Preload which is best more or less?

[Automania]

Hi guys I've being trying to set the preload up, I have one piece of wire at 0.020 and another at 0.062. Now the problem I've got is that with the shims I'm having problems, on one bank for example, I can get all the preloads with those figures except the fact I either have one where the small wire won't go in or where a couple are bigger than the 0.062.

I was just wondering which was better to have some to small of a gap or too large of a gap, obviously it'd be better to get it right but without adjustable pushrods I think I'm going to struggle. Any ideas much appreciated, cheers mike

[sidecar]

To a degree this sort of thing depends on what type of engine you are building, if its a bog stock lump with a stock cam then even if some of your pre-load readings are at either end of the scale they will be fine. If you are building a 'hot' motor with skimmed heads and a high lift cam then this sort of thing is important. The reason is that Rover controlled the max revs by allowing the valves to float at say 5800 RPM. What happens at these revs is that the followers then pump up with oil which causes the valves to be held open even when the followers are on the cam base circle, this causes the engine to mis-fire and lose power so that the driver changes up a gear. If the pre-load was set to say 40 thou then the valve will be held open 40 X 1.6 thou. If the minimum valve to piston clearance in the 'danger zone' was less than this then you would be in trouble!

I run an engine which I guess you would call stage III, it has piston cut outs for the valves, adjustable push rods and each pre-load set to 20 thou.

[Automania]

Ok it's got a crower 50229, not sure about the heads, I took them somewhere and they gave them a very light skim, but not sure if they had anything before this, I doubt it, although they have been reconditioned before. It's going in a land rover so it's never going to be revved hard. I'm not sure what my options are to be honest, I could probably do with some more shims, the set I got only had three sizes (8 of each) but I could do with some more variations, or I could get adjustable pushrods but the cost and the redrilling of the heads for these make it a none starter really as the heads are on now.
Cheers mike

[JSF55]

I got a 50229 in my 3.9 i set all the gaps around the higher mark, .060 and found it quite noisey, i did use the rhodes lifters with it which are louder. but it seemed more so than my last engine, 3.5 with a hurricane cam. i had the rocker covers off to clean them up and decided whilst i was in there to reduce the preload, next shim down, can't remember the size, but it made it quiter and i've had no issues with it, what followers are you using ?
edit ... have you tried swapping some of the pushrods around?

[stevieturbo]

I'd sooner run a higher figure than a lower one.

Too low and if the lifter didnt remain in control, it could end up flying up and down and not being held securely by the valve spring.

Run too much pre-load and this is les likely to happen. Worst case and all the oil got pumped out of the lifter, you'd end up with just a small valve clearance, similar to a solid lifter setup ( although with very different cam profiles used )

But hydraulic setups are pretty versatile and allow for a lot of error.

[sidecar]

The pressure on the push rod and inner cup of the follower that the oil pressure exerts will remain the same regardless of the pre-load figure so as long as there is always some pre-load the push rods are not any more likely to come out of the cup with more or less pre-load. The pressure that the valve spring exerts on the valve train remains the same regardless of the pre-load figure too.

[stevieturbo]

The pressure on the push rod and inner cup of the follower that the oil pressure exerts will remain the same regardless of the pre-load figure so as long as there is always some pre-load the push rods are not any more likely to come out of the cup with more or less pre-load. The pressure that the valve spring exerts on the valve train remains the same regardless of the pre-load figure too.

That assumes oil pressure does always remain sufficient to maintain the contact. It may not always be the case. Also if you run minimal pre-load, then under a valve bounce scenario there is more risk of problems compared to a high pre-load which would automatically take up some of that slack.

I cant see any positives from running a low preload figure.

[sidecar]

That assumes oil pressure does always remain sufficient to maintain the contact. It may not always be the case. Also if you run minimal pre-load, then under a valve bounce scenario there is more risk of problems compared to a high pre-load which would automatically take up some of that slack.

I cant see any positives from running a low preload figure.

The oil gets trapped in the lifter as soon as it lifts off it's base circle, as the oil is not compressible the valve then starts to lift off its seat. The oil pressure is only required to get the oil into the lifter whilst its on the base circle or a few degrees off the base circle but no more than that. Very little pressure or quantity of oil is required so the pump should always be able to cope with the demand.

The positive side of running low pre-load figures is that if the valve floats it it will not allow the lifter to be pumped up by a large amount. A lifter that is pumped up say 60 thou will cause the valve to be held open an extra 90 odd thou until the lifter bleeds down the excess oil which is can only do within a few degrees around the base circle. If this situation occurs during the critical period when the valves are close to the piston say at the end of the exhaust stroke when the exhaust valve can float due to it not being able to close as quick as the cam 'wants' it to close then you could end up with a load of bent valves.

