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| hydraulic lifter pre load https://slantsix.org/forum/viewtopic.php?t=47918 |
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| Author: | DadTruck [ Wed Feb 15, 2012 10:39 am ] |
| Post subject: | hydraulic lifter pre load |
about all of the internet articles and posting refer to a target hydraulic lifter preload of .020 to .060 When I disassembled the 83 slant motor last summer I did the routien of setting #1 cly so both valves were fully closed, used a razor blade to mark a line in the crud in on the push rods in line with the valve cover rail. loosened the rocker shaft and re cut the line in the pushrods after they drifted up. they both showed the push rod moved up .090 to .100 this is measuring a scratch in push rod crud,, but there is no way it could be .020 to .060 Checked the full plunger travel on a new and on an original 83 hydraulic lifter,, the lifter push rod seat fully up to fully down is a distance of .180,,, So the measurements I got of .090 to .100 puts the lifter pushrod seat right in the middle of available travel,, seems right, is it?? On this subject, the 1983 FSM under the heading of Tappets gives a range of .060 to .210 for "Dry Lash", don't see how one could ever get to .210, the pocket is .180 deep? is the slant hydraulic lifter just a lot different for preload than all other motors? regards DT |
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| Author: | raPoM [ Wed Feb 15, 2012 11:08 am ] |
| Post subject: | |
John- I am glad you brought this up,I want to know this too. I want to bump my 87 up to 8.5-9-1 comp,but am unsure of exactly how much I can get away with milling before running into problems. |
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| Author: | Joshie225 [ Wed Feb 15, 2012 11:46 am ] |
| Post subject: | |
Yes, the hydraulic slant lifters have a ton of plunger travel. So long as you maintain about .010" or so from bottoming out you should be fine. |
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| Author: | DadTruck [ Wed Feb 15, 2012 2:45 pm ] |
| Post subject: | |
Josh I thought some more about that "dry lash" factory spec of .060 to .210 wonder if that is a measurement of the gap at the valve stem to rocker arm tip? If so, considering the 1.5 rocker ratio, and an overall plunger travel of .180,,I think what they are recommending is keeping the spool .040 from the top ( .040 x 1.5) which results in a the .060 value at the valve tip and .040 from the bottom (.140 x 1.5) which is the .210 value at the valve tip. so it looks like a lifter pre load of .040 to .140 with 1.5 rocker arms would give a dry lash of .060 to .210 I'll give this a shot when I build my motor, to see if with non pumped up lifters I can translate the dry lash to pre load. regards DT |
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| Author: | Doc [ Wed Feb 15, 2012 3:20 pm ] |
| Post subject: | |
As you know... Getting all the valve stem heights the same (even) is the "key to success" with a non - adjustable rocker arm hydro head. DD |
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| Author: | CNC-Dude [ Fri Feb 24, 2012 12:41 pm ] |
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You can also gain RPM by having less lifter preload. This keeps the lifters from floating until higher in the RPM range. You can usually get another 500 or so RPM on the high end. Its also common for roundy-round racers and even Stock Eliminator drag racers limited to hydraulic cams to run about .002 valve lash, thus not preloading the lifters at all, and are able to run up above 7000 RPM. |
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| Author: | Joshie225 [ Fri Feb 24, 2012 1:23 pm ] |
| Post subject: | |
Then there are guys who run hydraulic lifters nearly bottomed out so that they don't collapse. This has shown to be a big power improvement with aggressive hydraulic roller cams. |
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| Author: | SLANTEDRAM [ Sat Feb 25, 2012 4:24 pm ] |
| Post subject: | |
I just measured the valve lash on my hydro build- .130" at the valve. Which translates to about .090" at the lifter- I also determined that the factory style rocker arms only have about a 1.42:1 ratio. I calculated this by taking all of the lash out under the rocker tip with feeler gauges and measuring actual valve lift- My cam is advertised with .395" lift, but in reality the actual valve lift only measured in @ .375" |
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