PeachParts Mercedes-Benz Forum - What is your Diesel engine cranking speed?

It will take something like my laser tachometer reading off the harmonic balancer to get accurate information. It can count that slow with great accuracy as well. Even ten rotations per minute do not seem to be much of a challenge for the cheap unit. Ten dollars plus mailing and made in china does not mean it is not deadly acurate. Or you can buy one in north america for sixty if it makes you feel better. Same unit.

If the car battery is really shakey you will probably not get enough consistancy. If it is that bad though you would just be waisting your time. The battery needs charged and checked or replaced before doing anything else.

The tachometr has to read the reflective tape only twice to get it's information. . So even if rpms were dropping it will still average and record the last two revolutions that you choose just before turning the tachometer off. So it is more than useable.

There is a narrow protuding portion of the balancer to fasten the reflective tape under there between the belt grooves and reading it vertically from the bottom. Enough clearance to do it if one side of the front end is jacked up and blocked or front end on ramps. .

I still on occasion see people crawl under cars on just a jack when driving by. Much less than years ago thank god. . It is not because people have gotten smarter in general with time. There are just fewer people that can or are willing to repair their own cars.

I would do the test but do not have a really good battery to try to generate a standard for the five cylinder or four cylinder engines. Since I do no winter driving on the old diesel mercedes keeping the batteries in optimum condition is not a great priority. As long as they start the car with a reasonable reserve they are good to go for me. Allow again for some strange reason I always seem to aquire mercedes cars with really good engines. None have just average compression. This is just payback for my innability to win major lotteries. ;)

Since starters always deteriorate from use and age to some extent. The best we can hope for is to develop a normal usable range. Also specifying what is really too slow. There will never normally be a too fast. :D

So much also depends on the condition of the engine.This is the major vairiable since a low compression engine will crank faster but start harder than one with excellent compression. I have one of mine waiting for new alternator belts. If that engine will turn at all it will start. I am serious if it groans over in warm weather it goes.

The reason I learnt this is the belt adjuster was at the end of it's arc on the alternator. Alternator of course was loose enough that no consistant real charging was occuring. Since the previous owner had not spared any money keeping things up it kind of suprised me. Sounds like mecedes only expected those belts to have about 15-20 thousand miles of useable life from what I can tell.

Thats the best reason I can come up with for their strange length of one thousand and thirty seven mm. It seems to me .A slightly shorter belt would last longer. The engineers calculated side belt wear from a 9.5mm belt width. This originall size since then has been replaced with a ten mm standard industry belt width. So you might get a little longer service life from a pair of belts of say 1020 mm length. They should go on as the 1037mm belts tend to centre the alternator arc adjustment. Thats even before any initial runnning stretch if it occurs. Belt life is fundementally totally finished at about seven point five mm in top width. If you change belts with more than the 8 mm top width left it means that brand is not stable or was not prestretched properly in manufature. Try another brand. I guess I am just playing around trying to get the best belt life possible. Consistant with reliability.

I have a couple of old mercedes I have not removed, cleaned and treated the main electrical connections with anti oxidation compound yet. The next one I do I will record the revs prior to the cleaning and after. Just maybe there will always be a small gain even when the connections have seemed to be operating normally. The ear is not sensitive enough for this test unless you had really poor connections when you start. All this is likely to prove is that it was always just been in my head.:) If by chance I find a consistant difference by tachometer test will post about it.

Remember the majority of those connections have never been disturbed since the cars where manufactured 20-30 years ago. Anything moist air can reach will oxidise to some extent with time. Okay perhaps not in the arizona desert.:P Gotta cover your posterior around here or someone else will. :rolleyes:

Anyways an excellent ideal to establish basic norms. . We are approaching restoration country with these older 123s. Yet a few of mine are still far too good for that. I am starting to feel that the newer mercedes diesels models are not ever going to get there in fairly high numbers. It is probable that the production numbers were far too small even if the desire existed.