just what the guys said.

lowriderdog37 · #9 04-14-2008, 11:31 PM

Oh yeah, I also rigged up the boost gauge today. I am running right at 14 PSI max, and the whining sound comes at about 8-10 PSI, and just gets louder as the boost goes up.

lowriderdog37 · #10 04-15-2008, 10:32 AM

anything?

#11 04-15-2008, 10:43 AM

Check the exhaust manifold for cracks, the manifold gasket and turbo gasket for black streaks that would show exhaust leaking.

lowriderdog37 · #12 04-15-2008, 11:28 AM

OK, Exhaust and intake manifolds look clear of cracks. There is no sign of unusual oil or soot leakage. I do know that the gasket from the manifold at the turbo leaks...I can see exhaust coming out of it after getting off the freeway and opening the hood. I tightened the exhaust manifold bolts, the ones I could get to...they each took about 1/8th of a turn, much like everything else on this car.

Thinking about it now...I think all of the oil on the intake side is probably coming from the excessive blowby I am getting. I don't think there is anything to worry about there.

I am considering taking the air filter off the turbo and take it around the block. If it's coming from the turbo...it'll be a lot louder then right? I am somewhat worried about driving it at all without the air filter at all though. The big problem is that I can not replicate the sound in park or neutral. Anything else?