Camshaft timing clarification - PeachParts Mercedes-Benz Forum

billhard · #1 04-07-2011, 05:29 PM

I have read several threads as well as the FSM about camshaft timing the 616 in my w115. There is one step I can't seem to get my clouded by home brewed ale brain to digest, could someone clarify?

In this DIY WIKI step #3 says Just remove valve lash. The FSM manual says "Screw cap nut upward at intake valve of No. 1 cylinder until valve clearance is just cancelled.

I know these are two ways of describing the same thing, but I guess I need three since I don't get it. What is valve lash, when is valve clearance just cancelled?

leathermang · #2 04-07-2011, 05:52 PM

Valve Lash is the distance left open for heat expansion of the valves so they will be seated during normal temperature operating of the engine..
If there were no ' lash ' then as they expanded from combustion heat they would cease to clamp against the head properly ( and this is very important to not burning the valve because at least half the COOLING OF THE VALVES is by the convection of heat to the head when it is closed..)
So to take up the lash... eliminate it.... you screw up that top adjusting nut ( there is technically only the cap nut...and the next one down is just its lock nut ) to take out that space.. thus... AS SOON as the Cam LOBE starts to rise... it will be reflected in the movement of the valve.. which you will be measuring with your dial indicator typically ) but can be done with feeler gauges )....
Valve lash is JUST cancelled when you have eliminated that space.. IE, you are not going to screw up that cap nut and put Pressure on the Cam... only eliminate the open distance referred to as the lash....

Chas H · #3 04-07-2011, 05:55 PM

Valve lash and valve clearance are the same. "Valve lash just cancelled" means zero clearance with no movement of the valve towards open.

billhard · #4 04-07-2011, 06:56 PM

OK so what is meant is instead of having the correct running gap between cam lobe and pad on intake valve for cylinder #1 i should reduce that distance to zero so the pad is touching the cam lobe?

Marvelicious · #5 04-07-2011, 07:11 PM

Quote:

Originally Posted by billhard

...There is one step I can't seem to get my clouded by home brewed ale brain to digest...

Ha. Life begins at 1.080 OG.

billhard · #6 04-07-2011, 07:15 PM

Quote:

Originally Posted by Marvelicious

Ha. Life begins at 1.080 OG.

It sure keeps me smiling.

Chas H · #7 04-07-2011, 07:23 PM

Quote:

Originally Posted by billhard

OK so what is meant is instead of having the correct running gap between cam lobe and pad on intake valve for cylinder #1 i should reduce that distance to zero so the pad is touching the cam lobe?

Yes.

billhard · #8 04-07-2011, 07:45 PM

Thanks guys or perhaps gals.

tangofox007 · #9 04-08-2011, 08:04 PM

Quote:

Originally Posted by leathermang

...at least half the COOLING OF THE VALVES is by the convection of heat to the head when it is closed..)

Conduction.

leathermang · #10 04-08-2011, 11:33 PM

Quote:

Originally Posted by tangofox007

Conduction.

Correct. This is the second thread in two minutes I had to plead injured knee drugs affecting my answer.... LOL
I know my thought process was ' heat conveyed ' to the head...and it came out convection...