Stock '83 460 Compression Test
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Stock '83 460 Compression Test
Hello all. I've been a lurker around here for quite a while, but it this is my first post.
I just picked up a 1983 motorhome that runs on the E350 chassis with a 460. It's got 138,000 on the clock but seems to still be running strong. I'm planning a long trip next summer with the family and want to get everything ready. All in all the motorhome is in excellent used condition. When purchasing I was completely prepared to refresh the engine if needed
My first step was to do a compression test to get some empirical data on the health of the engine. The test showed a high of 150 pounds and a low of 120. In between are a 130, several 135s, a 140 and a 145. From my research it look like as long as the lowest is at least 75% of the highest it passes. These results fall in that range but just barely.
So, in the opinion of this deep dark corner of the internet, would you call this good and trust it for an 8000 mile trip? Or, call it questionable enough to warrant a rebuild?
I just picked up a 1983 motorhome that runs on the E350 chassis with a 460. It's got 138,000 on the clock but seems to still be running strong. I'm planning a long trip next summer with the family and want to get everything ready. All in all the motorhome is in excellent used condition. When purchasing I was completely prepared to refresh the engine if needed
My first step was to do a compression test to get some empirical data on the health of the engine. The test showed a high of 150 pounds and a low of 120. In between are a 130, several 135s, a 140 and a 145. From my research it look like as long as the lowest is at least 75% of the highest it passes. These results fall in that range but just barely.
So, in the opinion of this deep dark corner of the internet, would you call this good and trust it for an 8000 mile trip? Or, call it questionable enough to warrant a rebuild?
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Ok, Not sure exactly what to test for on vacuum. I just went and put the gauge on. Connected it to the back of the manifold., I disconnected a line that goes to the transmission (I think) to connect the gauge. At idle, 600 RPM, it fluctuates between 16-17HG. At 800 RPM it fluctuates between 20 and 21HG. At 1000 RPM it's solid at 22 HG.
Does this give the info you would need? Is there some other test that I should run?
BTW. Thank you for your help. It's really appreciated.
Does this give the info you would need? Is there some other test that I should run?
BTW. Thank you for your help. It's really appreciated.
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Vacuum gauge test wants a source of constant vacuum, at factory idle. A high RPM will camouflage the result. 600 or less RPM is OK. At Sea level a healthy stock engine in good condition should pull 18" to 20" Hg steady needle. Vacuum gauge test is a very useful tool in engine diagnostics and tuning.
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Ok, so the vacuum is low and inconsistent. Is this because some of the cylinders are sealing better than others?
What's your opinion of this engine running strong for another 10k miles? If a rebuild is necessary I'd rather do it my self. I don't want to get caught at the mercy of a random mechanic that I don't know.
What's your opinion of this engine running strong for another 10k miles? If a rebuild is necessary I'd rather do it my self. I don't want to get caught at the mercy of a random mechanic that I don't know.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Low vacuum indication isn't necessarily rings. Late ignition timing is one possibility, maybe an intake manifold leak. What altitude do you live at? It's also important to see a steady reading. If it fluctuates or is erratic, could be worn valve guides or a bad valve for example. Worn rings are tested by blipping the throttle hard, the needle should drop to no more than around 5 or so, and then rebound to + 25 say, something like that. There are a bunch more tests and indications that can be gleaned from a gauge than just that chart, lots of websites and info about how to use one. Learn as much as you can using the resources available.
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Cargo Master
Joined: May 2001
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For that year motor your numbers are ok. It is a retarded valve timing motor. It will not show as good a numbers as a straight up timed motor. It is also a motor home and probably doesn't get driven a lot that can effect the numbers.
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