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post #1 of (permalink) Old 12-13-2000, 09:54 AM
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I think i have found my problem :o(

Hey Guys,

I think i found out my idling problem.

Here are the results from the Compression test on my 258 inline 6cyl.

#6 (plug black and dry)
1st try- 135
2nd try- 132
#5 (plug black and dry)
1st try- 130
2nd try- 130
#4 (plug black and dry)
1st try- 130
2nd try- 130
#3 (a tad wet and black)
1st try- 115
2nd try- 115
#2 (plug black and dry)
1st try- 130
2nd try- 125
#1 (normal color but wet)
1st try- 0
2nd try- 0

Is this a stuck valve? smoked rings? blown piston? or with my luck a combination?

thanks

[b]Boston Mangler
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post #2 of (permalink) Old 12-13-2000, 10:00 AM
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Re: I think i have found my problem :o(

what SHOULD the compression be of a stock 79 258 motor?

thanks

[b]Boston Mangler
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post #3 of (permalink) Old 12-13-2000, 10:09 AM
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Re: I think i have found my problem :o(

[img]/wwwthreads_images/icons/smile.gif[/img] You could pop the valve cover and eyeball the valve gear to see if you have a valve stuck open. Any little piece of carbon on the stem can do it.[img]/wwwthreads_images/icons/crazy.gif[/img] 258's are supposed to be 8.0:1 compression as manufactured.[img]/wwwthreads_images/icons/tongue.gif[/img]

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post #4 of (permalink) Old 12-13-2000, 10:24 AM
 
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Re: I think i have found my problem :o(

if you have an air compressor, CHOCK THE WHEELS, put it in NEUTRAL

rotate the engine until the valves are closed on that dead cylinder ( itll be pointing at that plug wire on the distrib cap)
hook air line to your compression guage hose ( right where the gauge plugs in) and pressurize the #1 cylinder at about 40 Psi

see where the noise comes from, itll tell you bad exh valve seal, bad intake valve seal, bad rings, bad head gasket.

just listen for hte hiss, increase the pressure if you need to to hear it escaping that cylinder.

I figure anything 120 or over is fine compression, I had a 304 that ran well, and was driveable although it made little power, it tested at 30psi dry and 50psi wet, in all 8 cylinders.





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post #5 of (permalink) Old 12-13-2000, 10:25 AM
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Re: I think i have found my problem :o(

Could be a stuck valve, especially after sitting for 8 months. Pop the valve cover off and have a look inside, to see iff everything is in order. You could try running your engine a bit with some cleaner in there. I don't think its the piston or rings, unless there's a hole in the piston
I'd personally try the engine flush first. Lemme know if you want a hand.

post #6 of (permalink) Old 12-13-2000, 11:00 AM
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Re: I think i have found my problem :o(

have you checked your oil? if that plug is wet.. im assuming from water.. then it sounds like a head gasket.. therefore you would have water in your oil pan.. drain the oil.. if it has water in it.. itll be a milking color..
also.. thats a 258? those numbers are a tad bit low.. supposed to be 150.. granted 130 is about at the tolerance for the low side.. but.. i would replace the rings in all the cylinders anyways.. and throw some new bearings in it.. and you do have that one other cylinder that is low..
drain your oil.. if you have a bad piston.. you'll have metal in the oil.. milky.. bad head gasket.. if the oil is fine.. you just gave it an oil change.. and then i would pull the valve cover off.. and have a look see..


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post #7 of (permalink) Old 12-13-2000, 11:33 AM
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Re: I think i have found my problem :o(

Mangler - check for a broken valve spring too - this will let the valve stay open and not close all the way. I had one on my F250 and it was broken such that it was REAL hard to see, but when you looked close at it, it was not closing the valve.

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post #8 of (permalink) Old 12-13-2000, 12:11 PM
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Re: I think i have found my problem :o(

Hey Guys,

Thanks for all the advice. I just pulled the cover and sure enough the # 1 cylinder has a stuck valve. It is the 2nd valve in (from the front) and the one with the longer pushrod. It is stuck completly compressed and i couldnt free it. The push rod was just kinda laying in its hole not connector to the rocker, must have fallen out of place when the spring compressed and move the rocker.

Time for a 4.0L head and EFI

Thanks Again

Boston Mangler
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http://ct-web.unh.edu/yankeetoys/kspeicher/

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post #9 of (permalink) Old 12-13-2000, 12:21 PM
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Re: I think i have found my problem :o(

Wow,
almost sounds like an easy fix to me. Is the rod warn down on the end? or is it the rocker? You could just pull some rockers from an engine at a yard and replace it. If it is the rod, same solution. Shouldn't be too hard to find one in a yard.

Good luck


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post #10 of (permalink) Old 12-13-2000, 01:57 PM
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Re: I think i have found my problem :o(

Is the rocker or pushrod damaged? If not then you could just work the valve loose with some penetrating oil and some light tapping. Or, if the stuff is damaged, just go the the yard and grab a rocker arm and it's matching pushrod and throw them in there. I'll give you a hand if you'd like...
Tom

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