Another blowby question - PeachParts Mercedes-Benz Forum

mach0415 · #1 02-19-2011, 05:42 PM

A little history first:
Last night I went to pick up my second 1985 300SD. Now I have 2 silver on blue SD's. Honestly, this car is in better shape, cosmetically than my original purchase. I answered a C-list ad actually for 4 brand new Good Year 205 75 r14 tires on bundt wheels for 300 bucks. The seller mentioned that the car was acting up and he parked it after he had new tires installed, and that the car was for sale too. I got pics e-mailed to me and figured, what the heck, if anything major was wrong, it would be a good parts car if the price was right. I got the whole thing for $575 and he threw in a new set of brake pads. All electronics work! Sunroof, windows, odometer, original first aid kit, etc. The paint is fair, but absolutely no rust or dents. I am still trying to wipe the grin off my face.
Cutting to the chase:
Engine is skipping, will barely pull, will not accelerate and has tremendous blow-by. I know a cylinder is dead and more than likely has a lower end issue. I have not had it long enough to do a compression test. My question is this: DO you all think it would be wise to pull the pan first to see if shavings and or a piston skirt/ring is sitting in the sump? OR Do you all think it may be only a stuck ring. I should also note that while spinning over, as the engine is turning there is a faster spot in the turning process, as if there is low compression on one cylinder out of five. This has not had WVO in it. I would not say that there is a ton of smoke coming out the tailpipe, but there is some. I am going to inspect the tap on the intake (ALDA banjo bolt). I may be soliciting a good long or short block. Let me know what you all think.

barry123400 · #2 02-19-2011, 05:51 PM

Maybe the guy just did not believe in valve adjustments. Although some really tight valves ability to result in a lot of smoke and and blowby is questionable. How about an injector stuck open?

Head gasket failure around the area of the oil pressure feed is not common on the 617s either unfortunatly. Was he running wvo or is there any evidence he was? Other than that stuck rings seem not likely.

junqueyardjim · #3 02-19-2011, 05:52 PM

It really seems like a good deal! I would try to drive it hard and get it as loose as possible, then adjust the valves, run it again and then do a compression test. Makes sure you are up on all fluids. Maybe adjust the valves first - room temperature is the best. Keep your ear open for strange, (harsh) noises.

mach0415 · #4 02-19-2011, 06:01 PM

Quote:

Originally Posted by barry123400

Maybe the guy just did not believe in valve adjustments. Although some really tight valves ability to result in a lot of smoke and and blowby is questionable. How about an injector stuck open?

Head gasket failure around the area of the oil pressure feed is not common on the 617s either unfortunatly. Was he running wvo or is there any evidence he was? Other than that stuck rings seem not likely.

Valve adjustment would be in order just from the peace of mind aspect of getting another car. He was not running WVO. He stated that this happened rather suddenly and has already replaced the fuel filters. I can deal with the low power issue, though it will not increase RPMs at WOT. My biggest question is whether or not nasty blowby through the oil cap can be cause by anything other than a lower end issue. All my training tells me that blowby is stuck or broken rings or a damaged piston.

layback40 · #5 02-19-2011, 06:24 PM

Quote:

Originally Posted by mach0415

Valve adjustment would be in order just from the peace of mind aspect of getting another car. He was not running WVO. He stated that this happened rather suddenly and has already replaced the fuel filters. I can deal with the low power issue, though it will not increase RPMs at WOT. My biggest question is whether or not nasty blowby through the oil cap can be cause by anything other than a lower end issue. All my training tells me that blowby is stuck or broken rings or a damaged piston.

