missing on cylinder

[rwmastel]

Nice tips!  Is a compression test done with the engine hot or cold?

Can I use the compression test guage to perform a leak down test, or is that a different tool?

What am I looking for or what should I do when taking the valve cover off and inspecting for a tight valve?

More background
This problem occurred all of a sudden.  I drove the car for the second day straight on a long drive (relatively speaking), a little more than 1 hour on the highway each way.  This second day I drove to my destination a little faster, about 80 mph.   :evil:   After the car sat for about 6 hours, I started it and it ran really rough.  I drove it anyway and it mostly smoothed out once hot again, but the miss never goes away completly.  Of course, it returns every time the car is started cold.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[A Dalton]

You can warm the engine a bit ..
 I would wait up on the valve cover removal til you get some comp pressure readings.....
 Leak test is in conjuction with pressure , but a little different
 we can go over that later, too...

[Cees Klumper]

Rodd - I would maybe check/retorque the headbolts. Did you run into high engine temperatures on your 80 mph drive? The leakdown test involves putting air pressure in the cylinders (valves closed) and then using a gauge to measure how long it takes for the air to leak out (hence the term 'leakdown test'), indicating I suppose the condition of the valves/seats and the pistons/rings.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[rwmastel]

No dangerously high engine temps, but maybe slightly above normal (85c to 90c) on longer uphill stretches.

If a valve is "stuck" then I assume it must be stuck wide open, as the cam lobe would have pushed the valve all the way down into the cylinder.  Does this mean the piston would have come up and hit the valve and ruined it?  If I have a stuck valve, is that a 100% guarantee that I need major cylinder head repair?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[rwmastel]

quote:Originally posted by cees klumper

Rodd - I remove injectors with a crowfoot wrench, the same one that I use for setting valve clearances, 17 mm I believe. They are not in too tight. There's a thin washer beneath the injectors, that sometimes stays behind, so make sure that on installation, there is only one washer beneath each injector.

I used the 17mm crowfoot to remove the fuel line from the injector.  Those things were stuck tight!  The injector was 19mm and I used a normal socket for that.  No need for an extra deep socket.  They required a serious effort to get loose as well.  The washers stuck to the injectors this time.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[rwmastel]

To borrow a line from history and Hollywood, "Huston, we have a problem."

Here are my compression readings in psi.  Keep in mind that I already knew I had a well worn engine with below average compression.  I'm on at least the third timing chain and have unkown actual milage.

#1 - 135
#2 - 130
#3 - 135
#4 - 40
#5 - 120
#6 - 140

So, what do I look for when taking the valve cover off?  What simple inspections can I do?  I will re-torque the head bolts because I've done this before and it's "regular" maintenance.

If I'm going to be removing rocker arms, tension springs, ball studs, valve springs, cones, retainers, etc. (can you tell I opened my parts book?), then I'll be needing expert assistance.

Thanks everyone!  Even though I may have a huge expensive fix on my hands, I feel better troubleshooting as much as I can myself.  Maybe we can disassemble a 230SL head at the next tech session!

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[A Dalton]

You may be jumping to the worst conclusions..

  you  may just have a tight valve that just needs adjusting.. like Mickeys did..

 Take off cover and turn the engine over til you see that both valves
on # 4 are fully closed .  This will mean the piston is on the compression stroke.  Now, get a feeler gauge and slide it between the cam lobe and the rocker ... If the clearance is too tight , the valve needs to be adjusted so it will be able to close all the way..[ in other words, so the cam does not hold the valve slightly open cuz there is no clearence between the valve and the cam]
 The specs are aprox .007 on the exhaust and .004 on the intake..
 Report back your findings
 Remember , when checking for clearance , it is best done when the cam lobe is facing straight up from the valve .. that way, you know the rocker is on the lowest spot of the cam [ Cam Base Circle]
 That is where you need clearance... there is no clearance when the cam lobe is pushing the valve open..

[rwmastel]

Oh man, now I need to buy feeler gauges!     Oh well, the fun continues.....

Would a stuck valve always be stuck in the full open position, or could it partially close and then be pushed open again every time the cam lobe operated it?

If stuck fully open, would the piston contact the valve?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[A Dalton]

<<Would a stuck valve always be stuck in the full open position, or could it partially close and then be pushed open again every time the cam lobe operated it?
 It will be open just a tiny bit , not even enough for you to see .
That is why you need valve adjustment to make sure the low spot on the cam is not keeping it from completely closing.

