Miss Firing

[glennard]

Rolf, Before you take the head off(a BIG undertaking for a first timer), 1)adjust all valves- 0.003" on intakes and 0.004" on exhaust. 2)make sure crank at TDC corresponds to cam shaft at mark(#1 lobes in a V) and rotor on #1.  Check to make sure the oil filter housing has the cylindrical seal on the center stub. If this has been missing, you have had no oil filtration and #6 rings may be tight. Then do a "5 minute Motor Flush".  This might loosen the rings.  Hope springs---
  If you take the head off, remember the 2 M6 cap screws in the chain vestibule and the head bolt order of loosening.

    150 lbs compression is a beautiful thing!

[Rolf]

Glennard... I checked all the items you suggested plus the flush and oil seal. I still get lousy compression readins sooooooooooo I guess the head comes off.

quote:Originally posted by glennard

Rolf, Before you take the head off(a BIG undertaking for a first timer), 1)adjust all valves- 0.003" on intakes and 0.004" on exhaust. 2)make sure crank at TDC corresponds to cam shaft at mark(#1 lobes in a V) and rotor on #1.  Check to make sure the oil filter housing has the cylindrical seal on the center stub. If this has been missing, you have had no oil filtration and #6 rings may be tight. Then do a "5 minute Motor Flush".  This might loosen the rings.  Hope springs---
  If you take the head off, remember the 2 M6 cap screws in the chain vestibule and the head bolt order of loosening.

    150 lbs compression is a beautiful thing!

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[glennard]

Rolf, Sorry to hear it didn't work.  Just a little 30 minute detour on the slim chance it might work.  Check with JA on what other diagnostic test to run-(for guides, seals, chain, etc.) before you lift the head.

[Benz Dr.]

Sounds like tight valve rockers and now one or more are probably burned out from lack of adjustment. Set valves at .003 intake and .007 exhaust.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[Rolf]

Dan,

  The number 6 intake valve was tight, compression was zero. I couldn't get any feeler gauge thru it. I adjusted to .003" and now get 25 psi. The compression does not increase after squirting oil in the cyliner. My guess as your educated one is valves.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[glennard]

Rolf, Whoops-dislexic moment.  0.003" om inlet - add 0.004" for 0.007 on exhaust.  Some do 0.008 on exhaust.  On a well running engine you can balance an old Jefferson nickel on the oil cap - ah, a Perfect Pagoda Pit-a-Pat!

[ja17]

Hello Rolf,

I agree with Dan, sounds like a valve problem. If you want to isolate the problem do this test: Remove both rocker arms over the bad #6 cylinder. Blow air into #6 cylinder. Listen for air leaking past the intake valve by opening the throttle valve and listening with a hose. Do the same at the exhaust tail pipe.

Some compression guages come with a hose which can be hooked up to shop air at one end and the spark plug hole at the other for performing such a test.

Joe Alexander
Blacklick, Ohio

[Rolf]

Update on Miss Firing...  I did what you suggested Joe and removed both rocker arms from the #6 cylinder and blew air through the intake. I heard air rushing through the intake. I took another look at the #6 valves and springs and found the intake spring higher than the rest. After further investigation, I found the keeper (valve collet) completely destroyed. Looked as if someone had chewed it but good. I also found excessive wear on the rotocap and the shim was distorted. After removing both the intake and exhaust rocker arms,I raised the intake valve, it seemed to be resting on the head. I blew more air into the intake and it seemed to hold. I have ordered the necessary parts and after installation, I will do another compression test. I got between 145 and 155 psi on all cylinders except the #6, when I did the compression test with the motor at operating temp (180 dgrees F.)

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[glennard]

MB gods are with you!  The keepers/collet can get out of place with the 'screw driver' push.  Are the valve stems straight?  Are collet grooves OK?  Guides?  seals? springs?  It is a miracle if the head doesn't have to be lifted.  JA to the rescue again!

