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1983 380 SL
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Discussion Starter #501
Looks interesting, but if you already reamed to 9.00 wont it just pass right through. 9.00-8.99 = ~ 0.0004 inch, not much.
I only reamed one... the one that was sticking when I pressed the valve tightly against it's seat. Also, even though I used a 6 flute reamer, the general thought is that it doesn't make a perfectly smooth round hole. However, when you drive a ball broach of precise dimension through the guide it makes it smooth on the inside and more perfectly round (there's no such thing as perfect).

I've done a bunch of reading on this topic and from what I can tell, you first install the guides, then ream them to get to a precise size and then run a ball broach through them to make them more smooth and as close to perfectly round as possible. The ball broach also makes the interference fit tighter.

I test fit each of the new valve guides using the existing valve stems and the fit was perfect (as close as I could tell). The very act of pounding them in with an air hammer creates some distortion which is first corrected with a reamer and then perfected with a ball broach. Inasmuch as I don't have a 8.99mm reamer, and in consideration of the fact that all the valves still slide smoothly inside the new guides once they were installed, I'll skip the reamer part and go directly to the 8.99mm broach. If the broach slides through without resistance I'll at least know that the clearance is good. If I can't get the broach through the guide then I'll need to spring for a 8.99mm reamer, but the difference between a 8.99mm and a 9.00mm reamer is .01mm or .000393 so I don't expect that I'll have any difficulty getting the ball broach through the guides that weren't reamed.

There is a third step which I am omitting entirely... core drilling. Core drilling is used to make the hole in the head where the valve guide is pressed in and the valve seat circumference, concentric to each other. I have no way of doing it so I'll just have to accept any out of concentricity issues that may arise and hope that the hand lapping of the valve seat to the valve will be good enough. If it's out by more than a few tenths then hand lapping will not likely be able to correct it in which case the valve may not seal perfectly. I'll paint layout blueing on the valve seats when I hand lap them and that will enable me to determine if the valve is contacting the seat uniformly or if there is a concentricity issue. I'm not sure what to do if the concentricity is way off. I'll cross that bridge when I get there but I must assume that the valve guide holes in the heads were already core drilled at the factory to be concentric with the valve seats and given that I'm not replacing the seats it's a good bet that they are already concentric.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,196 Posts
I only reamed one... the one that was sticking when I pressed the valve tightly against it's seat. Also, even though I used a 6 flute reamer, the general thought is that it doesn't make a perfectly smooth round hole. However, when you drive a ball broach of precise dimension through the guide it makes it smooth on the inside and more perfectly round (there's no such thing as perfect).

I've done a bunch of reading on this topic and from what I can tell, you first install the guides, then ream them to get to a precise size and then run a ball broach through them to make them more smooth and as close to perfectly round as possible. The ball broach also makes the interference fit tighter.

I test fit each of the new valve guides using the existing valve stems and the fit was perfect (as close as I could tell). The very act of pounding them in with an air hammer creates some distortion which is first corrected with a reamer and then perfected with a ball broach. Inasmuch as I don't have a 8.99mm reamer, and in consideration of the fact that all the valves still slide smoothly inside the new guides once they were installed, I'll skip the reamer part and go directly to the 8.99mm broach. If the broach slides through without resistance I'll at least know that the clearance is good. If I can't get the broach through the guide then I'll need to spring for a 8.99mm reamer, but the difference between a 8.99mm and a 9.00mm reamer is .01mm or .000393 so I don't expect that I'll have any difficulty getting the ball broach through the guides that weren't reamed.

There is a third step which I am omitting entirely... core drilling. Core drilling is used to make the hole in the head where the valve guide is pressed in and the valve seat circumference, concentric to each other. I have no way of doing it so I'll just have to accept any out of concentricity issues that may arise and hope that the hand lapping of the valve seat to the valve will be good enough. If it's out by more than a few tenths then hand lapping will not likely be able to correct it in which case the valve may not seal perfectly. I'll paint layout blueing on the valve seats when I hand lap them and that will enable me to determine if the valve is contacting the seat uniformly or if there is a concentricity issue. I'm not sure what to do if the concentricity is way off. I'll cross that bridge when I get there but I must assume that the valve guide holes in the heads were already core drilled at the factory to be concentric with the valve seats and given that I'm not replacing the seats it's a good bet that they are already concentric.
Good info. The stuff your talking about is way beyond what me or most of my fellow MB techs ever did. That's like a NACAR build.
 

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Premium Member
1983 380 SL
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2,823 Posts
Discussion Starter #503
Good info. The stuff your talking about is way beyond what me or most of my fellow MB techs ever did. That's like a NACAR build.
Don't go by me... coming up on 3 years in this forum I have learned to go the extra mile (excuse the pun) with these magnificent engines. I've owned my 380 for 36 years and I remember well how incredibly smooth running this engine can be. I used to demonstrate this to others when the car was new by balancing a nickel on it's edge on the air cleaner with the engine running. If not for the sound you might think the engine wasn't running. All I want to do is be able to balance a nickel on the air filter cover with the engine running again. Fat chance I know... but what is an obsession if not impractical.
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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Registered
1984 380 SL
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44 Posts
Just a thought don’t know if you’re hire shops have these, bit expensive to buy for 1 job! but the mandrel will fit perfectly in your valve guide then you can cut the seat concentric to the valve guide and just finish lap the valves,
I have used these in the UK cracking little tool..
 

