Tech Info - LT5 New Rebuild Zero Compression
11-02-2011, 10:07 AM
#1
Tech Contributor
Thread Starter
Tech Info - LT5 New Rebuild Issues (Lifters and Camshafts)
Tech Info - LT5 New Rebuild Issues (Lifters and Camshafts)
Zero Compression as a result of Valve Stem Clearance, Hydraulic Lifter aberrations, and camshaft regrinds during engine rebuilds is discussed in several posts.
Post 2. Lifters
Post 3. Lifters and Valve Stem dimensions (reground valves)
Post 4. Valve Stem Clearance Measurement Tool
Post 5. Camshaft Measurements
Post 6. Valve Stem Clearance Measurements for Stock Valves and Regrind Camshaft
Post 7. Regrind Camshafts Performance
Post 8. BAD Z
Post 9. Reserved
Post 10. Valve Stem Clearance Measurements for Stock Valves and Stock Camshafts
The first thing to check is for locked hydraulic lifters. It may be as simple as the lifters are hydraulically locked extended (uncompressed) when they were installed which they usually will bleed down over time. If that is the case, recheck the compression at a later date to see if the lifters did in fact bleed down (that may not happen rapidly if there is already oil pumped around the lifter). Rotate the crankshaft/camshafts such that as many valves are open as possible and leave the engine sit in that condition to bleed down those associated lifters. The lifters will not extend (uncompress) past the base circle once bled down (valves will then completely close).
Associated issues are discussed in the posts cited above. There are also variations in lifter geometry (lifter unplunged height) also discussed. You can also reset the lifters by removing them and thrapping them smartly on a hard surface unseating the plunger.
You may be able to turn the engine over (hot wire starter) getting oil pressure to help reset the lifters (camshafts and camcovers installed) If the engine sits for several days, some of those lifters bleed down and are then pumped up during initial start up (but less likely a quick bleed down if you have had oil pressure around the lifter and the lifter has not failed in any way).
If the issue is lifters, you may have to remove camshafts....but not the heads....if the issue is valve stem lengths, you would have to remove the heads.
The posts cited above may help if the low compression issue is valve stem clearance, lifters, or camshafts geometry including reground valves and reground camshafts.
Last UPDATE of post 1 Feb, 2013
Zero Compression as a result of Valve Stem Clearance, Hydraulic Lifter aberrations, and camshaft regrinds during engine rebuilds is discussed in several posts.
Post 2. Lifters
Post 3. Lifters and Valve Stem dimensions (reground valves)
Post 4. Valve Stem Clearance Measurement Tool
Post 5. Camshaft Measurements
Post 6. Valve Stem Clearance Measurements for Stock Valves and Regrind Camshaft
Post 7. Regrind Camshafts Performance
Post 8. BAD Z
Post 9. Reserved
Post 10. Valve Stem Clearance Measurements for Stock Valves and Stock Camshafts
The first thing to check is for locked hydraulic lifters. It may be as simple as the lifters are hydraulically locked extended (uncompressed) when they were installed which they usually will bleed down over time. If that is the case, recheck the compression at a later date to see if the lifters did in fact bleed down (that may not happen rapidly if there is already oil pumped around the lifter). Rotate the crankshaft/camshafts such that as many valves are open as possible and leave the engine sit in that condition to bleed down those associated lifters. The lifters will not extend (uncompress) past the base circle once bled down (valves will then completely close).
Associated issues are discussed in the posts cited above. There are also variations in lifter geometry (lifter unplunged height) also discussed. You can also reset the lifters by removing them and thrapping them smartly on a hard surface unseating the plunger.
You may be able to turn the engine over (hot wire starter) getting oil pressure to help reset the lifters (camshafts and camcovers installed) If the engine sits for several days, some of those lifters bleed down and are then pumped up during initial start up (but less likely a quick bleed down if you have had oil pressure around the lifter and the lifter has not failed in any way).
If the issue is lifters, you may have to remove camshafts....but not the heads....if the issue is valve stem lengths, you would have to remove the heads.
The posts cited above may help if the low compression issue is valve stem clearance, lifters, or camshafts geometry including reground valves and reground camshafts.
Last UPDATE of post 1 Feb, 2013
Last edited by Dynomite; 03-31-2013 at 07:15 PM.
