8 replies to this topic

[happydude2012]

Ok chaps

AC asked i measure lobe lift on my engine to determine if my cams had it.

Presumably i can do this with the engine in? 

 

How?

 

ha ha

 

sorry lads ive never done this and id like to learn - anyone got a video or diagram?

thanks

[Cooperman]

You need a Dial Test Indicator (DTI) with a magnetic base.

Use the DTI to measure the movement of the rocker on the push-rod side of each rocker from lowest point to highest point. That is the lobe lift, but the actual valve clearance must be added to this figure, so it must be measured with a feeler gauge or, alternatively, the valve clearance re-set to zero before doing the measuring.

[GraemeC]

Why add valve clearance to that measurement - is lobe lift not irrespective of clearance?
I can see the value in setting to zero, just to ensure everything on the cam side of the rockers stays in contact and there chance of float to give poor readings.

[happydude2012]

ok - ive bought one of the magnetic based DTIs and damn it im going to learn this.

So cooperman, i can do this with the rockers on? VERY COOL!  i assumed that id have to remove them and use the pushrods or something.

Im also after buying a compression tester - which ill be asking loads of questions about.

[Cooperman]

If the rocker is physically held onto the push rod end, then there is no need to consider the valve clearance, but there is a chance that the initial valve clearance will be under the push rod tip, not at the valve stem top.

The best way is simply to remove the valve clearance. That is what I always do as it removes any chance of error. Alternatively the rocker can be physically held down onto the push rod top during the initial setting of the DTI to zero.

In fact, if the rocker is on the valve stem, the amount to be deducted is the valve clearance divided by the rocker ratio.

Just removing the possibility of error caused by the valve to rocker clearance is important. 

[happydude2012]

do i do this on every rocker to check lift on each one? 

or just the end one?

[Retroman]

I would check each one, you can then tell if one or more is worn

[happydude2012]

got it! thanks chaps

the more i look at the symptoms, the more it sounds like a worn cam lobe.

Rocker tapping on a cold engine gradually fading when the oil dampens it -  , the odd backfire/crack at high revs in neutral.

I think im dooooomed lads.

 

nice generic but useful article here on symptoms if anyones interested.

 

https://itstillruns....ft-6293277.html

[Cooperman]

do i do this on every rocker to check lift on each one? 

or just the end one?

 

do i do this on every rocker to check lift on each one? 

or just the end one?

If checking for lobe wear, then each one needs to be checked.