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Registered
1979 450SL UK spec
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1,311 Posts
Discussion Starter #1
I came across this a couple of years ago when changing the valve guide seals. The valve guide came out with the seal when I tried to pull it off.



I had held the valve in place with rope compressed in the cylinder and the guide pushed back into place easily.



I buttoned the engine back up and decided to fix the issue later.

My plan is to remove the guide again and measure it carefully to see how badly worn it is, I'm not sure if it's a worn guide, or head, or both.

Replacement guide on an old valve.



Depending on what I find I may glue (with Loctite 648) the original back in place or glue in a standard size replacement. The diameter of the standard guide should be 14.04mm, I have a replacement which measures 14.06mm so very slightly oversize (by 8/10th of a thou). The next up repair size is 14.24mm but that would need a head off solution.



If there is wear in the head guide bore, I may be able to increase the hold of the guide by applying a slight knurl, but clearly it will be critical that guide does not get compressed too much and grip down on the valve.

In preparation for the job I decided to make up a tool which will help push the guide back down into the bore if finger pressure is insufficient. That gave me an excuse to make this purchase.



....and make up this tool.





Fitted to the guide.



I'm pretty sure I will need to grind away ~50% of the shaft to allow it to fit round the cam shaft but I'll do that once I get the cam covers off.

I will start the job as soon as the weather warms up a bit, temps here are ~2 or 3 degC this week, too cold on the fingers, around 10degC would be better.
 

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Premium Member
2007 ML320CDI, 1959 220SE, 1971 280SL, 1982 380SL
Joined
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626 Posts
I came across this a couple of years ago when changing the valve guide seals. The valve guide came out with the seal when I tried to pull it off.



I had held the valve in place with rope compressed in the cylinder and the guide pushed back into place easily.



I buttoned the engine back up and decided to fix the issue later.

My plan is to remove the guide again and measure it carefully to see how badly worn it is, I'm not sure if it's a worn guide, or head, or both.

Replacement guide on an old valve.



Depending on what I find I may glue (with Loctite 648) the original back in place or glue in a standard size replacement. The diameter of the standard guide should be 14.04mm, I have a replacement which measures 14.06mm so very slightly oversize (by 8/10th of a thou). The next up repair size is 14.24mm but that would need a head off solution.



If there is wear in the head guide bore, I may be able to increase the hold of the guide by applying a slight knurl, but clearly it will be critical that guide does not get compressed too much and grip down on the valve.

In preparation for the job I decided to make up a tool which will help push the guide back down into the bore if finger pressure is insufficient. That gave me an excuse to make this purchase.



....and make up this tool.





Fitted to the guide.



I'm pretty sure I will need to grind away ~50% of the shaft to allow it to fit round the cam shaft but I'll do that once I get the cam covers off.

I will start the job as soon as the weather warms up a bit, temps here are ~2 or 3 degC this week, too cold on the fingers, around 10degC would be better.
 

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Premium Member
2007 ML320CDI, 1959 220SE, 1971 280SL, 1982 380SL
Joined
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626 Posts
Loose valve guides are not uncommon in these engines. Often it occurs as a result of overheating, but not always. If one is loose, they all need changing. The engine will pull oil around the loose valve guides There are oversized diameter valve guides available. Installation requires removal of the head and then boring the guide hole to a specified diameter. The head is heated in an oven and the guide is placed in a freezer. They will then be insertable into the head. I have not seen locktite or glues work to correct this problem
 

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Registered
1979 450SL UK spec
Joined
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1,311 Posts
Discussion Starter #4
There is only 1 loose valve guide, I have tested all of them and only one pulled out. It certainly is not worth pulling the head at this stage. Have you tried Loctite 648, its good up to around 200degC and luckily it is an intake valve guide that is loose.


LOCTITE® 648 is designed for the bonding of cylindrical fitting parts. The product cures when confined in the absence of air between close-fitting metal surfaces and prevents loosening and leakage due to shock and vibration. It exhibits a robust curing performance. The product also works on passive substrates and offers high-temperature performance and good oil tolerance.

Retaining Compound - high strength. High temperature resistance. Ideal for retention of parts with a clearance or interference fit.
  • High temperature resistance
  • Proven to be tolerant of minor contamination due to industrial oils
  • High strength on all metals, including passive substrates (e.g. stainless steel)
  • Ideal for retention of parts with a clearance or interference fit
 

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Premium Member
1983 380SL, 2000 S430, 1991 420SEL (retired) - RHD
Joined
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5,356 Posts
I came across this a couple of years ago when changing the valve guide seals. The valve guide came out with the seal when I tried to pull it off.



I had held the valve in place with rope compressed in the cylinder and the guide pushed back into place easily.



I buttoned the engine back up and decided to fix the issue later.

My plan is to remove the guide again and measure it carefully to see how badly worn it is, I'm not sure if it's a worn guide, or head, or both.

Replacement guide on an old valve.



Depending on what I find I may glue (with Loctite 648) the original back in place or glue in a standard size replacement. The diameter of the standard guide should be 14.04mm, I have a replacement which measures 14.06mm so very slightly oversize (by 8/10th of a thou). The next up repair size is 14.24mm but that would need a head off solution.



If there is wear in the head guide bore, I may be able to increase the hold of the guide by applying a slight knurl, but clearly it will be critical that guide does not get compressed too much and grip down on the valve.

