Tight exhaust valves and loose intake valves? - PeachParts Mercedes-Benz Forum

bipolardave · #1 06-20-2016, 09:59 PM

I recently adjusted my valves. Over the last 12,000 miles, my exhaust valves tightened to the point that they had almost no clearance (spec is .30 mm) and the intakes were loose at ~.20mm (spec is .10mm).

Unless I'm mistaken, valves tend to work tighter over time and not loose.

My hunch is that the mechanic who adjusted them previously confused the valves and adjusted the intakes to .3mm and the exhaust to .1mm. Each valve then tightened up .1mm since the last adjustment.

Thoughts?

leathermang · #2 06-20-2016, 10:55 PM

That is easy to do....
and certainly a possibility...
and yes, on an overhead cam it wears tighter...
so now that you are doing it yourself you don't have to worry about that shop guy getting it wrong... I think it is nice to put some kind of mark on them as you start.. a bit of tape or something... color coded tape can take the iffyness out of the procedure... if you think it out to start with..

jt20 · #3 06-20-2016, 11:13 PM

I agree.

Just to be certain, try spinning the valve with the nuts tight so that the valve stem turns.

Leave the feeler in between the cam and rocker to see if it changes much.

Unlikely that all of them would have this issue at the same time... its just good info to find while youre in there.

VW1300 · #4 06-20-2016, 11:36 PM

I do my bug valves once a year, sometimes I find a loose intake valve - it happens.

Diesel911 · #5 06-21-2016, 01:45 AM

Quote:

Originally Posted by bipolardave

I recently adjusted my valves. Over the last 12,000 miles, my exhaust valves tightened to the point that they had almost no clearance (spec is .30 mm) and the intakes were loose at ~.20mm (spec is .10mm).

Unless I'm mistaken, valves tend to work tighter over time and not loose.

My hunch is that the mechanic who adjusted them previously confused the valves and adjusted the intakes to .3mm and the exhaust to .1mm. Each valve then tightened up .1mm since the last adjustment.

Thoughts?

Does the 240D have valve rotators on all of the Valves or only the Exhaust Valves? If so the Valve Rotators could be the reason as the rotation tends to wear them a tiny bit each time they move.

Also if the Engine had not had a Valve Adjusment for a long time crud buids up between the Valve face and the Vave Seat on the Exhaust Valve more then on the Intakes. After a Valve Adjusment that crud wears off some and your Exhaust Valves can get tighter.
There is recommendations in other threads that on Engines that have not had the Valves re-ajusted for an extended of time that after the newest Valve Adjustment the Car Should be driven sever hundred miles and then at least check the Valves to see if they have tightend up.

97 SL320 · #6 06-21-2016, 07:11 PM

The type of cam system has little bearing as to a valve going tight or lose.

Things that make valves go tight:

Valve face wear.

Valve seat wear

Valve seat sinking in the head ( mostly with aluminum heads especially if overheated )

Valve stem stretching.

Things that make a valve go loose:

camshaft wear.

Rocker / follower / pushrod wear.

Valve tip worn concave. ( this will look like a valve going tight if measured with a flat feeler gauge between stem and actuator. )

valve seat falling out of the head and cocking in the bore. ( See also aluminum heads overheating )

leathermang · #7 06-21-2016, 07:37 PM

Quote:

Originally Posted by 97 SL320

The type of cam system has little bearing as to a valve going tight or lose........

It is spelled ' LOOSE'...
and your statement is wrong.
and the fact that an overhead cam wears in a fashion which lessens the valve lash means that not adjusting properly on a regular basis puts your engine at risk of burning valves....

97 SL320 · #8 06-21-2016, 08:21 PM

Oh gee, attack me for a typo when you don't have any logic to attack the intent of my words.

Please expand on _exactly_ what wears on a OHC valve train that causes the valve lash to tighten up.

leathermang · #9 06-21-2016, 09:19 PM

Quote:

Originally Posted by 97 SL320

Oh gee, attack me for a typo when you don't have any logic to attack the intent of my words.

