Engine rattling sounds when on partial throttle
 

My 85 300D KaliKar (California model) is making a LOT of rattling sounds when I drive at partial throttle.

What I mean by partial throttle is the situation of driving at a constant 30 MPH. You are not mashing the accelerator pedal to increase speed, just holding it constant. I hear these sounds when holding any steady speed from about 15 up to 40 MPH. The sounds are even more pronounced when I am holding the throttle slightly open and rolling down a slight incline.

I have also noticed that the sounds are lessened when the engine is fully warmed-up.

Please note that this is a KaliKar, so the usual air cleaner bracket issues don't exist on my car. And I changed the motor mounts about 8 months ago and they appear fine.

The slight incline point I made above worries me; could this be a slack timing chain possibility--tensioner at full extension but not quite enough to take all slack out, engine being rotated by going downhill but not because of the throttle. I have no indication of any timing chain/tensioner maintenance by previous owners.

Any advice appreciated.

belts?
 

hi mate

did you checked your belts?



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It is true that loose belts can cause some very metallic sounding noises under the hood.;)

Checking belts
 

I have not checked the belts, but will this morning. :)

btw if you find them 9.5mm go for 10mm in case of replacement....

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Are you familiar with injector nailing? Can't hear your problem of course but my 240d does it at partial throttle; Pretty common in mercedes diesels I hear.

Things that cause abnormal nailing:
Bad Fuel
Air leak on the suction side of the Fuel Supply/Lift Pump to include the Hand Prmer
Late Fuel Injection Pump timing and I also found out that advanced timing beyond spec will also nail.
Injectors that have worn out Nozzles or the Pop Pressure is low
Valves out of adjustment
Late Valve Timing due to Timing Chain Stretch or Timing Gear wear (maybe)
Low Compression

Other things I have done
 

I guess I should mention what else I have done to the engine:

• Cleaned fuel injectors, rebuilt with with Monark nozzles, all pop tested at 2050 psi (within 50psi of each other), new heat shields
• Replaced hand primer with new model
• I have performed several value adjustments (several learning attempts)
• Compression test; all measurements seemed acceptable

since when
 

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since when rattling has appear? before or after learning attempts :)

was it sudden or it was developed from tiny noise?

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The sound has developed slowly over the last few months. I haven't adjusted the valves for several months. Maybe I should do that again for good measure.

it has to be biiiig chain slack to produce noise..so I dont think that is the issue

while checking belts do check

vac pump
water pump

as to my understanding those 2 things are most common front noise makers

valve adjustment in such short period would have sense only if previously
badly adjusted....

good luck


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Is there a belt tensioning device on that car? They tend to make noise when worn.