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Premium Member
1983 380 SL
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2,823 Posts
Discussion Starter #506
Just a thought don’t know if you’re hire shops have these, bit expensive to buy for 1 job! but the mandrel will fit perfectly in your valve guide then you can cut the seat concentric to the valve guide and just finish lap the valves,
I have used these in the UK cracking little tool..
Thanks for the link... I'll consider it once I layout blue the seats and see where the valves actually contact the seats. It may not be necessary to recut the seats, but if it is I'd need one cutter for the intake and one for the exhaust... they aren't the same angle. One is 30 degrees and the other is 45 degrees.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
Joined
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10,196 Posts
Just a thought don’t know if you’re hire shops have these, bit expensive to buy for 1 job! but the mandrel will fit perfectly in your valve guide then you can cut the seat concentric to the valve guide and just finish lap the valves,
I have used these in the UK cracking little tool..
That's how I used to do it on lawn mowers. I still have that kit. Some of the people who use it in automotive say its better than the standard valve seat grinder. Certainly is cheaper.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
Joined
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10,196 Posts
Thanks for the link... I'll consider it once I layout blue the seats and see where the valves actually contact the seats. It may not be necessary to recut the seats, but if it is I'd need one cutter for the intake and one for the exhaust... they aren't the same angle. One is 30 degrees and the other is 45 degrees.
You can get one cutter with 45° on one side and 30° on the other. But I would also recommend you get a 15° and 60° cutter to do a 3 angel grind with a uniform seat width. I'm always happy to watch other people spend money. :)
 

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1984 380 SL
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44 Posts
As above, the one I had had 2 different angles 30/45 one on each side, unfortunately it went missing when we moved premises.. shame it was used quite a bit on our plant equipment.. it may come to light one day:rolleyes:
 

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1998 ML320, 1975 280C
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124 Posts
You should NOT have to put blueing on the valves. The first go with compound will let you know how close you are. It will make marks that you cannot mistake, and is easy to measure.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,196 Posts
You should NOT have to put blueing on the valves. The first go with compound will let you know how close you are. It will make marks that you cannot mistake, and is easy to measure.
Depend on if you are using seats and valves cut to the same angle. Agree, if the angles are the same or you want to use the valves over without cutting them, than just go by the valve grinding compound. In some cases people will cut the seats to 1° more than the valve to get a better seal. In that case you don't use VG compound at all or you will defeat the 1° interference fit. My lawn mower valve grind kit comes with a 31° and 46° cutter head.
 

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1983 380 SL
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2,823 Posts
Discussion Starter #512
You should NOT have to put blueing on the valves. The first go with compound will let you know how close you are. It will make marks that you cannot mistake, and is easy to measure.
Sorry for getting the procedure wrong. You put the blue on the valve (not the seat) and then pop the valve against the seat (do not rotate). Where the valve contacts the seat the blue will be removed resulting in a circle on the valve which will show any concentricity variations. It may be that this procedure only works with valves that are cut 1 degree off from the seat. I've never done it myself.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
Joined
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10,196 Posts
Sorry for getting the procedure wrong. You put the blue on the valve (not the seat) and then pop the valve against the seat (do not rotate). Where the valve contacts the seat the blue will be removed resulting in a circle on the valve which will show any concentricity variations. It may be that this procedure only works with valves that are cut 1 degree off from the seat. I've never done it myself.
I wouldn't loose too much sleep on this. In auto school we used chalk.
 

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1983 380 SL
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2,823 Posts
Discussion Starter #515
Thanks for the video. It would be great to see the installation video too. I see from the instructions that the max overlap is 0.025 and min is 0.007, so would be interesting to measure the head bore withe the guide removed.
@RaceDiagnostics I was thinking of you when I went to remove the valve guides from the other head, so I decided to video the process. I had a small speaking part in the video and I can't believe how New York I sound. Oh well... I'm guessing a Hollywood career is out of the question.

The actual process of removing the 8 guides took less than a minute.
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,196 Posts
How have you guys been heating your heads to 80° C?
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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29,507 Posts
How have you guys been heating your heads to 80° C?
After washing the hub caps in the dish washer, they take the heads out of the oven?
 

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1983 380 SL
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2,823 Posts
Discussion Starter #519
How have you guys been heating your heads to 80° C?
My powder coat oven measures 2 feet square by 3 feet deep. It has a digital control where I can set any temperature I want up to about 500f but I seldom run it over 400f. It has an internal high temperature fan to circulate the inside air to provide even heating.

Here's a picture... That's the front sway bar in the oven.
MercPowderCoatOven1.jpg
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
Joined
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29,507 Posts
My powder coat oven measures 2 feet square by 3 feet deep. It has a digital control where I can set any temperature I want up to about 500f but I seldom run it over 400f. It has an internal high temperature fan to circulate the inside air to provide even heating.

Here's a picture... That's the front sway bar in the oven.
View attachment 2633335
Wow. Great set up!
 
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