I was just thinking as a rule of thumb after even basic machine work on block,heads,valves.
Are there after market head gaskets avail for 258s? how thick?
With even a mild street cam,checking preload on lifters would be the norm?
So i went and found this..
.The function of any lifter, hydraulic or mechanical (solid) is to ride the eccentric slope of the camshaft's lobes and effect the opening and closing of the intake and exhaust valves. Hydraulic lifters have the ability to automatically adjust themselves and maintain zero clearance in the valve train by supporting the pushrod plunger on a small chamber of pressurized oil, regulated by a precisely controlled oil bleed rate. Valve train noise is prevented because the lifter is preloaded, eliminating any clearance.
Hydraulic lifter preload is the distance the pushrod plunger is depressed below the retaining lock. Preload should be between .020"-.060" for the lifter to perform properly. With too little preload, the valve train will be noisy and the retaining lock may fail (break or pop out) due to excessive hydraulic force against the retainer. Conversely, too great a preload (more than .060") will produce excessive lifter pump-up, causing the valves to open longer and lift higher, drastically reducing cylinder pressure and hurting engine performance. The engine will also have very low vacuum, causing it to idle very poorly.If preload needs to be adjusted, there are several different avenues the engine builder can travel, each dependent upon what type of mounting the rocker arms use.
Probably one of the simplest ways to change preload is to change pushrods.
A longer pushrod increases preload and a shorter pushrod decreases preload. Adjustable pushrods are also available.
When should hydraulic lifter preload be checked? Something as simple as changing a camshaft or installing thinner (or thicker) head gaskets may affect lifter preload. Other engine machining operations such as valve grinding, decking the block, or milling the heads will, for sure, have a serious effect on preload. A good rule of thumb is that any time a cylinder head has work done, or has new components installed, is a good time to check and adjust preload.
I read back and saw why i started the adj push rod talk.
>Posted by: 85AmCfreak
« on: October 19, 2016, 03:56:43 AM » Insert Quote
Ok first of all welcome to the forum.
When replacing the rocker arm bridges there is no adjustment to the valves. Actually there is no adjustment period. They are hydraulic lifters.
Randy(thinking out loud again)H.
hi, the question was do the plastic valve cover hold down studs on the rocker bridges affect valve adjustment, no, they do not.
Also, unless one is doing a full race motor with roller rockers, high lift cam/springs, etc, custom pushrods are NOT needed. good luck, gz