Hello I am trying to get a doner engine running and swap it into my 300 SD. The car was in an accident and had heavy front end damage with 200,000 showing on odometer so I assumed ran ok up until accident. How many yrs. it sat I do not know but all the brakes were rusted fast when I trailered it home. Must have sat 20-25 yrs. Well I had hopes to get this engine running but not sure if I should waste any more time at the moment as the compression numbers looked very bleak they were #1 cyl. (200) #2 (240) #3 (200) #4 (100) and #5 (380) wish they all were like 5 any way this check was taken after a valve adj. on cold engine never got it running yet. Why would #4 be so low? I will try to start the car tomorrow but with those low numbers do not know if I will succeed. Should I waste any more time on this engine or move on to another? Could this engine just maybe need a valve Job to make it a good running engine?

A leak-down test will tell you where the problem is. Not easy on a 617 since you have to have your balancer marked at TDC, 72, 144, 216 and 288 degress but since you have the engine out it should be easier

If it sat that long without running, you will have pitted cylinder bores. You may get the engine running, but it probably won't be great and it will always burn oil. The low compression could be valves not fully closing due to rust or corrosion built up on the valve seats/faces and/or stuck compression rings. You might be time and money ahead to find a known-good runner.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

You could pull the valve cover, turn the engine until both rockers of the cylinder being tested are on the base circle of the camshaft. Put air in the cylinder either through an injector hole or glow plug hole and listen for the leak. You have to make an adapter to do this.

This isn't as perfect as a leakdown test with gauges because the piston is at the top and you don't have gauges; but, we already know the leaks are bigger than acceptable. This is the same thing leakdown readings would tell us. At this point we want to know the location of the leak.

Christina, Is there any feasible way to get a borescope into the cylinders? Looking inside may tell something such as scoring or corrosion. Phone endoscopes are around $25-30.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Tuna fish here

endoscope through a prechamber hole or an open valve somehow.

I got a cheap usb one for a laptop years ago I don't remember the price

Probably not worth the effort. If other good engines can still be found in your region at reasonable prices. I said probably as you have no solid indication of what the actual reason is. I would still try to start it. See what the compression numbers where like after it ran awhile.

It had not run for a long time so look hard for past vegetable oil use in the craze. If it was a past veggie engine I would pass it by. A veggie diet may be good for people. Not as often for these engines. The rings could be glued solidly in the lands with sitting.

I would not assume the cylinders were pitted. I'd have a look at them with the scope. I'd think with the wide variation that you have problems related to the valves.

I agree with Barry, try to get it started and run it for awhile. ....and if it has been veggied I'd pass on it.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Good news I got the engine running today still in the car and it sounded great I did'nt run it higher then idle about 45 seconds as had no radiator on it. I was so happy with the sound of it but the compression numbers have to be dealt with so I guess with the replies is I should try to determine where the leaks are. Can I make a fitting out of an old glow plug or can I purchase a fitting to put some air in the cyl. I will hook up a radiator and run the engine to operating temp. and take some more compression readings and maybe run about 4 qts. of marvel mystery in it to loosen up the rings if they are stuck fast. I will probably not get much done on it tomorrow as I have to put a radiator on a sprinter but will report back on how this progresses and if I can get those compression numbers to read a little higher.

Try to adapt something from the compression tester.

Are you putting the MMO in the cylinders or the crankcase? Due to gravity it would be more effective in the cylinders in which case a couple of ounces in each is sufficient. Four quarts is too much unless in crankcase, two quarts added to oil would probably be enough.

Glad to hear you got it running.

Good luck!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Two early for a compression test again. Needs some running. The expansion and contraction help with repeated cycles. Ability to start alone means probably no vegie oil use.

Should probably change the oil. As you will probably not be getting it hot enough to boil off condensation. Plus it is old and oxidized Oil. Some miracle oil in the base oil will help perhaps as well.

If it was able to idle reasonably well your initial compression numbers were wrong. Or some stuff cleared of the valve seats very fast. Perhaps the valve stems where sticking in the guides a little. Does not really matter as it now has a chance. With those numbers if it did not take a pull start to get it running. It to me is pretty amazing. Plus makes the first compression readings suspect.

Harbor Freight has an inexpensive leak down tester. Their compression gauge has the fitting that matches the glow plug hole.

I'll see later today whether the parts play together without modifications. Degree wheels are inexpensive.

Follow the instructions with the HF leakdown by the letter, including the part about max input pressure (?30 or 40 psi on the one I got?, anyways, you can break it if supply pressure is too high.

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CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

Did you check your compression by just pressing the rubber seal against an opening or do you have an adapter already?

pelicanparts sells one for $24 but it looks like you may have to remove the schrader valve from it:


https://www.pelicanparts.com/Mercedes-Benz/catalog/ShopCart/TOOL/POR_TOOL_MERCED_pg79.htm


OTC tolls makes the best leak-down tester. Most others are low pressure only and you have to set them up.

As mentioned, you'll need to change the oil A.S.A.P., I'd suggest pouring a goodly bit of MMO, SeaFoam or whatever your favorite snake oil is, in the cylinders, turn the engine 360 degrees by hand and allow to sit at least 48 hours, then drain the old nasty oil and re fill , start it (with cooling system !), run it a bit , allow to cool, re check the valves and then re test the compression .

I've made a good living resurrecting old dormant engines but, some valves are always open at rest so over the years of sitting the average used junker engine is going to have crusty valve seats that will need bedding in again at the very least .

Corroded cylinder walls too in many cases .

Let the snake oil do it's thing and soften the crap in the ring lands, you already paid for the donor car, might as well invest some labor into it .

Expect a lot of smoke for a while when you start it after soaking the cylinders .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Good deal! I agree with Nate and Barry. I'll bet $5 it will make a good engine for you.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.