DEAD cylinder: Valve + rocker arm craziness - PeachParts Mercedes-Benz Forum

blankenship · #1 02-18-2008, 08:37 PM

so, i added a '77 280e to the stable this weekend, and should probably lay down the story and give some background info before posing my question(s):

got her cheap because the non-mechanically-inclined owner said the motor was blown in 2004 because he'd run it out of oil, and she's been sitting since.
to quote him: "I was driving down the street and suddenly the car went poof and stopped suddenly. I had it towed to the mechanic who said it had run out of oil and blew the engine."

BUT

After I towed her home, I checked the oil, and there was some in there. It appeared normal consistency, with no water or milkiness. I added two quarts, which totally topped her up, and she took 1 quart of coolant. I turned the key and she turned over.

Her fuel gauge red empty, so I added 4 gallons of fresh gas, and she kinda / sorta started, and kinda / sorta ran a few times for 10-30 seconds, until abrubtly stopping each time. No noticable water in the oil or oil in the coolant afterwords. I got REALLY excited.

Anywho:
I did a compression test on her today, and got a ZERO reading (multiple times) on cylinder #1, thought #2-6 were all between 100-110 (cold).

I pulled the valve cover, and noticed that the #1 valve intake clearance big enough to stack a couple pennies in. that cylinder's exhaust valve was too big, too, but not nearly as bad. The other valves are slightly out of adjustment, but nothing major. I can see no broken springs or scarred cam lobes, but after removing the spring clamp from the adjusting screw on the #1 cylinder, the rocker arm basically just came off in my hand, revealing a little slotted metal fitting where the "Pressure Pad" is notated on the diagram below. It seems the adjusting screw won't get even get close to adjusting the clearance correctly, as there's just way too much play in there.

Wondering now, what's going on? Does any of this indicate the motor is truly "blown," and there's something wrong with the #1 cylinder/valve, or could it be something simple?

Johnhef · #2 02-18-2008, 10:10 PM

had a 560SEL recntly in a similar situation, 0psi on cyl 7, pulled the valve cover and found the arm laying loose and the 'pressure pad' laying lose in the head. its possible the pad ws installed incorrectly (car had a valve job done previously) and allowed the arm to come out. We replaced the arm and the pad and the car ran fine after that.

t walgamuth · #3 02-18-2008, 10:58 PM

Well, you have to get the valves working correctly to get compression, so the first thing is to get them sorted out. Replace any parts that are not correct. YOu can figure that out by comparing the bad ones to the others that are working correctly. Once you get all the valves sorted you should be getting more like 130 psi on the compression I would think.

It sounds like the porr engine has not been cared for....but it may still respond to some tlc.

Those 280es are really really tough engines.

Tom W

blankenship · #4 02-19-2008, 12:37 PM

right, sorting out the valves is obviously the first item of business, i guess my question is what to do about that first valve with its lolling rocker arm.

my 'pressure pad' wasn't laying loose in the head like Johnhef's..mine was actually still sitting there on top of the 'valve spring retainer' until i removed it with a magnet. (see photos to see the pad in place, removed, etc).

i guess, my best guesses would be:

1. the pressure pad is worn out, broken, installed incorrectly. it sounds like they make varying thicknesses of the pressure pad discs? does mine show wear or ?

2. the valve adjustment bolt and its threaded bush is worn out? (although, it takes quite a bit of effort to turn the bolt, and i'd guess that when they're worn out, they're easy to turn)

3. or, something more menacing, like the intake valve is stuck in the down position (?) or the spring is broken somewhere i can't see, or ?

thoughts?

meltedpanda · #5 02-19-2008, 01:53 PM

well the pressure pad looks fine, I think what has happened here is the spring has collapsed ( doubtfull) or the valve sleeve has migrated south not allowing the vavle stem to rise properly. There is not enough spring showing If that is the case you may have a hole in your piston
I would take out the sprk plug get that cylinder to TDC, then compress spring remove keepers and see what that valve is doing. You can use the air method or rope method to keep the vavle from fallign further. That will also let you evaluate the spring

ctaylor738 · #6 02-19-2008, 02:19 PM

If you had that much clearance, you're 'way outside what either the adjusters or the hockey pucks can correct. I think you will find that either the guide has dropped down, or the valve seat came loose. Obviously either will prevent the valve from closing all the way.

