Topic: Valve Adjustment Frustrations

[The Lone Builder]

Not strictly new; I posted similar question, but got no responses.

U've just completed rebuild of 750K2. Before putting head cover on, I rechecked the valve clearances. They seemed to have changed, so I reset them following the procedure in HM book.

The problem is that every time I rotate the engine and recheck, the gap seems to have changed. Now the last post on this issue noted that the end of the adjuster screws did not sit flat on the valve tops. The pic is of "adjusted" exhaust valve.

A bit of research led me to TT's post regarding concave/convex surfaces and the difficulty of setting gaps.

IF your adjuster mating surfaces have worn convex and concave, you can't use a flat feeler gauge to measure true gap.
However, if you know the thread pitch, for example 0.9 mm, then one full turn will create 0.9 mm gap, 1/4 turn will make 0.225mm gap, etc.  In this case .05 mm would 20 degrees rotational movement open from when zero lash was acheived.

I'm not sure what a non-flat feeler guage is, but ....

In my case the end of the screw seems to be very slightly convex and the valve end flat.

If I set the gap at the narrowest point, it is obviously larger elsewhere; is this the way to go?

I may be worrying needlessly, but I'd like to be sure before putting the cover on.

Thanks for assistance

Sean

[flybox1]

The gap is always set at the narrowest point.
Picture above looks correct and I believe these are the  'non-flat' feeler gauges.

[TwoTired]

There used to be tool offered to adjust tappets that had a dial mounted and calibrated for the thread pitch of the adjuster screw.  The handle would operate the lock nut and the dial would engage the adjuster screw.  Loosen lock nut with handle, turn dial for zero lash (finger tight), then back it out the proper number of increments on the dial to acheive the desired gap.  Then tighten lock nut with handle and move on to next adjuster.  It is very fast for production use.  Such a tool does not take into account adjuster stretch or metal ditortion from the tightening process.  But with routine use, that can be factored in with the tool's increment settings to result in very accurate and consitent settings.

The bit about concave/convex mating surfaces is that it emulates a ball and socket arrangement where a flat thicknes guage can not conform to curvatures, and is therefore inaccurate as a tool to measure clearances. This will result in actual tappet clearance greater than that of the thickness gauge.

Cheers,

[rotortiller]

What you will find is nut torque changes the reading so best to compensate with the feeler gauge drag prior to torque down. 

[bagatyr]

I just did a valve adjustment and found the same thing as rotortiller. The nut will decrease the gap as it's tightened by just a hair. Also make sure you are not pressing down with the screwdriver, that will also decrease the gap while you're measuring.

[The Lone Builder]

Thanks for the input folks.

Sounds like an amazing machine TT; do you have a pic of this tool?

Will retry without putting any pressure on the screwdriver.

Cheers

Sean

[Killer Canary]

www.motionpro.com/product/08-0073
I've never trusted myself with feeler gauges.

[DaveBarbier]

Try setting the clearance .001” over the recommended and when you tighten it down it should close up getting you right in the ball park. Thats what I do at least.

[Keith]

After adjusting the valve, lightly feel for free play between the rocker and the valve tip. Then, insert the next thinnest feeler gauge, it should slide between the valve and rocker with no resistance. The next size thicker than the correct gauge should not slide through....A go-no go gauge.