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1979 450SL UK spec
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1,435 Posts
Discussion Starter #1 (Edited)

[UPDATE, the thread has developed into an engine swap as it ended up being cheaper to do that, so there are wider topics also discussed around the gearbox as well as engine]


Finally it's time to start my top end rebuild. I have established already that I have virtually no compression in cylinder number 8 and suspect its a problem with the exhaust valve seat. I also have a tell tale blast of smoke after starting the engine indicating a problem with the valve stems and seals. Although the car is a 1979 450, at some point in the past it has had a 1976 350 engine transplanted into it.

The job is said to be beyond what a novice should take on but the cost to get it done in a shop is too high compared to the value of the car, I therefore decided to try it myself. I have collected the special tools needed and have both the Haynes manual and I have printed off all of the Mercedes engine CD. My experience so far has been basic car maintenaince, brake pads, rotors and a couple of 4 cylinder cam belts (but nothing in the last 10 years), so this job it massive compared to any previous ones for me.

First I removed the battery, air filter housing, radiator fan, alternator, wiring loom to the engine front end, spark plug leads and cam covers.

I am documenting each step, photographed everything and individulally bagged all the removed components.

So here are three of the pics. What are your thoughts on chain stretch

Left CAM (viewed from front of car)



Crank



Right CAM (viewed from front of car)

 

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Always Remembered RIP
1979 280sl 4 sp w/ac 1957 MGA 1998 volvo xc/70 2004 F150
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6,050 Posts
Thats not a lot of stretch, you can get an offset woodruff key to compensate for it. If you made it this far, you are more than able to complete the job. I would suggest that you send the heads out to be redone though.
 

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1979 450SL UK spec
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Discussion Starter #4
I was surprised to see both CAM marks completely aligned and an offset at the crank, I guess that means it is a newish chain but that the crank pulley is worn. But as suggested it should be possible to fix this with the offset keys.
 

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Premium Member
'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,334 Posts
It looks to me like the cam marks don't line up perfectly. Might gain another degree but avoiding parallax error. Then make sure tensioner is tight. and have someone hold tension on crank so driver side (passenger in UK) doesn't rotate back (due to valve springs?)

I am no expert at this (or any other mechanical work for that matter) but when I did my chain, I got varying readings until I worked out a way of consistently lining up the marks. I still had some "stretch" showing with the new chain, but didn't think it was significant.

An experienced MB mechanic told me , that if I wanted to use a Woodruf key to correct cam timing, I should use the 2mm valve lift method per the shop manual to determine more accurately how much of an adjustment is required.
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,196 Posts
I was surprised to see both CAM marks completely aligned and an offset at the crank, I guess that means it is a newish chain but that the crank pulley is worn. But as suggested it should be possible to fix this with the offset keys.
First thing to consider is how is the timing with a new chain. I assume you are going to put a new chain in prior to finishing the head rebuild. Then consider the offset keys. also remember those timing marks are only assembly reference marks. The correct timing procedure is a dial indicator procedure in the engine manual which is quite involved.
 

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1979 450SL UK spec
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Discussion Starter #7
Well I'm in two minds about replacing the chain right now. The left cam sprocket it badly worn and the right looks new, so I think I will leave the decision on whether to change the chain till after I get the heads and new sprocket back on.

I rotated the crank round again tonight and got the left cam spot on while holding it tight, the right one was then off by just a fraction and the carnk was at 4 degrees after tdc.

As you say the correct way to check the timing is shown in document 5-215, and of course needs yet another special tool.
 

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1979 450SL UK spec
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Discussion Starter #8
Progress from tonight in the garage.

I removed the spark plugs, some were in good condition some a little oily. Next it was the distributor and then I unbolted the power steering pump and mounting plate. I have not drained the power steering system and instead have been able to lift the pump over to one side.

Next I had a good look down into the heads which revealed a bit of a shocker!

Have a look at the slide rail.

 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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Progress from tonight in the garage.

I removed the spark plugs, some were in good condition some a little oily. Next it was the distributor and then I unbolted the power steering pump and mounting plate. I have not drained the power steering system and instead have been able to lift the pump over to one side.

Next I had a good look down into the heads which revealed a bit of a shocker!

Have a look at the slide rail.

This picture should be placed in the EGv107 somewhere.
For those who question.
 

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It Is What It Is, Dude
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22,841 Posts
.


You could put it in the Components and Locations.


Or....


Link to it in one of the chain entries. Or both.


You guys can all do links or reposts to any of the threads in the EGv107, just as we all post reference links and pics as a matter of course. I'd like to see a lot more of that happening, 'cuz we can't give everything it's own entry.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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Is there a way to test the chain tensioner, to see if it should be replaced?
Briefly, remove valve covers, set timing marks on the cams, then measure degrees stretch on the crank pulley. Covered in the EGv107 and manual, IIRC...
Have fun!

oops... need to read closer. Tensioner!
 

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US spec MB560SL 1986, Audi A4 and A6, Ford Taunus 1964 17M and 2.0 1975
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1,419 Posts
"Is there a way to test the chain tensioner, to see if it should be replaced? "

When I opened the passenger side valve cover I noticed that the chain was not tensioned, so the chain was loose in few minutes after the engine stop. The new Febi- tensioner keeps the chain always tensioned. My car is 560SL -86.
 

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89 R107, 05 CDI
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2,536 Posts
Progress from tonight in the garage.

I removed the spark plugs, some were in good condition some a little oily. Next it was the distributor and then I unbolted the power steering pump and mounting plate. I have not drained the power steering system and instead have been able to lift the pump over to one side.

Next I had a good look down into the heads which revealed a bit of a shocker!

Have a look at the slide rail.

Yowzer!! You are luuucky!!! Good catch!

That gives me fits to look at...

I'm driving Penny straight to the dealer to get that stuff changed out in the spring.

Good luck with the rest of the job and enjoy the snow driving!!
 
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