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  #31  
Old 04-22-2009, 07:25 PM
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Hello guys:
Yesterday I brought my 1982 MB 617 engine with 244Kmiles to a mechanic and explained to him about the leak from rear oil seal (the rope seal) and also I mentioned to him about the pressure on crank case. He took the dipstick from it's place and with engine running in about 1700 RPM with his thumb he plugged the tube for dipstick. He said that there are no pressure from crank case. The next test that he did was to open the oil refill cap on top of the valve cover and he said that the blowby or pressure in that place is too much. At this point we start to discuss why the pressure is too much and according with his experience he said that most engines have this pressure too high when valve guides are worn out causing pressure from combustion or stroke to flow into the valve cover building that kind of pressure. I asked him about the piston seals or rings be worn out and his answer was that if the piston rings were bad that pressure will coming through the dipstick tube because a leak from stroke will go to crank case and then out through dipstick tube and not from valve cover as it is now.
It make some sense to me but I would like to hear what you folks have to say about it.
Thanks

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  #32  
Old 04-23-2009, 01:18 AM
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LOL!
At idle the only pressure that could get by worn Valve Stems/Valve Guides/Valve Stem seals would be from the Exhaust side of the Valve System. At higher speeds even more so. (an exhaust restrection like a collasped Muffler could also raise the pressure.)

At higher RPMS if you have a Turbo the intake would also be under pressure and some pressure could leak by worn Exhaust Valves/Valve Guides/Valve Stem Seals.

Since the area under the Valve Cover is connected to the rest of the Crankcase by way of the space where the Timing Chain/Timing Gears are the pressure should be close to the same in the Crankcase and the in the Valve Cover. So no matter if Blow-by is causing the pressure or worn Valve Stem/Seals is causing the pressure or both of them are contributing to the pressure the space is connceted and the pressure should be similar.

Blow-by past worn Pistons and Rings as a cause of high Crankcase Pressure is just too well known to comment further on.

I do not know how it happens but some good Mechanics do not know how some of the things they work on function and some Mechanics know all of the Theory of how things work but are not good Mechanics.
This is why you need to learn the why and wherefores for yourself so that you can decide what is resonable when they tell you something.

Right of wrong my opinion:
Unfortunately the comment by the Mechanic on Blow-by not being the possible cause of the high Crankcase Pressure makes me suspect that the Mechanic was trying to sell you a Cylinder Head Job; something that he can do in his shop.
And, not a Engine rebuild job that would fix the Blow-by problem; that you would not go for because it is too expensive or it is more than he could handle.

If you want to you can find out if the Valve Stems/Guides are worn without removing the Cylinder Head. The FSM has instructions on how to do so.
To do this you should pull of the Valve Stem Seals from the ones you plan to check (you do not have to check all if you find a few are worn beyond spec.) but you would need to buy a set of Valve Stem Seals as after removing the old brittle ones they probably will not be reusable.
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Last edited by Diesel911; 04-23-2009 at 01:26 AM.
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  #33  
Old 04-23-2009, 01:39 AM
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Try this test but be careful.
At idle remove the Dipstick; now plug the breather hole in the top of the Valve comver (with the Oil Fill Cap installed). Now that the pressure has no place to go I am betting it will push Oil up the Dipstick Tube.
If it will not push Oil out of the tube at Idle try increasing the Engine speed a little at a time.
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  #34  
Old 04-23-2009, 10:30 AM
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Quote:
Originally Posted by nyko46 View Post
Hello guys:
Yesterday I brought my 1982 MB 617 engine with 244Kmiles to a mechanic and explained to him about the leak from rear oil seal (the rope seal) and also I mentioned to him about the pressure on crank case. He took the dipstick from it's place and with engine running in about 1700 RPM with his thumb he plugged the tube for dipstick. He said that there are no pressure from crank case. The next test that he did was to open the oil refill cap on top of the valve cover and he said that the blowby or pressure in that place is too much. At this point we start to discuss why the pressure is too much and according with his experience he said that most engines have this pressure too high when valve guides are worn out causing pressure from combustion or stroke to flow into the valve cover building that kind of pressure. I asked him about the piston seals or rings be worn out and his answer was that if the piston rings were bad that pressure will coming through the dipstick tube because a leak from stroke will go to crank case and then out through dipstick tube and not from valve cover as it is now.
It make some sense to me but I would like to hear what you folks have to say about it.
Thanks

Hi

Find another mechanic. That guy doesn't know his a** from a hole in the ground!

