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LOL!! Not a chemist but after 40 years of car resto,you pick up quite a bit.As a kid,we had a big ol iron tub filled with a Lewis Lye solution over a wood fire.Cleaned up heads,blocks great.Stuck an aluminum intake in it,had a few beers,forgot about it till the next day.Went to get it out and it was freakin GONE.Lesson number 3....
 

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A quart in 400miles is still better than my brothers' old Vega at 40k miles. LOL

1986 w/ 70k miles... how much oil was it using before the head work? Fwiw... rebuilt heads may not have been rebuilt correctly.

Does the RV smoke... on cold start up? ...under load? ...during deceleration? Is the pcv hose, from the pcv valve to the carb, dripping wet / oil in the intake?

'Cylinder walls looked good'... was the cross hatch still visible? Any burnished dark gray areas or shiny glazed areas? Glazed walls can be improved somewhat with top engine cleaners (SeaFoam). Lightly stuck oil rings can be freed up with engine oil flushes (Marvels). Burnished walls will require a hone.
 

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Discussion Starter · #26 ·
I did receive my leak down tester and next week I will start the leak down test and check for vacuum at the PCV grommet per Scotty's advice. Cross hatch was still visible and no shinny areas that I recall. Yes, it did burn oil before, and it did appear to be sucked in on the intake port. I had many motorcycles and car engines done at this machine shop and have confidence of his workmanship. Of course, there is always a chance of human error. I will post what the leak down rates are
 

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A leak down test is about percentage lost yes, as the manufacturer typically provides a spec. However, leak down tests are more about observation of WHERE the leak down occurs. If you hear the hissing in the crankcase, it's rings, if you hear the hissing in the tailpipe, it's exhaust valves, if you hear it at the carb, it's intake valves. It's also wise to check the neighbor cylinders to check the head gasket.
 

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Discussion Starter · #28 ·
Update.
Installed a combination vacuum gauge / fuel pressure gauge in place of the PCV valve. With the oil fill tube taped off and the tube that goes to the air cleaner taped off the gauge read zero. Made no difference if the engine was under load or revved up. Thought I would see some needle movement, of course I have never done this before.
Performed a leak down test and cranking compression test on 7 cylinders, did not do #5 due to difficulty of getting access. The leak down test indicated issues, only one of the cylinders that I performed leaked air into the crankcase, the others were valve leakage which is a disappointment since the heads were rebuilt. I performed the compression test and leak down tests several times to confirm the numbers.
#1 - 22% leakage, 135 PSI compression
#2 - 7% leakage, 145 PSI compression
#3 - 22% leakage, 145 PSI compression
#4 - 22% leakage, 150 PSI compression
#5 - did not do
#6 - 22% leakage, 150 PSI compression
#7 - 2% leakage, 150 PSI compression
#8 - 7% leakage, 150 PSI compression
 

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How long ago were they rebuilt and do they offer some warranty? Looks to me like the heads are coming off for inspection, which will give you a great look at the walls as well.

It's important to note that this doesn't rule out poor ring seal, only confirms that the valves are worse.
 

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Discussion Starter · #30 ·
How long ago were they rebuilt and do they offer some warranty? Looks to me like the heads are coming off for inspection, which will give you a great look at the walls as well.

It's important to note that this doesn't rule out poor ring seal, only confirms that the valves are worse.
The heads were done last fall, they have about 7,000 miles on them. I did the heads because I had a stutter / miss when accelerating, blowing air in the cylinder indicated exhaust valve leakage. When the heads come off again, the engine comes out for a rebuild, no picnic working on a E350 in the engine bay. Currently the engine runs amazing, starts right up whether warm or cold, accelerates briskly with smooth power delivery. Without the above testing the only issue I was aware of was oil consumption. Having never done a leak down test before I find it quite interesting there is not a direct correlation between cranking compression and the leak down numbers.
 

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That 0 vacuum gauge reading doesn't sound right... Hook everything up the way it's supposed to be then check it off a direct manifold vacuum port.. you should be getting something like 15-20 in at idle.. from there you can do a few diagnostic checks going by a few charts that you can find on goggle... If you're getting 0 in of vacuum then you've got it hooked up wrong... Engine won't pull in fuel at that low vacuum...
 

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That 0 vacuum gauge reading doesn't sound right... Hook everything up the way it's supposed to be then check it off a direct manifold vacuum port.. you should be getting something like 15-20 in at idle.. from there you can do a few diagnostic checks going by a few charts that you can find on goggle... If you're getting 0 in of vacuum then you've got it hooked up wrong... Engine won't pull in fuel at that low vacuum...
Sounds like he had it hooked up to look for crankcase pressure, not manifold vacuum.
 

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Discussion Starter · #34 ·
K, I thought we were using it to check for valve guide or ring blow-by..
I used the vacuum gauge to check crankcase pressure / vacuum not manifold vacuum. Check performed to check possibility of intake manifold gasket leak. Manifold vacuum is 20 to 21" at idle. If the engine did not use so much oil, I would not of performed all the above tests. Nice idle, strong vacuum, nice power for a stock 460. I did borrow a friend's bore scope to look down the spark plug hole and it does appear oil is getting pass the piston rings.
 

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Now that's weird, that much vacuum should mean that the rings are sealing good... There is one thing that I can think of that may be causing this... If the cylinders are tapered at the bottom of the bore, there would be your usage of oil consumption. One way to tell put the vacuum gauge on it and take it down the road. If it doesn't hold a decent amount of vacuum at a cruise, or recover vacuum when you lean on it going down the road, then that's where your oil it going.. If the bores are tapered at the bottom you'll lose ring tension at the bottom of the bore and that's where all the oil is being used. Make sense??
 

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Discussion Starter · #36 ·
Now that's weird, that much vacuum should mean that the rings are sealing good... There is one thing that I can think of that may be causing this... If the cylinders are tapered at the bottom of the bore, there would be your usage of oil consumption. One way to tell put the vacuum gauge on it and take it down the road. If it doesn't hold a decent amount of vacuum at a cruise, or recover vacuum when you lean on it going down the road, then that's where your oil it going.. If the bores are tapered at the bottom you'll lose ring tension at the bottom of the bore and that's where all the oil is being used. Make sense??
Last fall after the cylinder head replacement I did drive it on the road with a vacuum gauge connected to get an idea of what dual stage power valve would work. I was surprised at the vacuum level, at cruising it was in the 16 to 17 range, it took a good bit of throttle to bring it down to 12 inches of vacuum. Keep in mind this is a 9000-pound class C RV with the wind resistance that comes with it. My plan is major engine work this winter, not sure if I am going to rebuild the engine myself or get a crate motor. I did do some checking for someone to install a crate motor but the shops I checked just were not interested. Short staffed and enough other work to do.
 
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