Hydraulic tappets

Hi all,

Just got a question about hydraulic tappets- (bucket style). When installing them new, are people bleeding them to fill them with oil, or installing them as is and they will pump up once the engine is running and at oil pressure?

Also, with increased oil pressure. If you are using a lighter spring, if the oil pressure exceeds the installed pressure of the spring. Is it possible for the pressure within the tappet to override the pressure of the spring and open up the valve slightly, losing power?

a/ some do, some don't. Some just soak them overnight in oil so it will be drawn into the tappet to lubricate the piston in the body, rather than leaving it dry, initially.

What one should bear in mind is that the normal operating position will be somewhere between fully compressed and fully extended (but not actually reaching either), and if one fully primes the oil reservoir, it will mean the valve may be held off the seat until the tappet "leaks down" (loses enough oil to allow the valve to close), whereas with the option of installing them (relatively) dry meaning there will be excess clearance until the tappets recive enough oil to fill their reservoir and bleed out any trapped air - this can take anything from a few minutes to 15 minutes, or more.

b/ not something I've considered, but if you ran a REALLY low installed seat loading, and a really high (cold?) oil pressure, I suppose it is theoretically possible. Don't be confused by the oil "pressure" and the actual force the piston within the tapped body is applying - depending on the specific tapped design, it will normally be significantly less than 1"^2.

As an aside, the first part of a/ is basically what happens when hydraulic tappets suffer valve float - the oil takes up the momentary increase in clearance.

Oil pressure reaching the hydraulic lifter is also generally a LOT lower than what you'd measure in a block oil gallery.

Personally I've just soaked them, but I can't say that's best.

I've seen people manually bleed them, but the engine still didn't sound great on first start, so it seemed like a lot of work for potentially no benefit. I'm curious what others think.