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1983 380 SL
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3,093 Posts
Discussion Starter #641 (Edited)
I couldn't wait, I modified my plan to hone the bore in the tower to just Scotch Brite it. I took my exhaust pipe expander (which was the perfect size) and wrapped a Scotch Brite pad around it (also a perfect fit) and rotated the expander by hand. I had originally planned on rotating it with my drill but at the last minute I decided to go by hand first and if that did nothing, then use the drill.

Here is the exhaust pipe expander sitting on the Scotch Brite pad.

ExhaustPipeExpander1.jpg

And then inserted in the cam tower.

ExhaustPipeExpander2.jpg

And the tower after spinning the Scotch Brite inside the bore of the tower after adjusting the expander to provide moderate outward pressure. Nothing too tight... just moderate pressure.

MercNbr2TowerHoned.jpg

And the result... No more binding

MercTower2Fixed.jpg
 

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1983 380 SL
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3,093 Posts
Discussion Starter #643
Great result, we are all relieved!
It's impressive just how tight these tolerances must be. I examined that bearing surface under 10x magnification before I used the Scotch Brite on it and I couldn't detect any problem or scratch (that I could feel with my fingernail) or anything else that might cause binding, but after the Scotch Brite treatment, the binding was gone. Amazing.
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,504 Posts
Looks good. Did you measure the bore after to see how much you took off?
 

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1983 380 SL
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3,093 Posts
Discussion Starter #647
Looks good. Did you measure the bore after to see how much you took off?
No, I don't think I actually took anything off... I probably just removed a few tenths of suirface dust or a stray atom of aluminum.
 

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1983 380 SL
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3,093 Posts
Discussion Starter #648
You have the patience of Job! :)
I know you're all going to think I'm crazy but the drivers side cam spins more freely than the passenger side (the one that had the binding problem). Although it's not binding anymore, if I let it sit for a few minutes and then try to spin the cam, I can feel some resistance before it starts spinning, but once spinning it spins with little effort. If I put this engine together with that little discrepancy between heads it will drive me crazy knowing that there is a difference that shouldn't be there.
I contacted the guy I bought the cam tower from on eBay and asked him to expedite the shipment. I'm going to wait for the replacement cam tower to arrive and see if it makes a difference before I continue with the assembly of the engine. I'll clean parts while I wait.
 

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1998 ML320, 1975 280C
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184 Posts
When you first cleaned the parts, did you oil the aluminum after? As a welder I know how fast it will oxidize, and you may have a coating of aluminum oxide on the inside of the bore. That would be all you need to make things tight, and it's great for removing metal off turning surfaces.
 

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1983 380 SL
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3,093 Posts
Discussion Starter #650
When you first cleaned the parts, did you oil the aluminum after? As a welder I know how fast it will oxidize, and you may have a coating of aluminum oxide on the inside of the bore. That would be all you need to make things tight, and it's great for removing metal off turning surfaces.
I've had these cam towers and the cam on and off so many times I can't remember what I did the first time, but all subsequent times I've been certain to oil both the cam and the tower.
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,504 Posts
Don't forget as the engine warms up they will loosen. But your initial start after sitting for a month is where you need to be concerned about galling.
 

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1983 380 SL
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3,093 Posts
Discussion Starter #652
Don't forget as the engine warms up they will loosen. But your initial start after sitting for a month is where you need to be concerned about galling.
Yes, I've considered that but the cam on the drivers side slides in so effortlessly and rotates so smooth that I feel I should make the passenger side head do the same.
You know how it is... sometimes good enough just isn't good enough.
 

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1983 380 SL
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3,093 Posts
Discussion Starter #653
Finally got back to assembling the engine after blowing out my right knee, tearing the meniscus and causing a sleight fracture.

Right out of the gate when I got back to the engine I ran into a problem... I came across and entry about the distributor drive gear that makes no sense to me.

According to the manual, with the engine at ignition TDC the distributor drive gear must be installed in such an orientation that the indicators on the distributor drive gear (vertical green arrow in the picture below) must align with the indicated position on the head (horizontal green arrow in the picture).

The manual says that if this is not done, then you may not be able to position the distributor for proper ignition timing.
I just don't see that as being true. As I see it, the distributor orientation is completely controlled by where the rotor is positioned when the small gear at the end of the distributor shaft is engage with the distributor drive gear.

