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Old 05-01-2004, 02:12 PM
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How to test piston rings?

Hey,

I have my engine apart, I have no idea how many miles it has, its a 350 4 bolt main. I want to know if it needs new piston rings? are they hard to install? Is there any kind of test i can do to see if the present ones are still any good?

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Old 05-01-2004, 02:31 PM
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I would do a compression check, then add a little oil into the cylinders. Recheck the compression. If the compression values go up significantly after adding the oil then the rings are worn.
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Old 05-01-2004, 03:10 PM
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I did a compression check and thats why i took it apart, cylider number 5 was at 30 psi. and the rest were above 150, cylinder number 7 was at 180. Do i have to remove the connecting rods off of the crank to change the piston rings?
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Old 05-01-2004, 03:17 PM
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Quote:
Originally posted by Echofive
[ Do i have to remove the connecting rods off of the crank to change the piston rings? [/B]
YES! You probably either have a bent valve or you have tightened a rocker down too far on cyl. 5 !! Just the oil control rings would probably net you 30 p.s.i. !!
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Old 05-01-2004, 03:21 PM
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Something else i just thought of, The oil would turn black pretty quickley after changing it. I have cahnged the oil/filter 3 times in the last 8 months becasue of that reason. It would get pretty Dark.
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Old 05-01-2004, 04:18 PM
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If you have never done a set of rings on anything, I suggest you get someone local to give you a hand. It is not hard at all but, there is more to it than just popping on a new set. Since you did have low compression I would suggest replacing them. You will want to at the very least run a dingle ball hone in the cylinders to knock the glaze off and give the new rings a surface to set to.

Yes, you have to remove all the pistons but, you do not have to remove the pistons from the rods. Since this is your first shot at it I don't think you need to get to carried away (total rebuild). If there is not a major ridge at the top of the cylinders you should be able to get by with a "shade tre" overhaul. Rings, bearings, gaskets. Be very careful because if you drop a piston it will break (I assume they are cast). Once you have the pistons out make sure you clean the groove the rings ride in (ring lands), this can be done using one of the old rings broken in half.

If you are on a real tight budget the above advice will work for you. If you have a little money to spend then you might as well do a complete rebuild, pistons, bore the block, balance etc... That is the best way to go it you want to make HP or want it to last for a long time. Don't get me wrong I have seen some "shade tree" overhauls run for years.

Royce
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Old 05-02-2004, 12:18 AM
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Yes, I think I will get new rings, when i take of the rod caps I have to mark them right? Tonight I sanded teh suface of the deck, the timing chain cover surface, and oil pan surface. swith fine sandpaper to get all the old gasket off and to make it look clean. I am also doing this to the heads. Im using Laquer thinner to clean with. How fine of a sandpaper should I use on these surfaces?
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Old 05-02-2004, 10:57 AM
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Lets hope that you have a bad or mis adjusted valve. If a ring caused the compression to be that low it would most likely be a broken ring rather than a worn ring. A broken ring would tear up the cylinder wall quickly. Since your heads are off a cheap and dirty test for your valve would be to turn the heads with the ports facing up and fill the port with solvent and see if any leaks past the valves. As for cleaning the deck surface of he block and heads use a scraper as much as possible before sanding. If you must sand 400 grit buy hand or 180-220 in a D/A sander.
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Old 05-02-2004, 01:12 PM
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I dont think it is a misadjusted valve, because the compression used to be ok on all the cylinders this jsut recently happened after the car being pushed at kinda high RPM's. (I dont have a tach) The car seemed a little weak so decided to do a compression test and found that, its been apart since. I'll try that leak test today, and report back later on.
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Old 05-02-2004, 10:34 PM
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Ok, today i pulled my pistons and marked the from which cylinder and put the caps on the ends they correspond to and the direction they go. I also have someone to help me put the pistons back in afterwords.

Ok, today i pulled my pistons and marked the from which cylinder and put the caps on the ends they correspond to and the direction they go. I also have someone to help me put the pistons back in afterwords.


I also did the head test the heads with water in the intake ports only two intake valves leaked one on each head, not quicley but they did leak. I then turned the heads over to do the exhaust ports and one on each side leaked right through the water port ?
is this normal?

I can get some 291 casting heads for free, should i grab these? Would they yeild more performance then the stock 993's i have now?
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Old 05-02-2004, 10:49 PM
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Quote:
Originally posted by Echofive
Ok, today i pulled my pistons and marked the from which cylinder and put the caps on the ends they correspond to and the direction they go. I also have someone to help me put the pistons back in afterwords.

Ok, today i pulled my pistons and marked the from which cylinder and put the caps on the ends they correspond to and the direction they go. I also have someone to help me put the pistons back in afterwords.


I also did the head test the heads with water in the intake ports only two intake valves leaked one on each head, not quicley but they did leak. I then turned the heads over to do the exhaust ports and one on each side leaked right through the water port ?
is this normal?

I can get some 291 casting heads for free, should i grab these? Would they yeild more performance then the stock 993's i have now?
The was the exhaust crossover that the water ran through and that's ok. How about the valves on the cylinder that only have 30 psi? Did they leak? You've allready got it apart and you know that the valves ar starting to leak. Now is the time to do something about that.
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Old 05-02-2004, 11:14 PM
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Just for future reference, water has too much surface tension to really tell you much. But in this case you did find some valves that allowed water through, so you know they're leaking pretty good.
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Old 05-03-2004, 12:29 AM
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Is there a better liqued to use than water? Gasoline?
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Old 05-03-2004, 04:59 AM
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Laquer thinner.
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Old 05-03-2004, 08:44 PM
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Should I slap t hose 291's on instead of my 993's? will they at least overflow the 993's by a little? given they are in the same general condition.
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