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  #31  
Old 09-30-2008, 12:32 AM
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okay, thanks. so am i correct in assuming that the cam being retarded would lessen the chances of pinging?

a new cylinder head would be pricey, and undesirable anyway given the few km the engine has traveled since extensive work was carried out.

how can i measure the head with it fitted? measure from where to where, and what is the correct figure?



Quote:
Originally Posted by Arthur Dalton View Post
Looking @ engine from the front...... The engine runs CW, so if cam indicator alignment requires turning the crank CW past TDC for the cam to align. [ as I believe is what you suggest] , then the valve timing would be retarded.


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  #32  
Old 09-30-2008, 01:54 AM
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It would be better to retard the ignition timing to stop the pinging. There is a small dial type indicator at the base of the distributor with a slotted adjuster. The adjuster sould be to the right on the dial if the ignotion is set to spec and moved to the left to retart the timing.
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  #33  
Old 09-30-2008, 03:28 AM
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I have to agree w/those who mentioned shaving the head. Machine shops will sometimes forget to hone out the cylinder domes after the head shaving, which in turn increases the compression. If this is your case, the only way to get rid of the pinging is to remove the head again and have the domes honed. (We are assuming that you have an OE head gasket w/correct thickness).
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  #34  
Old 10-07-2008, 09:10 PM
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hi again guys

so is there a way i can measure head thickness with the head installed, and what is the correct measurement?

also, if it related to compression, wouldn't it make more sense for it to ping when the engine is at operating temperature? it is FAR worse when the engine is cold.
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  #35  
Old 10-07-2008, 09:36 PM
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Pinging

I can remember when a head like this was trued it might have a lot of metal shaved off of it. Mercedes has a minimum thickness for this head but I cannot find out what it is.

To compensate for taking metal off the head during the resurface a thicker head gasket would be used. This is not just a Mercedes thing, it was common to all cars at that time.

If the head is thinner then the combustion chamber is lower on the cylinder. This would increase compression and cause the engine to need higher octain fuel, or a thicker head gasket.

Thicker head gaskets were used on a lot of car sent to the far ease as the octane of gasoline there tended to be about 70 at the highest. All cars sent to this area had the thicker head gaskets in order to quckly and cheaply lower engine compression.

Try some octane boost and see if that stops it. You may just need to get the head redone.

Pooka
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  #36  
Old 10-07-2008, 09:57 PM
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If the fuel had sat in the tank for four months would this cause pinging and if so how do resolve the problem?
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  #37  
Old 10-07-2008, 10:54 PM
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4 month old fuel wouldn't do that,as for pinging when cold,well that's new to me,in fact I am wondering if it is pinging and not a broken piston. ( as it warms up the break closes quietning down) .
Pinging happens regardless of engine temp except when an engine is overheated. i have the specs for cylinder heads,I'll post them up as soon as i find them.
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  #38  
Old 10-07-2008, 11:05 PM
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Hello,

Yes the pinging should get worse as the engine temperature increases. So you are correct in that something is not making sense. Do you have the correct distributor on the car? Some in that era were vacuum advance and others vacuum retard. Check for correct function with a timing light if you have not yet.

Measuring the head with it in place can be difficult. Do you have service records so you can possibly check the invoices from the machine shop? I believe the stock head thickness is 85mm, 84mm is the minimum thickness.
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1964 220SE Rally (La Carrera Panamericana someday)
1966 Unimog 404s (Swedish Army)
1969 300SEL 6.3 (sold)
1969 280SL Pagoda
1973 280SEL 4.5
1974 450SLC FIA Rally car (standard trans)
1982 300D turbo (winter driver)
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  #39  
Old 10-09-2008, 07:56 AM
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measure the head from the surface where it sits on the block to the surface where the cam cover sits. yes you measure it on the engine,use a caliper to get as accurate measurement as possible ( without the head gasket thickness)
Stock height is is 84.8 - 85 mm. Maximum allowable to be removed on a 220 is 0.8 mm.
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  #40  
Old 10-09-2008, 08:38 PM
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hi guys

thanks for all the help so far.

i played with it a bit more. i started by adjusting the valves, which were a little loose, but all by approximately equal amounts. to make the camshaft markings line up, i have to turn the engine clockwise about seven degrees (on the crank). i think the offset cam keys come in 2, 3, 4, 5 degrees. is this measured at the crank or by angle at the cam sprocket, ie, which one do i need to order to bring it into time?

i tried octane booster, which didn't make a difference.

timed at 3 degrees before top dead centre, the pinging when cold is unbearable. as it warms up much of it goes away.

as an experiment i retarded the timing when cold, to the point the car would backfire. the pinging went away. the aim of this was to eliminate mechanical noise.

it is difficult to measure even with a caliper, but the head seems to be 84mm.

short of bringing the cam back into perfect timing, i've run out ideas!
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  #41  
Old 10-09-2008, 10:30 PM
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You need to replace the timing chain,which is not difficult. There is far too much wear there to set the timing with amount of accuracy. 84mm should be OK,If it were 83 i would suspect that the head had been planed too far.
I would start by replacing the chain and overhauling the distributor to ensure the vacuum and mechanical advance are both working correctly.
let us know how it runs then and if it still pings,how about posting a video on Youtube so we can have a listen?
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  #42  
Old 10-10-2008, 12:33 AM
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The offset key required will be 1/2 the degrees the alignment of crank was from TDC . So, you would want the .9mm key [[3/20' degree] for a correction @ crank of 6-1/2 degrees - part #621-991-02-67.
If the head has been cut , don't expect a new chain to bring the crank/cam back into alignment.
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  #43  
Old 10-10-2008, 02:06 AM
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7 degrees on the crank is NOT where I would be putting in Offset keys.
Machining the head won't give that much slack either ,so like i said earlier just change the timing chain ,start with the basics and work from there.
If you think about it for minute,if the chain so worn you would put an offset key in to bring the timing to spec,what position is the tensioner In?.It would connecting with the head by now and not keeping the chain tight ,thus exacerbating the problem. And,because changing a timing chain in one of those is so easy,why bother with off an set key?


In fact in all these years I have only used them once and that was on a AMG equiped engine which required me to dial in the cams to keep the perfomance at the projected levels.
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  #44  
Old 10-10-2008, 08:50 PM
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What is the engine temp under pinging condition.Normal or high
mak
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  #45  
Old 10-10-2008, 09:20 PM
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Hello,

Seven degrees of chain stretch is not enough to cause this type of severe pinging in my opinion. I have seen engines set up one chain link off (18 degrees) and not have pinging issues. However offset keys are cheap!

This is a fairly low compression engine (8.7 : 1) compared to the later M130 engines (9.5 :1).

Without actually hearing the noise itself I am not sure it is even engine pre-ignition. The cold engine pinging situation really has me thinking it may be something else. Possibly a broken ring and damaged piston?

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Blacklick, Ohio
1964 220SE Rally (La Carrera Panamericana someday)
1966 Unimog 404s (Swedish Army)
1969 300SEL 6.3 (sold)
1969 280SL Pagoda
1973 280SEL 4.5
1974 450SLC FIA Rally car (standard trans)
1982 300D turbo (winter driver)
1986 560SEC
1989 Unimog FLU419 (US Army)
1991 300TE (wife)
2002 SLK 32 AMG (350 hp)
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