frijolee

iTrader: (12)

I'm looking for a good "how things work" answer to help me in checking piston to valve clearances. The problem is that I know that hydraulic lifters are supposed to adjust valve lash to zero but not how they do it, nor how I'm supposed to know if they've collapsed or not. Does anyone have a good link to a tech article they could point me to or feel like writing a good techie responce on how they work?

One the practical side I'm about to check ptov clearances using clay. My understanding of the process goes like this:

1) heads off
2) cover any selected piston face in the valve region with clay at least .200 thick.
3) assemble and torque down head with gasket
4) use adjustable length pushrods to take all play out of the two rockers for the piston in question
5) spin the crank a minimum of 2 full revolutions
6) tear down and check thickness of clay below maximum depressions for each valve
7) if you don't have 0.080 and 0.100 clearance on intake and exhaust you need to flycut you pistons.

-Any flaws in my methodology?

-Any tricks for keeping a stock head gasket whole so you can torque it twice?

-How will I know if a given lifter is collapsing and shows me more clearance than I actually have? Will it stay collapsed so I'd have play in the rocker thereafter?

I recognize that solid lifters are the optimum way to go for checking clearances but I'm only doing this once on one engine and I'm trying to minimize my cost (dumb logic if I blow an engine I know). Are solid lifters a requirement? What are the downsides of using my hydraulic lifters in this application?

PS If it matters my engine is damn near dry. I had it hanging upside down on a stand for a week with the heads off waiting for rod bolts.

ShevrolayZ28

iTrader: (4)

In general, you are ok doing this way, but you need to install a special light tension valve spring if you're going to do it with hydrolic lifters installed, or if you plan to turn the motor over with an adjustable pushrod installed.

Another way to do it involves using a degree wheel, low tension valve springs, and a dial indicator.

ROCNDAV

iTrader: (100)

I've been at this point in my project for a long while now. I have old lifters, so I used a combination of JBweld and washers to make two "solid" lifters. Maybe you can do this as well if you have old ones laying around.

Disassemble the lifter and clean it out. place washers inside the lifter and some jb weld to take up the slop. place the cap and retainer back on. wait a day or so for the jb weld to harden.

frijolee

iTrader: (12)

I'm trying to avoid taking the springs apart if possible (more tools, more parts). Are the adjustable pushrods incapable of carrying the tensile load of a regular valvespring?

If I had to go to the effort of installing a light duty tension spring I'd go the dial indicator method instead of using clay. I thought the whole point of going clay way to avoid light duty springs...

Andrew91GT

iTrader: (6)

Heavy springs will depress the springs in the lifters making an accurate P/V measurement impossible. You can use the heavy springs if you use a solid lifter to check P/V clearance.

frijolee

iTrader: (12)

So the problem is in the lifter having a lesser spring rate than does the valvespring, not the adjustability of the pushrod. That makes more sense.

vettenuts

iTrader: (4)

I am not sure the adjustable pushrod is up to the task either, especially if extended out a ways. I think the checking spring method is a better approach, more accurate results to instead of trying to measure a dissected piece of clay.

mr2guru

iTrader: (16)

gotta use check springs or modded/solid lifters.

ROCNDAV

iTrader: (100)

not trying to hijack your thread frijoee, hopefully I am asking a question to help the both of us out.


I adjusted my pushrods until they were tight against the rockers. I pulled off the rockers and measured the pushrod length with a set of digital 8" calipers. I measure 7.202". I modified (as mentioned above, in another post) my old hyd lifters with washers and jb weld, so they are what I would call "pumped up" / "solid" lifters.

1. How much difference is there in a pumped up verus a dry lifter? I take it that I need to calculate for somewhere in the middle of the two. I don't want to have too much preload, which I believe will collapse my new stock lifters, nor do I want to tick, and rattle all day long either.

2. Can I unscrew/extend the adjustable pushrod out .050", .100" and see what differences I get in both the clay and to check coild bind? Wouldnt this give me the same results as trying a 7.25/7.300 pushrod?

3. Am I measuring the pushrods correctly? Because I measured 7.202, do I assume that these are 7.200's? or would I add a theoretical amount to compensate for the flat/holes on the ends? I am using Cran Cams adjustable checking pushrods PN 99725-2 (6.125-7.500)

Unlike frijolee, my block was decked .010 and my AFR 225's were milled for 66CCs, so I'm sure I will need shorter pushrods than the normal 7.4's that everyone uses.

frijolee

iTrader: (12)

I'm still looking for a good theoretical explanation for how hydraulic lifters actually work.

From a few of the above responses I'm picturing a diaphram driven by both a preloaded spring (of lower rate than the valve spring) and by oil pressure (hence how slop is removed and the startup clatter goes away...) The combination of oil pressure plus spring is then sufficient to overcome the force required to open the valvespring and the lifter moves smoothly thereafter.

vettenuts

iTrader: (4)

If you are measuring the pushrod with a vernier, you are measuring OAL or overall length. Pushrods come in gauge length, not the same measurement. So the 7.202 you measure would be closer to a 7.185 pushrod length. Comp has a very good explanation of this on their website. If you use the Comp adjustable pushrod, there is a line on it that measures in gauge length as you unscrew it, and the lines are aligned in 0.050" increments.