Good Luick,

Joseph
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  #35  
Old 04-23-2009, 06:21 PM
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Quote:
Originally Posted by Diesel911 View Post
LOL!
At idle the only pressure that could get by worn Valve Stems/Valve Guides/Valve Stem seals would be from the Exhaust side of the Valve System. At higher speeds even more so. (an exhaust restrection like a collasped Muffler could also raise the pressure.)

At higher RPMS if you have a Turbo the intake would also be under pressure and some pressure could leak by worn Exhaust Valves/Valve Guides/Valve Stem Seals.

Since the area under the Valve Cover is connected to the rest of the Crankcase by way of the space where the Timing Chain/Timing Gears are the pressure should be close to the same in the Crankcase and the in the Valve Cover. So no matter if Blow-by is causing the pressure or worn Valve Stem/Seals is causing the pressure or both of them are contributing to the pressure the space is connceted and the pressure should be similar.

Blow-by past worn Pistons and Rings as a cause of high Crankcase Pressure is just too well known to comment further on.

I do not know how it happens but some good Mechanics do not know how some of the things they work on function and some Mechanics know all of the Theory of how things work but are not good Mechanics.
This is why you need to learn the why and wherefores for yourself so that you can decide what is resonable when they tell you something.

Right of wrong my opinion:
Unfortunately the comment by the Mechanic on Blow-by not being the possible cause of the high Crankcase Pressure makes me suspect that the Mechanic was trying to sell you a Cylinder Head Job; something that he can do in his shop.
And, not a Engine rebuild job that would fix the Blow-by problem; that you would not go for because it is too expensive or it is more than he could handle.

If you want to you can find out if the Valve Stems/Guides are worn without removing the Cylinder Head. The FSM has instructions on how to do so.
To do this you should pull of the Valve Stem Seals from the ones you plan to check (you do not have to check all if you find a few are worn beyond spec.) but you would need to buy a set of Valve Stem Seals as after removing the old brittle ones they probably will not be reusable.

Dear Diesel911:
Your comments were realy helpful.
By the way, what means FSM?
About your suggestion of "plug the breather at the top of valve cover and check if the oil will come out from dipstick tube", I already did with the oil fill cap in place and the answer is: The oil came out from dipstick tube.
Also with dipstick removed from tube and breather removed from valve cover there still pressure coming out of oil fill cap if I remove it.
Now what should I do next?
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  #36  
Old 04-23-2009, 06:45 PM
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Quote:
Originally Posted by nyko46 View Post
Dear Diesel911:

Now what should I do next?

make sure your oil level is not too high.

then, a compression test.

and pray
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  #37  
Old 04-23-2009, 06:57 PM
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As jt20 said a compression test would give you more info. It would tell you if it is a worn out Cylinder/Piston/Rings issue or not.

It also could tell you something I think was not mentioned here is a leaking Head Gasket. It could show up as 1 obviously low cylinder compared to the other cylinders or 2 low cylinders next to each other with the others being obviously higher.

FSM = Factory Service Manual (If bought from the Mercedes Classic Center $19.99 + $7 shipping; you get it on 2 CDs).

As for what to do- if your Engine is worn out the choice is to Rebuild the engine, Replace the Engine with a used one or drive the Car until it will not run any more (use the Oil Fill Cap hole and make something to add some more ventilation so that the pressure is not high enough to force Oil out of the Rear Main Oil Sea).
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Last edited by Diesel911; 04-23-2009 at 07:07 PM.
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  #38  
Old 04-23-2009, 07:31 PM
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Quote:
Originally Posted by Diesel911 View Post
As jt20 said a compression test would give you more info. It would tell you if it is a worn out Cylinder/Piston/Rings issue or not.

It also could tell you something I think was not mentioned here is a leaking Head Gasket. It could show up as 1 obviously low cylinder compared to the other cylinders or 2 low cylinders next to each other with the others being obviously higher.

FSM = Factory Service Manual (If bought from the Mercedes Classic Center $19.99 + $7 shipping; you get it on 2 CDs).

