piston to valve clearance and lifter preload.
#1224111
04/29/12 10:38 AM
04/29/12 10:38 AM
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Joined: Jul 2003
Posts: 3,378
Rancho Cordova, CA
Exit1965
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OP
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Rancho Cordova, CA
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I am checking piston to valve clearance using the playdo method. I'm using a hydraulic lifter with the pushrod seat welded to the top, i.e. 0 preload is possible.
Let's say I have .030" preload with my pushrods and rocker arms, measured of course on the base circle of the cam.
Now I use the lifter that is welded to prevent any preload. So on the base circle, when the rockers (non adjustable) are tightened down, the cam is pushing that pushrod up by .030", which translates to ~.045" at the valve using ~1.5 ratio rocker arms.
So does that mean when doing the P-V clearance measurement, that .045" should be added to the final measurement of the thinnest point of the Playdo?
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Re: piston to valve clearance and lifter preload.
[Re: Exit1965]
#1224113
04/29/12 06:24 PM
04/29/12 06:24 PM
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Joined: Oct 2011
Posts: 559
Idaho
LaRoy Engines
mopar
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mopar
Joined: Oct 2011
Posts: 559
Idaho
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Please describe the exact method you are using to check the piston to valve clearance. Let's not worry about preload just yet, as it my be irrelevant, depending upon your procedure.
Last edited by heyoldguy; 04/29/12 06:25 PM.
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Re: piston to valve clearance and lifter preload.
[Re: LaRoy Engines]
#1224114
04/29/12 06:40 PM
04/29/12 06:40 PM
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Joined: Jul 2003
Posts: 3,378
Rancho Cordova, CA
Exit1965
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Ok - piece of playdo laid across the piston. Put head gasket on, install head, install 2 hydraulic lifters which are welded so the cup doesn't move, then pushrods, install rocker shaft.
Rotate engine a couple of times. Pull head off and measure playdo at thinnest area.
The way I figure it, since I know I have preload with my pushrods and rockers, when I tighten down the rocker shaft, it lifts the valves by the amount of preload. Since it's obviously not pushing the lifter's cup in any. Therefore whatever preload (times 1.5 for the rocker arm ratio) should be added to the measurement of the playdo since the valves were open that much more through the rotations.
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Re: piston to valve clearance and lifter preload.
[Re: Exit1965]
#1224116
04/29/12 06:48 PM
04/29/12 06:48 PM
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Joined: Mar 2003
Posts: 4,848
Memphis
HemiRick
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Memphis
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Yes add the preload times 1.5 to your measurement.
Take care,
Rick
68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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Re: piston to valve clearance and lifter preload.
[Re: Cab_Burge]
#1224119
04/29/12 11:05 PM
04/29/12 11:05 PM
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Joined: Jul 2003
Posts: 3,378
Rancho Cordova, CA
Exit1965
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Quote:
Now, if I was using your method I would subtract the .045 from the claythickness (Playdoh) I've added by doing it your way (.045 preload)
Im not understanding why you would subtract .045 instead of adding it?
If the lifter is not allowed to have preload and lifts the valve up by .030 * 1.5 on the base circle of the cam, is it not pushing the valve another .045" into the playdo? So if there is .100", it's was lifted an extra .045" so it's actually .145".
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Re: piston to valve clearance and lifter preload.
[Re: LaRoy Engines]
#1224121
04/30/12 09:05 AM
04/30/12 09:05 AM
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Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
70Cuda383
Too Many Posts
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Too Many Posts
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Marysville, O-H-I-O
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here's my take.
I flat out wouldn't do it the way you are. you're assuming the preload that you'll have with your combo. what if you only have .020 of preload? or .040 preload? had the decks or heads shaved at all? what head gasket are you using compared to the factory steel shim? stock pushrods?
if I were you, i would take your modified solid lifter, and if you don't have adjustable rockers, then buy an adjustable/threaded checker pushrod. thread it so that you have "zero lash" when the cam is on the base circle and the valve is closed, THEN do your checking, and you'll remove all variables from what your actual PtoV is.
**Photobucket sucks**
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Re: piston to valve clearance and lifter preload.
