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1979 450SL UK spec
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Discussion Starter #123
^ or find a respected rebuilder and see what they would use...
That is easier said then done, there is no engine builder in the country I live in (Scotland) who has any clue about these engines, let alone anyone who's advice I would trust.
 

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1983 380 SL
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3,489 Posts
Well it's all clear as mud to me, maybe I should start a poll on grey iron or chrome plated.
There is little doubt that Chrome rings are superior to cast rings under certain conditions, and this difference is reflected in the price. Chrome rings are more expensive by a factor of two or more.
However, the question to be answered isn't "are Chrome rings good but cast are bad"... it's more of "are cast rings good enough for what we need them to do" and the answer is a resounding "Yes".

If you can find chrome rings for your ride (I couldn't) and you don't mind paying double... then go for it but I doubt that you will be able to detect any difference in engine performance throughout the life of the rings.

Note: I think our engines were fitted with Chrome rings from the factory, but I could be remembering that wrong.
 

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1979 450SL UK spec
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Discussion Starter #125 (Edited)
Well I managed to pick up two full sets, one chrome plated, the other grey iron, both sets for ~ £35 each, I think they were miss priced. So the question is which one to use since both are sitting here.

 

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1979 450SL UK spec
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Discussion Starter #126
Too busy to get out to the garage today, but did do some more measuring of the old and new valve guides and the head valve guide bores.

The valve guide situation is a bit odd, in EPC the original size that was used is no longer available and has been replaced by a fractionally bigger set, EPC refers to these as "repair stage 1", whereas in the workshop manual there is no mention of the original size, it refers to the EPC stage 1 as the "standard dimension". I think that at some stage when Mercedes realised that they had a problem with loose valve guides they dropped the original size and adopted the 1st oversize as the standard replacement.

Here are the old and new guides, I also purchased a single EPC oversize 2 in case I needed it for the problems I had on the intake of cylinder 1.



You can see here that the old cylinder 1 valve guide easily slips into the head.



The good news after doing all the measurement is that I wont need to bore out the head for the "oversize 2" valve guide as it is well within the recommend overlap.



Still got to check the other head but don't expect any issues there.

Next I did an inspection of all the valve seats for damage, good news again there, there were no chips or damage. They are supposed to have a 3 angle grind but its not very obvious.

Cylinder 1 exhaust



Cylinder 1 intake.



The remainder of the valve seats on the first head were the same.
 

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1983 380 SL
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3,489 Posts
Are you going to have the valves reground? The recommendation when changing valve guides is to have the valves and the seats reground in order to maintain concentricity.
I opted not to do that but instead I painted the valves and seats with blue Dykem and used the old tried and true method of the rubber suction cup handle spun between your palms, with valve grinding compound applied to the valve, to regrind the valves and seats. It takes quite a while to get them to remove all the Dykem evenly but I did eventually get it.

Also, new valve guides should be reamed to size and then have a ball broach passed thru twice in order to retain smooth straight surfaces inside the guide.

Ball Broach. Guide-Liner Sizing Ball Broaches
 

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1979 450SL UK spec
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Discussion Starter #128
I will check with Dykem as you did and take it from there, I would like to buy the new seat cutters from Nuway but it will be close to £300 to buy the set.

I bought expensive 8.99mm and 10.99mm reamers to resize the guides after fitting, ball broaches are unobtainable in Europe.
 

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1983 380 SL
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Why 10.99mm reamers? Do the exhaust and intake valves have different size stems? On the 380 they're both 9mm.
 

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1979 450SL UK spec
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Discussion Starter #131
I opted not to spend several hundred dollars on "new" cam towers due primarily to the fact that they can be replaced, (with some difficulty), once the engine is placed back in the car and running. If at that time I observe an unacceptable level of ticking, then I'll make the decision... or not... to spend the roughly $600 bucks to replace one side (drivers) of the cam towers. I believe the cost to replace the cam itself would add an additional several hundred dollars.
Well I brought all the parts indoors and let them stabilise at 20degC and remeasured everything, there was a slight improvement but not much.



Given that the cams and bearings are relatively easy to change, I have no ticking sound or symptoms and that it will be the best part of £1000 to change (bearing towers, camshaft, rocker arms and maybe shims), I will take your advice and reuse what I have. The worst that will happen is that I'll put off the expense for a year and have a project for next winter.
 

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1983 380 SL
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Well I brought all the parts indoors and let them stabilise at 20degC and remeasured everything, there was a slight improvement but not much.



Given that the cams and bearings are relatively easy to change, I have no ticking sound or symptoms and that it will be the best part of £1000 to change (bearing towers, camshaft, rocker arms and maybe shims), I will take your advice and reuse what I have. The worst that will happen is that I'll put off the expense for a year and have a project for next winter.
I would suggest buying a replacement #5 cam tower (your right side) on ebay. You will likely be able to find one closer to spec and without the deep scratches visible on yours. I was able to find 2 cam towers at a reasonable price from 2 separate sellers and I was pleased with their condition.

Oh no! I just searched eBay for your rear cam tower and there were none listed. Maybe Fonzi has one.
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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Well I managed to pick up two full sets, one chrome plated, the other grey iron, both sets for ~ £35 each, I think they were miss priced. So the question is which one to use since both are sitting here.

As long as you are going to hone use the chrome.
 

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Discussion Starter #139
I spent a long time in the garage today but made limited progress.

First I stripped down the second head.



The tray is now full!



Next was a lot of scrubbing in the hot degreaser bath.



I then checked both heads for flatness, both were good. but both heads don't look great, do you think they will seal ok or do they need skimmed?



Next I went back to the sheared bolt on the first head.



Built up with weld.



Then nut welded on.



I managed to get the bolt turning but had to go through this process a lot of times. I think the thread has galled since I am making such slow progress.



It is now sitting in a puddle of "plus gas" overnight to see if that helps.

I then went on to try to clean up the valves, I will leave them in this oven cleaner overnight, but don't have a good feeling of success. The main ingredient is Potassium Hydroxide. Does anyone have a suggestion of the best way to do this?

 

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1983 380 SL
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3,489 Posts
I then went on to try to clean up the valves, I will leave them in this oven cleaner overnight, but don't have a good feeling of success. The main ingredient is Potassium Hydroxide. Does anyone have a suggestion of the best way to do this?
Put the valve stem in your drill motor and spin the valve in a scotch bright pad. The valve will come out looking new.
Took a photo.
MercCleanValve.jpg
 
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