to replace timing chain guides, must I remove cylinder head? - PeachParts Mercedes-Benz Forum

ktlimq · #1 03-31-2004, 07:36 PM

1992 300D.

Then should I replace head gasket (even if there is no leak yet) at that job?

md21722 · #2 04-01-2004, 08:26 AM

Why do you want to change the chain rails?

They usually last the life of the motor.

md21722 · #3 04-01-2004, 08:30 AM

Generally speaking, its not a good idea to pull the head on a well running engine. There are all sort of things that MAY go wrong as a result of pulling the head. If the engine is well cared for, the timing chain will last the life of the motor. So will the rails. There were some problems with head gaskets, but if its not leaking, overheating, or mixing fluids, I'd leave it alone. Head gaskets are not PM. If the chain isn't "stretched" past its wear limit, I would leave it alone.

md21722 · #4 04-01-2004, 08:32 AM

To answer your original question, I'm not sure. I believe the upper rail can be done with the head in place. Two slide pins need to be removed. They are pulled out with a slide hammer or an extractor type tool. The tensioner rail may need removal of the timing cover ($$$).

ktlimq · #5 04-01-2004, 09:06 AM

I am not sure but it seems that tensioner rail needs removal of cylinder head.
An upper guiding rail and a lower guiding rail can be replaced without removal of cylinder head.

Of course not. I do not want to remove cylinder head. I am going to do an oil analysis to see whether my engine mixes fluids.

I get 25 mpg compared to 30 mpg last summer (with almost the same highway and city ratio). A dealer tech said timing chain (even if it were stretched) might not be responsible for 20% decrease in mpg.
He said it might not even be worth measuring timing chain stretch or worrying about the chain.

While an indi recommended immediately replacing chain without even measuring the stretch on my 230 000 mile car.

md21722 · #6 04-01-2004, 10:21 AM

One of the easiest ways to check the timing chain "stretch" is to remove the valve cover & line up the marks on the cam and read the pointer on the crank pulley. The # of degrees it reads would be the "stretch". This has been covered repeatedly in previous threads so a search should bring up pictures & other goodies. Larry Bible will probably say it needs to be done with a dial indicator. However, many of us are getting useful #'s without using the dial indicator. Have a new valve cover gasket handy when you do this if the gasket hasn't been changed in a while. There is NO reason to change the chain just because your car has 230Kmi - unless you like spending money. Same with the rails. Diagnose the problem before throwing money at it. With fuel economy decreases, there are a lot of EXPENSIVE things that can be changed without fixing your problem. Its not like changing a $2 part to see if it helps. Also worthwhile to check pump timing. A restricted catalytic converter, dirty injectors, air intake issues, dragging brakes are also possibilities. Operating in the winter will reduce fuel economy. The fuel is lower BTU so it won't gell. Cars take longer to warm up (and they don't run as efficiency when cold). Fuel QUALITY also makes a big difference. In my MB's fuel economy can vary 20% based on station to station differences even in the same season. Even if your head gasket is blown you may not have any fuel economy issues with that.

ktlimq · #7 04-04-2004, 04:05 PM

Thank you for your replies.

About the station, I have been using Power Petroleum, because it has been offering diesel fuel at lowest price in my town. But, I will try Citgo next time. Mobil and Shell diesel stations are more distant from my place.

joe p · #8 04-04-2004, 06:25 PM

If you chose to replace the chain and rails you DO NOT need to remove the head for the tensioner rail. Remove the lower cover, break the old rail and remove the pieces, remove the big pin with a stud puller, place the new rail in its proper location and drive the big pin home. Nothing to it and it saves pulling a head for no real reason.

Joe

ktlimq · #9 05-05-2004, 03:49 PM

A shop's invoice:

Found valve cover gasket leaking, R&R air intake tube and valve cover gasket, to replace valve cover.
Also found timing chain stretched to max-spec. Customer declined to repair.

(I did not ask about timing chain or cam gasket, but they themselves inspected it and even replaced valve gasket without calling me.)

Now I just recived phone call from another mechanic. In this case, I told the mechanic to inspect timing chain. He said the stretch is less than 1 degree.

Shall I have the timing chain inspected by another mechanic?

md21722 · #10 05-05-2004, 04:04 PM

Why not just measure it yourself?

I have talked to a few mechanics and none knew how to check a diesel timing chain. They usually saw "we never change them".

If the car has oil changes by the book, it should last the life of the car. Its not like a gas motor where it will rattle and break rails.

ktlimq · #11 05-05-2004, 04:38 PM

The mechanic said the wear condition of cam sprocket is fine, and the chain "feels tight" too.

I have no experience working on car engine.
I am not sure I can correctly remove and install things correctly (especially the things above cam cover - turbo related stuff? ).

md21722 · #12 05-05-2004, 04:49 PM

How long have you owned the car & how often do you change the oil?

ktlimq · #13 05-05-2004, 05:05 PM

I bought it last May.

Dealer's (used car dealer, not MB dealer) oil change at purchase.
After 4000 miles (Castrol 20W-50).
After 4076 miles (Castrol 10W-40).
After 2778 miles (synthetic 20W-50) in April, 2004.

ktlimq · #14 05-05-2004, 05:14 PM

By the way, on this board, I readd that we must not rotate the crank reverse direction. But the tech rotated the crank a little reverse to check tightness. He said when he worked on stretched chain, he could feel free play when he rotated crank back and forth.

md21722 · #15 05-06-2004, 08:41 AM

Turning the engine in reverse a 1/4" or so won't hurt it. I've never heard that rocking it back and forth can "feel" stretch. That sounds ridiculous to me.

Severe service oil changes are 2500 mile intervals (city driving, winter months). The Castrol 10w-40 and 20w-50 oils aren't rated for diesel service. I wouldn't go more than 3000 miles on those oils. Get Chevron 15w-40 or Mobil 1300S 15w-40 or Shell Rotella 15w-40 (truck diesel oil) next time.

Regards,