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202 Rocker Geometry & Lifter Adjustment |
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The principle for adjusting a hydraulic lifter is the same regardless whether they can actually be adjusted or not dependent on the rocker fulcrum design. The objective is to ensure the push rod socket is pushed into the lifter a predefined distance that will allow the lifter to automatically take up zero clearance in the valve train for the life of the engine. (I have an article on Hydraulic lifter operation in the Engine section, please refer to this for further explanation). The ideal setting of 50 yrs ago was approx .030" to .050" of plunger movement into the lifter equating to 3/8 to 1/2 turn of the fulcrum bolt after zero lash, but can be much more these days because the cylinder head would have been machined several times which means the head sits lower and pushes the pushrod into the lifter further. You can go deeper and also shallower if you wish, the lifter will still do its job within a full working range from about .020" up to .160" (4mm max) but the danger with working close to the extremity of 4mm are the problems called lifter pump up and solid lifter lock. With lifter pump-up (which by the way can happen even at .030" adjustment) you will lose compression and the engine may stop and won't restart until the lifters bleed down. So the safer option is to stick a little closer to the loose side rather than the tight side. With solid lifter lock the plunger hits the end of its travel within the lifter bore and becomes a solid tappet. This will cause permanent valve opening and develop a permanent engine miss-fire with lack of compression in the cylinders affected. The engine used is a Holden 202 which utilises an aluminium rocker post bridge to joint a pair of rockers from the same cylinder. Other engines may use individual rocker posts, one for each valve, however the principle for adjusting them is exactly the same. The method I show in the video is for adjusting the rocker geometry and as a consequence the lifter is also adjusted albiet not as you may think. After adjusting the geometry then if you need to adjust the hydraulic lifter to retain the original plunger depth and you will need to adjust it, then you have to change pushrod lengths. Since this is an expensive way of making adjustments, it is rarely to never done which leads to further problems. I have never come across an engine yet that someone has fitted shorter rods because they realised the hydraulic lifter was on near lock up. If you end up with a rod pushed through a rocker arm, I think you have a problem with pushrod lengths being too long or it has coil bind. I have several videos that I have done over the last 20 years on the subject. The following videos will cover exactly what dimensions we are chasing for correct geometry and at the same time covers off on lifter adjustment.
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The table below shows the relationship of how far the push rod socket is pushed into the lifter at various turns of the fulcrum bolt on a Holden 202 after achieving zero lash. This is for a 5/16" UNC bolt that has a pitch of .055" per thread. If your bolt is a different size then you will need to know the pitch to calculate what is required to adjust for one quarter turns of the bolt, either a shim or machining of the pedestal post. The formula for a 1:1.5 ratio rocker is calculated by multiplying the bolt movement distance by 1.68 as calculated by my CAD program.
Please Note: The above table is only for the lifters I was using in a Holden 202 engine. Other manufacturers of the same lifter may have different specs.
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