What am I missing?


MercDistDriveGear1 copy.jpg
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,504 Posts
I'm assuming the distributor drive gear has a different tooth count that the sprocket. If true yes.
 

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1983 380 SL
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3,093 Posts
Discussion Starter #655
The distributor gear has about 12 teeth... the distributor drive gear has about 36 teeth.
 

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1983 380 SL
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3,093 Posts
Discussion Starter #656 (Edited)
Well, one step forward two steps back.

While installing the cam followers (rockers) the engine gets harder and harder to turn by the balance bolt with each follower installed, which is to be expected... but when I install the followers on cylinder 7 or 8 the engine locks up, like the piston is hitting a valve.

I double checked the cam timing and it is dead nuts right on. wtf!!!

Update: I told a fellow gear-head at work about the engine appearing to lockup when I install followers 7 & 8 and he suggested I remove all the cam followers and just install the cam followers on 7 & 8 and see if the engine locks up. Well what do you know... with just 7 & 8 cam followers installed the crank turns fine. So apparently with all the cam followers installed the force required to turn the crank is sufficient to make it feel like the engine locked up but it's not. What a relief.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,504 Posts
Well, one step forward two steps back.

While installing the cam followers (rockers) the engine gets harder and harder to turn by the balance bolt with each follower installed, which is to be expected... but when I install the followers on cylinder 7 or 8 the engine locks up, like the piston is hitting a valve.

I double checked the cam timing and it is dead nuts right on. wtf!!!

Update: I told a fellow gear-head at work about the engine appearing to lockup when I install followers 7 & 8 and he suggested I remove all the cam followers and just install the cam followers on 7 & 8 and see if the engine locks up. Well what do you know... with just 7 & 8 cam followers installed the crank turns fine. So apparently with all the cam followers installed the force required to turn the crank is sufficient to make it feel like the engine locked up but it's not. What a relief.
Start by installing 7 & 8 first and see if you get the same feeling when you get to 1 & 2.
 

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1983 380 SL
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3,093 Posts
Discussion Starter #659
Start by installing 7 & 8 first and see if you get the same feeling when you get to 1 & 2.
Yup, that's what I did and with 7 & 8 installed alone the crank spun fine, so I installed them all and used more strength when turning the crank at the balance bolt and now it appears to be OK.

I have renewed respect for the power of an exploding fuel mixture... when running, the engine has no problem overcoming the inertia of all that metal. Of course when it's running there is no... or shouldn't be any... metal to metal contact. Everything is supposed to be riding on a film of oil .. but damn! At 2,000 or 3,000 rpm, with pistons flying up and down and valves opening and closing and rod and main journals spinning on their surfaces... it's amazing that it works at all.

I once read that an internal combustion engine is about 11% efficient at getting the power in the fuel to the wheels and I'm beginning to see why. The 11% number sounds low but with so much to be overcome just to move all the parts of the engine, I can believe it isn't terribly efficient.
 

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Premium Member
1986 560SL with M120 V12 Engine, 1988 560SL Stock
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10,504 Posts
Yup, that's what I did and with 7 & 8 installed alone the crank spun fine, so I installed them all and used more strength when turning the crank at the balance bolt and now it appears to be OK.

I have renewed respect for the power of an exploding fuel mixture... when running, the engine has no problem overcoming the inertia of all that metal. Of course when it's running there is no... or shouldn't be any... metal to metal contact. Everything is supposed to be riding on a film of oil .. but damn! At 2,000 or 3,000 rpm, with pistons flying up and down and valves opening and closing and rod and main journals spinning on their surfaces... it's amazing that it works at all.

I once read that an internal combustion engine is about 11% efficient at getting the power in the fuel to the wheels and I'm beginning to see why. The 11% number sounds low but with so much to be overcome just to move all the parts of the engine, I can believe it isn't terribly efficient.
Rule of thumb years ago (like 40 years ago) was 33% out the crank, 33% out the exhaust and 33% elsewhere (friction, radiator heat and block heat losses). It was actually more like 40, 30, 30. But I forgot which got the 40. I'm betting its a lot better now.
 
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