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Cylinder Cranking Pressure on Stock 426 Hemi #1417002 04/08/13 08:24 PM 04/08/13 08:24 PM
Joined: Jan 2003 Posts: 3,905 Minnesota 3twos OP master
3twos OP master Joined: Jan 2003 Posts: 3,905 Minnesota	What would be an anticipated cranking pressure for a stock 426 hemi with standard mechanical cam and pistons, etc.? Al & Sheila

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417003 04/08/13 10:07 PM 04/08/13 10:07 PM
Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska	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

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: RapidRobert] #1417004 04/08/13 11:40 PM 04/08/13 11:40 PM
Joined: Jan 2003 Posts: 3,905 Minnesota 3twos OP master
3twos OP master Joined: Jan 2003 Posts: 3,905 Minnesota	Quote: What would be a normal general (PSI) range expected on a cyl compression test on a stock Hemi That is what I was trying to figure out however I think I know it should probably be at least in the 130-140 psi range. I get 100 on all of the left bank cylinders and 85 on three of the right bank and one more cylinder at 75 psi. This is cranking with the starter motor, 3-4 revolutions. Obviously something is wrong, the engine runs but not a good idle and lot's of hesitation. It does go wide open throttle with no back firing. I am wondering where to start. I know nothing of the engine except it was supposed to be rebuilt 3k miles ago, maybe the cam is worn but there is not excessive clatter? Al & Sheila

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417005 04/08/13 11:56 PM 04/08/13 11:56 PM
Joined: Jan 2003 Posts: 15,976 Chilliwack B.C. Canada R RUNCHARGER I Live Here
RUNCHARGER I Live Here R Joined: Jan 2003 Posts: 15,976 Chilliwack B.C. Canada	You've got problems, it should be well over 150, I'm thinking more like 175 or 180. Did it just start this behaviour? Timing chain jumped? Sheldon

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417006 04/09/13 01:06 AM 04/09/13 01:06 AM
Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska	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

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417007 04/09/13 07:28 AM 04/09/13 07:28 AM
Joined: Mar 2007 Posts: 3,277 West Coast, USA jbc426 master
jbc426 master Joined: Mar 2007 Posts: 3,277 West Coast, USA	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)

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: jbc426] #1417008 04/09/13 09:49 AM 04/09/13 09:49 AM
Joined: Nov 2003 Posts: 1,029 Southeast Virginia 68jim super stock
68jim super stock Joined: Nov 2003 Posts: 1,029 Southeast Virginia	I seem to recall that last time I did mine, totally stock 68 hemi w/mech cam, it was around 180psi. I had the throttle wide open and all the plugs out of the motor. I was chasing down a miss and 7 cylinders were 180 and one was 10... Busted pushrod... Jim

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 68jim] #1417009 04/09/13 10:55 AM 04/09/13 10:55 AM
Joined: Jan 2003 Posts: 3,905 Minnesota 3twos OP master
3twos OP master Joined: Jan 2003 Posts: 3,905 Minnesota	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

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417010 04/09/13 02:46 PM 04/09/13 02:46 PM
Joined: Mar 2008 Posts: 5,746 Ontario, Canada Dodgem master
Dodgem master Joined: Mar 2008 Posts: 5,746 Ontario, Canada	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.

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: Dodgem] #1417011 04/09/13 03:04 PM 04/09/13 03:04 PM
Joined: Jan 2005 Posts: 1,527 minnesota Kirby pro stock
Kirby pro stock Joined: Jan 2005 Posts: 1,527 minnesota	Al- I'm wondering if they backed off the valve springs while it was in hibernation. Rings? Any blow by? That sucks!

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: Dodgem] #1417012 04/09/13 03:58 PM 04/09/13 03:58 PM
Joined: Jan 2003 Posts: 3,905 Minnesota 3twos OP master
3twos OP master Joined: Jan 2003 Posts: 3,905 Minnesota	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? Al & Sheila

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417013 04/09/13 04:17 PM 04/09/13 04:17 PM
Joined: Jun 2006 Posts: 5,161 CT GTX MATT master
GTX MATT master Joined: Jun 2006 Posts: 5,161 CT	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

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: GTX MATT] #1417014 04/09/13 05:48 PM 04/09/13 05:48 PM
Joined: Jan 2003 Posts: 16,376 D dogdays I Live Here
dogdays I Live Here D Joined: Jan 2003 Posts: 16,376	You are overanalyzing the problem. No way valves are going to wear that much in a couple of thousand miles. And, if you have lash on your exhaust valves you know that isn't the problem. So it's possible your measuring technique is incorrect or that something is basically wrong with the engine, like camshaft put in wrong and bent a couple of valves. A leakdown test like RR said would be a good place to start. And no, a couple of thousandths on the lash won't make a whole lot of difference on a compression check. R.

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417015 04/09/13 08:14 PM 04/09/13 08:14 PM
Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska	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

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417016 04/09/13 10:28 PM 04/09/13 10:28 PM
Joined: Mar 2008 Posts: 5,746 Ontario, Canada Dodgem master
Dodgem master Joined: Mar 2008 Posts: 5,746 Ontario, Canada	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!

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: RapidRobert] #1417017 04/09/13 10:49 PM 04/09/13 10:49 PM
Joined: Jan 2003 Posts: 3,905 Minnesota 3twos OP master
3twos OP master Joined: Jan 2003 Posts: 3,905 Minnesota	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

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417018 04/10/13 12:59 AM 04/10/13 12:59 AM
Joined: Jan 2005 Posts: 1,527 minnesota Kirby pro stock
Kirby pro stock Joined: Jan 2005 Posts: 1,527 minnesota	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.

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: Kirby] #1417019 04/11/13 01:02 AM 04/11/13 01:02 AM
Joined: Jun 2004 Posts: 3,319 Chicago Burbs sthemi master
sthemi master Joined: Jun 2004 Posts: 3,319 Chicago Burbs	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. Video Little Red Wagon Indy Nats,BurnoutContest

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417020 04/11/13 01:58 AM 04/11/13 01:58 AM
Joined: Jul 2008 Posts: 607 Boise M Moparteacher mopar
Moparteacher mopar M Joined: Jul 2008 Posts: 607 Boise	1st. Install a battery charger to insure constant cranking rpm. 2nd. Tie the throttle back so no fuel in the cylinders. 3rd. Use a different gauge with a different schrader valve. The wrong type of valve will give low results. A tire schrader valve used in a compression tester gives the wrong readings. Crank each cylinder 5 times. get back to us. There is no sense to disassemble when a cranking compression, running compression, and leak-down will tell you what is wrong.

Re: Cylinder Cranking Pressure on Stock 426 Hemi [Re: 3twos] #1417021 04/11/13 07:04 AM 04/11/13 07:04 AM
Joined: Nov 2003 Posts: 2,715 closer to Canadian beer! torkrules I'm neurotic
torkrules I'm neurotic Joined: Nov 2003 Posts: 2,715 closer to Canadian beer!	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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