11-02-2011, 10:07 AM
#2
Tech Contributor
Thread Starter
Lifters
Lifters
Lifters when first installed may be locked unplunged or fully extended. One theory is that when you remove the camshaft, some of those lifters suck in oil essentially pumping themselves fully extended. When you reinstall the camshafts you now have valves staying open unless you can remove the oil from the lifter before you install the camshafts. This is in addition to the valve stem height issue from a new valve job exceeding the lifter limits which no amount of lifter oil relief will solve. This is also in addition to the scheme where you do NOT mix lifter locations when reinstalling used lifters to protect yourself from lifter wear aberrations and lifter locked position aberrations.
Once you crank the engine or run the engine for a few minutes lifters will bleed down. But for those lifters which extended and locked themselves fully extended during camshaft removal it is an issue because now those valves will open farther than they should when you crank the engine for a few minutes.
BUT still another issue involves the existence of several variants of the same HT 2236 Sealed Power Lifter.
Lifter on left is STOCK (91' LT5), Lifter second right (identical to stock) is new made in Mexico, Lifter third right is new made in China, Lifter fourth right is new made in Mexico. I wonder for those who bought new lifters.....how many installed several different variants of the same lifter in a single head without knowing it. Prolly would work fine but just kind of messy mechanic work.
BUT...... all the lifters cited above (except the left lifter which is stock) come in Sealed Power HT 2236 boxes (some made in China and some made in Mexico).
Then there is the Melling JB 2236 which is identical to the stock lifter (left lifter) of the above lifters.
I measured the LC (Lifter Compression) or difference between maximum and minimum height of the stock lifter and found .120 inches.
Also measured LH (Lifter height) or maximum height of stock lifter (uncompressed from plunger to top of lifter) and found .800 inches.
There is a variance in Lifter Height and Lifter Compression among lifters.....
The Mellings JB2236 are identical to stock original Lifters as you can get.
I received 16 JB2236 Lifters today from Clark Discount (Type in JB2236 in the Search By Key Word). Perfect...exactly what I was looking for :thumbsup:
Last UPDATE of post 2 July, 2012
Lifters when first installed may be locked unplunged or fully extended. One theory is that when you remove the camshaft, some of those lifters suck in oil essentially pumping themselves fully extended. When you reinstall the camshafts you now have valves staying open unless you can remove the oil from the lifter before you install the camshafts. This is in addition to the valve stem height issue from a new valve job exceeding the lifter limits which no amount of lifter oil relief will solve. This is also in addition to the scheme where you do NOT mix lifter locations when reinstalling used lifters to protect yourself from lifter wear aberrations and lifter locked position aberrations.
Once you crank the engine or run the engine for a few minutes lifters will bleed down. But for those lifters which extended and locked themselves fully extended during camshaft removal it is an issue because now those valves will open farther than they should when you crank the engine for a few minutes.
BUT still another issue involves the existence of several variants of the same HT 2236 Sealed Power Lifter.
Lifter on left is STOCK (91' LT5), Lifter second right (identical to stock) is new made in Mexico, Lifter third right is new made in China, Lifter fourth right is new made in Mexico. I wonder for those who bought new lifters.....how many installed several different variants of the same lifter in a single head without knowing it. Prolly would work fine but just kind of messy mechanic work.
BUT...... all the lifters cited above (except the left lifter which is stock) come in Sealed Power HT 2236 boxes (some made in China and some made in Mexico).
Then there is the Melling JB 2236 which is identical to the stock lifter (left lifter) of the above lifters.
I measured the LC (Lifter Compression) or difference between maximum and minimum height of the stock lifter and found .120 inches.
Also measured LH (Lifter height) or maximum height of stock lifter (uncompressed from plunger to top of lifter) and found .800 inches.
There is a variance in Lifter Height and Lifter Compression among lifters.....
The Mellings JB2236 are identical to stock original Lifters as you can get.
I received 16 JB2236 Lifters today from Clark Discount (Type in JB2236 in the Search By Key Word). Perfect...exactly what I was looking for :thumbsup:
Last UPDATE of post 2 July, 2012
Last edited by Dynomite; 11-30-2012 at 07:30 PM.
11-02-2011, 10:08 AM
#3
Tech Contributor
Thread Starter
Lifters and Valve Stem dimensions (reground valves)
Lifters and Valve Stem dimensions (reground valves)
Lifters can be compressed .120 fully loaded anything above that the lifter is totally plunged and will hang valves open. Cams take up .075 from base circle.
The Base circle is .075 above the main journals so when you bolt down the camshaft it will push the lifter down .075 plus the factory has the lifter set above the journal another .015 so a stock motor takes up .090 of the .120 leaving .030 for compression of the lifter to account for valve stem clearance apperations (valve regrind for example).
