nebulous

Hey, I have a 305 TPI, that until a few months ago was supercharged. It has always had an abnormally large amount of PCV, but I always just assumed that was because of the supercharger. In the last few months it has really been performing badly, and still has a lot of PCV gasses even superchargerless. Does this indicate bad rings? What are some of the main causes and symptoms of rings going bad, and what is the best way to check them?

82camaro

The 'best' way: Tear it down and look at the rings.


------------------
350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, current red metallic paint. Lots of other stuff...
82camaro

speedlvr

An easier way would be to get a compression test done to see if it's within specs.

WideOpenVTwin

Yes, a compression check, but to single the rings out as the problem (as opposed to the valves), do the check normal and then put some oil into the cylinder and do it again. If the compression increases then it's worn rings

ede

do a compression and leak down test and repost the results if you don't know what they tell you.

------------------
ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

nebulous

I'm not familiar with a leakdown check. What does that involve?

ede

basically you apply air preasue (100 psi makes the math easy) and hold it for a set period of time (usually 1 hour) and see how much leaks off (10% is common)

------------------
ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

AlexJH

I bought a leakdown kit to check if I had a blown head gasket.

Basically it is a compression tester that is hooked up to compressed air. You put the piston at TDC and attach the leakdown gauge, and pressurize it. Then listen at various points on the engine to see where the air is leaking out.

The kit cost me about $110 CDN, so about $70 US.

nebulous

I did a check on cylinders 1 and 2(all I had time for in the middle of the night), They came out 150psi and 120psi respectively. What are valid ranges for the 305tpi? Do they all have to be exactly the same? Also, It seems like at 9.5:1 compression on an atmosphere 139.65psi is as high as it can get. Is that affected by humidity/etc, or am I just not thinking straight?

RB83L69

When you compress a gas, it heats up. When you raise the temp, the pressure goes up. So if you could compress the gas in the cyl and then wait for it to cool down without leaking, then you could measure the static CR that way. In the real world it doesn't work like that.

I've got a nickel that says your #2 piston is melted down the side, on the side toward the spark plug. It results from detonation, or running lean, or both. You need to pop a head off and take a look at it, I think you will see your short block is toast.

------------------
"So many Mustangs, so little time..."
ICON Motorsports

nebulous

I took the heads off around 6k miles ago, and everything was in pristine condition. Could this damage have happened so suddenly? Also, how is my shortblock toast? Seems like I could just put new rings and pistons in, perhaps with a slight overbore. Am I wrong in this? Another thing: I just checked #3 and can get no reading at all on the checker. Is that even possible? I drove it 40 miles out here last night and it ran OK just not great. Any feedback would be greatly apriciated since Ive got it in the garage on ramps right behind me and am wonder what to do.

RB83L69

It can happen in one pass. Although, usually it occurs more gradually, as succcessive instances of the damage happen. Often it's not particularly visible from above until it's really severe, so it's not impossible that there was already started on the road to destruction the last time you saw it. The damage will be on the side of the piston, starting at the compression ring, and proceeding downward from there. It will look like the ring lands and the skirt melted and tried to seize to the bore. Usually the motor will continue to run OK until it gets like the guy that posted a few days ago where he had oil shooting out of his dipstick tube from all the blowby.

You are correct, you could just put in new pistons and rings, along with boring the block as required; I believe that's pretty much the definition of rebuilding a toasted short block, along with refreshing the crank if necessary and the bearings.

------------------
"So many Mustangs, so little time..."
ICON Motorsports

nebulous

This is what I came up with compression-wise(provided this board allows HTML)....

<table border=1>
<tr><td>psi</td><td colspan=2>cyl #</td><td>psi</td></tr>
<tr><td>150</td><td>8</td><td>7</td><td>150</td></tr>
<tr><td>150</td><td>6</td><td>5</td><td>140</td></tr>
<tr><td>145</td><td>4</td><td>3</td><td>0</td></tr>
<tr><td>120</td><td>2</td><td>1</td><td>160</td></tr>
</table>

[This message has been edited by nebulous (edited August 10, 2001).]