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rough idle, low compression
Topic Started: Nov 24 2011, 12:22 AM (3,011 Views)
AlexK
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Hi Guys,

I've had my '92 5sp 1.0L 2dr for a few weeks working on it and I'm finally driving it after fixing the timing belt, water pump, door handles, window regs, wheel bearings (which I thought was a transmission noise so I opened up the trans too). The idle is rough and not much power at low RPMs, and hard starting. That sounds like bad valves to me. So I did a compression test and got 108, 108, 80 psi. I'm at high altitude here in Reno, NV so I would expect 135 or so.

The plugs are tan and there is no exhaust smoke, so I'm assuming the rings are OK and it's just the valves. Do you agree? I ordered a $200 rebuilt head on ebay. I can't wait to see what these little pistons and valves look like!
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mcmancuso
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A good way to check the valves: (with the engine running) Put a dollar bill up to the tailpipe and if it sucks it up intermittently you may have a burned valve. Though with the overall low numbers I'd say it needs rings too. Do a wet compression test, if the numbers don't go up, its just valves, if they go up quite a bit then you need rings.
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allmountain40
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Im inclined to suspect rings also since all 3 cylinders are low. Definitly do the wet test as described above. :thumb
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Bad Bent
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Facetious Educated Donkey

You'll have a new drive train soon. :scared

Here is a link to the wet test that mcmancuso suggests and note the WOT point.
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wayn
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rings are easy once you get the head off. Do it.

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AlexK
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I'm using a Harbor Freight Tools compression tester and it's crap. the pressure is supposed to stay in the gage until it's released, however mine slowly bleeds down. I oiled the check valves and release valve on the tester and tried again, this time watching the gauge needle while cranking and applying WOT. These numbers are more accurate than before. Remember I'm at high altitude where the ambient pressure is 12.5 psia as opposed to 14.7 psia at sea level, so 150 psi on the compression test is like 176 psi at sea level.

cyl dry wet
1 150 155
2 155 160
3 110 115

This says my rings are probably OK and my #3 cylinder likely has a bad exhaust valve. I ordered a rebuilt head on ebay as well as a head gasket, cam seal, and timing belt tensioner (mine makes noise). After reading other threads I know to use 5-30W oil in the Metro and I might do a Seafoam clean to get the carbon out of my engine. This should keep the new lifters happy.

Thanks for the tips.
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Woodie
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I'd put rings in it anyway.
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Johnny Mullet
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Fear the Mullet

Woodie
Nov 25 2011, 05:11 AM
I'd put rings in it anyway.
:timeout

And listen to Woodie :hein
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idmetro
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I too vote for a new set of rings. Having owned a series of Metros and having read enough horror stories about rebuilding the head without touching the bottom end and winding up with an engine that generates its own Austin Powers smokescreen I have made up my mind that unless it is a financial necessity to do only the head I will at least put in new rings along with the head on any G10 that has >100k miles on it. The chances of having to do it over are just too high for my liking...
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AlexK
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OK so I should do the rings too. Should I hone the cylinders while the pistons are out too? What should I order now, just all new piston rings?

There are lots of different brands available at a wide range of prices. Is there a brand and/or supplier the community here prefers?
Edited by AlexK, Nov 25 2011, 01:54 PM.
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AlexK
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I did my first fillup where I kept track of the odometer. I went 409 miles on 7.22 gallons = 56.6 mpg! With that kind of gas mileage maybe I don't want to change anything at all! It seems too high to believe but I checked my odometer against the mile markers today and it's right on. I clicked the gas pump off twice to be sure the tank was full. I'm still suspicious, we'll see what the next tank yields.
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clarkdw


Drive it and enjoy the fuel savings till it proves to need something. With mileage like that I wouldn't touch it unless it was absolutely belching smoke. :thumb
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wizard93
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THESE RINGS should work just fine for your engine. I'm glad you decided to go ahead and throw rings in it while the head is off. I would do at least a light hone on the cylinder walls to make sure the new rings break in properly. I've always used THIS KIND OF HONE on engines I've rebuilt with good results, but some people prefer the "bunch of grapes" hones that are out there. But yeah, be sure to hone those cylinders, even if you still see a slight cross-hatch pattern in the bores, if you can't feel the cross-hatch pattern with your fingernail, then your new rings won't seat.
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idmetro
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:gp on the honing, you don;t want to go to the effort of doing the job and not have it work. I used these rings http://www.store.partsdinosaur.com/product2411.html on my rebuild and so far have 30k miles on them with no incident. Take advantage of the your current situation and start acquiring parts towards the coming rebuild. Good Luck!
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AlexK
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Thanks for the tips. I bought the rings, gaskets, and hone. I recently bought a '94 XFI in addition to the '92 referenced in this thread. It could use some head work too (compression test yields 135, 155, 135)so I'm going to do them both. I need to buy a set of gapless rings for the XFI.
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