Noise at front of Engine 280SL

[Jeff]

Hi All,

Looking for some help determining the source of an intermittent noise I notice from the front of the engine bay on my M130 '69 280SL Pagoda. (Please see Youtube video link below.) The engine was professionally rebuilt 10 years and approx 6000 miles ago.

The sound only occurs at low revs, but not idle. Engine appears strong, is in tune, freely revs to 5500, sounds good and pulls well. Initially I though it was the fan blade glancing the radiator when the engine was a bit unsettled, just before returning to idle, as it sounds like light metal intermittently hitting aluminum. Then I thought it could be the fan pulley occasionally hitting the crankshart pulley.

I removed the alternator/fan belt and pulley to rule them and the water pump bearings out,  but the sound is still there.

Any suggestions on what this could be would be most appreciated.

https://youtu.be/tdj1XMP7LgU

Jeff

[mdsalemi]

Wow—that’s a severe and distinct enough sound that if anything was hitting anything else, there’d have to be some kind of wear marks visible.

If no evidence of any external markings from that…maybe something internal to accessories that are bolted on? Viscous fan clutch, alternator, water pump, even starter.

You may need one of those mechanic’s stethoscopes to try and pinpoint the sound to a specific location.

[Vander]

Is the fan hitting the top of the radiator? The sound sounds like it is happening off screen, there appears to be chipped paint on the top of the radiator at the 26-30 second mark.

[su8pack1]

Is the fan hitting the top of the radiator? The sound sounds like it is happening off screen, there appears to be chipped paint on the top of the radiator at the 26-30 second mark.

I agree, something is loose if that is the case.

[Jeff]

Today I removed all the  belt (power steering and Fan/alternator) and the sound was still there. I would think it would show somhow at higher revs, if the sound was internal to the engine. Best I can tell it sounds like its coming from somewhere near or in the air box or throttle valve, but no parts there I can think of that would generate that sound and no obvious wear signs visible around front of engine.

[Charles 230SL]

Jeff, try listening to it with the valve cover cap off. Just wondering if it could be occasional timing chain clatter

[Vander]

Record another video with the belts  and components off.

[Benz Dr.]

The popping sound is separate from the engine noise. I've seen a lean idle mixture cause a backfire in the intake manifold that sounds just like that.

The last strange internal engine sound I ran into turned out to be the helical drive gears. Remove your tack cable at the cylinder head and find a small wood screw that will fit into the end of the drive gear shaft. Lift it up and down. Anything more than a small amount of play is not good. If it will move 3 -4 mm you are headed for big trouble.

I had a 280SE coupe in last year and the drive gears lost all of their teeth so that the oil pump no longer turned. It broke three cam bearings and destroyed camshaft. Luckily, the engine was idling in traffic when this happened. Crank was OK because oil pressure goes to the cam last. 

[rwmastel]

You may need one of those mechanic’s stethoscopes to try and pinpoint the sound to a specific location.

Or just use a length of hose and point it at various things, listening for the noise.

[Cees Klumper]

This reminds me of Kees Schilperoort's 'Raden Maar' radio show from the late sixties.

To me Dan's idea of light backfiring due to lean mixture so far seems most likely. Try enriching the idle mixture a couple of clicks and see iif it makes a difference? Is the sound also there at higher rpms?

[mdsalemi]

Everybody is quite interested in this now, and please report back on when you find the solution.

Too often, a problem is reported a number of solutions are suggested and then we never hear from the original poster again!

At first, to me, it definitely sounded like a mechanical sound. But then Dr. Benz indicates it may be slight backfiring. These kind of assessments have us all very curious.

[Pawel66]

Sort of throwing ideas to be checked, sorry if completely irrelevant...

The screws holding the viscose cooling fan clutch may come very close to water pump screws (at least this is what i observed on my engine). You may check of there are no marks there.

[Benz Dr.]

Fan is not hitting the rad. That's just a bit of paint coming off of the solder around the end cap.

I can't say for sure but there may be two different noises. The main one is a lean back fire and the secondary one is possibly coming from deeper inside the engine. Proper tools could quickly focus on the noise.

[Jeff]

Thats for the great suggestions. I will look to adjust the fuel mixture in the next couple of days as per Benz Dr suggestion and report back.

[kampala]

Is the sound the clicking that occasionally occurs?

This to me sounds like a solenoid clicking on and off. What solenoids are on this car?  CSV, Injection pump, CSS?

[rwmastel]

Jeff,

I see your other two videos on your YouTube channel.  Does this mean its fixed?

[Jeff]

Firstly a massive thank you for your interest and responses....proving once again how good this group is.

I'm delighted to say that Benz Dr wins the meat platter, as the issue was exactly as he described.....the engine was running too lean and backfiring in the exhaust manifold. Thank you very much Benz Dr, I was beginning to think this could be an internal engine issue.

As he indicated, it was much easier to detect (and feel) once I separated the air box from the throttle butterfly, as you can hear in the attached link. The other link is the car running post fuel adjustment.

Still needs a bit of work to get the idle speed down by about 300rpm, but the issue is resolved.

https://youtube.com/shorts/OOOBHQW6Dus

https://youtube.com/shorts/U9rqun3but0

Thanks again - Jeff

[mdsalemi]

…Benz Dr wins the meat platter, as the issue was exactly as he described...

…and THAT IS WHY he’s “Dr. Benz”…

Not much he hasn’t seen—or heard—on Pagodas!

[cfm65@me.com]

Well done Doc

[BobH]

Amazing to be able to diagnose a problem just by listening to a video!