- 3 Min Read
- By: Alex Fiehl
Mercedes 450SL Timing Chain - Part 1
One of the most challenging jobs on the 1975 450SL will be the timing chain. It starts out innocently enough but will take on a life of it’s own.
1975 Mercedes 450SL timing chain
While learning can be a challenge, it’s always worth the time and in the process we will discover how to and how not to do something. You will also gain a great deal of knowledge on how your Mercedes 450Sl really works and how Mercedes did things.
Evaluating the Mercedes Timing Chain
First Evaluation: If your 1975 450SL has 100,000 miles on the odometer and has not had the double-row timing chain replaced, DO IT! (NOTE: a few model years came with single row chains that were prone to break). You will be presented with one of three options. First, you will do it yourself, second you will take it to a shop to do it for you, or if you are fortunate, you will help a friend do the deed who has a shop.
Second Evaluation: Regardless of whether or not the chain has been replaced, if you have recently acquired a 450SL check the timing for your self. The following is a step by step procedure on how to check the timing:
Step 1: Remove righthand valve cover. That will be the left cover if you are in front, facing the car. 10mm socket required to remove valve cover bolts.
Step 2: Remove spark plug number 1. It is the plug closest to the front of the engine.
Step 3: Use a Vacuum/Pressure gauge by threading appropriate brass fitting in to spark plug hole
and connecting vacuum line and gauge. Do not tighten, just snug to stopping point.
Step 4: Use either a 27mm or 22mm on a breaker bar to turn the engine over in a clockwise
direction only. (NOTE: In order to turn the engine over with the radiator, fan and shroud still in place, you will need to utilize the bolt on the power steering pulley. Otherwise, you will turn the engine by the crankshaft pulley bolt.) Turn slowly.
Step 5: While rotating engine, observe gauge. When pressure begins to build, start watching for your timing marks to align. When the timing marks align at this stage, the engine is at TDC.
NOTE: Should you continue past the timing marks, your gauge would begin to register on the vacuum side. If you do miss the mark, start over). Having the engine at TDC matters, don’t just align the marks, as different readings can take place at different positions. The image shows the marks you will need to look for on the top of your camshaft and gear.
Step 6: Now that the camshaft timing marks are aligned and the engine is at TDC, you will now look at the timing marks on the vibration damper (harmonic balancer) as indicated in photo.
Step 7: Look at the position of the pointer and corresponding number or line. (NOTE: The timing “pointer” is attached to the lower right corner of the water pump). The marks are in increments of 5. In the case of this photo, the engine is 10° (degrees) after TDC, indicating the timing is 10° off. In this case, my odometer has 110,000 miles recorded and I know the timing chain has not been replaced. Again, in this case I know the 10° is due to chain stretch and worn gears, so time for a new chain. One way to tell if the chain has been replaced is to look at the guides that are visible after removing the valve covers. If they are chocolate colored and grooved, they are old. One would hope if the previous owner had put a new chain in they would have replaced all the guides, but don’t take chances.
Step 8: Knowing you need to replace the chain before the timing gets worse and engine damage occurs, it is time to order the necessary parts and they are as follows: 1X double row timing chain, 1X Tensioning guide/rail (NOTE: Only the rail should need to be renewed, but check the metal guide for damage), 6X Slide rails (NOTE: These rails are not all the same), 1X Chain tensioner (NOTE: This part also serves as the connection point for the emissions air pump.), 2X Camshaft sprocket, 1X Crankshaft sprocket, 1X Chain Link Press (Baum Tools, part number 000-5843), 1X yellow paint marker.
If you are at 200K miles and on your second chain, you should pay close attention to your oil pump, oil pump chain and driven gear for wear and replace if needed. The guide wheel should not need to be replaced but check carefully for excessive wear. Also check tension spring and clamp for excessive wear.
Checking all your Mercedes timing chain parts
Once you have received all your parts, it is critical to verify each and everyone against the specified Mercedes part number. There are many chassis number splits and it is critical that the parts be exact for your chassis. There are also Federal and California variants, which can also cause a world of confusion if you are not careful when ordering. FCP is very helpful when placing a parts order.
Step 9: Now the fun begins! Stay tuned for the next blog post as we prep to get the chain out.
Helpful tools for your Mercedes
This Fuel-O-Vac® Compound Meter (fuel/pressure/vacuum gauge) is a great tool to have in the garage.