If you do one valve job you should be ok. If you do a second or third valve job or even a poor valve job the valve will sink into the seat which will bring the valve farther into the lifter bore. This will result in having to grind the valve stems to compensate for the valve seat changes.
If the valve seat is ground and the valve stem comes higher into the lifter bore (more than .035) the valves will hang open and will result in very low compression #'s.
All of the above is an easy fix by just grinding the valve stems. Be careful when grinding valve stems to make sure you don't take off too much not leaving enough valve stem above the retainer (at least .020-.025). If inadequate valve stem above the retainer, the lifter can knock the keepers out which will cause even bigger iisues.
Example Lifter and Valve Stem Clearance Measurements (Valves reground)
All dimensions are in inches. (Actual numbers for stock lifter in Dark Green).
LC.....(Lifter Compression) difference between maximum and minimum height of lifter typical .120.
LIP.....(Lifter initial compression) camshaft in neutral position .090 Stock setting.
LRP.....(Lifter remaining compression) compression of lifter to account for changes in valve stem position .030 Stock setting.
LH......(Lifter height) from plunger to top of lifter (not compressed). (.800 measured stock lifter).
VC......(Valve clearance) distance between valve stem and journal (valve closed). (.750 measured after valve recondition).
Preset.....Height of uncompressed lifter above journal typical .015. (measured .047 avg after valve reconditioned. Recommended .005).
PL......Preload is half the difference between journal diameter and camshaft base circle diameter typical .075. (.080 stock cam shaft).
An example after a valve regrind Preset=.047 is different than stock .015. Which Preset (.047 avg) is too much.
A Mellings JB 2236 lifter is very close in gemetry to the stock lifter (left lifter) in the photos in the post above .
The Mellings JB 2236 Lifter Height LH is .794
Last UPDATE of post 3 July, 2012
Lifters can be compressed .120 fully loaded anything above that the lifter is totally plunged and will hang valves open. Cams take up .075 from base circle.
The Base circle is .075 above the main journals so when you bolt down the camshaft it will push the lifter down .075 plus the factory has the lifter set above the journal another .015 so a stock motor takes up .090 of the .120 leaving .030 for compression of the lifter to account for valve stem clearance apperations (valve regrind for example).
If you do one valve job you should be ok. If you do a second or third valve job or even a poor valve job the valve will sink into the seat which will bring the valve farther into the lifter bore. This will result in having to grind the valve stems to compensate for the valve seat changes.
If the valve seat is ground and the valve stem comes higher into the lifter bore (more than .035) the valves will hang open and will result in very low compression #'s.
All of the above is an easy fix by just grinding the valve stems. Be careful when grinding valve stems to make sure you don't take off too much not leaving enough valve stem above the retainer (at least .020-.025). If inadequate valve stem above the retainer, the lifter can knock the keepers out which will cause even bigger iisues.
Example Lifter and Valve Stem Clearance Measurements (Valves reground)
All dimensions are in inches. (Actual numbers for stock lifter in Dark Green).
LC.....(Lifter Compression) difference between maximum and minimum height of lifter typical .120.
LIP.....(Lifter initial compression) camshaft in neutral position .090 Stock setting.
LRP.....(Lifter remaining compression) compression of lifter to account for changes in valve stem position .030 Stock setting.
LH......(Lifter height) from plunger to top of lifter (not compressed). (.800 measured stock lifter).
VC......(Valve clearance) distance between valve stem and journal (valve closed). (.750 measured after valve recondition).
Preset.....Height of uncompressed lifter above journal typical .015. (measured .047 avg after valve reconditioned. Recommended .005).
PL......Preload is half the difference between journal diameter and camshaft base circle diameter typical .075. (.080 stock cam shaft).
An example after a valve regrind Preset=.047 is different than stock .015. Which Preset (.047 avg) is too much.
A Mellings JB 2236 lifter is very close in gemetry to the stock lifter (left lifter) in the photos in the post above .
The Mellings JB 2236 Lifter Height LH is .794
Last UPDATE of post 3 July, 2012
Last edited by Dynomite; 10-02-2013 at 08:19 AM.
11-02-2011, 10:08 AM
#4
Tech Contributor
Thread Starter
Valve Stem Clearance Measurement Tool
Valve Stem Clearance Measurement Tool
The Valve Stem Clearance Measurement Tool consists of a 14 inch aluminum round stock 1.140 diameter (all in inches) with a dial gage inserted at the center (with a countersunk set screw). This valve stem clearance measurement tool allows the measurement of valve stem clearance (shortest distance to journal surface) on the axis of the valve stem. The dial gage is set to zero on the journal surface. The aluminum round stock is lightly lubricated during the measurements.
