Chain Guides Replaced - PeachParts Mercedes-Benz Forum

wbain5280 · #1 04-18-2007, 11:59 PM

Today, I finished replacing the chain guides on my 420SEL. Some were actually missing or only a small piece was left. There were sone sections down inside the open area of the open area of the head where the chain goes and the chain wore out some material of the head itself. The chain had rubbed on some of the pins and wore a groove in them. I'm suprised this engine didn't self destruct. I will post pics of this operation as soon as I upload the pics.

I had to smash the distributor cap as the screws holding it on were frozen but the cap needed replacing anyway. I also have new wires on the way.

I also found that the passenger side sprocket is off by what looks like one tooth. I'll install the tensioner and check it the offset and realign it properly. I suspect I'll need a new chain.

Hit Man X · #2 04-19-2007, 03:52 AM

Looks like you saved the motor!

Did you do the tensioner lining too? The lining is very inexpensive and easy to swap.

wbain5280 · #3 04-19-2007, 05:54 AM

Yes, I did the curver tensioner chain guide, the old one was loose.

wbain5280 · #4 04-22-2007, 02:41 AM

jhodg5ck · #5 04-22-2007, 11:04 AM

that 2nd to last picture of your timing, is that where it ended up after all the work?

I'm going to wager your upper gears are quite worn (As well as the other gears but they're a PITA to get to).

How many miles are on that engine?

Jonathan

stevebfl · #6 04-22-2007, 11:16 AM

You have more than chain stretch involved with that timing issue. Somewhere the gear has been put on wrong. Move the gear forward a tooth. That gap is more than a tooth wide. Back when it was practical to dial indicate and compensate timing I used to see right side gears as much as 14degrees retarded after 250k miles. Fourteen degrees is a little over an 1/8 inch. A one tooth movement will change the timing 18 degrees.

Don't even think about offset woodruf keys unless you plan to do a real dial indicated measurement of timing.

karim · #7 02-05-2008, 10:32 PM

A question for Steve: I have changed chain guides,banana link ,hydraulic tensioner,and timing chain (420sel) the timing is exactly as it was prior to this work ie: with harmonic balancer @ tdc left cam is "spot on" on the mark while the right cam is lagging by a couple of MM from its respective index mark. As the engine ran well to begin with do you believe it is a common occurence?will jumping one tooth on the cam gear over advance it? When I match the cams simoultaneously to their respective index the harmonic balancer is showing 5 degrees retarded,is it worth investigating further?

stevebfl · #8 02-06-2008, 08:29 AM

I wouldn't worry too much about the marks. They always are a little retarded at the cams. If there is a significant difference between heads, it might be worth testing it completely. It's been years since I have done it, but the concept is to dial indicate the valve openning of cyl 1 and 6. In a hydraulic lifter car I think one is supposed to remove the hydraulic and replace it with an adjuster from the older mechanical lifter engines. Then one adjusts all the freeplay out and turns the motor till the valve is depressed 2mm. At that exact point the degree measurement is observed on the crank and compared to the appropriate value for that valve from the TDM (technical data manual).

If it is off 5deg or more then offset keys are available (or atleast they were) to correct. They were available in 2,3,4, and 5 deg. This is cam degree which is doubled at the crank, so it really is 4, 6, 8, and 10 degs. Since a single tooth is 18 degrees one can get about anything within 2 degs by using the offset to advance or retard. In other words I used to see a lot of chains stretched such that the right cam was 14 deg retarded (at the crank). By jumping the chain a tooth it became 4 degrees advanced, then using an offset key to retard it 4 deg it was perfect.

karim · #9 02-06-2008, 09:23 AM

Steve thank you for your informative response. I take it then at the cam my lag is 2.5 degrees ,which as you suggested , not worth worrying about. It's good to get some ones perspective on things.I will proceed and button the old girl up .

jhodg5ck · #10 08-04-2012, 08:15 AM

yup, passenger side.

As an update to the general procedure, i STRONGLY recommend getting your hands on a valve spring compressor and removing ALL the rockers.. I'm seeing so, so many fail these days. Even if the cams etc all look OK it pays to inspect the rockers before it becomes a problem.

You can thank the modified oils and their lack of anti wear/zinc-phosphate additives for the problem.

It is Rare for me to open a car up and not find rockers that are in need or replacing.

Jonathan

macdoe · #11 08-04-2012, 02:00 PM

Yes I agree with you on that. The pass. side cam looks to have some scoring on a couple of lobes. It is not really bad and is basically on the irrellevant slope of that cam. I took the oil tube off to clean out the holes. It looks like this was caused by a lack of oil to the cam oiler tube or a hole got plugged up for a bit and then cleared itself. I have a good set of used cams but I am pretty sure I mixed up all the rocker arms when it got dissassembled, plus that engine had timing chain failure so I am not sure about using those rockers.

I might have to save up to buy lots of parts for that and do that job down the road....I would like to change the head gaskets at the same time since I would have to loosen some head bolts to get the cams out and I don't like loosening head bolts unless the head is coming off. And if the heads are coming off then I may as well take the timing cover off and do the lower guides and then may as well replace all the rubber in the intake tract and then I will be into may as well drop a +145 load of money into it territory. If I go that far then I may as well have the heads re-done too.

I can't afford it right now but it is on my mind that the rockers and such should be done. Good point especially if you are experiencing that type of phenom. Thanks for that info.