Tune up help for a '74 450SL
 

I am going to be helping a friend with a tune up on her '74 450SL. She has had the car for a year and a tune up has not been done. She is experiencing sluggish acceleration, and some miss firing/sputtering.

My oldest Benz I have had in the past was a 1980 300SD. My oldest gas Benz is currently a '92 190E 2.6, which has it's timing computer controlled . So what I am saying is it's been a vey long time since I have had to deal with checking/seting the timing on a gas engine. I still have a timing light, but I need to know the specs for her car. She is in the midst of getting a manual for the car, but I would like to know what is involved now.

I have searched some threads and I see different numbers being thrown around. Does anyone know the factory specs for this engine and year. Also, what sparkplugs would be recommended. I am sure the ones listed in her original owner's manual have long since been superceeded. Per the parts catalog here, it shows a Bosch resistor plug. Is that correct? I thought Benz's used non-resistor plugs.

Any info you guys/gals can provide for doing a tune up, especially with regard to timing specs, would be greatly appreciated.

Correct, non-resistor plugs. The Bosch ones are hard to find but NGK non-resistor ones were still plentiful and a good choice last I looked.

5°ATDC timing with the vac connected should be the goal (7°BTDC without the vac lines connected). This is idle speed. It should get a good point, if you have an RPM gauge or timing light you can check spark advance it may serve you better. The likely culprit is dirty ignition points and/or dirty EFI trigger points.

Thanks for the numbers. I do have a timing light and the car of course has a RPM guage in it. Now as far as the ignition points and efi trigger points go, how do you clean these. I have never owned a car with points in the distributor (assuming that's where they are), or EFI points.

Thanks again.

Ignition points, if it has it (and I believe 74 does, I think 75 was the cutoff year) are simply replaced, and then set dwell with a dwell meter. The EFI trigger points are housed in the side of the distributor. Unplug them, remove the dist cap, and pull the distributor (mark where the rotor goes first) and then remove the points. Clean with a dollar bill, index card, business card. or some other non-abrasive material and re-install. If heavily oiled use electrical contact (not carb or brake) cleaner.

go to SL forum and search my name, if its a Djet , all the information you will ever need is there - trust me hahaha:)

When you have the distributor out, clean the breaker plate, advance weights, vacuum diaphragm also. free advance weights make for good running.

These are tricky, delicate, mechanical analog computers.

40 years of old lube gets sticky.

I have a friend with a 380SL with sluggish response needing this job.

Thanks for all the tips. I just checked both Bosch and NGK websites and neither one list non resistor plugs. In vain I went to the local Autozone and they didn't list any plug by any manufacture, that was non-resistor.

NGK should be available

Also worth checking the seals around the injectors. I did a lot of work on a 78 450sl, that had a poor idle and discovered that some "genius" had put gobs of silicone around the injectors. New seals, and it ran like it was supposed to. Tested it at over 150mph on the highway outside Cambridge England. :D

She had the seals looked at and some were replaced. From the couple of times I looked at the engine, all appeared to be up to snuff, no Mcparts. It has a brand new set of wires, Beru I believe. The dist. cap appears new also.

Ron, if you could get me the NGK part number, that would be great. Is there that great of a difference in the plugs, between resistor and non resistor? Also is the difference so great that it's worth turning over every stone to find them? Most of the guys at Pepboys, Autozone, etc, only know what is in the computer. In other words they don't know anything on their own, probably never heard of non-resistor plugs. That's why I went directly to NGK and Bosch's websites and they don't list anything. Thye both have the usual search engines/drop down menus for selcting parts. Again for both sites, they list resistor plugs.

Thanks again for everyone's tips/advice. This is her first Benz and I don't want her to get frustrated with the car and give up.

If the vehicle originally had non-resistor plugs, then it probably has resistance wires. Adding resistor plugs will cause an undesired drop in ignition voltage.

Here are the non-resistor NGK, BP5ES, $2.07 per plug, right from our forum sponsor's part site. Click "Buy Parts" above for the full catalog :)
NGK Spark Plug BP5ES NGK,W0133-1641869 - PeachParts

The wires for the D-Jet cars must be solid core. The boots and end caps themselves have the resistors. If memory serves, the boot for the plug is 5k ohms and the boot that goes on the dizzy cap is 1k ohms. Use a multimeter and make sure each wire is close to 6k ohms (give or take about 200). If the resistance is too high then the car will have no power, especially under load! A lot of aftermarket wire sets for the D-Jet cars for whatever reason cross with the more modern 560, 420, 500 etc engines and they are not the same and not compatible!

Speaking on the behalf of my friend and obviously me, thanks for all the tips. Just spent yesterday sorting out her car. The spark plug wires were new and fine. As a matter of fact the 5 ohms resistor rating was stamped on the metal sleeve around the boot. However this is what we found. All of her plugs were Bosch, yet 3 of them were newer than the others and they were resistor plugs. The others were WD7C plugs. So for 3 of the cylinders she had resistor plugs connected to resistor wires. So that certainly didn't help. The condition of the plugs were fine except #6. Though the electrode was ok, there was oil on the threads. We checked the valve cover gasket and it wasn't coming from there. Any ideas on this one?
Next we check her timing. Someone previously/kindly put a white mark on the 5 ATDC. Using a timing light we discovered 2 things, her idle was too low, reading about 680 and the timing was way off. We also found that the vaccuum hose going to the vaccuum advance on the distributor was hard and easily slid off the plastic line. So we replaced that and another vaccuum hose on the left side of the engine. After replacing the plugs, setting the timing and idle, and those 2 vaccuum lines, she is a completely different car. Cost wise this really down to about $16 for the plugs (NGKs non resistor). The car is running real nice.
While we had the plugs out, I used my video borescope to have a look inside each cylinder. We could still see the boring marks from when the engine was made in 1974!!!!. We also saw some carbon on the pistons, but ther is nothing we can do about that.

Now the next issue for the car is her running temp. She is running very hot, like about 210 f . Coolant has been flushed/replaced by me. I used Zerek GS-05 which is the same stuff that Mercedes packages in their white bottles but charges twice as much. I mixed it 50/50 and the level is fine. I could not fine the drain plugs on the block, so I could only dump out what was in the radiator. When refilling it, she took a bit over 2 1/2 gallons. My immediate thoughts for the high temps are either a partially closed thermostat, clogged radiator, or worse a failing water pump. Any ideas of this issue?

look at the easy stuff first, T stat , then make sure she is burped ( no air pockets) and then look at the radiator for clogging

The cause of high temperatures, is very often a timing problem. Too much retard. These engines need to be advanced. The timing should be set to about 27-30deg BTDC at 3000rpm. To get this, your distributor should be turned ccw almost to the end of the slot in the clamp plate. If you can't get the timing to advance that much, then you need to open up distributor and free up centrifugal weights. (There is a DIY on this here and on Benzworld 107 forum (another good source for the D-Jets) Temperature should be down at about 180F. If timing is as above and yo still get high temps, then time to look at tstat and make sure it works and is installed properly.

You should be fine with the NGK plugs, but these cars also run fine with resistor plugs and new Bosch wires. Basically resistor just moves from end of wire into the plug.