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Car Forum / Mercedes-Benz Cars / January 2008Valve Stem Seals Again
I replaced the valve stem seals on my 560sl a while ago, but the car recently started blowing blue smoke on start up, and three plugs are now oily. I would therefore like to replace the seals on just those plugs now and the others later, if I need to, rather than replacing all of the seals now. I was thus wondering whether I need to remove all the plugs and/or rocker arms to turn the engine by hand, or whether I can get away with removing just the rocker arm and plug of each cylnder, as I'm working on it. Also, I was wondering whether I should clean out or replace the camshaft oiler tubes while I'm in there, considering that the car has about 175k on it? Thanks in advance for the help. Larry It is much easier to remove all plugs to turn engine over. Yes, just replace those three. Yes, replace the oil tube as it does get brittle. Thanks Tiger. You're the best :-) >It is much easier to remove all plugs to turn engine over. > >Yes, just replace those three. > >Yes, replace the oil tube as it does get brittle. You may want to check the guides on those oil burning cylinders. They are probably loose in the head and go up and down like a hydraulic pump! > Thanks Tiger. You're the best :-) > [quoted text clipped - 3 lines] > > > >Yes, replace the oil tube as it does get brittle. Thanks, Karl. I was wondering how much pressure to put on those guides when I installed them, and what held them in place while the stems were rapidly moving up and down. Seemed to me they would be prone to come loose, and maybe they did. Did you or anyone else have this happen to seals, and is there any sure way to avoid it in the future? Larry >You may want to check the guides on those oil burning cylinders. >They are probably loose in the head and go up and down like a hydraulic [quoted text clipped - 7 lines] >> > >> >Yes, replace the oil tube as it does get brittle. The guides are a very tight press fit. They come in over-sizes on the outside dimension. We would freeze the guides in liquid R-12 and pound them in with special drivers. They have a ring on them to stop them in the correct position and the special drivers limit their depth when installing. If they slide out with no or very little pressure, you need new guides. 11 are the guides here: http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=107048&M=117%2E967&GA=722%2E313&L=76 5%2E707&CT=M&cat=14M&SID=01&SGR=065&SGN=06 Standard on the intakes are 14mm and the exhausts are 15mm. Repair size I is 0.20mm over and repair size II is 0.40mm over. The ring is #14. You need the heads off and the valves out to do this correctly and then a valve resurface. [I have replaced one guide in the car, but I do not recommend this!] > Thanks, Karl. I was wondering how much pressure to put on those guides > when I installed them, and what held them in place while the stems [quoted text clipped - 15 lines] > >> > > >> >Yes, replace the oil tube as it does get brittle. Oops! I thought you were talking about the seals coming loose. If the oil burning is, as you speculate, caused by the guides -- which I hope it isn't -- I guess I'm just going to have to live with it, since I can't afford a valve job right now. Then again, since the car's only using a quart every 500 miles or so, I can live with it. Thanks for your input, though, Karl. It's always appreciated. Larry >The guides are a very tight press fit. They come in over-sizes on the >outside dimension. We would freeze the guides in liquid R-12 and pound them [quoted text clipped - 33 lines] >> >> > >> >> >Yes, replace the oil tube as it does get brittle. >The guides are a very tight press fit. They come in over-sizes on the >outside dimension. We would freeze the guides in liquid R-12 and pound them [quoted text clipped - 13 lines] >valve resurface. [I have replaced one guide in the car, but I do not >recommend this!] Karl, As it turns out, your suspicion was right on. When I removed the rocker and springs on the valve that was burning oil, I saw that the guide was loose. Can you tell me how one goes about replacing a guide without removing the head, how difficult it is, and why you don't recommend it? (I can guess but I'd still like to hear it from you ). I'm asking because I can't afford a complete valve job right now, but I';d like to stop burning oil, if possible? Thanks very much in advance. >The ring is #14. It also just occurred to me. Is this just a brass ring that goes around the guide, and if so, does the valve stem seal hold it in place? If that's that case, maybe the valve stem seal lifted up, allowing the ring to move up and down? But, then again, I'm pretty sure that the guide and ring were moving up and down together, and I tried pushing the seal down to hold the ring in place, but