Soon, the joys of pulling the M110 cam box and head.

blankenship · #7 02-19-2008, 02:54 PM

thanks for the input, fellers.

questions:
1. does it matter that the springs on that cylinder look the same as on the others? or that i can see the valve stem inside of them, and what i imagine is the (white?) stem seal the same as on the other cylinders? (see attached photos for a couple different views of the area)

2. can i remove and test the valve spring without having to remove the camshaft housing? and can i remove it without a special spring compressor, magnetic lifter for collets, and the other special tools it says are required in the service manual?

3. is there an easy way to tell if you've got a hole in the piston? or if the valve guide or seat dropped, is there anyway i tell without removing the danged camshaft housing (which sounds like it might be a little out of my league, requiring lots of special tools, etc.)

ctaylor738 · #8 02-19-2008, 03:34 PM

To remove the spring, you need a compressor that hooks under the cam. You can get the colletts out with needle nose pliers.

Since your have zero compression on that cylinder, obviously something catastrophic has happened, as has been suggested. I'm not aware of a way to tell which catastrphe has occurred without pulling the head.

To pull the cam box/head you do need several hundred dollars worth of special tools:

- spring compressor
- screw- or impact-type pin puller
- 17 and 19 mm hex bit sockets

It's a lot of work, but not rocket science.

meltedpanda · #9 02-19-2008, 03:55 PM

well, what if you rotated to TDC at that piston and then used compressed air to see of it would hold, my thought is that is will not because the valve is down, but it may confirm that this is the issue and not the piston. If per chance the air pressure closes the valve then it may be as simple as a sleeve, welll that is not simple, granted, but at least you could R/O hole in the piston.
I just dont see how a sleeve could migrate that far south and not contact the top of the cylider. I guess the other possibility is the valve stem is bent, perhaps as a result of a colision with the cylider head??
If it were me , I would go about removing keepers and see of the valve can be pulled up manually. On the one I did the valve seal actually came out with it - not good, but I was getting it to seal with air

300SDog · #10 02-19-2008, 06:10 PM

Yep, it sounds like something weird with valve guide, seat or stem that keeps the valve from closing. Strikes me that pulling the head and camshaft carrier is next logical choice. Heck ye probly wanna eyeball the bores, wiggle-test valve guides and reconnoitre valve seats anyhow based on vehicle's sketchy history.

And pulling cyl head and cam carrier on the m110 aint that tough!

To pull the m110 camshaft carrier it's wise to have an old ice cube tray for sorting parts, keepin all rockers in exact order to their respective lobes and valves. Say one side for intake and other for exhaust marking one end of tray as "front" or #1cyl. This will be helpful since you're pulling the rockers in varied order - step 1 to camshaft carrier removal. Look for worn surfaces with core metal exposed on rocker surfaces when you do this, as I'm sure you know already.

Then TDC the engine after you've pulled the rockers - and paint mark the chain to sprocket teeth for easier reassembly. Slack the chain tensioner and entire operation can be accomplished without breaking the chain you understand. Plus you will want to wire or bungee the chain to prevent it from dropping when you use rubber hammer to knock the sprockets off the camshaft ends - yer next mechanical step after pulling rockers.

The rest will be common sense - unbolting and pulling camshaft stantions and lifting the carrier thats surprisingly light in weight. Dry gasket underneath probly doesnt even need replacing. Did this myself, it took less than couple of hours recovering junkyard m110 cam & carriers using no special tools at all.

Then with cam carrier outa the way cyl head's gonna be piece of cake - just dont drop or forget 6mm allens down in the chain gallery that oughta be packed with rags first.

