PeachParts Mercedes-Benz Forum - View Single Post

tcane · #12 02-15-2002, 10:47 PM

Before getting a junkyard engine I would do a TDI to find out what's wrong with yours. It sounds like #1 rod is bent since the roughness is on every rotation of the crank. One rod costs about $100 and replacing the bent rod would seem to be the least expensive and least time consuming way to fix your engine. Also, M-B rods for the 300D come in 5 weight groups with rods having a weight within 4 grams of each other are grouped together and then installed into a particular engine, then once that engine is assembled, the engine is dynamically balanced and the flywheel has material removed to achieve a balanced engine. Replacing one rod requires matching the weight of the replacement rod to the ones already in your engine to keep the engine's balance and avoid vibration. A machine shop can do the weighing and matching for you - unless you have the equipment to do this. You would be very lucky to find a junkyard engine with the same rods as your engine - unless the crank is ruined in your engine (unlikely) then you would use the crank, all the rods, and the flywheel from the junkyard engine to keep the engine's balance.

I just removed a 300D engine, rebuilt that engine, and I am getting ready to install it this weekend. I made my own engine hoist sling because the engine comes out at a 45 degree angle to clear the firewall. Look at your engine and you will see attached to the back of the head a stamped piece of metal with a large diameter hole in either end - this is the attachment point M-B uses to hoist the engine. On the front of the head connect the hoist chain to the bolt with a 19mm head located about in the center that connects the AC bracket (York compressor) or another bracket to the head. Get the picture? The hoist chain is a single chain connected to the front of the head that then splits into a Y attaching to the bracket connected to the back of the head. I made my hoist chain using 5/16" chain, one piece is four feet long and another piece that is two feet long. Connect the two foot long piece to the four foot long piece about in the middle of the four foot long piece with a strong 5/16" bolt with thick washers on either side. This set-up keeps the engine straight up and down so it is easier to hoist it out of the car (if you use a hoist chain/sling that attaches to only one place front and back the engine will tilt to one side making it harder to remove). Then I used two 5/16" quick links that I connect to the chain and then connect the quick links to the engine lift (I used two quick links for security). The quick links are oval in shape with a nut that completes the oval to ensure a strong connection. Attach the quick links on the single chain about mid-way between the oil filler cap and the throttle linkage on the valve cover so the engine can be hoisted at the extreme angle needed to get it out of the engine compartment. I did find one problem with the 5/16" chain - the 19mm bolt on the front of the head has a shank dia. of 12mm that is slightly larger than the inside dia. of the chain link - so I used a file to remove a bit of material so the bolt slides through the chain. You can use a 3/8" chain and 3/8" quick links to avoid having to file on the chain. The chain hoist costs about $10 to make - well worth it in my opinion.

Removing the engine is pretty straight forward, but I strongly urge you to get the Haynes manual because it has very good instructions on removing the engine. Other than the lock nuts on the flex disc I mentioned before, the other things that are unusual are the removal of the engine shock (you need either a 7mm or 8mm open end wrench to hold the shaft to remove the nut holding the shock to the frame) and the transmission stays attached to the engine when removing the engine - so the transmission mount cross member needs to be removed and a jack to hold the trans and engine up (both the M-B and Haynes manual leave the cross member in place). It is very hard to reach the top bolts attaching the trans to the engine and they will need a lot of force to loosen that is hard to do when laying on your back underneath the car (now, if you can put your car on a lift that is a whole different story . . .).

Pistons and liners are the same price for both the 240D and 300D, and have the same dimensions (91.00mm pistons). In mid 1978 M-B changed the piston diameter to 90.90mm to reduce engine displacement below 3,000cc for tax purposes in countries using engine displacement as the basis for the tax rate charged). The 90.90 pistons cost the same as the 91.00 pistons. The liners are the same for the 240D and all 300D's. These parts are easy to find.

If the pistons are in good condition and measure to within spec using a micrometer, and the cylinder liners are worn beyond spec (the stock piston rings are chrome faced and hard on liners, especially the early engines, Larry and I have corresponded about this and techs I've talked to confirm this) then you can R&R the liners for about $275 machine shop cost (R&R liners, boring and honing, mill the block), plus about $175 for all new liners ($35 each), plus about $170 for new rings (I know where they cost $94). New pistons cost about $130 each for standard size plus boring/honing to size. Or, 91.50mm oversize pistons cost about $150 each plus boring/honing (and increase displacement to almost 186 cu.in. from 183 - feel the power!).

Or, if your engine is in really bad shape and you have the GM-type AC compressor in your car then you might want to consider getting a turbo 300D since your salvage yard sells them cheap. As I understand it, you can put the turbo in your car with minimal modifications (especially if you have the GM type AC since the AC lines are routed similarly). If you have the York AC then the turbo can still be done, it just takes a bit more work. I'm sure some other members know about this swap and can provide more info than I can. A turbo would make your car really fly! Also, the 300 engine blocks are the same other than the length of some of the threaded studs various accessories are mounted to - so any 1977-1985 300D engine will fit into your car.

One thing I will caution you about getting a junkyard engine - take the time to remove the head before buying or removing the engine from the car (if the place you're buying from is cheap because you remove the engine). If the engine has a blown head gasket and this has damaged the head and/or especially the block significantly - then it is far better to find another engine. Check the oil pan also for debris. I bought a junkyard engine to replace mine because a blown head gasket ruined the head and block. I pulled the head off one engine that was in worse condition than mine (took me about 2 hours to remove the head). The next engine was all but perfect upon removing the head and the inside was very clean. I could even see the different colors of the two types of valve stem seals it was so clean (turns out the engine was a nearly fresh rebuild with a lot of new parts and oversize 91.50mm pistons). I bought that engine and stripped it all the way down to check everything and other than a minor amount of rust in two cylinders (that honed out) the engine is in very good condition. New rings, lap the valves, new gaskets and seals, and a rebuilt engine is nearly ready to drop into my car (plus some other work besides the engine). The biggest problem with this engine is it is one of the filthiest engines I have ever seen (it looked like when a quart of oil was added that 3/4 went into the engine and 1/4 was poured all over the engine and the hood pad disintergrated all over the engine mixing with the oil - in many places the crud was 1/2" thick or more). Turns out the front crankshaft seal wore a big groove in the crank spacer ring and the resulting oil leak was very severe (I removed one of the engine mounts from the block and poured a lot of oil out of it!!). I've spent more time cleaning and scraping off oil/dirt/crud than I have on mechanical work.

From reading a lot of Larry Bible's replies, I believe he takes issue with the 5 cylinder engine because it is harder to remove and install when compared to the 240D because it is longer (the extreme 45 degree angle to clear the firewall), it is easier to install the 300D with the trans removed (meaning you have to install the trans separately and more work), and the 240D can be installed with the trans attached to the engine. The 300D's one additional cylinder means it costs 20% more to rebuild over the 240D (one more piston, one more liner, camshaft costs more, etc., etc.) and more cost to have machine shop work done. Larry has some issues with the 300D's reliability and he believes the 240D is more reliable. Also, the power of the non-turbo 300D (77 horsepower) is not enough over the 240D (70 horsepower) to justify the additional cost. That said, I am not putting myself in Larry's place by saying the above as Larry can tell you what he thinks - I'm just repeating what I've read and I will freely admit I have not read everything Larry has written and he will probably take issue with what I wrote and correct me letting you and I know what he really thinks.

Oops, sorry this is too long.
Good Luck!
Tom