If stuck fully open, would the piston contact the valve?>>
 If it were full open , you would have NO compression.. and , yes , the piston would hit it , but only ONCE...

[Ben]

Remember to set /check your valve clearances with the engine stone cold !!

Regards,
Ben in Ireland.
'64 230SL 4sp.
'03 CLK Kompressor

[rwmastel]

I bought feeler guages today.  Supprisingly inexpensive tool!  I'm not sure when I'll get to use them, probably the weekend of 11/27.

About the torque of head bolts:  I did a search on this forum and I saw where people suggested it with engine cold and others with engine hot.  Which should I do for regular maintenance?  Also, it's always stated to torque the bolts in the proper sequence.  What is this sequence?  I have not looked in Haynes or BBB yet, it's probably there.  I have seen 70 ft. lbs listed as the proper torque, is that correct?

Many Thanks,

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[rwmastel]

Tonight I removed my valve cover.  Since I had the lead from the coil to the distributor disconnected, and because I am just worried about cylinder #4, I simply used the starter to move the cam lobes.  They were not exactly straight up, but close.  On the rocker arm closer to the firewall, the .005 guage would fit through, but not the .006 gauge.  On the rocker arm closer to the radiator, the .006 gauge would fit through, but not the .007 gauge.

Saturday I will re-tighten the head bolts and do this again.  The BBB says to tighten them in 4 steps.

 - With the engine cold:
Tighten in specified order at 4 mkp (28.9 ft-lb)
Tighten in specified order at 6 mkp (43.4 ft-lb)
Tighten in specified order at 9 mkp (65.1 ft-lb)
 - With the engine hot (80C, 176F)
Tighten in specified order again at 9 mkp (65.1 ft-lb)

This is less than the 80 ft-lb that's been recommended on this Forum, so I checked two other sources:

Glenn's Mercedes Benz Repair & Tune-up Guide says:
Torque spec for 230SL is 8 mkp (58 ft-lb)

Haynes Mercedes Benz 230/25/280 Repair Manual says:
230-series cars use 58 ft-lb cold and 65 ft-lb hot
280-series cars use 72 ft-lb cold and 80 ft-lb hot

I hope this clears up head bolt torque specs for the different cars.  I'll be following the BBB specs.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[rwmastel]

What size hex drive do I need for the head bolts?  They look like about 10mm or 12mm.  I want to buy the right tool on my lunch hour today.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Cees Klumper]

Rodd - pretty sure it's 10 mm hex bolts.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[Naj ✝︎]

Rod,
Did you get the 10mm hex?

Couple of points:
The three stage procedure you quoted is for when fitting a new head gasket i.e. when you have had the head off.
For retorqueing the head, the procedure is to loosen each bolt a few turns and retighten to the final setting, following the tightening sequence bolts 1 thru 14.
This should be done with the engine warm (80 degrees C).

I guess you have the earlier BBB for the 230sl and the specs are on page 00-0/27?
Also read the notes on the opposite page 00-0/26, especially note 2) and 4).

Hope this helps.
naj

65 230SL
68 280SL

[ja17]

Hello Rodd,
Try the hillbilly leak down test it works and requires no expensive testers.
If your compression is down to 40lb in one cylinder (taken with warm eng.), the problem will be obvious. Remove both rocker arms on the low cylinder. If you have a compressor and air hook up hose for the spark plug hole....  connect an air line from the compressor to the cylinder and listen for air leaks. The air will leak off in one of four places 1)exhaust valve (listen for leak at exhaust tail pipes), 2) intake valve (listen for leak at intake with venturi open, 3) broken rings listen for air leak in engine from open oil filler cap, 4)head gasket (listen for air leaking from coolant resivour).
Yes a cylinder head removal and analysis would be great at the tech session.



Joe Alexander
Blacklick, Ohio

[rwmastel]

Naj,
I got a set of Craftsman 3/8 inch drive hex head sockets (4mm, 5mm, 6mm, 7mm, 8mm, 10mm) for $12.49, so I hope they are not 12mm bolts!!

Yes, I have the version of the BBB that covers the 230SL and 250SL, not the 280SL.  I found the info you mentioned on pages 00-0/26 and 00-0/27.  I originally found my info on page 01-4/1.  Having read on since then, there is retighten instructions on page 01-4/3, step 36.  What a great book!

Since the retightening is to be done with coolant at 80c, I guess I'll be putting the valve cover back on and going for a drive tomorrow (Saturday) morning.