A standard engine will never run clearances that are close enough for this to happen but it could certainly happen on a modified engine. I have measured several and it does not take a massive head skim or change of camshaft duration before the valves are too close to the pistons even without any lifter pump up, throw that in and the two will hit unless eyebrows are cut into the pistons. It's not even the peak lift of the cam that matters here, its the duration that the valves are open and by how much in the 20 degree BTDC to 20 ATDC period when the valves are 'on the rock' (Having said that a high lift cam will generally have more duration because it needs it in order to get the valves open to the higher figure and then close them again without exceeding acceleration limits)

[stevieturbo]

The above assumes the oil gets trapped and actually stays trapped. The lifter will not be a perfect seal, so some oil will be able to bleed off during operation. If you use a light pre-load and some does bleed off removing all preload altogether, you risk lifter damage and camshaft damage from the hammering effect that will take place as the lifter no longer follows the profile.

[sidecar]

There is no way that the 50-60 PSI of pressure that the oil pump produces could ever withstand the pressures that the valve springs generate, Very roughly I have worked it out below, I assumed that the inner piston is 0.5" in diameter, in fact I think that it is smaller therefore the PSI figure that I have come up with is on the low side.

The 'over the nose' pressure that the valve springs produce is up at something like 250lbs
The inner piston has an area of about 0.2" squared.
So the pressure of the oil is 250/0.2 which is...............



1250 PSI


On a knackered old engine with worn out lifters yes there will be some bleeding out of this oil at low RPM but as the oil system can not even feed the lifters when they are more than a few degrees off the base circle then the oil pump can do nothing about this. That and the fact it has 60 PSI to push the oil into a cavity where the oil is already at 1250 PSI so even if it could all that would happen is all of the oil in the lifter would be forced straight out of it.


Finally most engines do in fact keep the oil trapped in the lifters even when they are switched off, the open valves remain open for weeks and will only lose a small amount of oil which is why most engine will only rattle for a second after start up.

One other thing, with a solid lifter setup a clearance gap is actually setup by the engine builder on purpose yet those engines do not throw their push rods all over the place with a mild valve bounce so why should a hydraulic setup do this even if the preload is minimal, it still has some which a solid system does not have at all.


Bleed down lifters actually lose oil by design, they don't mis-place pushrods or hammer the cam as far as I know. (Not that I would use bleed down lifters anyway).

[Automania]

I'm back on this today, after I've fitted the flywheel back on. I'm going to have a swap around of the rods as suggested above, hopefully that might get them a little closer, presuming it's the rods that are different sizes and not the rockers?

So it seems a little split on which is best but seems I'm better off with a little too much than too little?

[Automania]

There is no way that the 50-60 PSI of pressure that the oil pump produces could ever withstand the pressures that the valve springs generate, Very roughly I have worked it out below, I assumed that the inner piston is 0.5" in diameter, in fact I think that it is smaller therefore the PSI figure that I have come up with is on the low side.

The 'over the nose' pressure that the valve springs produce is up at something like 250lbs
The inner piston has an area of about 0.2" squared.
So the pressure of the oil is 250/0.2 which is...............



1250 PSI


On a knackered old engine with worn out lifters yes there will be some bleeding out of this oil at low RPM but as the oil system can not even feed the lifters when they are more than a few degrees off the base circle then the oil pump can do nothing about this. That and the fact it has 60 PSI to push the oil into a cavity where the oil is already at 1250 PSI so even if it could all that would happen is all of the oil in the lifter would be forced straight out of it.


Finally most engines do in fact keep the oil trapped in the lifters even when they are switched off, the open valves remain open for weeks and will only lose a small amount of oil which is why most engine will only rattle for a second after start up.

One other thing, with a solid lifter setup a clearance gap is actually setup by the engine builder on purpose yet those engines do not throw their push rods all over the place with a mild valve bounce so why should a hydraulic setup do this even if the preload is minimal, it still has some which a solid system does not have at all.


Bleed down lifters actually lose oil by design, they don't mis-place pushrods or hammer the cam as far as I know. (Not that I would use bleed down lifters anyway).

Does the rocker ratio need to be taken into account on the above equation?

[sidecar]

There is no way that the 50-60 PSI of pressure that the oil pump produces could ever withstand the pressures that the valve springs generate, Very roughly I have worked it out below, I assumed that the inner piston is 0.5" in diameter, in fact I think that it is smaller therefore the PSI figure that I have come up with is on the low side.