[Rolf]

The springs are ok as are the grooves and valve stems. It seems when the keepers were eaten, by some unknown alien, the valve stayed right there. It might have been riding on the piston. It seems the only thing that saved further damage is the way the valves are in correlation to the pistons. I just needed new keepers, the rotocap and shim for that piston. I will know if further work is needed after I assemble it all and blow some air down the cylinder and finally, if the air holds, a compression test. Thank You Joe. kiss kiss

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[ja17]

Hello Rolf,

Glad you have pin pointed the problem area. I fear that a valve guide may have come loose in the head when the engine was hot (the mysterious noise you heard). This condition could release the keepers and raise havoc while the engine was running. The condition is commonly known as "dropping a valve".

When the engine cooled the valve guide could have tightened up once again. It sounds like you must remove the valve retainers and springs. Caution, caution the valve will drop into the cylinder and may not be retrievable if you are not very careful. Compressed air is usually used to hold the valve closed and from dropping in the cylinder during these kind of procedures. This is done during valve seal replacement. I cannot understand what is holding the vlave up if the keepers are gone? unless something is bent? Anyway applying compressed air to the cylinders will send the piston to BDC (bottom dead center) and the valve will be able to drop completely into the cylinder, so be careful. Moving the piston to the top and not using compressed air will hold an intake valve almost completely up safely as it rests on the piston top. However exhaust valves will still fall about an inch even with the piston at the top.

Loose keepers  may get washed back under the rear cam tower where there is a large oil drain passage leading directly back to the oil pan below. If the keepers have gone this route they may harmlessly end up in the oil pan. You may see them again at some oil change in the future!

Anyway, while the springs and such are off, check the valve guide to make sure it is tight in the head. If all seems ok, re-assemble and see how the compression does. If you are not completely familiar with any of these procedures let us know so we can help guide you.

Joe Alexander
Blacklick, Ohio

[Ben]

Its ounds indeed like it dropped a valve, and the noise you heard was probably the valve being hit by the piston, a quick "machine gun fire" sound.

As Joe says there may be other damage to the valve seat or valve itself. Measure the height on the closed valve against another and also the height of the guide.

When I did my rebuild I discovered several loose guides, the engine smoked but performed fine !

Best of luck !

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

[Rolf]

Hello All,

  It seems the valve didn't drop all the way because a piece of the keeper was sorta jammed keeping the valve from falling completely. I was lucky I guess for that. The guides do not seem to be loose. I'll see about the valves after I blow air down the spark plug hole and then, if everything seems ok, do another compression test. I have my fingers and toes crossed for when I get to that point. I removed the valve retainers and springs with the piston up and tied the valve off with thin tie wrap around the indentation on the valve stem. I will post more as the plot thickens or comes to a conclusion. Thank you all for your help and guidance.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[ja17]

Hello Rolf,

Installing the valve keepers will be a real difficult job without a special tool (spring compressor).  At least the intake is easier to hook up than an exhaust valve. If you have problems getting any of the bits and pieces you need let me know.



Joe Alexander
Blacklick, Ohio

[glennard]

Try the 1" box stock for the spring compressor.  A notch at one end to fit around the ball stud and a cut out at the valve for a magnet to lift out the keeper.  The BBB, Haynes, Clymer, Chilton - one of them has a picture.  Still have to hold the valve up.

[tuultyme]

What attachment do you use to apply air pressure to the cylinder while tring to replace the valve seals? Is there an easy way to remove the valve retainer without removing the head?  And finally is there anything special that is needed to remove and replace the valve seal.

From Joe
"When the engine cooled the valve guide could have tightened up once again. It sounds like you must remove the valve retainers and springs. Caution, caution the valve will drop into the cylinder and may not be retrievable if you are not very careful. Compressed air is usually used to hold the valve closed and from dropping in the cylinder during these kind of procedures. This is done during valve seal replacement. Anyway applying compressed air to the cylinders will send the piston to BDC (bottom dead center) and the valve will be able to drop completely into the cylinder, so be careful. Moving the piston to the top and not using compressed air will hold an intake valve almost completely up safely as it rests on the piston top. However exhaust valves will still fall about an inch even with the piston at the top."

Bruce; 268Blaugrun(green) 1970 280SL; IL

[ja17]

Hello Bruce,

I will get some photos of the tools and post them with information soon!



