1981 380SL noisey engine how to diagnose? - Mercedes-Benz Forum

 
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post #1 of 8 (permalink) Old 06-14-2005, 11:00 PM Thread Starter
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1981 380SL noisey engine how to diagnose?

Hi all I'm new to the forum here and thought I would give this a try.
I have a 1981 380SL I bought last summer for 1500 bucks. yes you can imagine she is old with 128,000 miles and not only shows a little age but the poor thing was so abused in a former life. However I thought it would be fun to have and work on a little at a time while driving it.
However...
The engine starts good, idles fine but has a constant clicking noise which I thought sounded like a tapped out of adjustment. The tappets on this ebgine are hydrolically managed. I pulled the valve covers and checked the tappets and all seemed good and tight. The timing chain seems to have good tension as well so I am somewhat at a loss as to what is causing this noise. you can really hear it when the engine idles and it settles out somewhat when up to highway speed but is still there a little. When you let up on the gas you can really hear it too.
My father (who is more experianced with diesel engines) thinks it could be ignition timing. But I think it sounds quite metalic in nature.
I am wondering if anyone has any experiance with diagnosing this sort of thing and what I should be looking at to find and eliminate this noise.
BTW the engine has the double row timing chain setup which I was very pleased to see when I opened it up.
Thanks in advance to all
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post #2 of 8 (permalink) Old 06-15-2005, 07:07 PM
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RE: 1981 380SL noisey engine how to diagnose?

It could be a broken piston skirt. It would cause the floating in and out tapping you are talking about (The wrist pin flops around) . It is a fluke but I've heard of it happening. I seen an A-one mechanic get bull whipped from a similar problem. They completely replaced everything from valves to lifters. It sounds just like a lifter knocking. When they took the oil pan off, they found the piece of piston skirt laying in it.

I don't mean to scare you but it could be this or a jillion other things. Just a thought.

Glad to hear you have the double chain mod kit. My friend had a 380 SL and wasn't so lucky!
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post #3 of 8 (permalink) Old 06-15-2005, 09:11 PM
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RE: 1981 380SL noisey engine how to diagnose?

That mileage is not really that old for these cars – what’s the condition of the cam lobes?

Post in the r107 forum, btw – you’ll get more responses.
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post #4 of 8 (permalink) Old 06-17-2005, 11:37 PM
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RE: 1981 380SL noisey engine how to diagnose?

Not timing, probably a valvetrain issue. I'm guessing a cam lobe failure or poor oil pressure to your tappets. I'm not exactly sure how your engines tappets are setup, but if they're not getting enough oil pressure, it will be unable to maintain a tight valvetrain. Some hyd tappets will stick in the compressed position and cause that noise as well, but usually once they stick they stay stuck and the noise would be constant.
I'd say try to determine where the noise is coming from exactly. I would try to feel and wiggle the valvetrain and turn the motor over by hand a ¼ turn, feel, turn, feel until you’ve made at least 2 revolutions. Two engine revolutions = one cam revolution, this will allow you to see a complete opening/closing cycle of each valve. Hopefully you will be able to spot the offending part. Sometimes when finding the part is difficult I will run a motor with the valve cover off to locate it by sound. Some engines will sling or squirt oil so be prepared.

If your valvetrain is hopelessly loose due to wear, pour in a couple quarts of "honey oil", I use the HyperLube stuff. It's super thick oil intended to reduce oil burning and it should quiet that motor way down and reduce further wear. I've used it on many tired engines with great success. My '85 190E developed a horrible valvetrain noise a few years ago, I didn't even bother to look at it, I simply poured in 2qts of that goo and its been so quiet that I'd forgotten about it until I read your post. (That’s substituting 2qts, not adding)
It will also help if you have a broken skirt. It fills gaps and cushions parts from hard contact, it’s an all-around helper for shot-out engines.
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post #5 of 8 (permalink) Old 06-18-2005, 09:08 AM
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RE: 1981 380SL noisey engine how to diagnose?

Quote:
Chevota - 6/18/2005 1:37 AM

I'm guessing a cam lobe failure...
Correct, or better excessive cam lobe wear. If not properly oiled the cam lobes on the M116/117s can wear excessively. A kind of pitting or grooving results on the lobe resulting in noise.

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post #6 of 8 (permalink) Old 06-18-2005, 08:24 PM
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RE: 1981 380SL noisey engine how to diagnose?

Fyi: Crower cams can rebuild lobes if a cheap replacement can't be found. crower.com
I think they were kinda spendy, like $50 per lobe.
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post #7 of 8 (permalink) Old 07-13-2005, 09:39 PM Thread Starter
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RE: 1981 380SL noisey engine how to diagnose?

hey all thanks for the information. greatly appreciated.
well I did tear into it with my dad and we looked it over. The lobes on the cam are in super condition with hardly any wear that I can see or feel. verey smooth with NO grooves.
I did however find one hydrolic tapped spacer which was at the time loose. OK however the next day I went out to work on it some more trying to figure out how I can replace this and all of a sudden (and mind you I did not touch the engine again after finding this) it was so tight I could no longer wiggle it. so now I have no clue.
I think I am going to try the motor honey route and see what that does. It is a pretty nice little care and I love driving it. I found a rebuilt engine on ebay but the guy wants 3500 bucks for it and well the car is not worth that much. I only gave 1500 bucks total for the car as it sits now. I have driven it and have put close to 1000 miles on it. I just want the engine to be quiet. My dad says to drive it till it blows up and call the junk yard.
So timing is not it I take it from the posts. And I didn't quite agree with this either to be honest cause the sound is so metalic I thought it had to be valve train. I am going to replace the timing chain tensioner. cheap part and couldn't hurt either.
well that is all for now. I do appreciate all the ideas though. Sure wish that engine was half the price on ebay I would then possibly consider replacing the engine with a rebuilt one. Oh well I will keep my eyes open.
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post #8 of 8 (permalink) Old 07-14-2005, 07:49 PM
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RE: 1981 380SL noisey engine how to diagnose?

why not properly clean out the varnish causing the lifter to stick? Use a can of Berrymans transmission cleaner with a warm (not hot) engine. Runit a few minutes,let it sit an hour, run a few minutes,etc for a day or two.Never get it HOT. Then drain the oil and refill, adding one pint of Marvel Mystery Oil to the crankcase.
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