Mark,
It is highly unlikely that the bad blowby is caused by anything else.
The fact that 1 cylinder is dead is probably a good hint. Dont bother taking the sump off for a look, you wont find much. A compression test will confirm if you have a bad cylinder. An Italian tune up may only put a rod through the block if the piston is real bad.
Best keep your eye out for a good replacement motor if you wish to keep the car going.

mach0415 · #6 02-19-2011, 07:11 PM

Quote:

Originally Posted by layback40

Mark,
It is highly unlikely that the bad blowby is caused by anything else.
The fact that 1 cylinder is dead is probably a good hint. Dont bother taking the sump off for a look, you wont find much. A compression test will confirm if you have a bad cylinder. An Italian tune up may only put a rod through the block if the piston is real bad.
Best keep your eye out for a good replacement motor if you wish to keep the car going.

Unfortunately, this is what I know and am afraid is going to be the demise of another 617.

ngarover · #7 02-19-2011, 07:44 PM

what's interesting is I have a ton of blowby on my 81 300d. There's video showing it puffing out the oil cap, and it tosses a crap load of oil into the air cleaner....

Still, it runs like a clock, smooth as ever, and I just today to it for a 5 hour round trip averaging 60-65mph and only used up half a tank of fuel doing it...

mach0415 · #8 02-19-2011, 07:51 PM

Yeah, the funny thing is that there is a lot of blowby on this thing, and it will even toss the oil cap off, but it doesn't feel like the expected 50 psi or whatever. I am tempted to pull the pan just to see if there is/are any bits in there. Especially since he said it happened out of nowhere. It needs to be resealed anyway, as it appears to have leaks from the pan area. What is that vid?

ngarover · #9 02-19-2011, 07:53 PM

Quote:

Originally Posted by mach0415

Yeah, the funny thing is that there is a lot of blowby on this thing, and it will even toss the oil cap off, but it doesn't feel like the expected 50 psi or whatever. I am tempted to pull the pan just to see if there is/are any bits in there. Especially since he said it happened out of nowhere. It needs to be resealed anyway, as it appears to have leaks from the pan area. What is that vid?

Video from the day I got it home....
http://www.youtube.com/user/NGARover#p/u/8/E-CZcvp_Ay4

mach0415 · #10 02-19-2011, 08:07 PM

Its probably close to yours, maybe a little more, but yours has no skip, right? Mine has a completely dead hole. It does not knock, so perhaps an injector is not firing. There is just a string of #@%! that I am going to chase down. Compression test first. If low, I will pull injectors and soak for a week or more in MMO. I would assume that this thing should at least rise above 900 rpms even with a dead hole. I think this is a very neglected 617. While I am at it, timing chain stretch will be checked. If all else shows low, I'll locate a 617 and yank it.

mach0415 · #11 02-19-2011, 08:22 PM

The PO stated that he thought the fuel pump primer was leaking. Do these leak externally? OR Do they suck air and this ends up in the injection system? If so, this could be the cause for a skip and low power, correct? The blowby is entirely separate issue at that point anyway. BUT, does a leaking primer pump cause a constant misfire? This is an older black primer pump and it does not seem to have the same resistance my 276,000 mile 1985 SD does.

layback40 · #12 02-19-2011, 09:10 PM

Quote:

Originally Posted by mach0415

Its probably close to yours, maybe a little more, but yours has no skip, right? Mine has a completely dead hole. It does not knock, so perhaps an injector is not firing. There is just a string of #@%! that I am going to chase down. Compression test first. If low, I will pull injectors and soak for a week or more in MMO. I would assume that this thing should at least rise above 900 rpms even with a dead hole. I think this is a very neglected 617. While I am at it, timing chain stretch will be checked. If all else shows low, I'll locate a 617 and yank it.

If compression is low, then MMO may work. Dont like your chances though!!
If you yank it, you will see the more with the head off than the sump removed.
Has it got good oil pressure?
Good Luck !!!

mach0415 · #13 02-19-2011, 09:16 PM

Quote:

Originally Posted by layback40

If compression is low, then MMO may work. Dont like your chances though!!
If you yank it, you will see the more with the head off than the sump removed.
Has it got good oil pressure?
Good Luck !!!

It has great oil pressure 3 bar at all times above idle and 2 hot at idle