Engine and Transmission Tech

Hi Guys,

I'm in the process of learning things regarding valve to piston clearance measurements when using hydraulic lifters.

As I understand one should measure the clearance by using a solid lifter and adjust for zero lash (when possible) or to using a solid lifter with your actual lifter pre-load correction.

Either way one should regard a clearance of approx .100" for the inlet valve. Some say an absolute minimum of .050" could be ok to.

This clearance is for: expanding components due to heat, valve bounce and pump up action when revving the engine to high.

I hope I'm correct up to now.

But the following thing is bothering me because I don't understand this. How does a lifter looks like in a pumped up state due to high revving on the end of the opening movement of the inlet valve (maximum lift)?

This in three situations:
1- Standard lifter
2- High revving lifter
3- Roads Bleed down lifter

In case of lifter C one should take into account a additional clearance of not 1.6 (rocker ration) times the pre-load but als times the pre-load with .030" for the small plunger in the middle.

I made a drawing to explain things.

Many thanks for your help

Frank

Frank, Your using sbc lifters ? The "rumor" is the LS inner spring(lifter), allows more rpm before pump-up. If your using oem Rover rockers, ratio is closer to 1.55/1. The most any hydraulic lifter can pump up, is up to the retainer ring. Rhodes we're considered "cool" at one time, but oem style lifters got better for higher rpm. , ie. LS/etc. Problem with Rhodes is they don't adjuct equally. Oil pressure available to each lifter varies with clearances involved,(bleed-off). Valve spring pressures is another variable. IF you converted to Volvo adjustable rockers, could only benefit the cause. Cheers, roverman.

What happened to the old fashion way of setting chevy hydralics to zero lash starting the engine with the valve covers off, tightening or loosing rocker arm until clicking or + clearances went away and then giving the adjustment another 1/2 turn or so(clockwise) to load lifter hydralics correctly?

David, This isn't a sbc. Rockers are non-adjustable, hence my suggestion of "Volvo's". Engine Masters had a good "lifter/preload" shoot-out, about a year ago, enlightening. Cheers, roverman.

Volvo adjustable rockers are new to me. What volvo engine/car should I look for when trying to by these? I can't find them at my usual addresses like RealSteel and V8tuner in the UK.

I understand what is mentioned regarding equal oil pressure and the bleeddown lifters. I'm running these lifters in my SuperSeven and like them a lot since I can't here the ticking noise anyway :-)

So as I understand it is lifter 'B' that would be the one to make/lock 9I used 2 comp glue) to be used as a solid lifter to do the v-p clearance measurement with zero lash. I did the zero lash by shimming the pedestals and zeroed the lash by inserting a feeler gauge during that one turn.

Kind regards,

Frank

Frank, Use the "search box" at top of page. Archived as Volvo rockers for Rover V8, sbb and 215 Olds. Very sturdy rockers, came with my GT 1 Huffaker TR 8, with serious mech roller cam( 8k rpm). add: I had a plan to use sbc pedestle/shaft mounted roller rockers. Make a one piece, solid shaft,(oil thru push rods) and make shaft towers to fit. Too many diversions ! Cheers, roverman.



Edited 1 time(s). Last edit at 04/03/2012 01:48PM by roverman.

For this engine I have already new steel rockers from v8tuner and new shafts.

What do you consider to be the absolute minimum clearance for inlet and exhaust valve regarding their distance to the piston. I see .100"inlet and .110" exhaust. But I also see Inlet .080" and Exhaust .090".

This 3.9 +020 has the cast 9.35:1 CR pistons with normal rods and has a maximum rev of 6300 rpm with Rhoads bleed down lifters. I use a Crower 50232 .488" valve lift cam set to a lifter preload of .020-.030". Single springs.

I did some calculations with the heads I'm now preparing and would like to skim the heads so the v-p clearance drops to .080 thou for the inlet.

Kind regards,

Frank



Edited 1 time(s). Last edit at 04/04/2012 02:17PM by Frank.de.Kleuver.

Hi Frank,
Conventional practice is to mill the heads to reach your required compression ratio and squish areas.
Valve clearance is dealt with second and is generally obtained by milling the pistons.
However, if your approach fulfills all three criteria at once so much the better.
Regarding valve to piston clearance. .080" is a little tight on an engine like yours.
Lets consider that minimum deck height is .040" for your bore size and engine configuration.
What that means is that at in certain engine running conditions it will aproach 0" so we must subtract .040" from your valve to piston clearance. Looks OK as it still leaves .040".
But you have a .030 lifter preload. As the lifters pump up you need to subtract .030" x 1.55 (your rocker ratio) which comes out to.0465". You are now inside your pistons by .0015". Probably a survivable incident, but throw in some valve float or valve train harmonics and because the valve train is now out of control your new engine is now junk.
I think the .100" and .110" figures are much more realistic. Especially on a street engine that will see some carbon build up.
The smaller figures are more suited to a very tight solid lifter forged race engine.
Even at .040" some of our bigger bore honda race engines will leave a light witness mark on the head if the driver has to hit it hard.
Cheers
Fred



Edited 1 time(s). Last edit at 04/05/2012 01:52AM by DiDueColpi.