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Author Topic: Lost compression in single cylinder...  (Read 3652 times)

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Offline Liane

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Lost compression in single cylinder...
« on: May 02, 2015, 04:02:23 PM »
Hello, and thank you for reading...

I have a 1978 Pinto Wagon with the Cologne 2.8l v6.. I was wondering if there are common issues with this motor, and with the cylinders themselves. Please be descriptive as I have much to learn.

As much help as you can provide is greatly appreciated!

Liane M.

Offline pinto_one

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Re: Lost compression in single cylinder...
« Reply #1 on: May 02, 2015, 05:50:53 PM »
The number one issue on the 2.8 is the factory timing gear on the cam, if it was changed it was very reliable, only every 15 thousand miles you should adjust the valves, I do mine every 7 to 8 thousand to keep them quiet, if you lost compression on one cylinder you may have a burnt valve there, check the valve clearance and see if one may be set too tight, also check for vacuum leaks,  hope this helps you,
76 Pinto sedan V6 , 79 pinto cruiser wagon V6 soon to be diesel or 4.0

Offline dick1172762

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Re: Lost compression in single cylinder...
« Reply #2 on: May 02, 2015, 06:51:29 PM »
Or a blown head gasket or cracked head. UGH or DOS UGH!
Its better to be a has-been, than a never was.

Offline Liane

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Re: Lost compression in single cylinder...
« Reply #3 on: May 02, 2015, 08:00:10 PM »
Thank you very much for the responses!

Offline Wittsend

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Re: Lost compression in single cylinder...
« Reply #4 on: May 04, 2015, 10:36:16 AM »
Can you give the readings of your cylinders? Is there a total loss of compression, or is the one cylinder decreased from the others? Compression loss comes from many causes. Excessive mileage or lack of oil can wear the cylinder walls and piston rings. Piston rings can break. Pistons can get holes in them. Cylinder heads can crack or warp. Head gaskets can fail. Some engines (thought I don't think it is a problem with your engine) can have the head bolts stretch or loosen. Camshafts can wear. Valves can become mis-adjusted. Valves can burn.

Leakage at the head can sometimes be determined by coolant leakage.  It can show externally, internally (milky white-ish oil) - or dampness/misfires on the spark plug. A burnt valve usually sounds like a misfire. A worn cam will show as excessive valve clearance and a ticking noise. Rings and cylinder wall problems can somewhat be determined by putting about a tablespoon full of oil in the cylinder and then re-checking the compression. This will show a temporary rise in pressure as the oil momentarily creates better sealing. So, there are a few of the things you can start with and report back.

Offline pinto_one

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Re: Lost compression in single cylinder...
« Reply #5 on: May 04, 2015, 12:02:13 PM »
If you can find one to borrow or rent use a cylinder leak down gauge, I use them when I do a 100 inspection on aircraft engines,  it will let you know if you have a valve or piston ring problem,  I do all the cylinders and write it down , I do this on the aircraft I work on and enter the info log books for past history of the engine , if all are good next thing I would look at is plug wires , a bad plug, or something in the ignition system,  if that does not show up any thing last I would check for a worn cam , lobe almost gone, these are a few ways we can point you in the right direction on fixing whats wrong . As Wittsend said give us some numbers , and a extra note is to keep the fan belt in great shape , if you lose it it will run hot quickly, and Will crack a head in no time, the later 2.8s in the bronco II/Rangers had all three belts go over the top water pump pulley to help with that problem , (ask me how I know)  good luck ,
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Offline jonz2pinto

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Re: Lost compression in single cylinder...
« Reply #6 on: May 04, 2015, 03:07:03 PM »
A  trick  showed to me to check for exhaust valve problem is to hold a piece of paper to exhaust tip and see if it sucks the paper in.It worked on a pinto with a burnt valve for me.Sometimes you can can hear a spitting type sound at tip also similar to a miss.
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Offline dick1172762

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Re: Lost compression in single cylinder...
« Reply #7 on: May 04, 2015, 05:34:44 PM »
I heard of that trick in 1948 and its still a good one. Use a 9x11 sheet of paper to get the full use of the trick.
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Offline Wittsend

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Re: Lost compression in single cylinder...
« Reply #8 on: May 05, 2015, 11:18:52 AM »
Just a quick notation regarding Pinto_One's second post.  He is giving a proper rundown on checks for loss of power that would include checking the ignition system. I'm assuming that you have already determined (given the subject title) that compression is down in one cylinder and therefore the recommended ignition test would not have any bearing on that (specifically).  Being that you stated you have much to learn I didn't want you to associate an ignition problem as a cause of low compression and follow that path.

 His recommended leakdown test is superior to the compression test I recommended. 

Offline amc49

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Re: Lost compression in single cylinder...
« Reply #9 on: May 05, 2015, 10:27:33 PM »
Just a tip..........

'A  trick  showed to me to check for exhaust valve problem is to hold a piece of paper to exhaust tip and see if it sucks the paper in.'

'I heard of that trick in 1948 and its still a good one. Use a 9x11 sheet of paper to get the full use of the trick.'

FYI, the trick works but much better on interference type exhaust with multiple cylinders that interfere with each other (normal common non-header log type manifolds). I simply use my hand and listen carefully, you'll hear the spit of the non working cylinder in the longer stream of normal pressure bumps there. Between hand being sucked back in and noise you can generally tell the misfire. HOWEVER, when working on a proper tuned exhaust and/or say single cylinder firing down its' own pipe it is NORMAL to feel the pipe suk after the pressure pulse, it's the normal vacuum pulse that follows any positive pulse down a pipe. That negative pulse gets buried in all the positives in a multi-cylinder engine and more with the more cylinders to interfere with it.

I remember back in dirt biking days watching a parked Honda 305 Superhawk with high straight pipes in 4 foot weeds first blasting the weeds out of the way then trying to suk them back into the pipe with every pulse at idle. You could easily feel it too, within 1 inch you could hardly stop hand from being pulled back to get burned on pipe end with the negative pulse.

Offline 65ShelbyClone

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Re: Lost compression in single cylinder...
« Reply #10 on: May 16, 2015, 10:38:03 AM »
Higher-RPM engines like the Hawk's also tend to have more cam overlap that promotes reversion (pulling exhaust back in) at lower engine speeds.

A regular misfire at idle can also do that because the cylinder has less than atmospheric pressure it on the intake stroke. Nothing fires and expands on the power stroke so the pressure remains below ambient when the exhaust valve opens, causing air to rush in.

I heard of that trick in 1948 and its still a good one. Use a 9x11 sheet of paper to get the full use of the trick.

Do you think an A3 size would work better since it's a metric engine?
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