The 'over the nose' pressure that the valve springs produce is up at something like 250lbs
The inner piston has an area of about 0.2" squared.
So the pressure of the oil is 250/0.2 which is...............



1250 PSI


On a knackered old engine with worn out lifters yes there will be some bleeding out of this oil at low RPM but as the oil system can not even feed the lifters when they are more than a few degrees off the base circle then the oil pump can do nothing about this. That and the fact it has 60 PSI to push the oil into a cavity where the oil is already at 1250 PSI so even if it could all that would happen is all of the oil in the lifter would be forced straight out of it.


Finally most engines do in fact keep the oil trapped in the lifters even when they are switched off, the open valves remain open for weeks and will only lose a small amount of oil which is why most engine will only rattle for a second after start up.

One other thing, with a solid lifter setup a clearance gap is actually setup by the engine builder on purpose yet those engines do not throw their push rods all over the place with a mild valve bounce so why should a hydraulic setup do this even if the preload is minimal, it still has some which a solid system does not have at all.


Bleed down lifters actually lose oil by design, they don't mis-place pushrods or hammer the cam as far as I know. (Not that I would use bleed down lifters anyway).

Does the rocker ratio need to be taken into account on the above equation?

Aha, it probably does and in fact due to the way that the rockers work I think that they will increase the pressure within the lifter even more.

Anyway the point that was trying get across is that the pump pressure is so low compared to what else is going on it can't have anything to do with actually lifting the valves. The system is 'sealed' once the lifter is off the base circle.

[Automania]

There is no way that the 50-60 PSI of pressure that the oil pump produces could ever withstand the pressures that the valve springs generate, Very roughly I have worked it out below, I assumed that the inner piston is 0.5" in diameter, in fact I think that it is smaller therefore the PSI figure that I have come up with is on the low side.

The 'over the nose' pressure that the valve springs produce is up at something like 250lbs
The inner piston has an area of about 0.2" squared.
So the pressure of the oil is 250/0.2 which is...............



1250 PSI


On a knackered old engine with worn out lifters yes there will be some bleeding out of this oil at low RPM but as the oil system can not even feed the lifters when they are more than a few degrees off the base circle then the oil pump can do nothing about this. That and the fact it has 60 PSI to push the oil into a cavity where the oil is already at 1250 PSI so even if it could all that would happen is all of the oil in the lifter would be forced straight out of it.


Finally most engines do in fact keep the oil trapped in the lifters even when they are switched off, the open valves remain open for weeks and will only lose a small amount of oil which is why most engine will only rattle for a second after start up.

One other thing, with a solid lifter setup a clearance gap is actually setup by the engine builder on purpose yet those engines do not throw their push rods all over the place with a mild valve bounce so why should a hydraulic setup do this even if the preload is minimal, it still has some which a solid system does not have at all.


Bleed down lifters actually lose oil by design, they don't mis-place pushrods or hammer the cam as far as I know. (Not that I would use bleed down lifters anyway).

Does the rocker ratio need to be taken into account on the above equation?

Aha, it probably does and in fact due to the way that the rockers work I think that they will increase the pressure within the lifter even more.

Anyway the point that was trying get across is that the pump pressure is so low compared to what else is going on it can't have anything to do with actually lifting the valves. The system is 'sealed' once the lifter is off the base circle.

Ah I get you now, yep can see your point.

[Automania]

Ok I've had another go at this and wrote down the clearances.

The sizes of rod I had were 0.062, 0.045, 0.027, 0.020 and 0.015"

These are the measurements I got, it might not make sense but the numbers are the rod I could get in then the next one I couldn't, so the clearance would be between the two values, hopefully ivennot over complicated it too much

1. 0.027-0.045
2. 0.062-0.045
3. 0.045-0.027
4. 0.027-0.020
5. 0.045-0.027
6. 0.027-0.020
7. 0.020-0.015
8. None of my rods fit in the gap.

N/s bank
9. Gap is bigger than my largest rod (0.062)
10. 0.062-0.045
11. 0.045-0.027
12. 0.062-0.045
13. 0.045-0.027
14. Gap bigger than 0.062
15. 0.045-0.027
16. 0.045-0.027

So the way I look at it their all pretty good, but I'm bothered about no.8, any ideas what to do with this?
I'm going to try and find an old set of feeler gauges and see if I can get the actual clearance.

Any help from an adult much appreciated