Engine Pinking and Timing Chain

[iamamanc]

Hi

94 W124 OM606 non Turbo

Got my injectors re-balanced for £25 each, the performance has greatly improved, a lot more pull on hills and is overall a lot more responsive -BUT - It's started nailing (pinking) under 1200 revs. The guy who did them said he had set the pop pressure at 160 because after ca 1000 miles the springs will settle back down and allow pop at 130-140 lbs of pressure which is optimal, which could cause nailing.
After a lot of reading and brain picking it seems that having the injectors balanced has highlighted the off timing of the fuel pump and valves, which is a common cause of nailing.
The easy (!!??) thing to do would be to reset the pump and valve timing to compensate for the optimal setting of the injectors. A MB mechanic (over 50 who lends me tools) said that given the age and mileage of my car the chain would have some stretch and renewing the timing chain and tensioner should pull everything back together again. So I ordered a chain, tensioner + seal, sliding rail and three sprocket bolts for £200 and will set about it next week.
Any thoughts or tips on this undertaking

Cheers
Adrian

 

[Dieselman]

I'll be interested to see if it fixes the problem as retarded timing isn't usually the cause of nailing.
The nailing is due to the rate of rise of temperature in the cylinder being high.
You could check the chain stretch aby checking the cam timing against crank timing, anything upto 5 deg is acceptable. The pump timing can be checked and set independantly of the chain and should be 14 deg ATDC measured via the port in the side of the pump.

I suspect the injectors are not delivering properly at low opening and maybe either dribbling or not spraying properly.

 

[iamamanc]

Hi dieselman
The guy who did the injectors guarantees they are set bang on, balance, pop and spray patten. I also drove around for about 20 miles then checked for fuel and/or compression leaks (bubbles) of which there were none.
To be honest I suspect that the injectors need to be "run in" but it seems like a good excuse to replace the timing chain. I have been meaning to do this due to a lack of any history when buying the car and deep suspicions of "clocking".
I intend checking the pump timing before I change the chain (I even have the thing that locks it up) and again after. And will then make any adjustments if needed
I wanted a multivalve 124 and was prepared to look past the initial flaws.
But still - any pointers on changing the chain would be appreciated

Cheers
Adrian