Hydraulic Lifters - How Do They work?

[Tony Hunt]

Gentlemen,
A recent discussion about hydraulic tappets (lifters in US-speak) revealed that, although I am familiar with the principle by which OHC hydraulics work, the idea of the same thing on a pushrod engine with adjustable clearances created a number of anomalies:
1. How do you set the adjustment up? And from that, how do you adjust them on an engine with oil in it, when the lifter is 'solid'. Is it possible to push them down to the bottom of their travel, then adjust from there? If so, what are the parameters?
2. How do you know when the hydraulic lifter is operating comfortably within its adjustment range?
Could anyone supply an extract from a Ford manual explaining the whole business, with diagrams if possible?
I have found that data on the 302SVO engine is non-existent in UK.

 

Tony, I'll try to exoplain the best I can.

Hydaulic lifters do not have clearance, solid lifters do. Hydraulic lifters have preload and/or lash, which to say is when the pushrod contacts the lifter and there is no clearance the adjustment nut (on adjustable valvetrains) is tightened .020 to .060 more and then secured, on bolt down (or non-adjustable rockers) the preload is measured when the rocker is completely bolted down, and if out fo spec then typically shims are used.

The proper way to adjust is with a dial indiacator, but an accepted way (again adjustable rockers only)is to run down the rocker nut, turning the pushrod with your fingers until you can not turn it anymore (that is refered to as zero lash), using either rocker clips or an old valve cover with the center cut out (so oil doesnt spray everywhere), you would then start the engine, working with one at a time back off the rocker nuts until they make a "clacking" noise, then tighten until the noise goes away and give it 1/2 turn more, with bolt down rockers this is not possible to do, shims and a dial guage works best. Hope this helps.

 

[Tony Hunt]

Many thanks, Chris.
The solid lifter problem is easy - the traditional TR/MGB ohv method of adjustment works - with the lifter on the heel of the cam and the engine cold, set the clearance with a dial guage, feelers - or you even used to be able to get a tool which took wear of the rocker into account by setting so many thou of clearance per turn of the tool.
With hydraulic lifters, how do you know, when you adjust to zero clearance, if the hydraulic adjuster is at the bottom, top or middle of its range?
Does running the engine, and backing off until the clearance opens, automatically pump the adjuster fully up?
The half turn extra on this new, zero-clearance position would then presumably push the adjuster down towards the middle of its range?
This is so hard describe! /ubbthreads/images/graemlins/confused.gif

 

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Does running the engine, and backing off until the clearance opens, automatically pump the adjuster fully up?
The half turn extra on this new, zero-clearance position would then presumably push the adjuster down towards the middle of its range?

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Yes, when you run the engine the lifters pump up and fill with oil and the extra 1/2 turn preloads it. The pushrod actuates the spring loaded plunger within the lifter, when you initially install them and turn them between your fingers to achieve the zero lash make sure the cam is rotated so the valve is in the closed position (doing them this way one at a time), setting all 16 to zero lash, starting the engine (it will be pretty noisy until oil pressure builds) and then using the "backing off" procedure (again one at a time) unitl you go around to them all, keeping in mind that this procedure is for ADJUSTABLE ROCKERS, you must determine which kind you have, early Ford, up to '68 or so were adjustable, later ones were positive stop, and sometime in the 70's they went to bolt down.

Any Ford shop manual will detail this for you, you could even probably find it on line (Mustang guys perhaps), I hope I was able to help and make this a little more understandable.

 

[Tony Hunt]

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I hope I was able to help and make this a little more understandable

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Eminently so. Many thanks, Chris.

 

[Ian Anderson]

Tony

As promised at last night's meeting herewith a link to the RPI site where they give information on the Rover stuff. Presumably this is similar to the Ford set up and someone can confirm / reject the similaritiies.

This is the link
http://www.rpiv8.com/engine-4.htm#worntappets

Ian