Rotating the aluminum round stock valve stem clearance measurement tool in the journal slightly moving the tip of the dial gauge back and forth across the tip of the valve stem will give you a minimum valve stem clearance. The valve clearance to journal varies from the sides of the valve stem tip by .002 with minimum clearance at the center of the valve stem tip.
The valve stem clearance is the shortest distance from the end of the valve stem to the bottom surface of the camshaft bearing journal
Once you set a zero at the journal, all 32 valve clearances can be measured in about 5 minutes. I have checked all valves several times and get within .001 each time checked so the measurements are very repeatable. The .001 variance depends on exactly where the dial gage plunger is set on top of the valve stem.
Valve Stem Clearance Measurements (Stock Llfters)
Zero at the journal.
Checking valve stem clearance.
The stock lifter height unplunged is .800. The maximum lifter plunge is .120. Camshaft base circle Preload is .080.
The example valve stem clearance as measured below to the journal is .739. The dial gage shows .261 which to get to 1.0 which is the zero setting above we would go .739.
The lifter will Preset above the journal .800-.739 or .061 in this case. Adding Preset and camshaft Preload we get .136 which exceeds the maximum lifter plunge of .120. The valve will stay open. Lifter Preset is the height of the top of the lifter (unplunged) above the journal surface.
You may think you have extra clearance with the camshafts in the neutral position (using the stock retainers) being able to plung the lifter a tad. However, do not be mislead, when you install the camcovers, you loose that excess clearance the stock retainers provide and can end up with a valve in the open position.
Last UPDATE of post 4 Feb, 2013
The Valve Stem Clearance Measurement Tool consists of a 14 inch aluminum round stock 1.140 diameter (all in inches) with a dial gage inserted at the center (with a countersunk set screw). This valve stem clearance measurement tool allows the measurement of valve stem clearance (shortest distance to journal surface) on the axis of the valve stem. The dial gage is set to zero on the journal surface. The aluminum round stock is lightly lubricated during the measurements.
Rotating the aluminum round stock valve stem clearance measurement tool in the journal slightly moving the tip of the dial gauge back and forth across the tip of the valve stem will give you a minimum valve stem clearance. The valve clearance to journal varies from the sides of the valve stem tip by .002 with minimum clearance at the center of the valve stem tip.
The valve stem clearance is the shortest distance from the end of the valve stem to the bottom surface of the camshaft bearing journal
Once you set a zero at the journal, all 32 valve clearances can be measured in about 5 minutes. I have checked all valves several times and get within .001 each time checked so the measurements are very repeatable. The .001 variance depends on exactly where the dial gage plunger is set on top of the valve stem.
Valve Stem Clearance Measurements (Stock Llfters)
Zero at the journal.
Checking valve stem clearance.
The stock lifter height unplunged is .800. The maximum lifter plunge is .120. Camshaft base circle Preload is .080.
The example valve stem clearance as measured below to the journal is .739. The dial gage shows .261 which to get to 1.0 which is the zero setting above we would go .739.
The lifter will Preset above the journal .800-.739 or .061 in this case. Adding Preset and camshaft Preload we get .136 which exceeds the maximum lifter plunge of .120. The valve will stay open. Lifter Preset is the height of the top of the lifter (unplunged) above the journal surface.
You may think you have extra clearance with the camshafts in the neutral position (using the stock retainers) being able to plung the lifter a tad. However, do not be mislead, when you install the camcovers, you loose that excess clearance the stock retainers provide and can end up with a valve in the open position.
Last UPDATE of post 4 Feb, 2013
Last edited by Dynomite; 02-17-2013 at 01:36 AM.
11-02-2011, 10:08 AM
#5
Tech Contributor
Thread Starter
Camshaft and Lifter Measurements
Camshaft and Lifter Measurements (Stock and Regrind) all in inches
Stock Camshafts
Journal diameter is 1.140.
Base circle is 1.300.
The Preload would be (1.300 - 1.140)/2 = .160/2 = .080 (read in reverse since extended)
Regrind Camshafts
Journal diameter is 1.140.
Base circle Intake cams is 1.150.
Base circle Exhaust cams is 1.220.