Joe Alexander
Blacklick, Ohio

[Rolf]

Hello All,

  Update on Miss Firing. I received the parts and installed them. I blew some air into #6 cylinder and it held. I warmed up the car to operating temp and did a compression test. I got from 145 psi to 155 psi in all the cylinders. I am sure glad I didn't have to remove the head. It seems that all the trouble was in the top end. I took the car for a ride and it performed marvelously. Thank you for all your help.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[J. Huber]

Very impressive bit of troubleshooting Rolf. I'd say you are really lucky to be so mechanically inclined. I think a lot of us would have received the ol' "yep, engine's shot -- you need a rebuild..." not because our mechanics are inept or greedy -- but because of the time involved to explore...

James
63 230SL

[Rolf]

James,

  Let us not forget the ones who gave me reliable advise. I have worked on motors before but it was some time ago and nothing as  this motor. I like simple ones such as my bike.  Thank you all again.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[glennard]

Rolf, How about a short recap?  What failed?  What parts were replaced?  Any ideas why?  Adjustments afterwards?  Advice?  Thanx

[Rolf]

Recap on Miss Firing

  The keeper was all chewed up. Possibly from not being installed correctly or a possible flaw. I don't know how else it could have loosened up. The rotor cap showed signs of being rubbed and the shim was bent. It seems the rocker arm was not riding where it was supposed to be. The rotor cap was at a slight angle instead of being straight and the shim was also not sitting where it was designed to. There were no signs of wear on the valve stem, shining areas indicating rubbing. The rotor cap showed signs of wearing, around the hole to one side was really shiney. The shim was bent to a degree and unusable. I had tried to readjust the clearance between the rocker arm and cam  but, no matter how much I turned it to increase the clearance, I still could not get a feeler gauge to clear. I replaced the rotor cap, shim and keepers and was able to obtain the necessary clearance between the rocker arm and cam. The groove in the valve stem were unaffected by all this, as was the valve guides. I had also asked a buddy of mine who restores classic USA cars to take a look at what had happened. He told me he had never seen anything like this before. So, I cannot say for certain what the cause was. I believe it was shoddy installation by a previous mechanic who worked on the car for a previous owner. I believe this because after I got the car, I found out the throttle linkage was installed incorrectly, among other so called repairs on the car. I haven't had the time, as of yet, to take the car out for a decent ride. I guess, when I do, that will be the true test. I have driven it around town and have not experienced any problems. I did a compression test and the readings are between 145 and 155 PSI on the cyclinders.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[Rolf]

Final on Miss Firing....  Fisrt off, I would like to thank all those who gave me guidance with the problem. After it did it the second time, dropped valve. It seems someone did grind the end of the valve too short and that was the cause of my problem. I did what Al said he did to one of his, so many years ago. I ground the valve side of the thrust washer at a 45 degree angle so more of it would pass through the retaining ring to ensure the washer rode on the stem and not the retaining ring. So far I have put 150 miles on the car and no problem. I know this is a "quick" fix and I shall be removing the head over the winter to properly correct the problem. New valves, springs, keepers, retaining rings and thrust washers all around plus having the head and valve seats checked. Thank you all again.

Rolf
1966 230SL Auto
1992 300D
1991 FLHS

[al_lieffring]

Hey Rolf

I'm glad that I was able to help you find what turned out to ba a very obscure defect in your valve train.

For everyone else, because the correspondence between Rolf and myself were off forum. It should be mentioned that my suggestion to Rolf was that the offending valve stem may have been ground off to make more valve adjustment clearance. When the stem has been ground too short the the slotted pad that the rocker arm rests against will make contact with the valve spring cap before it makes contact with the stem. when this happens the spring pressure that holds the valve keepers in plase is loostened when the valve opens and will eventualy cause the keepers to fall out.

I suggested that he should grind some extra clearance around the outer edge of the base of the valve pad and then aply grease to the pad to make sure that the contact was against the valve stem, not the spring cap.

Al Lieffring
66 230Sl
Jones'n for a new gas tank