Joe,
An air compressor is yet another tool I don't have (see below).

I hope I have my bad cylinder resolved long before July 30, but I'm always willing to let my car get torn apart for the greater good!

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[ja17]

Hello Rodd,
The head bolts are 10mm allen socket. Be sure to loosen the radiator cap to relieve pressure in the cooling system before beginning the re-torque. Yes the 230-SL uses a lower torque spec than the 280 even though the head bolts are the same diameter and configuration.

Also make sure the valve adjustment is correct on your low cylinder.

A $15.00 air tank (Harbor Freight) can be used instead of a compressor for your leakdown test!



Joe Alexander
Blacklick, Ohio

[Naj ✝︎]

Rodd,
After reading all the posts again, I think Joe is right - a leak down test is in order.

Maybe time for Arthur to convey his leak down test lesson

quote:Leak test is in conjuction with pressure , but a little different
we can go over that later, too...

naj

65 230SL
68 280SL

[glennard]

quote:Originally posted by rwmastel

Oh man, now I need to buy feeler gauges!     Oh well, the fun continues.....

Would a stuck valve always be stuck in the full open position, or could it partially close and then be pushed open again every time the cam lobe operated it?

If stuck fully open, would the piston contact the valve?

Rodd
Powell, Ohio, USA
 
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

40 psi - Sounds like a burnt exhaust valve on #4.  Wheezs?

[Benz Dr.]

I've never seen a stuck valve in a benz engine that was running. The fact that you have some compression tells me it's not stuck open. The valve guide will come loose if the valve stem is grabbing or galling but alloy valve guides are pretty slippery which is why they need very little lubrication.
You can have a burned valve and still have some compression reading because all the air won't leak through before you get some reading on the guage. A compression tester is therefore only useful in relation to a comparison of all cylinders. A leak down tester is more accurate and a vacuum tester is deadly accurate. This is the tool I use for all of my rebuilding. If a hair falls on the valve seat while placing a valve it will show up as a leak - it's that exact.

You WILL remove the head. In fact you might as well plan on a rebuild pretty soon. Fixing the head on an engine with any bottom end wear will often result in a spun rod bearing or broken rings. It's the old saying about weakest link.......

Daniel G Caron

[rwmastel]

quote:40 psi - Sounds like a burnt exhaust valve on #4.

quote:You can have a burned valve and still have some compression reading because all the air won't leak through before you get some reading on the guage.

Can someone define "burnt valve".  Was it left on the stove too long?  

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Naj ✝︎]

Rodd,

The sealing edge of the valve head literaly burns off and so the valve cannot seal anymore.
One cause of valve burn is not enough valve clearance at the tappett so the valve does not fully close and therefore gets too hot as it is not able to dissipate any heat to the valve seat / head.
Can also burn when too much 'meat' is taken off the valve head when refacing old valves.
Not doubt others here will add to causes of valve burning.

naj


65 230SL
68 280SL

[glennard]

quote:Originally posted by naj

Rodd,

The sealing edge of the valve head literaly burns off and so the valve cannot seal anymore.
One cause of valve burn is not enough valve clearance at the tappett so the valve does not fully close and therefore gets too hot as it is not able to dissipate any heat to the valve seat / head.
Can also burn when too much 'meat' is taken off the valve head when refacing old valves.
Not doubt others here will add to causes of valve burning.

naj


65 230SL
68 280SL

Somebody must have a pix of a burnt valve- just a little 'V' at the edge.  Don't think his valves were ever adjusted!

[Benz Dr.]

I have a few from a 220SE and the only ones I've ever seen - this isn't common. Only the valve burns away and not the seat which proves the hardness of the seats and also the heat dissapating abilities of the head. The valves are somewhat softer than the valve seats I believe.

I'm not sure what caused this on this engine as it was like this when I bought the car. These cars use manifold injection and all 3 injectors fire at the same time with 2 different sets of 3 runing from only 2 injection elements on a mechanical injection pump. The 230SL engine is really only a highly modified 220SE engine as they're both 127 engines.
The 220SEb was the engine I learned about injection on and it's a lot harder to make one run right than a 113 car. All the injectors have to be matched to within a few PSI of each other or the weakest of the 3 will spray before the other 2. If one is barely working it will burn out valves and could have been the problem here.
I replaced the 2 bad valves and did the head with injector matching. Now it starts and runs better than any car I own.

Daniel G Caron