NEED HELP: 4.6L Triton with low compression in cyl # 4 - FordTough.ca - Home of Canadian Ford Truck Enthusiasts
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post #1 of 13 (permalink) Old 04-12-2014, 10:42 PM Thread Starter
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Question 4.6L Triton with low compression in cyl # 4

Hi folks

I have a '98 F150 with 4.6L Triton with low compression in cyl # 4 @ approx. 30#; all other cyl are at 140# or so. Would it be a burnt valve, bent valve, cam? Any ideas before I rip it apart?

Any harm if I drive it like that? I have not have it on the road yet.

Thanks
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post #2 of 13 (permalink) Old 04-12-2014, 10:50 PM
 
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First thing I would look at on that one is threads in spark plug hole. Is it blowing by any with the compression tester screwed in? Welcome to the site by the way.

Such is life. Just passing through.

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post #3 of 13 (permalink) Old 04-14-2014, 10:36 PM
 
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So what's up with this one? Any further word?

Such is life. Just passing through.

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post #4 of 13 (permalink) Old 04-15-2014, 06:51 AM
 
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Park it and pull the head off. You'll have to whether it's a valve or a set of rings or a head gasket or a cracked head/block. Driving it will just do more damage.

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post #5 of 13 (permalink) Old 04-20-2014, 03:10 PM
 
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Leak down test time.

I know it's at the back and it's a pain in the rear, but turn the crank by hand until you feel #4 on its compression stroke. You can get a neat little tool that whistles as in indicator - it's pretty much a necessity as it's impossible to get your finger down the spark plug well.

The leak down tester will flow regulated air into the cylinder. At this point your listening for air coming out the exhaust (exhaust valve), intake (one of the intake valves) or through the oil fill (piston rings).

Good luck.

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post #6 of 13 (permalink) Old 04-21-2014, 11:29 AM Thread Starter
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While holding the crank shaft with a Johnson bar, I put air in the cylinder with piston all the way up; the air would give the piston a good jolt. I moved the piston up & down several times while pressurized with air; at one point, lots of air came out from the oil fill hole so I suspect a ****ed up piston. I inspected with my Borescope and found something weird on the piston that I can't figure out what it is.



It's the best picture I could get. Does that look like a damaged piston or what the heck is it?

Is it possible to remove that piston from the bottom without removing the crankshaft? This is just my spare truck while I rebuild the trany in my F350 so I don't want to spend too much $ as I will sell it once I get my F350 back on the road.

Any idea if the piston will slide by the crank & block?
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post #7 of 13 (permalink) Old 04-21-2014, 09:00 PM
 
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At this point the head needs to come off. You need to see what's all buggered in there.

Moreover, even if the piston will get around the crank (and it should), you'll need the head off to get the rings compressed anyway.

2003 GMC Sierra 3500 -- dually, 4x4, hasn't blown up yet and that's what i look for in a truck

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post #8 of 13 (permalink) Old 04-21-2014, 09:48 PM
 
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Hard to tell but looks like pre ignition or detonation of some kind has blown right through the ring lands and probably burnt a valve also. As Varsity Tyler said, time to pull the head. Once you do the repair then you will have to find out what caused it or it will happen again.

Such is life. Just passing through.

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post #9 of 13 (permalink) Old 04-22-2014, 09:38 AM Thread Starter
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Thanks for the bad news. LMAO I already have too much money invested in this bad deal truck. Haven't even registered & driven it yet and it's starting to cost me more then book value. Damn it. I'll have to decide how much more I want to spend on it.

Thanks again for the input guys.
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post #10 of 13 (permalink) Old 04-27-2014, 07:26 PM Thread Starter
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Update:
Took the oil pan off today; pressurized the cylinder with air & from underneath, I could hear lots of air pissing out so I stuck a poly hose in one ear and other end toward the bottom of the piston and lots of air in one location. I viewed that location with the borescope and yup, piston has a burnt hole which is also the spot you see in that picture above
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