I bought a '79 300SD with a broken chain. Upon further investigation I found out that the chain broke on start-up. I am hoping that the lower end is okay. I know that the cam towers were broken so I will replace the head with a good one. If the lower end is no good then my following question will be moot. For right now we'll just say that the lower end is good.

My question is: How would a person install a new chain? Will the engine have to be removed? Will the person be able to feed the new chain in if they drop the lower pan? How, how, how?

Kevin

If you can get a hold of both ends of the chain you can pull in a new one with the engine in the car. If it broke on startup, it shouldn't have spun much after the break. My chain broke on startup and the chain was still on top of the valve sprocket...the other end was wrapped around the crankshaft sprocket.

I'm surprised the cam towers are broken with the chain break occurring during startup.

Good luck.

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1976 240D
1987 560SL
2007 E320 Bluetec
1998 C280 (now son’s car)
1982 240D Manual - Sold

Having dropped a chain while changing it, I have the following advice:

One, if it ran OK (no valve problems before the chain broke), remove the cam towers and cam. Press down on the valves and see if them move freely and close properly. If they do, I'd risk just installing the chain. With the followers out, you can rotate the engine and cam independetly without valve to piston interference. You will have to be able to turn the crank to check them all, but none of the ones on the 220D engine I just got were stuck. If the chain is still on the sproket, wire tie it in place.

Get new towers and re-install the cam minus followers.

Make some long wire hooks to fit the links on the chain. You will need several to that you can untangle the chain once you get it free and pulled part way up. Flat sliver solder or braze rods are just the right width to fit into the links sideways. A steep hook will let you pull up on a link or side plate. Coat hanger wire will also work. Make the hooks deep enough that the chain won't slip.

If you can reach it, remove the bolt pin for the tensioner rail and pull the rail -- if the crank won't turn yet, leave it be.

Get a good light and peer down into the chain case. Probably need to remove the upper chain guide, but if the chain is still on the cam, wire tie it on and leave the upper guide in place. You will see the chain down there, it's very unlikely to have run into the oil pan.

Get a hook into whatever you can see and pull it up as far as you can. If you get a loop, work to the free end. If the crank won't turn, pull the chain up as much as you can and turn the crank gently BACKWARDS. Don't drop the chain as it can wind down into the oil pan. Crank should free up and release the chain. Don't turn any more than it takes to get the chain free.

Once you get the free end up, link new chain to old and roll through. Timing is probably all messed up, so just don't drop it down again! If you have the tool, or a helper, and the chain was still on the cam, go ahead and keep it on the cam as you go round.

Once you get it in place, crimp the link. Set crank to TDC and remove cam sprocket, set cam to TDC and re-install sproket. I'd stick some wire through the chain once you get the crank to TDC so you won't drop it again while messing about with the sproket.

Pull IP and set engine to 24 BTDC (non turbo) or 26 BTDC (turbo) on compression on #1, set IP to start mark, install IP and set timing with a drip tube.

Re-install cam followers in original position, replace valve cover, and start!

If the vavles are sticky, it time for a valve job, not a new head.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!