As for an explanation of the lifter, an excellent explanation is contained in David Vizard's book on SBC valve trains.

ShevrolayZ28

iTrader: (4)

Maybe this link will help some of you guys.

http://www.fordmuscle.com/fundamenta...ve/index.shtml

If you use the clay method you can get by without a dial indicator, solid test lifter, and degree wheel, but you will need the PR length checker and the test springs.

Grimes

iTrader: (3)

http://www.cranecams.com/?show=techarticle&id=2

ROCNDAV

iTrader: (100)

I dont see the lines on my pushrod tool, as others have mentioned as well. so would I take that 7.185 length and just add my desired preload amount?


Frijolee, here are some pictures of the internals of a hydraulic lifter that I disassembled.

Andrew91GT

iTrader: (6)

Every turn in the pushrod tool is .050".

ROCNDAV

iTrader: (100)

So when measuring the pushrod, you are only measureing the rod length itself, not including the ball ends?

frijolee

iTrader: (12)

Good links... Thanks. For my situation the cleanest, most straightforward method appears to be going with test springs and either a dial indicator or feeler gauges. Although it means more parts to purchase, if everything works out I might get away with only torquing the head once (vs guaranteed removal with clay). While I did throw down for ARP head bolts I had already purchased stock head gaskets so I figured I might as well use them.

I seem to have answered my own question about the easiest way to keep a graphite head gasket whole: it's the obvious logic that you only use it once (even if the car wouldn't be fired up between torquing).

ROCNDAV

iTrader: (100)

frijolee, do you still have your old gaskets? can you use them for claying then use the new ones for fianal torquing? THat was one of the reasons I decided to go with mls gaskets and ARP studs, because I nknew I would have these heads on and off several times.

frijolee

iTrader: (12)

I bought my engine with heads off. The old head gaskets practically split in half and the halves that were on the block have been carefully scraped away. Those graphite bastards do leave some crazy residue behind. I bought the stock head gaskets before I ran across a deal on ported heads and cam.

I haven't done any real research on the cometics or other reusable gaskets but I have a harder time trusting their ability to reseal without decking everything perfectly flat. Then again the only reason mine aren't as flat as I'd like is the tiny bits of graphite still remaining (I've been over the surfaces probably a dozen times now and I can still see imperfections), so maybe this is just a catch 22 situation.

Joel

frijolee

iTrader: (12)

This is a pretty good article. However, as I thought about it a bit more I wanted to clarify something about lifter preload.

According to the above: lifter preload is the amount the lifter can collapse due to the greater spring rate of the valvesprings (measured with the valve closed). It's worth noting that oil pressure must be absent to correctly measure deflection hence the bleed down period required.

I have a theory which if correct explains why adjustable pushrods are recommended (but perhaps not required). I'm waiting on a valvespring tool and check springs but my revised plan of attack looks like this:

1) install check springs for both valves on a given piston
2) heads should be installed normally using hydraulic lifters, gaskets, etc. Everything torqued to normal specs.
3) use adjustable length pushrods on chamber with check springs. Dial valve lash to zero
4) spin crank and locate closest point of contact by manually forcing valves further into camber than is required.
5) use dial indicator to measure valve travel (ie clearance) or feeler gauges to measure the gap between rocker tip and end of valve
6) you need 0.080 on intake and 0.100 on exhaust. If you don't have it you get to alter timing, cuts you pistons, or run a different cam.

Here's where I started thinking, what do adjustable length pushrods actually buy us? If I just used the regular pushrods in conjunction with check springs the only thing that changes is that the valve won't close at the way (the check spring will "give" in opposition to the normal practice where the lifter "gives" a distance which by definition equals lifter preload.)

If I know my lifter preload (seems easy enough to measure) and I know my rocker ratio I should be able to calculate out how much further a valve should be driven with the lifter 100% extended (aka pumped up all the way to the stop). When people talk about the best practice method of using a solid lifter, adjustable pushrods and zero lash what are they really measuring? It's certainly not the closest a piston and valve can actually get... You're basicaly measuring the p to v clearance at nominal lifter preload. With more oil pressure the lifter extends even further. As I see it this is WHY we need 0.080 and 0.100 clearance. Those numbers always seemed way to large to account for thermal expansion and tolerances of stretching parts.

As I see it the clearance has to account for the 0.020 to 0.060 of lifter preload. Not coincidentally the rocker ratio 1.7 multiplied times our maximum preload 0.060 = 0.102. Which is pretty damn close to the minimum allowable clearance on our exhaust side.

I'm going to measure preload on a couple of pistons to be sure it's pretty uniform. After that I'll try a bit of math and see if I can return my adjustable push-rods unused.

Joel