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  #1  
Old 05-09-2013, 04:33 PM
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What's Your Valvetrain Horror Story?

Do you have one? I'd like a better idea of how bad things can get, what kind of weird stuff happens what people forgo adjustments, etc. I recently had a conversation with a guy that adjusted his valves to inch specs rather than mm, and the car apparently sounded like a diesel with all the hammering.

More generally, what's the furthest out of spec you've seen valves -- how much do you think it takes for real catastrophic damage to be caused to the valves, rockers, etc..?
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Old 05-09-2013, 05:21 PM
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I think valves can get tight when they are not adjusted-leading to burnt valves.
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Old 05-09-2013, 05:38 PM
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I understand the theory behind correct valvetrain maintenance and lash adjustment.

What I'm interested in here are those off the wall stories, the outliers, that define what CAN and MIGHT happen under certain conditions. This all helps to define the limitations of certain systems. So for example, has anyone had catastrophic valvetrain failure? A valve lose adjustment rapidly?
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Old 05-10-2013, 02:51 AM
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Well here's mine

OM617 rocker arm problem?

Turned out a Mercedes expert fitted the groups of rocker arms in the wrong order on my engine - it took a long time for the penny to drop!

I've also had a refurbished head back from a machine shop that had a OM615 valve (smaller diameter) in my non turbo OM617 head...

...and a broken valve guide that leaked oil into the exhaust. Oh happy days!

http://www.peachparts.com/shopforum/diesel-discussion/276144-om-617-manifold-oil.html
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  #5  
Old 05-10-2013, 10:36 AM
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I have lots of valve train stories. If you leave the rocker pounding against the cam lobe long enough it will wear the lobe down to nothing, which I've seen. Valve lash adjustments are important; done correctly, your cam should never wear out.

I had a ticking noise in an engine but only at idle. We adjusted the valves and it still ticked. Turned out it was loose or worn valve stem keepers and eventually the keepers broke and.......... the valve dropped into the cylinder smashing the piston. Not nice......

Rocker geometry is very important on older enginea such as the 127 through 130. Get this wrong and you can wipe out a set of valve guides in a couple of miles.
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  #6  
Old 05-10-2013, 10:52 PM
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Quote:
Originally Posted by Coastal220 View Post
I understand the theory behind correct valvetrain maintenance and lash adjustment.

What I'm interested in here are those off the wall stories, the outliers, that define what CAN and MIGHT happen under certain conditions. This all helps to define the limitations of certain systems. So for example, has anyone had catastrophic valvetrain failure? A valve lose adjustment rapidly?
Fairly common if the adjuster has a weak interference fit. On the older gas engines a torque wrench should be used to determine if they are within specs.
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  #7  
Old 05-14-2013, 11:34 PM
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My worst valve issue with a Mercedes was Summer of '82 on my '61 Ponton 180, where #1 exhaust valve burned so badly that there was a narrow pie-slice notch cut right through the valve head. Plus all the intake-valves had deep grooves worn round their edges. Fixed by my only Mercedes valve-job.

But I've had a whole litany of valvtrain troubles with a pair of early '70s Audi Super-90 wagons
powered by a high-compression, slant-four pushrod engine designed by Daimler-Benz when they owned the company in the mid '60s.

First time was May '79 with Audi #1, when a coolant thermostat stuck on a trip and the engine overheated enough for the #2 intake valve guide to loosen in the head and move up & down with the valve, causing much oil-burning and huge clouds of blue smoke. Cured by my first Audi valve job

Next time was early '82 on Audi #2.
(Three days before Air-Florida flight-90 landed on the 14th street bridge!)
On a bitter cold afternoon, while going about 60 mph, the top of #2 exhaust valve snapped off and buried itself sideways in #2 piston, spltting said piston down one side and gouging out a crater in the head.
A junkyard head with a valve-job and a set of new pistons finally got it going two months later.
Good thing I had a '66 230 Fintail as my backup in the meantime!

Third time was Summer '84 when #3 intake-pushrod bored a hole through it's rocker-arm. Ordered one pushrod and a set of rockers from Audi, but only got five rockers as Audi informed me that was all that was left in their world-wide inventory. so I just replaced the one.
(Anyone need a rocker-arm for a 1970-72, 1760 cc pushrod Audi Super-90 engine?)

Finally, Fall '87 the accelerator stuck to the floor. Then several seconds of over-revving knocked #1 exhaust valve seat loose and cocked it in the head. So I lost compression in that cylinder. leading to my third and final Audi valve-job.

That car was over 20 years old in the early'90s when I retired it for a broken rear suspension torsion bar. At that point, new (or used) Audi Super-90 parts were pretty much extinct.

By then, I'd gotten back into Mercedes with a '72 W115 220. followed by a '72 W114 250. Later a 60 Fintail and several W123 diesels. Never had any valvetrain issues with any of them!

Happy Motoring, Mark
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Last edited by Mark DiSilvestro; 05-15-2013 at 12:04 AM.
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