[Re: Rapid340]
#1224124
04/30/12 12:40 PM
04/30/12 12:40 PM
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Joined: Apr 2005
Posts: 12,271
Overpriced Housing Central
RobX4406
I Live Here
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I Live Here
Joined: Apr 2005
Posts: 12,271
Overpriced Housing Central
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Quote:
With a hydraulic lifter, the potential is there for RPM's to exceed the engine speed at which the valve spring maintains control of valvetrain motion. If this happens (maybe overrev or springs becoming weak over time) the lifter could pump up to the retainer clip. The safest thing to do is to allow for this scenario by subtracting plunger depth X rocker ratio from your static piston to valve clearance. If you have an adjustable valvetrain you can set lifter preload to a low setting and minimize effects on P/V clearance.
Yep!
Measure it with the static solid/welded lifter and make sure you have enough VtoP clearance as that will be the closest it will be in a real time situation.
Just for fun, think about this. Valve to piston clearance .080 intake. If the plunger actually preloads at .060 and you multiply by the 1.5 ratio (mostly fantasy here on stock stuff or a SB with the rotten lifter angle) and that's .090 at the valve... What happens to the .080 clearance you measured when the lifter pumps up? It's gone!
Without an adjustable push rod/rocker to get slack/preload out you might be chasing your tail.
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Re: piston to valve clearance and lifter preload.
[Re: Exit1965]
#1224125
04/30/12 02:33 PM
04/30/12 02:33 PM
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Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
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Ontario, Canada
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Hydraulic lifters don't pump up to the retainer ring or all hydraulic engines would hold the valves open all the time resulting in no compression. They do in fact self adjust to the point of the pre load and stay they especially with anti pump up lifters. Factory pre load is about .070 all factory motors did not hold the valve .070 off the seat. SO if you have non adjustable valve train a welded lifter will likely hold the valve open .045 to .060 than the proper lifter when installed. So check and get back to us I have a few of these which come in handy for degreeing a hydraulic cam with non adjustable rockers and checking valve clearence in the same as you can set it to 0. http://www.summitracing.com/parts/CRO-70006-1/http://www.summitracing.com/parts/CRO-70009-1/I have the old Mopar performance ones! 
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Re: piston to valve clearance and lifter preload.
[Re: 70Cuda383]
#1224129
04/30/12 10:14 PM
04/30/12 10:14 PM
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Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
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master
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
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Quote:
Quote:
Hydraulic lifters don't pump up to the retainer ring or all hydraulic engines would hold the valves open all the time resulting in no compression. They do in fact self adjust to the point of the pre load and stay they especially with anti pump up lifters.
What happens when you over-rev the motor, and you go into valve float? the valve is hung open from the lifter ramping up off the cam. it's possible at that moment, for the lifter to pump up to the retainer clip because there's nothing holding it down.
what happens after everything seats back down? wouldn't you then have the valves hung open until the lifter bleeds back down?
that might just take long enough that on the next engine cycle, you hang the valve open and hit a piston.
You need to be smacked in the head for not having the proper valve springs, and no rev limiter.
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Re: piston to valve clearance and lifter preload.
[Re: Dodgem]
#1224130
04/30/12 11:28 PM
04/30/12 11:28 PM
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Joined: May 2011
Posts: 4,489
northern,Ohio,USA
Clanton
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northern,Ohio,USA
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Quote:
Quote:
Quote:
Hydraulic lifters don't pump up to the retainer ring or all hydraulic engines would hold the valves open all the time resulting in no compression. They do in fact self adjust to the point of the pre load and stay they especially with anti pump up lifters.
What happens when you over-rev the motor, and you go into valve float? the valve is hung open from the lifter ramping up off the cam. it's possible at that moment, for the lifter to pump up to the retainer clip because there's nothing holding it down.
what happens after everything seats back down? wouldn't you then have the valves hung open until the lifter bleeds back down?
that might just take long enough that on the next engine cycle, you hang the valve open and hit a piston.
You need to be smacked in the head for not having the proper valve springs, and no rev limiter.
i thaught that is how i got extra lift out of the cam.  
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Now, if I was using your method I would subtract the .045 from the claythickness (Playdoh) I've added by doing it your way (.045 preload)
