86 560SEL what happened?? :( - Page 3 - PeachParts Mercedes-Benz Forum

rsmartin · #31 02-28-2008, 10:29 PM

I'm the orginal poster of this thread.....

Well it's been 5 months and finally my mechanic has decided to look into the "dead" 560SEL. He's a diesel guy and really dislikes the "gassers" but yesterday he decided to have a look. Here's what we found.

He dropped the oil pan first to see if any pieces in there. Crystal clean.

So off come the valve covers. Upper chain rails have NO discernable wear.

The cams are still in alignment, so it appears no chain jump.

BUT the hydraulic tensioner is soft and does not hold the chain tight.

I'll try to explain what happens as best I can...

If he turns the left cam slightly to take some slack out of the chain he can turn the main crank maybe 15 degrees until it binds. if you turn the left cam backwards you bring everything back to where it was again... so you can only turn the engine maybe 15 degrees back and forth... make any sense?

so we can only surmise that a lower guide has broken and has jammed something up?

but since the cams are not out of alignment with each other or with the distributor, it seems that there shouldn't have been any valve damage??

you see i'm trying to see if anyone can give me any reason NOT to do a complete upper end overhaul, i.e. pull the heads, valve job, replace chain, tensioner and guides, etc.

at 64K miles, doing all that would basically give me a new engine, right?

what you all think i should do?

Tomguy · #32 02-28-2008, 11:29 PM

You really need to find out if the cams ARE aligned right and, honestly, the only way to tell is if the engine is at TDC for the #1 cyl and the notches on both cams line up with the towers. You can't really tell otherwise, because 20° at the crank is 10° on the cam and it's really hard to tell 10° of cam movement, and that's exactly 1 tooth.

The engine's being bound up, and unless you take the heads off you can't tell if there is piston damage but if the engine's being bound, you'll need at least 1 valve, even if it's just from the starter. The flywheel alone weighs enough that 100RPMs of momentum on it would seriously bend a valve. Make it your own DIY project. Take the heads off. I did heads on my 4.5 (an m117) in 1 weekend, with no prior experience, and I bet you could at least pull them off yourself to see what kind of damage is done. Find a used replacement head at a pick-and-pull junkyard for $50 or so, have the stems and seals replaced on that one and the other presumably still good side, and you're set until 200k at least.

rsmartin · #33 02-28-2008, 11:44 PM

everything was lined up at top dead center ... but come to think of it, why would the engine lock at top dead center on #1 cylinder. I saw the marks lined up on the cams and towers myself. but what would cause the engine to stop right at top dead center.

i don't have the time or tools to do it myself.... i'll spend the bucks if i really need to. my mechanic said the same thing as you... hard to believe that there isn't a bent valve due to trying to start it.

pawoSD · #34 02-29-2008, 01:54 AM

With only 64k on it I'd probably have the engine repaired and then enjoy it another 150k.

whunter · #35 02-29-2008, 02:23 AM

If all the plugs are removed, and it still locks = bent valves.

Caused by the bad chain tensioner.

Strife · #36 02-29-2008, 02:44 AM

An interesting post, a few points:

1. Every GM small-block V8 (including some Hi-Po) I've seen had nylon on the cam gears from the factory. Of course, you could use that timing chain as a collar for a big dog...

2. I've read that recently-made MB tensioners have an extra valve to prevent leakdown, whereas other mfr's (Febi, for example) may not. I don't know if this is true but if it is my next preventative tensioner replacement on my cars will be genuine MB; I'll look at the price difference as catastrophic insurance.

3. An unexplored area on timing failure is the possibility of a binding camshaft from bearing misalignment or lack of oil to the bearings. When I replaced my 380's camshaft I was amazed at the high-precision fit in this area. Even the smallest unmeasurable (with my tools) misalignment caused binding. The final adjustments were made with a plastic mallet and some patience before final torquing and spin testing. Even a little binding can cause a dry spot on the bearing and eventual heating/wear, etc. If a cam binds, something is going to slip or break at the weakest point, and those points on these engines are made of plastic.

