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post #1 of (permalink) Old 06-16-2003, 03:50 PM Thread Starter
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O/T cylinder leak test for 258

hi there

i'm looking to do a leak test on my 258. what's the easiest way to be sure that the cylinder is at TDC? i've got a tool that will run air through the cylinder and measure how much is leaking. the person i am borrowing the tool from told me less than 20% leakage from a 20 year old engine would be okay.

the reason i am doing this is because i'm getting blue exhaust and trying to pinpoint the problem...are the rings bad, are the valves not closing properly or something else...

also, i have two conflicting reports...one person who believes the 1st cylinder is more likely to be worn because it runs cooler and a second person who believes the 6 cylinder would be more worn because it runs hottest. what do you all think?

thanks
patrick
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post #2 of (permalink) Old 06-16-2003, 04:28 PM
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Re: O/T cylinder leak test for 258

1. Easiest way to determine the stroke...
2. There are two easy ways:[*]Know the stroke of the 1st cylinder.
then follow the firing sequence through the rest of the cylinders.[*]Pull the valve cover and watch for the valves to close.
3. Now the trick is to do it while using the starter to rotate the engine...
4. Me, I rotate the engine by hand,
5. Feel for compression on the upstroke... then,
6. When the pistion tops out... that TDC for that cylinder.


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post #3 of (permalink) Old 06-24-2003, 04:25 PM Thread Starter
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Re: O/T cylinder leak test for 258

hi there

so i got around to doing the leak test...sort of

so i pulled the valve cover and i turn the engine by hand and watch the rocker arms go up and down.

1. when standing on the passenger side, for each pair of valves which valve is the intake (right or left)?

2. will the rocker arms be up or down when the valves are closed (i'm guessing up because i never seem them both down)?

3. how do you "feel" for the compression stroke?

when trying the leak test on cylinder #6 i get 40% leakage. I'm hoping i'm doing something wrong. i hear the leaking from what i think are the valves (rather than the exhaust which would indicate leakage around the cylinders) which makes me think that i don't have the cylinder in the right spot.

any comments/suggestions?

thanks
patrick
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post #4 of (permalink) Old 06-24-2003, 05:39 PM
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Re: O/T cylinder leak test for 258

</font><blockquote><font class="small">In reply to:</font><hr />
how do you "feel" for the compression stroke?

[/ QUOTE ]1. Put your finger in the spark plug hole of the cylinder you want to test.
2. Manually rotate the engine.
3. You'll feel compression building up on your finger.
4. In fact, it'll eventually blow your finger outta the plug hole.
5. Then you know you're on the compression up stroke.
6. The larger valve is the ehaust valve.
7. On the compression and power stroke the valves will be closed,
9. That translates to the both rocker arms completely up.
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post #5 of (permalink) Old 06-25-2003, 02:09 PM Thread Starter
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Re: O/T cylinder leak test for 258

hi there

so...here's the update.

i did the cylinder leak test and got consistant results which i'm hoping means i did it right rather than consistantly wrong.

what i got was between 45 and 50% leakage for each cylinder. the person who loaned me the leak test machine said to not worry about anything over 20%. well, 50% is well over 20%.

it sounds as though the leaking is coming from the top of the motor through the valves (rather than through the exhaust which i was told would indicate ring deteriation).

so what should be my next step? i really don't feel comfortable taking the engine apart anymore than it is already (which is just the valve cover off and some of he vacuum lines disconnected).

thanks for any help!!
patrick
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post #6 of (permalink) Old 06-25-2003, 02:39 PM
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Re: O/T cylinder leak test for 258

1. From the description the problem is burned intake valves or seats.
2. To really tell it'd take head removal... which isn't hard.
3. Did you also do a compression test?
4. A bad intake wouldn't cause blue smoke...,
5. Unless the valve seals are also worn.
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post #7 of (permalink) Old 06-25-2003, 03:40 PM Thread Starter
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Re: O/T cylinder leak test for 258

hi there

i have not done a compression test. are they easy enough to do while the engine is in it's current state (nothing hooked up)?

in looking at the sparkplugs i've noticed quite a bit of black on them...i remember vaguely seeing a series of pictures that show how spark plugs wear can indicate what's going on...can anybody tell me where i saw that?

i don't image it's hard to take the head off...it's the putting it back on correctly that i'm worried about.
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post #8 of (permalink) Old 06-25-2003, 06:19 PM
 
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Re: O/T cylinder leak test for 258

compression check is not hard to do at all. read over two articles and if you have any more questions come back and fire away.
you can get compression test kit or gauge at your favorite auto store.
welcome to the wonderful world of jeeps

Article 1
Article 2
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post #9 of (permalink) Old 06-26-2003, 10:33 AM Thread Starter
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Re: O/T cylinder leak test for 258

hi there

thanks for the links to the articles.

couple questions...it mentions that in order to do a compression test you should have oil in the engine to get a good seal around the rings. would that be necessary for a leak test as well? i have run the engine since november or so. what i'm thinking is that since i don't have oil in there my leak test may be producing results that are high (maybe if oil where in there i'd be getting leaks around 35-40% instead of 45-50%).

also...doesn't a leak test tell me pretty much the same thing as a compression test...that air is leaking (so that compression can't be built up)?

any idea of what a "valve job" would cost me if i had a professional do it...not some hack like me who doesn't know what they are doing? how bout a "ring job"? a complete overhaul? what about increasing the volume of the engine by boring out the cylinders. seeing as i have no experience in this world i don't know if these things cost $50, $500, or $5000.

thanks alot
patrick
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post #10 of (permalink) Old 06-26-2003, 11:07 AM
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Re: O/T cylinder leak test for 258

1. A compression test should be done[*]dry, no oil in cylinders [*]wet, oil in cylinders
2. If a reading is low, and the PSI goes up with oil,
3. You know the rings are worn.
4. If not... then the problem's in the valves.
5. A leak-down test should be done dry.
6. It tells you the path of escaping compression, over time.
7. A valve job will cost about $200 to $300,
8. If you pull and reinstall the head.
9. Your symptoms pointed to the valves,
10. Were the engine mine I'd do a compression test,
11. To see how the rings fared,
13. Pull the head,
14. Take it to a machine shop for refurbish,
15. And remove the carbon from the top of each piston,
16. And install the rebuilt head,
17. And go from there if the Compression test was OK.
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