The Preload Intake cams would be (1.150 - 1.140)/2 = .010/2 = .005
The Preload Exhaust cams would be (1.220 - 1.140)/2 = .080/2 = .040
..........Stock Camshaft Journal Diameter.....................Stock Camshaft Preload
Lifter internal depth of plunger is .271 (Mellings JB 2236) (read in reverse since extended). Lifter external height is 1.065 (Mellings JB 2236)
Difference or lifter height in contact with camshaft and valve stem is 1.065 - .271 = .794 (Mellings JB 2236) (Stock lifter is at .800)
Last UPDATE of post 5 Feb, 2013
Stock Camshafts
Journal diameter is 1.140.
Base circle is 1.300.
The Preload would be (1.300 - 1.140)/2 = .160/2 = .080 (read in reverse since extended)
Regrind Camshafts
Journal diameter is 1.140.
Base circle Intake cams is 1.150.
Base circle Exhaust cams is 1.220.
The Preload Intake cams would be (1.150 - 1.140)/2 = .010/2 = .005
The Preload Exhaust cams would be (1.220 - 1.140)/2 = .080/2 = .040
..........Stock Camshaft Journal Diameter.....................Stock Camshaft Preload
Lifter internal depth of plunger is .271 (Mellings JB 2236) (read in reverse since extended). Lifter external height is 1.065 (Mellings JB 2236)
Difference or lifter height in contact with camshaft and valve stem is 1.065 - .271 = .794 (Mellings JB 2236) (Stock lifter is at .800)
Last UPDATE of post 5 Feb, 2013
Last edited by Dynomite; 02-17-2013 at 01:21 AM.
11-02-2011, 10:08 AM
#6
Tech Contributor
Thread Starter
Valve Stem Clearance Measurements for Stock Valves and Regrind Camshafts
Valve Stem Clearance Measurements for Stock Valves and Regrind Camshafts using Mellings JB 2236 Lifters
Valves can be remove using a (modified) Lowes Valve Compressor, Removing keys, and Adpter
Last UPDATE of post 6 Dec, 2012
Valves can be remove using a (modified) Lowes Valve Compressor, Removing keys, and Adpter
Last UPDATE of post 6 Dec, 2012
Last edited by Dynomite; 02-17-2013 at 01:23 AM.
11-02-2011, 10:08 AM
#7
Tech Contributor
Thread Starter
Regrind Camshafts Performance
Regrind Camshafts Performance
The sound says it all.....perfect
Last UPDATE of post 7 July, 2012
The sound says it all.....perfect
Last UPDATE of post 7 July, 2012
Last edited by Dynomite; 09-25-2012 at 11:46 AM.
11-02-2011, 10:09 AM
#8
Tech Contributor
Thread Starter
Additional Information and Summary
BAD Z
1991 ZR-1 (LT5)
Marc Haibeck Chips (87 Octane and 91 Octane)
Pete Cams...........ZZZZZZOOOOOOOOM!!!!!!
Locobob Porting............ZZZZZZOOOOOOOOM!!!!!!
A26B Gaskets
Carter200 Machining
ZF Doc "C" Beam Plates
Doc Don's Bose
Over 115 mph in quarter mile down the street with no power shifts just cruising.
(I will keep the details secret for a challenge........just in case)
Click on photos (videos) to hear Pete's cams in action with SW ZR1CORVOR headers and SW ZR1CHAMSW exhaust.
Last UPDATE of post 8 Oct, 2012
1991 ZR-1 (LT5)
Marc Haibeck Chips (87 Octane and 91 Octane)
Pete Cams...........ZZZZZZOOOOOOOOM!!!!!!
Locobob Porting............ZZZZZZOOOOOOOOM!!!!!!
A26B Gaskets
Carter200 Machining
ZF Doc "C" Beam Plates
Doc Don's Bose
Over 115 mph in quarter mile down the street with no power shifts just cruising.
(I will keep the details secret for a challenge........just in case)
Click on photos (videos) to hear Pete's cams in action with SW ZR1CORVOR headers and SW ZR1CHAMSW exhaust.
Last UPDATE of post 8 Oct, 2012
Last edited by Dynomite; 10-14-2012 at 08:38 PM.
09-09-2012, 06:27 PM
#10
Tech Contributor
Thread Starter
Valve Stem Clearance Measurements for Stock Valves and Stock Camshafts
Valve Stem Clearance Measurements for Stock Valves and Stock Camshafts using Mellings JB 2236 Lifters
Last UPDATE of post 10 Oct, 2012
Last UPDATE of post 10 Oct, 2012
Last edited by Dynomite; 12-15-2012 at 03:41 PM.