As for what to do- if your Engine is worn out the choice is to Rebuild the engine, Replace the Engine with a used one or drive the Car until it will not run any more (use the Oil Fill Cap hole and make something to add some more ventilation so that the pressure is not high enough to force Oil out of the Rear Main Oil Sea).

Great help.
If is the same FSM = Factory Service Manual , I have it from Mercedes Benz with a different name:Model 126 Service Manual Library.
It also has 2 CDs and covers many other Mercedes Benz models like: 300SD, SDL,SE,SEL,350SD,SDL and eight more models.
I was thinking to buy a compression test kit just for that reason and I found this one at Amazon.com
http://www.amazon.com /Pro-Grade-Compression-Test-Diesel-Engines/dp/B0013G6ZYA/ref=sr_1_1?ie=UTF8&s=automotive&qid=1240529074&sr=8-1

Please let me know if it will be a good tool.

About used engine, I found an used for a reasonable price but the seller does not know about the compression on that engine. So it will be a risk taken and it is already removed from car.
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  #39  
Old 04-24-2009, 01:34 AM
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Quite a few members have used this on from Harbor Freight at $25 plus shipping. I bought for even less when it was on sale at one of their stores (you may have a store near you). However, I have never used it yet so I cannot comment on it. If I was you I would start another Thread and as who has used the Harbor Freight compression tester and the results.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=93644

I cannot compare the Amazon one to the Harbor Freight one. They may even be the same kit made in the same place. The Harbor Freight Kit has an adapter to take the compression through the Glow Plug hole and also has an adapter to do the same by way of the Injector Hole.

Buying an used Engine is always a gamble. If the Engine will crank over you can get some sort of a compression reading from it even if it is laying on a pallet.
However, even if the milage the Seller is telling you is correct this does not tell you if the Engine was overheated or run without Oil due to something like an Oil Cooler Hose leaking or just plain abused by the prior owner.
I think the best way to buy a used Engine is the get a whole car with some other problem like a bad body, trashed interior or bad transmission. This way you can run the Engine and maybe even test drive it.
It is a problem to get rid of it afterwards but there is other parts you can salvage form a whole car.
If you buy a used Engine buy itself you would be best off getting it from a Salvage Yard that gives or allows you to buy a warraty on the Engine.

Buying from the salvage yard would cost more but if you buy from a private seller and the Engine is no good you will have 2 no good Engines on your hands.

Another thought is to "Buddy Up" with someone local to buy a complete Car. You need the Engine but someone else may need the other parts on the car.
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  #40  
Old 04-24-2009, 10:20 AM
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Forgive me but I just don't get it. Is your car leaving a trail of white or blue smoke from the exhaust????? There is no mention I've seen. So far, all we have talked about is a pressure build up in the engine casing, causing oil to push out of the dipstick tube and the rear main seal. All engines have some blowby and pressure in the casing. That is why they provide for a means to vent the gases. If your engine is not venting gases from the crankcase, as it should, then why are you suddenly talking about the major expense of engine compression checks and possible replacement? You have said yourself that when you remove the breather hose, the oil no longer pushes up from the dipstick. I haven't seen here anything about finding the obstruction.

If you want to learn more about your engine, that's all well and good. But I don't understand the sudden jump to replacement engine, etc...
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  #41  
Old 04-24-2009, 10:31 AM
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X2. Drive it. I particularly would not be considering replacing the rear main seal on that engine. To do that, the engine must be removed. Why remove a questionable engine at significant expesne, only to replace it with one less oil leak? If you want a more informed opinion from the experts here, video your blowby from a warm engine with the oil fill cap off, post it here or on youtube and see what people think.
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  #42  
Old 04-24-2009, 10:56 AM
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Quote:
Originally Posted by nyko46 View Post
Dear Diesel911:

About your suggestion of "plug the breather at the top of valve cover and check if the oil will come out from dipstick tube", I already did with the oil fill cap in place and the answer is: The oil came out from dipstick tube.
Also with dipstick removed from tube and breather removed from valve cover there still pressure coming out of oil fill cap if I remove it.

CONFUSION:

I misinterpreted this quote to be: "I removed the breather hose and oil still came out of the dipstick tube.."

This is not an acceptable condition.

But it is wrong.

If you bring your engine to operating temperature, loosen the oil fill cap, rev the engine and the cap gets sucked back down, then your crankcase is breathing sufficiently.

sorry for the mix-up

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