New thoughts on Valve Adjustments - PeachParts Mercedes-Benz Forum

jt20 · #1 04-06-2010, 01:59 PM

I have a theory... oh boy..... and I think its kind of important.

I know for a fact that I have worn valve guides that need to be replaced. I have noticed, as have other members, that when you adjust the valves there may be a great variance in clearance if you spin the valve in the head.

This must be due to the worn guides. The sloppy camshaft arrangement puts a lateral force on the valve stem and wobbles it; this action ovalizes the valve seats.

When you spin the valve, it is mating the ovaled edges with the circular edges (head seat vs. valve seat) and causing the height discrepancy.

Perhaps this is well know... I couldn't find any info on it.

what I really want to figure out is.... How should we set the valves short of getting our heads rebuilt?

I think you want to set the valves at the TIGHTEST location only. Not a mixture, or an average of the heights.

The tightest location (smallest clearance) is where, presumably, the valve will spend most of its time.

leathermang · #2 04-06-2010, 02:05 PM

UH... have you factored in the valve rotators ?
And the fact that the safer situation... is too loose as compared to too tight..which might be catastrophic ?

jt20 · #3 04-06-2010, 02:11 PM

I have considered the rotators, and they are not supposed to change heights (and will not unless failed) and will not effect the valve height.

the discrepancies are not great enough to cause interference..... yet. And mine are quite bad. Adjusting at the tightest position will make the valve as short as possible, not long and potentially hazardous.

the premise is that, the valves will tend to stay in the position where they seat more fully when worn. But will rotate as intended when perfectly circle.

leathermang · #4 04-06-2010, 02:20 PM

When TCane showed me and TxBill how to set the valves he took into account that difference caused by rotating the top nut... but I do not know how you are going to rotate the actual valve to do this....

jt20 · #5 04-06-2010, 02:22 PM

please elaborate an what Tcane said.

I am big fan!

jt20 · #6 04-06-2010, 02:24 PM

rotating the valve happens with the nuts tightened. turn them together, the entire valve turns.

use your feeler to find the position where the feeler is tightest, or won't go in.

leathermang · #7 04-06-2010, 02:30 PM

I would be careful about using the jammed two top nuts situation to rotate the valves..
you can however use that special wrench on the sloted washer ( not its correct name) to turn the valves.
If you strip the threads from either of those clearance adjusting nuts you have to take the head off to correct the situation ! EEEEEAAAKKKKKKKKKK !!!!!

TCane used the standard method... but was just really careful about everything.

Alastair · #8 04-06-2010, 03:53 PM

Ive re-built a number of 615/6/7 heads over the years....

On high-milers, (200K+) Ive noticed that the seat in the head wears Oval--just slightly...

taking a worn head, replacing the guide and a new valve and use a grinding-paste, you'll find that one side contacts and the other doesnt...

--And, Its Always the Same Side of the head that this shows up --cant remember which, Injector side--I think

--Even if you Dont replace the guide, and use a new valve, the Same wear shows up on the head seat...

Obviously a head-seat cutter is used, But a 30 degree one is difficult to find in these parts! and Ive used a 45 degree before now, when the seats have been too bad...

the wear is caused by the slight side-thrust caused by the cam-follower, which moves through an arc, imparting that side thrust directly to the valve-stem....

Diesel911 · #9 04-07-2010, 01:34 AM

If you use a Valve seat Grinder insead of a cutter you can dress the Grinding Stones to what ever Angle you like.

I was told way back in Trade School that one of the syptoms of a worn out Valve Train is that it will not hold an adjustment. So what everyone has said seems logical.