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Roadside Jerry
Roadside Jerry, Auto Mechanic
Category: Car
Satisfied Customers: 2948
Experience:  Auto Mehanic 39 years,30 with the NYPD Fleet Service Division
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The lifters seem to pump up and hold the valves open

Customer Question

The lifters seem to pump up and hold the valves open after a short time running. I have details on previous repairs that may be pertenant.
Submitted: 8 years ago.
Category: Car
Expert:  Roadside Jerry replied 8 years ago.
Hello D Criss, The only reasons for the lifters to pump up are, defective lifters, oil pressure that is to high,or the valves were not corrected for the height when the head was rebuilt. When the valve seats and valves are machined,the stem height gets longer, the stem tip is supposed to be ground down by the rebuilder of the head to compensate for this.If the head is resurfaced,it also contributes to the problem. This can cause the lifters to not have enough clearance up give you the problem.If the problem began since the head was done,this is what you will have to look into. Thanks,Jerry.
Customer: replied 8 years ago.
Thank you. I think you have hit the nail on the head. One more thing...How is oil introduced into the lifters and how is excess oil pressure in the lifters relieved?
Expert:  Roadside Jerry replied 8 years ago.
Hi, I am going to send some info on lifters for you. Oil is feed under presure to the lifters throuh oil supply holes in the bore the ride in.When the cam comes up to the high spot the lifter check vlave closes,and the oil is trapped inside,making it allow the valve to open. When the valve is open the check valve in the lifter is supposes to open and release some oil. That is why you need the slight play in the valve train,if to tight the pressure cant be releases and the lifters pump up.

A hydraulic lifter, also known as a hydraulic tappet or a hydraulic lash adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. The Conventional means of adjusting valve actuation always require a small clearance to be left between the valve and its rocker or cam follower to allow for thermal expansion and wear. The hydraulic lifter was designed to ensure that the valve train always operates with zero clearance, leading to quieter operation and eliminating the need for periodic adjustment of valve clearance.

The hydraulic lifter consists of a hollow expanding piston situated between the camshaft and valve. It is operated either by a rocker mechanism, or in the case of one or more overhead camshafts , directly by the camshaft. The lifter is filled with engine oil intermittently from an oil galley via a small drilling. When the engine valve is closed, the lifter is free to fill with oil. When the valve is opening and the lifter is being operated by the camshaft, the oil feed is blocked and the lifter acts just as a solid one would, oil being incompressible.

[edit] History

The first firm to include hydraulic lifters in its design was Pierce-Arrow in the early 1930s. Hydraulic lifters were popular on automobiles designed in the 1980s, but most newer cars have reverted to bucket-and-shim mechanical lifters. Although these do not run as quietly and are not maintenance-free, they are cheaper and rarely need adjustment because the wear caused by operation is spread over a large area.[citation needed]

[edit] Disadvantages

There are a number of potential problems with hydraulic lifters. Frequently, the valvetrain will rattle loudly on startup due to oil draining from the lifters when the vehicle is parked. This is not considered significant provided the noise disappears within a couple of minutes, typically it usually only lasts a second or two. A rattle that does not go away can indicate a blocked oil feed or that one or more of the lifters has collapsed due to wear and is no longer opening its valve fully. The affected lifter should be replaced in the latter circumstances. In extremely rare circumstances, a lifter can "pump up" and create negative valve clearance so that its valve cannot close. This is more serious as burnt valves will result. In all cases it is important to follow the manufacturer's recommendations for oil viscosity and quI amality

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Customer: replied 8 years ago.
This is most interesting. Thank you. I have determined that the rocker screws have 20 threads per inch. A 1/4 turn will result in 0.0125 inch
lateral movement. I can losen the rocker screws one quarter turn AND THE ENGINEE RUNS FINE. I will have to return the head to the machine shop that did the work or maybe use two head gaskets. What do you think?
Expert:  Roadside Jerry replied 8 years ago.

Hi,I am glad to hear you found the problem. As far as the fix,the correct way would be to have the heads returned to the machine shop so the valves stem tips could be ground down that amount. I would believe that if you had available a small grinder and were able to keep any debris out of the engine it could possibly be done with the head still on the engine in the vehicle.I also might be tempted to clean the rocker screws and threads throughly and use loc tite on the threads and leave the adjustment set so it runs,or try to shim the rocker adjustment up, if possible. As far as 2 head gaskets,I found a company the makes head gasket shims of various thicknesses,it would be safer then using 2 gaskets I will send you a link,and a copy of a page from the site. Thanks for the accept,good luck,let me know how it works out for you,Jerry.