the seal wouldn't move . Besides, the guide should definitely have been anchored in the head, right? Thanks Karl or anyone for clarifying this for me. >>The guides are a very tight press fit. They come in over-sizes on the >>outside dimension. We would freeze the guides in liquid R-12 and pound them [quoted text clipped - 27 lines] > >Thanks very much in advance. The snap ring is just a thin piece of steel in a groove. It is there just to mark the depth of the guide when you drive it in. The guide is a tight press fit. They are driven in with a tool and a big hammer. You need to be very very lucky to be able to replace one in the car. The piston has to be lowered so the valve rests on it because it has to be at least half way down the guide when you drive the new guide down. Once you drive the new guide in, then you bring the piston up which brings the valve up. When it clears the top of the guide, you put air in the cylinder to close the valve so you can install the, valve stem seal, spring, retainer, and keepers. Hopefully, the valve seals compression...... Not a job for the faint at heart! > >The guides are a very tight press fit. They come in over-sizes on the > >outside dimension. We would freeze the guides in liquid R-12 and pound them [quoted text clipped - 27 lines] > > Thanks very much in advance. Thanks for the explanation, Karl. Can you tell me why engine manufacturers couldn't have made it much easier to replace valve guides sumply by screwing them into the head from above? Thanks >The snap ring is just a thin piece of steel in a groove. It is there just to >mark the depth of the guide when you drive it in. The guide is a tight press [quoted text clipped - 46 lines] >> >> Thanks very much in advance. They have been press-in from the beginning. They have to be a softer material then a valve stem. Wear is always going to happen. More than likely, cost is a factor. When MB came out with the 722.6 trans, we were amazed at the amount of crap in it, i.e. small bits of aluminum from the machining operations. They never flushed or deburred them! At one of the training classes, a tech asked why MB did not spend more time cleaning them. I said it was the cost factor. If you spend $15 more on each case then times it by 1 million cases, that equals $15 million dollars spent. Cheaper to have a few fail...... > Thanks for the explanation, Karl. Can you tell me why engine > manufacturers couldn't have made it much easier to replace valve [quoted text clipped - 17 lines] > >> > >> >The guides are a very tight press fit. They come in over-sizes on the > >> >outside dimension. We would freeze the guides in liquid R-12 and pound > >them [quoted text clipped - 31 lines] > >> > >> Thanks very much in advance. >The guides are a very tight press fit. They come in over-sizes on the >outside dimension. We would freeze the guides in liquid R-12 and pound them [quoted text clipped - 9 lines] > >The ring is #14. It just occurred to me. Is this just a brass ring that goes around the guide, and if so, does the valve stem seal hold it in place? If that's that case, maybe the valve stem seal lifted up, allowing the ring to move up and down? But, then again, I'm pretty sure that the guide and ring were moving up and down together, and I tried pushing the seal down to hold the ring in place, but the seal wouldn't move . Besides, the guide should definitely have been anchored in the head, right? Thanks Karl or anyone for clarifying this for me. You should be able to turn the motor by hand with all the spark plugs installed. Grab the drive belt(s) to say, the power steering or fan, and pull with one hand and push with the other and it will turn the motor in small increments. That's how I turn my diesel when adjusting its valves.  Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. Thanks for the advice, T.G.. However, I once tried rotating the engine by turning the power steering bolt to check for chain strectch, as you once suggested. But only the belts and alternator rotated. I would sure prefer to rotate the engine your way, rather than at the harmonic balancer, if at all possible. Did I do something wrong? >You should be able to turn the motor by hand with all the spark plugs >installed. Grab the drive belt(s) to say, the power steering or fan, and >pull with one hand and push with the other and it will turn the motor in >small increments. That's how I turn my diesel when adjusting its valves. The big bolt at the harmonic balancer is the proper position to turn over the engine. That is what the manual specified and what I did on my 380SE. Good point, but by pulling and pushing the belt itself with your two hands additional tension is applied. Try it. Signature© 2007 T.G.Lambach. Publication in any form requires prior written permission. |
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