And how many miles on this excellent recovery operation? At 125-150k expect chain is stretched and engine needs light head work to easily last another 150k miles at least. Reconnoitre new headgasket kit including valve seals, buncha valve guides and *maybe* a few exhaust valves is all you need assuming the bores look clean. These are sodium filled valves that should be replaced if seriously pitted and NOT reground maybe gently lapped is all. Question of exposing the core and valves gettin toasted in another 30-50k miles if ye try to regrind em. And for cryin out loud NEVER plane or shave alot of metal from cyl head unless its absolutely severely warped and flunks the simple straight-edge test. Cam carriers that require any resurfacing is entirely unheard of. Heat dispersal preventing cracked/warped alloy head chassis assembly is one reason MB went with pancake carrier arrangement on m110's. Dont let anybody shave the cyl head since it probly aint warped.

Meanwhile the M110 twincam engine is hot-ticket item in extremely high demand. Heck, it'll bolt into *any* MB chassis including coupes, convertibles and long wheelbase sedans from about 1969-80. Had one in my 4-spd Euro 280SEL and it ran like bat outa hell.

Deffinitely I'd recommend not bein scared of pulling cyl head to sort this engine out. But first I'd try what MP recommended above: basically TDC the engine, compress and remove #1 valve springs and reconnoitre valve guide wiggle and whatnot there. And then reassembling springs and rocker ye may accomplish really simple diagnosis like cracked spring, dislodged valve retainer bit, bent valve stem or seized/slipped guide before pulling the head. And as i've said: if bores look clean, no cracked pistons and nothing weird with cyl head - then light top end reconditioning and reassembly would probly not be waste of time. Under worst case scenario if nothin else, there's gotta be market for reconditioned m110 cyl heads out there.

300SDog · #11 02-19-2008, 06:14 PM

An afterthought......

Anybody heard of injector tip gettin spit loose and chomped by valve? Haint seen this myself but that dont mean it caint happen.

blankenship · #12 02-19-2008, 07:07 PM

I should have mentioned earlier, this baby's history isn't THAT suspect.
The PO's receipts (from 1998-2003) show that 30k ago (in '98), she had a FULL VALVE JOB, including:
REBUILDING THE HEAD ($740) and cleaning, reinstalling, new head gasket, adjusting valves, etc, to the total tune of $2000.

That's a GREAT step-by-step from 300SDog, really appreciated. But man, I'll tell you, it's the kind of job I'd sure like to SEE done (or have a veteran looking over my shoulder) before I attempt it personally/alone.

If I'm going to start by the easiest route:

-Can I get that spring + keeper off and inspect that valve without removing the camshaft housing?

-Do need to buy/build a spring compressor to get that one off, or can I work it with some other handy household tool?

-Once I get the springs and stuff off, how is an idiot like me going to diagnose a dislodged valve retainer bit, bent valve stem, or seized/slipped guide (with nothing to compare it to)? Will it be obvious?

-Is there ANY chance that all this could just be caused by a "collapsed" valve adjuster screw / threaded bushing?

meltedpanda · #13 02-19-2008, 07:25 PM

Hey Dog, perhaps us ol kentuckians can make a road trip to the great northwest

So Lee
You will need a spring compressor. There are all kinds, just get , find or borrow a good one compression of the spring will give you access to the retainers, may need a little wack to get them loose, pick em off and pull spring. Seals can be looked at , as can valve stem. However I think yours is going to be down and may need help up. Remember to TDC piston and either fill plug hole with rope or use compressed air. THis is so the valve does not fall into the piston area, although with it at TDC it cant go far. I'll betcha the valve sleeve is the culprit, however Dog has a point - something in the way, dunno I found a ball bearing once in an old dodge truck , punched a hole in the piston.

Ferdman · #14 02-20-2008, 06:02 AM

Lee, a small borescope would allow you to inspect the piston head through the spark plug hole. Ask around. A local independent tech may have one you could borrow.

meltedpanda · #15 02-20-2008, 08:32 AM

I got to thinking about this , and no matter what the issue the head will have to come off, that is unless the problem is north of the head, which only leaves the spring, which I doubt, but is possible.
Sleeve = head removal
Valve bent = head removal
Piston issue = head removal
but as DOg said not too big a job, and great wayto learn