Cylinder Cranking Pressure on Stock 426 Hemi
#1417002
04/08/13 08:24 PM
04/08/13 08:24 PM
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Joined: Jan 2003
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3twos
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What would be an anticipated cranking pressure for a stock 426 hemi with standard mechanical cam and pistons, etc.?
Al & Sheila
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 3twos]
#1417003
04/08/13 10:07 PM
04/08/13 10:07 PM
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Posts: 36,041 Lincoln Nebraska
RapidRobert
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Circle Track
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What would be a normal general (PSI) range expected on a cyl compression test on a stock Hemi
live every 24 hour block of time like it's your last day on earth
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 3twos]
#1417006
04/09/13 01:06 AM
04/09/13 01:06 AM
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RapidRobert
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I'd do a leakdown test on it & see where the air is escaping
live every 24 hour block of time like it's your last day on earth
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 3twos]
#1417007
04/09/13 07:28 AM
04/09/13 07:28 AM
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jbc426
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Are you holding the throttle wide open when cranking the motor? Squirt some oil into the cylinder and see how much higher the compression gets.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 68jim]
#1417009
04/09/13 10:55 AM
04/09/13 10:55 AM
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Joined: Jan 2003
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3twos
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I just got this car and the engine was supposedly rebuilt back in the mid late 90's with very little use since then. I am now wondering if the valves and seats were not hardened or set up for unleaded gas and now the valves are grinding into the seats and there is no valve lash any more. I think I will pull the covers tonight and see what I find.
Al & Sheila
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 3twos]
#1417010
04/09/13 02:46 PM
04/09/13 02:46 PM
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Dodgem
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Well if it is a solid cam give it some lash 28/32 is a good start and do the compression test again. If it is a hydraulic maybe it has way too much preload. But I see it is solid! I like 5 hits on compression all spark plugs out full throttle does not seem to make a big dif but they say full.
Last edited by Dodgem; 04/09/13 02:49 PM.
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 3twos]
#1417013
04/09/13 04:17 PM
04/09/13 04:17 PM
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GTX MATT
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No .25 might be the spec for a newer cam.
Are you sure your compression gauge is correct? And I wouldn't stop cranking so fast. I let them crank until they stop climbing.
My 98 Chevy Lumina with a 3.1 and 202k miles has 180 psi just for comparison.
My 68 440 in my Satellite had about 120 psi, needed rings. I did a full rebuild. At 120 psi I don't know how many miles were on it, I'd say more than 100K but it was clean. I measured a couple of bores and came up with around .004-.006 bore taper. (they say rebore at .004, I wouldn't be afraid to re-ring it but I wanted a fresh engine for once).
Less than 100 is bad news bears. Maybe they used the wrong size rings or something, or maybe never seated them properly and glazed the bore.
Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 3twos]
#1417015
04/09/13 08:14 PM
04/09/13 08:14 PM
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RapidRobert
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I just ran into an erroneous reading from a bad compression gauge (taking out the schrader valve (like whats in a tire valve stem) & spraying it all out with cleaner fixed it). If no leakdown tester you could use just the hose from that compression tester & if the schrader valve is in the integral fitting on the end of the hose then take it back out & if the valve is in the gauge head then screw the hose in the plug hole & connect it to shop air. Check several of the worst cyls & watch the rotor to get em at TDC & listen for where the air is escaping; carb (intake valve)/tailpipe (exhaust valve)/radiator (head gasket)/breather on valve cover(rings)
Last edited by RapidRobert; 04/09/13 09:02 PM.
live every 24 hour block of time like it's your last day on earth
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 3twos]
#1417016
04/09/13 10:28 PM
04/09/13 10:28 PM
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Dodgem
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Quote:
Quote:
Well if it is a solid cam give it some lash 28/32 is a good start and do the compression test again.
If it is a hydraulic maybe it has way too much preload.
But I see it is solid!
I like 5 hits on compression all spark plugs out full throttle does not seem to make a big dif but they say full.
I took one valve cover off at lunch and there appears to be some lash but no more than .025 so do you think a few thou could make a difference? It appears a leak down test would be the best way to see what is happening?
now as long as it has lash it should test fine. put some oil down the cylinders to see if it is ring seal!
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: RapidRobert]
#1417017
04/09/13 10:49 PM
04/09/13 10:49 PM
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3twos
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I did use the shop air and rigged up a line with regulator and hooked up to the plug holes however it seemed the air was all going into the crankcase and it was hard to figure out if the air was going out the exhaust or elswhere. I did find what looks like bad rocker arm geometry as a couple of the adjusters were backed up into the rocker arms and the cup on the pushrod was close to or touching the rocker arm. I set the lash on all of the valves which all of them were out of adjustment and all were less than the .028 and .032.The inside of the valve covers and lifter gallery were all very clean so i think this engine was rebuilt not many miles ago. Also the cam does not have bad lobes and there are no bent push rods.
Al & Sheila
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 3twos]
#1417018
04/10/13 12:59 AM
04/10/13 12:59 AM
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Posts: 1,527 minnesota
Kirby
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Quote:
I did use the shop air and rigged up a line with regulator and hooked up to the plug holes however it seemed the air was all going into the crankcase and it was hard to figure out if the air was going out the exhaust or elswhere. I did find what looks like bad rocker arm geometry as a couple of the adjusters were backed up into the rocker arms and the cup on the pushrod was close to or touching the rocker arm. I set the lash on all of the valves which all of them were out of adjustment and all were less than the .028 and .032.The inside of the valve covers and lifter gallery were all very clean so i think this engine was rebuilt not many miles ago. Also the cam does not have bad lobes and there are no bent push rods.
Al-my geometry was like that too. i ended up bending an exhaust valve. thus the new roller set up.
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: Kirby]
#1417019
04/11/13 01:02 AM
04/11/13 01:02 AM
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sthemi
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My stock compression Hemi, has 185-195 cranking pressure, with a fairly agressive hyd cam. Yours should be 150 minn. Might as well take it apart to see what is wrong before anything gets damaged.
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Re: Cylinder Cranking Pressure on Stock 426 Hemi
[Re: 3twos]
#1417021
04/11/13 07:04 AM
04/11/13 07:04 AM
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torkrules
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Quote:
What would be an anticipated cranking pressure for a stock 426 hemi with standard mechanical cam and pistons, etc.?
I would thing anywhere from 130psi to 160psi would be considered normal.
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