Please expand on _exactly_ what wears on a OHC valve train that causes the valve lash to tighten up.

Everyone else already knows this... and you would not take my word on it anyway..... so you will need to do your own research...

Frank Reiner · #10 06-21-2016, 10:35 PM

Quote:

Originally Posted by leathermang

Everyone else already knows this... and you would not take my word on it anyway..... so you will need to do your own research...

Well, almost everyone; I am indeed quite curious about the phenomenon.
How does valve clearance decrease as a result of wear, and in what way is it unique to OHC configurations? Does the phenomenon occur with bucket followers as well as finger followers?

leathermang · #11 06-21-2016, 10:46 PM

Frank, as the valve top which contacts the head.... and the head wear... the valve gets farther into the head... and thus closer to the cam... so it has less distance between the cam and the top of the valve... thus risking , if not checked regularly, having NO Clearance WHEN HOT.. thus not allowing the valve the approximately 50 percent of the time held tightly against the head which is important to the convection cooling of the valve...
In other words.. it can have SOME clearance.. but if not enough to allow the expansion of the valve when WARM.... then that lack of sufficient cooling can occur and burn the valve...

Frank Reiner · #12 06-21-2016, 11:10 PM

gl:

You have repeated the information concerning valve face and valve seat wear from post #6, a post written by another, without explaining your contention that loss of clearance is unique to OHC configurations.

ROLLGUY · #13 06-21-2016, 11:54 PM

Not that I am an expert in this, but as I see it, we are mostly talking about solid lifters/buckets/followers and not hydraulic. It would seem that on all engines, valve and seat wear accounts for most of the reduction in valve clearance, and very little cam/follower wear. On our iron head engines, valve adjustment is more critical, as failing to do so at the proper intervals can cause burned valves and or hard starting from lack of compression. I don't think loss of clearance from wearing valve and seat faces is unique to OHC engines, but it is not noticed with hydraulic lifters/followers etc, as it is with adjustable ones. It has been my experience that the exhaust valves on the 61X engines seem to get tight, whereas the intake stay the same or get looser.
As far as knowing what valves are intake or exhaust, I mark a "I" for intake, and
a "-" for exhaust on the cam oiling tube with a Sharpie (after wiping the oil off of course). I know the order, but for those that don't, it is quite easy. One can clearly see that the forward most port is an exhaust, so after marking that, they are two of each, alternating until the last one, which would be an intake. It looks like this: - I I - - I I - - I
Marking the valves first makes it (in my case) "Richard proof".

Diesel911 · #14 06-22-2016, 12:58 AM

Quote:

Originally Posted by 97 SL320

The type of cam system has little bearing as to a valve going tight or lose.

Things that make valves go tight:

Valve face wear.

Valve seat wear

Valve seat sinking in the head ( mostly with aluminum heads especially if overheated )

Valve stem stretching.

Things that make a valve go loose:

camshaft wear.

Rocker / follower / pushrod wear.

Valve tip worn concave. ( this will look like a valve going tight if measured with a flat feeler gauge between stem and actuator. )

valve seat falling out of the head and cocking in the bore. ( See also aluminum heads overheating )

Valve Rotators can cause both.

Diesel911 · #15 06-22-2016, 01:10 AM

The Fuel Injection Shop I worked in also occasionally rebuilt Cylinder Heads. A Customer brought in 2 Cylinder heads from a Ford gasoline V-8 Engine. This was a heavy duty Engine like might be used on a one ton truck.

The Intake Valves were in decent shape but all of the Exhaust Valve faces were worn to the extent that they were knife edged with some burned through. The Exhaust Valves had Valve Rotators on them but the Intake Valves did not have Rotators.

Those 2 Heads were the only Heads I have rebuilt that had valve ratators on it. None of the Diesel Heads I have worked on had valve rotators.