Lifter Pre Load checking

keanej

keanej

New Member
I have read the instructions on various web sites and I am still confused ?

With the cam on the back of the lobes the push rods are quite free - is this the point I am meant to be measuring the gap between the piston inside the lifter and the circlip ? ( Am I right in thinking I am not measuring anything to do with the pushrod ball and the circlip ? )

On the RPI web site it mentions 108 degrees, 108 from where - valve fully close ?, and given that measuring 108 without any equipment is going to be difficult is that the flat of the cam lobe against the bottom of the lifter ?

I assume that once the engine is running the lifter fills with oil and the piston in the lifter rises so there is less gap between that and the circlip - which takes up any play.
 
If you're refitting a new standard cam and followers to an engine that hasn't had the heads skimmed or the valve seats recut excessively I wouldn't be worrying about it. Setting that will only be necessary if you start changing things from standard spec. Do you think that Rover had a man with his little wire gauges checking all 16 clearances and then working out the mean shim size on every single engine as it went down the line? I don't think so. And if you've had the heads skimmed, but then fit composite gaskets you'll be near enough back to where you started anyway.

The RPI site shouldn't be taken as gospel either.......
 
Harvey

The cam wasn't that old, the lifters in good condition and rockers & shafts not worn.

I had a couple of push rods that had developed nipples - so I replaced all 16.

I have fitted later heads, one of which was skimmed very lightly, these had new valves in ( I am using the original rockers )

So on that basis I was checking the clearance - especially as I can't be sure that the heads haven't been skimmed before.

If I make sure that each push rod is free with a bit of play - is that a sufficient check - Must admit on the couple I have looked at so far there seemed to be a lot of play on the push rod which I why I wanted to check it. I suppose 40 - 60 thou is quite a bit anyway.
 
You can measure the heads to see how much has been skimmed off them using just a straight edge and feeler guages if you really want to know. Pushing the pushrod up and down is bound to be moving the piston in the lifter as well I would think.

I'd say if you do want to check it then take the reading with the lifter on the heel of the cam, (valve fully closed position).

One thing with RPI is they go on something alarming about checking this, and yet will happily sell you thicker composite gaskets to fit to unskimmed heads, and yet they don't sell rocker pedestals that have the same amount skimmed off the bottom as the as the shims they sell to correct the fault the other way.......
 
Checked all the lifters today, once I started to turn the engine over I could see how the lifters compress as the valve starts to open and rebound once the valve had closed - so it became obvious what I was meant to be measuring.

Passenger side bank are OK, say between 30 - 40 thou, drivers side ( the one I had skimmed ) will need shimming. I didn't have any wire thicker than 40 thou to measure the gap ( I would guess at 70 - 80 ) but as the shim kits have multiple sizes in I'll try a set and then measure the gap once fitted.

So waiting for the post man again.
 
Remember that the thickness of the shim under the pedestal is not the same thickness as the amount you are trying to reduce from the clearance in the follower, you have to take into account the rocker ratio. You also have to average it out to get shims of the same size under each pedestal.

I've not ever skimmed just one head, but the thought does occur that doing that could cause problems with the alignment of the inlet manifold when you try to refit it.
 
harveyp6 said:
Remember that the thickness of the shim under the pedestal is not the same thickness as the amount you are trying to reduce from the clearance in the follower, you have to take into account the rocker ratio. You also have to average it out to get shims of the same size under each pedestal.

I've not ever skimmed just one head, but the thought does occur that doing that could cause problems with the alignment of the inlet manifold when you try to refit it.
Click to expand...

I would have thought that it would upset the compression ratio a bit as well ? Ar you sure that you are comfortable with only skimming one head?

Bear in mind that you should test the pre-load with the tappets empty of oil - I don't know why, but I am told that this is correct.

The ratio is 1.6 on the Rover V8 so to adjust the pre-load by 25 thou, you need a 16 thou shim. (set of 16 thou shims)

Pre-load should be 40-60 thou btw

Richard
 
quattro said:
I would have thought that it would upset the compression ratio a bit as well ? Ar you sure that you are comfortable with only skimming one head?
Click to expand...

It will alter the cr, by how much obviously depends on how much has been taken off.
 
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