Valvetrain Geometry and hydraulic lifter preload

[turbodig]

My guide plate problems got me thinking about valvetrain geometry on hydraulic lifters...

The "Normal" method of checking geometry is with a solid lifter, and watching tip alignment.
I checked mine on assembly, and while it wasn't perfect, it wasn't far enough off to warrant different length pushrods.

I got to thinking, recently, that the above method of checking assumes that the lifter will be at full pump (ie, the plunger at max height) during normal operation. While it's possible that this might be the case at upper rpm pressure, it might not at lower pressures.

Seems to me, that this would negate any attempts at proper geometry at lower RPMs. A .020 longer/shorter pushrod could be negated by a touch extra preload. It would also indicate that the least amount of preload you could tolerate would be the best. (Assuming your geometry was checked at full pump)

You'd never really get accurate geometry, though, except at high RPM. I suppose high RPM is where you'd want it to be the best, but in the reality of day-to-day use, you operate in the 1500-2000 RPM area. This would mean less-than-optimal guide wear.

A roller tip really becomes a big deal in this, as the effects of bad alignment will be a lot less.

Once I fix my guideplates, I'm gonna play with different preload to see just how much it effects geometry and tip contact.

 

[Foot Performance]

Re: Valvetrain Geometry and hydraulic lifter preload

I would say when you are doing you preload checks myabe try to prime the motor as much as possible but I think setting it is just going to vary so much that it may not do any good becuase after rolling the engine over a couple of time lifter depth is bound to change (atleast I wold think maybe not)

 

[vanillagorilla]

Re: Valvetrain Geometry and hydraulic lifter preload

http://www.cranecams.com/?show=faq&id=3

This is the method that myself and others have always used. As long as you pre-load them properly, you can use your adj. pushrod to get the geometry right. Hyd. lifters should never fully pump up, even at high rpm. This causes the valves to hang open, which reduces power. If you suspect that's the case then you might want to look into getting some anti-pump up lifters.

 

[turbodig]

Re: Valvetrain Geometry and hydraulic lifter preload

http://www.cranecams.com/?show=faq&id=3

This is the method that myself and others have always used. As long as you pre-load them properly, you can use your adj. pushrod to get the geometry right. Hyd. lifters should never fully pump up, even at high rpm. This causes the valves to hang open, which reduces power. If you suspect that's the case then you might want to look into getting some anti-pump up lifters.

I don't think mine are; that's why I'm not sure that checking valvetrain geometry with a solid lifter does any good - you're never gonna run it that way, anyway.

The crane article references a non-adjustable valvetrain; I can understand pushrod length for that. But, in the case of an adjustable rocker, you can change your preload to whatever you'd like.

I can adjust preload to the .030 to .050... no problem there. If I can't guarantee, though, that the pushrod is going to stay at that position, it's pretty pointless to try to get the rocker tip to be in the middle. The plunger in the lifter effectively acts like a variable-length pushrod, within the range that the plunger moves.

I could see buying different length pushrods if you were *way* out of whack (ie, more than the .030 to .050 range), but anything short of that will be "soaked up" by the lifter.

Maybe I'm missing something here?

 

[vanillagorilla]

Re: Valvetrain Geometry and hydraulic lifter preload

I don't think you're missing anything. With a non-adjustable valvetrain, the only way to get proper geometry is with different length pushrods or valves. What ever it is when torque down is it. With adjustable rockers, you basically set the pre-load desired and lock the poly locks down. If the geometry isn't correct, then you need a different length pushrod. Sure you could probably bottom out the plunger with adj. rockers, but the proper pre-load is still needed.

It's pretty easy to get way out of wack though when you deck the block, mill the heads, run a cam with a smaller base circle etc. Not really things we run into in the syty world but...

 

[WyoSyclone]

Re: Valvetrain Geometry and hydraulic lifter preload

This topic is similar to that found on airplanes when one is calculating the differential throw of control surfaces (ailerons, elevator, rudder)..... I'll have to dig out my books and revisit all of those geometry equations. I guess the only real variables are valve stem tip height in relation to rocker centerline (valve seats cut evenly, valve stem lengths equal) and lifter plunger height.... base circle, and base circle to rocker centerline should be givens unless someone line bored the cam off center or milled the heads and/or block out of whack... sounds like a great opportunity for some laser-measuring equipment
Is it possible to blueprint the lifters to make sure they've all got similar plunger spring specs?

 

[vanillagorilla]

Re: Valvetrain Geometry and hydraulic lifter preload

Is it possible to blueprint the lifters to make sure they've all got similar plunger spring specs?

I think the "higher end" aftermarket hyd. lifters are blueprinted more or less. I know they modified orifice size and spring pressure/rate. I'm not sure about now, but it used to be that there were only 2 hyd. lifter manufacturers in the US. The aftermarket companies bought from them and then modified the lifter. You can tell by the e-clip style snap ring in place of the typical wire snap ring.

 

[turbodig]

Re: Valvetrain Geometry and hydraulic lifter preload

I think the "higher end" aftermarket hyd. lifters are blueprinted more or less. I know they modified orifice size and spring pressure/rate. I'm not sure about now, but it used to be that there were only 2 hyd. lifter manufacturers in the US. The aftermarket companies bought from them and then modified the lifter. You can tell by the e-clip style snap ring in place of the typical wire snap ring.

That's still the case, as far as I know. Stanadyne, and Johnson. (plus GM (Delphi))

Anyway, what my research seems to be finding is that once you get your preload set within spec, you check the tip pattern after running a few cycles. If it's good you're golden, otherwise you get new pushrods. Trying to check them static, it seems, is wasted time.

I actually have 2 out of the 3 done (block decked and heads milled), which I expected to screw up the geometry. It didn't, at least not bad, but then I was only doing a static check.
I'll re-check 'em once I get the new guide plates in.

 

[Don W.]

Re: Valvetrain Geometry and hydraulic lifter preload

I'm gonna chime in here with my

. Lifter "preload" and rocker geometry are two different things. Regarding preload I was always of the impression that a hyd lifter plunger should be at or near the center of its travel which is what I suspect the CompCams article is all about.

Rocker geometry is different, overlooked and also important. Two links that explain things.

http://www.compcams.com/information/Products/Pushrods/

The below link refers to the "Y" block and shimming a shaft rocker. All we have to do is adjust the rocker. The theory and desired result are the same.

http://www.eatonbalancing.com/blog/2007/12/10/rocker-arm-geometry/

So correct geometry AND correct preload may require fiddling with pushrod lengths on our engines.

Hyd lifters WILL "pump up" under high RPM conditions as valve float occurs causing the valves to remain open with consequent very rough running and immense power loss. Anti pump up lifters attempt to avoid this with high leakdown rates.