Lifter Preload
Discussion
I made the schoolboy error today of torquing down my inlet manifold on its new gasket and totally forgot about checking lifter preload.
My original heads were sent to V8D and turned into stage 3, they look as if they have had a light skim.
Cam is their MC1, lifters, pushrods and rockers are standard and it’s a composite head gasket as standard.
What I’m asking is how critical is it to check the preload on these engines?
My original heads were sent to V8D and turned into stage 3, they look as if they have had a light skim.
Cam is their MC1, lifters, pushrods and rockers are standard and it’s a composite head gasket as standard.
What I’m asking is how critical is it to check the preload on these engines?
Belle
You could try V8 Development's method of checking the preloads, see http://www.v8developments.co.uk/technical/valve_tr...
Setting The Pre-load
1) The 'pre-load' measurement is taken at the top of the follower and is the distance that the inner plunger is depressed below its retaining circlip. This is really very difficult to measure and we therefore have a slightly re-worked method for making the measurement.
2) With camshaft and followers fitted and the pushrods located on the followers, start to fit the rocker assemblies but do not tighten them down. Check that the camshaft lobe for number 1 inlet is 180 degrees opposite the follower (the follower is at the lowest point of its travel). Slowly tighten the rocker assemblies by turning each of the four bolts in succession (half a turn at a time) until the gaps at the valve side and the pushrod side are closed. At this point you should have no depression on the inner plunger in the follower (it should be at the top against the retaining clip) and the pushrod should be easily spun between your fingers but not able to move vertically up or down easily. Then using either feeler gauges or an accurate vernier caliper, measure the gap between the rocker pedestal and the cylinder head. This measurement will tell you what the pre-load will be without the rocker ratio being taken into account, in order to get the accurate pre-load measurement then use the formula;
Pedestal gap measurement x 1.6 = Pre-load at follower
3) we are looking in most cases for a pre-load of between 0.040" (40 thou) and 0.100" (100 thou) although this is not always the case so please ask if your installation is unusual or non standard.
4) Let us assume that your measured pedestal gap is 0.100" (100 thou). This would mean a pre-load of 160 thou which is too much and therefore the pedestals need 'shimming' to reduce the pre-load. By using the same calculation in reverse it follows that a 0.050" (50 thou) shim will reduce the pedestal gap to 0.050" and give us a pre-load of 0.080" (80 thou) which is acceptable. The shims generally come in thickness's of 0.016", 0.032" and 0.050" so it does not take a genius to adjust the pre-load to within parameters for most instances.
5) What if the pre-load is too low? This is more of a problem! There are a couple of decent solutions; a) have the pedestals machined down by 0.030" to 0.050" and then repeat the pre-load checking procedure or b) use adjustable pushrods to alter the length of the pushrod and therefore the pre-load on the follower. Both of these options have drawbacks! The pedestal machining is expensive, difficult and not always very accurate. The use of adjustable pushrods is a much better solution but most adjustable pushrods are slightly thicker than standard Rover versions and may need the guide holes in the cylinder heads 'opening' slightly to allow for contact free movement (this is a simple drilling exercise!).
You could try V8 Development's method of checking the preloads, see http://www.v8developments.co.uk/technical/valve_tr...
Setting The Pre-load
1) The 'pre-load' measurement is taken at the top of the follower and is the distance that the inner plunger is depressed below its retaining circlip. This is really very difficult to measure and we therefore have a slightly re-worked method for making the measurement.
2) With camshaft and followers fitted and the pushrods located on the followers, start to fit the rocker assemblies but do not tighten them down. Check that the camshaft lobe for number 1 inlet is 180 degrees opposite the follower (the follower is at the lowest point of its travel). Slowly tighten the rocker assemblies by turning each of the four bolts in succession (half a turn at a time) until the gaps at the valve side and the pushrod side are closed. At this point you should have no depression on the inner plunger in the follower (it should be at the top against the retaining clip) and the pushrod should be easily spun between your fingers but not able to move vertically up or down easily. Then using either feeler gauges or an accurate vernier caliper, measure the gap between the rocker pedestal and the cylinder head. This measurement will tell you what the pre-load will be without the rocker ratio being taken into account, in order to get the accurate pre-load measurement then use the formula;
Pedestal gap measurement x 1.6 = Pre-load at follower
3) we are looking in most cases for a pre-load of between 0.040" (40 thou) and 0.100" (100 thou) although this is not always the case so please ask if your installation is unusual or non standard.
4) Let us assume that your measured pedestal gap is 0.100" (100 thou). This would mean a pre-load of 160 thou which is too much and therefore the pedestals need 'shimming' to reduce the pre-load. By using the same calculation in reverse it follows that a 0.050" (50 thou) shim will reduce the pedestal gap to 0.050" and give us a pre-load of 0.080" (80 thou) which is acceptable. The shims generally come in thickness's of 0.016", 0.032" and 0.050" so it does not take a genius to adjust the pre-load to within parameters for most instances.
5) What if the pre-load is too low? This is more of a problem! There are a couple of decent solutions; a) have the pedestals machined down by 0.030" to 0.050" and then repeat the pre-load checking procedure or b) use adjustable pushrods to alter the length of the pushrod and therefore the pre-load on the follower. Both of these options have drawbacks! The pedestal machining is expensive, difficult and not always very accurate. The use of adjustable pushrods is a much better solution but most adjustable pushrods are slightly thicker than standard Rover versions and may need the guide holes in the cylinder heads 'opening' slightly to allow for contact free movement (this is a simple drilling exercise!).
stevesprint said:
.................................. The use of adjustable pushrods is a much better solution but most adjustable pushrods are slightly thicker than standard Rover versions and may need the guide holes in the cylinder heads 'opening' slightly to allow for contact free movement (this is a simple drilling exercise!).
Drilling itself is easy enough but you have no way of stopping the swarf from going down inside the engine unless you have the inlet removed and the whole valley stuffed with rags and paper towels.However, if,as you say, the heads have been skimmed it is far more likely you will need shims than the reverse.
Steve
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