Odds of Bad Rings at 155K - PeachParts Mercedes-Benz Forum

bgkast · #1 07-17-2006, 01:45 AM

I am trying to help diagnose and fix a hard starting '79 300D. The car has been sitting for 2 years and has a reported 155K miles on it. The owner can not remember if it was having this problem before the period of sitting. He says that the car starts fine if left plugged in, or if warmed up. It has had a new glow plug relay put in, but I don't believe that the plugs them selves had been checked. The owner also reports some blue smoke on start up that quickly disappears.

My plan is to check out the plugs, give a valve adjustment, check the battery, and replace the old diesel. If that doesn't do it where do you suggest I proceed.

It seems to me that this must be something other than a compression problem due to bad rings, assuming that the mileage is correct, and the car was not horribly neglected for its whole life. Anybody care to confirm/correct my thinking.

Thanks all. -Bryan

Jeremy5848 · #2 07-17-2006, 01:52 AM

Depending on the maintenance that this vehicle has had or not had, worn rings are less likely than other problem sources that should be checked first. Your plan of attack sounds good. If the valves have not been adjusted in many miles, they could be tight and that would cause some loss of compression and hence make the engine hard to start. The other things that you plan to do are also possibles. Definitely check the battery -- sitting for two years is hard on them. Fuel maybe. Glow plugs maybe. Others will no doubt have some good suggestions.

Motorhead · #3 07-17-2006, 04:12 AM

First thing to do is check the valves. I am sure that you will find some tight ones. I had a '79 300D that I bought that had sat for along time. It wouldn't start either. I pulled it to about 35mph for a 1/4 mile, turned the key on and put it in "S". It started right up. Pulling it turns the engine faster and the cylinder heat builds. I adjusted the valves and it started ok after that. If the fuel is two years old, don't worry about it. My 240 sat for 4 years and started right up. I DON'T recommend letting them sit that long but it started ok. Ran better when I put fresh fuel in it.

bgkast · #4 07-17-2006, 02:32 PM

Thanks for the help. Any thing else I should look at because it has been sitting? Breaks may be a bit iffy eh?

tangofox007 · #5 07-17-2006, 02:48 PM

When engines go unused, cylinder walls rust. It is very conceivable that the two years of "sitting" caused more distress than the 155k miles of driving. IP timing is also a possible factor for the hard start condition.

Motorhead · #6 07-17-2006, 08:21 PM

My 240 didn't have any brake issues other that the rotors were rusty. I am going to do a brake fluid flush. Like I said before, it isn't recommended to non-use store a car unless you go COMPLETELY through it to "pickle it".
Because the car is new to you, the BEST insurance you can do is changing ALL fluids and service the car. Have Fun with the car. Know it, work on it, enjoy it.

slarson80 · #7 07-17-2006, 08:39 PM

Made a world of difference in the startablity of my 79 when I first got it. Granted, the loops that where in there looked terrible.

300SDog · #8 07-17-2006, 09:29 PM

Bad rings with only 155k after 27 yrs?? Yes, I can see this happening same as TangoFox said, especially in northwest climate and humidity........ Here's the scenario: if one of these puppies sits outside (even under a car port) several years never being started then the rings will RUST from condensation within the bores, SEIZE in their grooves and CRACK when the engine is first started. And soon therafter cracked rings will do a number on the bores, going from bad to worst.

bgkast · #9 07-17-2006, 11:22 PM

I don't like that scenario.

I will check and see if this problem existed before the car was parked, and if it was occasionally started during its hibernation. Thanks.

kip Foss · #10 07-17-2006, 11:27 PM

Check your compression. If it is low squirt some oil into each cylinder. If the compression comes up then you have bad rings. If it doesn't come up they you probably have bad valves.

bgkast · #11 07-18-2006, 12:24 AM

That it the eventual plan. I'm going to start with the smaller stuff and progress up. Thank you.

Endust · #12 07-18-2006, 09:23 AM

Careful with the oil squirt into the cyl. There can be some problems associated with doing that on a diesel engine.

rrgrassi · #13 07-18-2006, 01:27 PM

Also, ya gotta remember, when an engine is shut off, not all cylinders will be exposed to humid air. Some valves are closed and some are open, just depending on where in the power cycle the individual cylinder was at the time os shutdown. If you are going to pour oil in the cylinder for the compression test, make sure the glow plugs do not heat. Best way this to do is remove the glow plugs and leave them out like you would sparke plugs on a gas engine. This will ensure no glow, and no compression except for the cylinder that you are testing. When you are done, then then replace the glow plugs.

bgkast · #14 07-18-2006, 08:06 PM

I'm hoping that the guy started it occationally.

Anybody in the Portland OR area want to loan me a compression tester this weekend?

bgkast · #15 07-22-2006, 02:30 AM

I adjusted the valves and it starts fine now. It has a fair amount of blow by though. Thanks for the help!