4. I don't think that there is a way to make an old-school "hi-perf" 2 valve per cylinder engine that is non-interference, because of compression and valve lift requirements.

stevebfl · #37 02-29-2008, 09:04 AM

Based upon your data, I would imagine that the chain isn't the issue. I will say that I have never seen valves keep a motor from turning with the starter. The starter will just bend them if they aren't closed.

I'm guessing that something has fallen into the motor, probably on #1 or #6 as that is why it stopped with the piston at the top.

As to chain issues, my shop has repaired hundreds of them on all versions of the 116 and 117 motors. A couple points of interest: there are only two rails that actually touch the chain when rolling in tention. They are the tentioner rail and the rail below it on the lower right side of the motor. The rails that cause all the problems are the three in the heads and I recommend them to be replaced every 75k or 5 years whichever comes first. They are dirt cheap but do take a few hours of labor to replace. If you DIY then it is cheap insurance. I see no point in any other level of preventative maintenance except maybe a new chain every 200-250k miles.

We just burried my all time mileage test case this week. It was a 90 420SEL that had 950,000 miles. Something finally gave in the lower end. We had done two chain jobs on that motor the last one over 450,000 miles ago. We replaced those rails almost every year as he drove 90,000 a year.

rsmartin · #38 02-29-2008, 10:11 AM

i called my mechanic and clarified a point. the engine was not stopped at top dead center. he was able to turn it to TDC by turning the crank, then turning the cam to unbind the chain, then turn the crank, then the cam, etc. so something is causing the chain to bind down low where we can't see. again, no debris was found in the oil pan.

i have a snake light with a camera attached. i think we'll try to look up from the bottom with the snake light camera and see what we see

but if you were me.... how would you proceed?

i'm thinking dive into the front first, taking off the chain cover and see what we find... replace chain and all guides since we're there already. assuming we find a problem .. say a broken guide down in the lower part of the chain area (not very good at the technical language) would you just go ahead and do the heads and valves as well? my mechanic (who is mainly a diesel guy - i have and 84 and 85 300SD) is thinking we just go for it and hopefully end up with a basically renewed engine that will go for the next decade.

i don't want to spend the thousands of dollars if not necessary but don't want to be penny wise and pound foolish.

rsmartin · #39 02-29-2008, 10:15 AM

here's picture of the car if anyone cares...

stevebfl · #40 02-29-2008, 10:17 AM

While the starter is strong enough to run right through interfering valves, turning it by hand won't be. I would remove all the rocker arms so the valves will be closed and see if you can turn the motor. The rockers won't be removable on valves that are being depressed so you might have to back the motor up to get all of them.

pawoSD · #41 02-29-2008, 10:25 AM

Quote:

Originally Posted by rsmartin

here's picture of the car if anyone cares...

Save it!! That is a BEAUTIFUL car!! Wow...its so flawlessly clean! That car has a looooong life ahead of it!

pmckechnie · #42 02-29-2008, 11:29 AM

What Steve said. Remove the rockers. I would also measure the hight of each valve and look for one or more that are shorter than the others. If they are all the same, you don't have any bent valves. At least you will know one way or the other.
By the way, I would sure fix it or sell it to me.

AZIRRIGATION · #43 02-29-2008, 02:59 PM

A dislodged valve seat can cause similar symptoms.

Check out this thread for information; "Exhaust valve for #4 cylinder sticks open about a 1/4 inch in 1987 MB 560 SEL".

Links to thread-- http://www.peachparts.com/shopforum/showthread.php?t=208049 AND http://www.benzworld.org/forums/w126-s-se-sec-sel-sd-sdl-class/1352311-exhaust-valve-4-cylinder-sticks-open-about-1-4-inch-1987-mb-560-sel-engine.html