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Old 07-20-2013, 07:35 PM   #43
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First of all if your mechanic does a compression test with the engine running ,get a new mechanic. Second a leakdown test is the logical next step but there is no reason to remove the rocker arms. A leak down is done at TDC with the valves closed. If you get a high leakage percentage listen to carb or injecter,exhaust and breather and around the head gasket for air inorder to determine where the leak is. If you find a leak in either the intake or exhaust then back of the rockers and retest to make sure it isn't a tight or pumped up lifter. Don't get your engine torn down until you know where the problem is. I can not tell you how many "mechanics" have brought me heads to repair and I have to tell them there is nothing wrong with them.
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Old 07-20-2013, 07:41 PM   #44
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Quote:
Originally Posted by MotorPro View Post
First of all if your mechanic does a compression test with the engine running ,get a new mechanic. Second a leakdown test is the logical next step but there is no reason to remove the rocker arms. A leak down is done at TDC with the valves closed. If you get a high leakage percentage listen to carb or injecter,exhaust and breather and around the head gasket for air inorder to determine where the leak is. If you find a leak in either the intake or exhaust then back of the rockers and retest to make sure it isn't a tight or pumped up lifter. Don't get your engine torn down until you know where the problem is. I can not tell you how many "mechanics" have brought me heads to repair and I have to tell them there is nothing wrong with them.
How do you know that each of the 8 cyl are at TDC without removing the valve covers? It is much easier to just loosen up the rockers if doing a cyl leak down test. Some hyd lifters do not allow the valve to fully close when the engine is off but while running it does. It saves a lot of time since this is in an Econoline chassis to loosen up the rockers right off the bat.

But as you stated, you want to be very certain on what you are after before tearing into your engine. Especially since this is in a van chassis and that 460 is in there really tight.
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Old 07-21-2013, 06:59 AM   #45
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Hook up the leak down tester then just tap the key(with ignition disconnected)until the guage shoots up.If you pull the rockers before the test it will not tell you if you have a tight or pumped up lifter. Hydrolic lifters should never not close the valve all the way unless the lifter is plugged and not releasing pressure. While a compresion is useful many things can give you a low reading ,rings valves ,gasket even a bad cam. A leak down will help you narrow down the problem.

JamesR I really agree with you on your leakdown suggestion. A majority of the mechanics I deal with have no idea what a leak down tester is much less how to do one.
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Old 07-21-2013, 06:00 PM   #46
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I'm not thinking 85lbs is particularly low as this engine is only 8.5-1 and the fact that all 8 cylinders are the same I am satisfied, at 70 thousand miles the engine is going to be a bit worn with the leak down test the issue is its very labour intensive to do because of that goofy plenum but true enough it would be a waste of time if I tore it apart and the valves were not the issue
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Old 07-22-2013, 11:28 PM   #47
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Ok guys need some opinions here I've been doing a fair amount of reading ( and stressing ) and have realized that 85psi is low but I am realizing a few things that the compression test was done cold which will cause a lower reading will it not? Understandably so no one wants to stick there hand willing fully into a hot engine compartment so I am thinking If my reading are the same across the board cold, they should be the same warm but a higher psi, am I wrong on this? As well it's a great suggestion to do a leak down test but really labor intensive could I not achieve the same result by doing a wet compression test, from my reading if the compression goes up it means ring problems and not valves, or vice versa if it doesn't change we can eliminate worn rings? And pin point the valves? Thanks guys I know I'm stretching here but I'm really not interested in wasting my time doing a valve job on a worn engine and by all honesty I'm sure by the time dust settled it will only take me a small amount of time more to actually replace the entire engine. And at 2300 for a reman engine it's not money i want to spend but it is less then what I'd lose if I sold it as is and paid the tax on a new one
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Old 08-02-2013, 07:33 PM   #48
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Hey guys wanted to give you a quick update, I started throwing some Hail Mary's at the ol gal with some Rislon ring lubricant as well as an additive to free up sticky valves, I think I got it!!! It's not 100% but it's almost non noticeable now so at the 20 bucks I threw at it I'm impressed and is going to save myself some bashed knuckles and mental grief. Thought I'd say something as I'm sure many people here have experienced te same issues I have and haven't known where to turn its worth a shot, I know it might only be temporary but ill take it for now
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Old 08-02-2013, 08:27 PM   #49
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If that doesn't work, try Restore. It works by filling the groves in the cylinders. I had a 70 Land Cruiser that was so worn out that the pistons were trying to swap holes. I used Restore every time it got weak.
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Old 08-03-2013, 08:17 AM   #50
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Mitchyb,
Your assessment of the compression questions was spot on.

TeJay
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Old 08-03-2013, 11:53 AM   #51
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If this is a carb type engine it might be the Idle adjustment. However I will tell you of a problem I had with a Dodge V-8 Van.

The thing idled very very rough.. Ran fine at speed but idled very very rough.

Finally I decided to "Shotgun" and the first thing I did was pull the PVC hose and plug it.. Engine smoothed down right quick... I pulled the PVC valve and found that there was nothing there.. NO valve, just an elbow.

78 cents later it was 100% (yes this was a while ago)
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Old 08-04-2013, 09:21 AM   #52
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It's been some time but that's exactly how we checked to see if the PCV system was operating. Remove the PCV valve and plug the bottom. If the RPM's changed then the system was providing a positive vacuum to the crankcase to vent the fumes. If the RPM's didn't change then something was already plugged and there was no vacuum leak. At idle the vacuum leak was minimal but as the RPM's increased and IMV changed the valve would open and allow more venting of the crankcase gases.

Good job catching the problem.

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