In preparation for the job I decided to make up a tool which will help push the guide back down into the bore if finger pressure is insufficient. That gave me an excuse to make this purchase.



....and make up this tool.





Fitted to the guide.



I'm pretty sure I will need to grind away ~50% of the shaft to allow it to fit round the cam shaft but I'll do that once I get the cam covers off.

I will start the job as soon as the weather warms up a bit, temps here are ~2 or 3 degC this week, too cold on the fingers, around 10degC would be better.
Great work as usual RD. Wish I had a lathe like that but SWMBO would kill me.:)
 

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Registered
560SL '88 Suzuki GS1000E '78
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165 Posts
Hi Jim,

I Think it's worth a try. If it won't work, you need to remove the head anyway. Fortunately it's an intake-valve, so the thermal stress is low. The only issue that could happen would be a misalignment between valve and valve seat so a little leackage could appear - but who cares...

Martin
 

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Registered
1985 380 SL
Joined
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91 Posts
Hi Jim,

I Think it's worth a try. If it won't work, you need to remove the head anyway. Fortunately it's an intake-valve, so the thermal stress is low. The only issue that could happen would be a misalignment between valve and valve seat so a little leackage could appear - but who cares...

Martin
Yes, and I would do a compression and leakdown test before and after to see if there is a change. If there is a leak the intake valve could burn and the leak get worse over time.
 

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Registered
1979 450SL UK spec
Joined
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1,311 Posts
Discussion Starter #9
Great work as usual RD. Wish I had a lathe like that but SWMBO would kill me.:)
I've been wanting/needing one since I retired and don't have access to the university workshop anymore, no chance to use any of their equipment now due to H&S and insurance/liability etc.

The choice was between an old well built lathe like a Myford that could turn into a restoration project in itself, or a modern Chinese unit. In the end I went for this 6 year old small Chinese unit imported and supported by a UK company. So far so good and should be just big enough for most of what I need to do. Watching lots of youtube videos showing what incredible work can be turned out on these lathes by old school time served machinists.

A couple of years ago I was offered this one for free as the University was scraping it, but I just didn't have the space.



It needs to fit in here and still leave space for both cars.



The only option was to give up on the beer fridge.



So out with the fridge an in with the lathe, it just fits in.



Next I need to work out where to fit a milling machine.
 

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'79 450SL, '04 CLK200 convertible; former A124, W210, A209.
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1,509 Posts
Fantastic work Jim, love it! Amazing how much useful equipment can be squeezed in as long as there's a good reason for it. :)
 

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Registered
1979 450SL UK spec
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1,311 Posts
Discussion Starter #11
Ok, after a ski holiday and then nearly three weeks of illness due to CV19, I got back into the garage this afternoon.

First removed the top hose and lost about 1/4l of coolant, mostly into a tray.



Removed the bolts from the fan cowl.



The the four bolts holding on the fan.



All came off easily as they haven't been on that long.



2626513


Next I removed the fixings for the fluid bottles.



Better access now.



Had a look at the spark plug for cylinder one which has the loose guide, very oily.



Then a look into the cylinder, I need a better bore scope with higher resolution, any suggestions? Wireless would seem the way to go so as not to strain any connection to a phone etc. I could make out some numbers and an arrow.



That's it for today.
 

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Registered
1979 450SL UK spec
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1,311 Posts
Discussion Starter #13
Yes, pretty sure I got it in either the Spitzbub in Saalbach (one of the bar staff unknowingly had it and was quarantined a few days later) or Salzburg airport which was overrun on the 14th March due to all the ski resorts shutting down. It was mobbed and there seemed to be a lot of ill people. I got it fairly bad but was not hospitalised and Kim had milder symptoms and was ill for about a week. We are both feeling a lot better now, good enough to get out to the garage anyway.
 

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'79 450SL, '04 CLK200 convertible; former A124, W210, A209.
Joined
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1,509 Posts
Holy cow Jim, I'm sorry to hear that but glad you and Kim are doing well! Looking at your postwith pics it sounds like you're back being your regular self, awesome! 🍀👍
 

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Registered
1979 450SL UK spec
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1,311 Posts
Discussion Starter #15
Set cylinder 1 to TDC.



Both valves closed.



Leak down test looked better than expected.



Cam cover off.



Chain guides still looking ok.



Rocker arm taken off.



6 feet of rope fed it with cylinder down then compressed against the valves.



Puck lifted off with a magnet.



Valve collets lifted out with a screwdriver and strong magnet.



Springs ready to be lifted out.





Valve seal and spring base lifted out.



Guide lifted out.



Old and new guide dimentions.



The correct diameter should be between 14.035 and 14.05mm, so the old one is undersized by ~0.1mm and the new one is oversized by .01mm.



I tried to fit the new guide by hand but it would not go in easily, or at all by hand. So decided to reuse the old guide.

First I cleaned up the bore and guide to remove all the oil with brake cleaner and compressed air.



Next I went over the old guide with an engraver to roughen up the surface, that took the diameter to ~14.04mm.



Next I smeared the guide with high temp LOCTITE® 648 and tapped it into place up to the cir-clip "stop".



I tested the valve movement and it was still free to move easily.



Next I started to rebuild everything back together.



I will leave it ~72 hours to cure before starting the engine back up.
 

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Registered
'79 450SL, '04 CLK200 convertible; former A124, W210, A209.
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1,509 Posts
Excellent work Jim, just excellent! Thanks for the detailed pics, they make all the difference 👌👍
 
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