Bad rings? Compression results

[nickblackgsx]

Just bought a 97 GST(knowing the possible engine problems) and checked compression and here are the results. I did two tests on each cylinder and then added a capful of oil to each cylinder and checked again.

1st 148 2nd 155 with oil 190
1st 135 2nd 138 with oil 165
1st 129 2nd 132 with oil 160
1st 140 2nd 138 with oil 180

The previous owner changed the headgasket himself and said it could possibly be a tooth out of time, I don't believe that could effect it that much could it? Could there be anything else that could cause theses results besides needing new rings? I believe if a bad headgasket job it would keep the compression down whether I added oil in the cylinders or not. Anyway, I just wanted to make sure it was the rings so I know what I have ahead of me!

Thanks in advance!

 

[NEpilot]

The problem with the oil and our cars is the shape of the pistons; when adding oil you are actually increasing the CR. The large difference "wet" could be the amount of oil you put in each hole.

Also, when you did the CR check did you let the car warm up and make sure it was floored when cranking?

The service limit is 130 I believe and depending on miles I wouldn't be overly concerned with those numbers. The bigger concern is when they are so different from each other. I would do a leak down test next to figure out where you are losing compression.

-Chris

 

[nickblackgsx]

The car has 103,xxx miles on it. And the car was warm and the throttle was held open during the test. The previous owner said the car was missing the knock sensor for a while and flooded the engine, couldn't that kill the rings? I don't have a leak down tester, where should I get one at? I just don't see why the rings would be bad with 103,xxx miles. The car does seem weak and slow compared to my other cars.

 

[BogusSVO]

First, check the timing belt, off one toth can make a diffrence in your comp. readings.

Whem the past owner chenged the HG, did he have any work done to the head?

Check Ebay or Harbor freight for a 2 gauge leak down tester appox $60

 

[nickblackgsx]

Ok, I will check the timing when I get a chance. I don't think he had anything done to the head. He didn't have the cash to put in it, used the same timing belt and all. Just a composite head gasket and some ARP's were added.

 

[BogusSVO]

Depending on how hot the head got when the HG blew, the head may have warped and "cracked" the valves of the seat so they do not fully seal also.

 

[NEpilot]

Is there a MBC on the car or does it appear there may have been one at some point? Removing the knock sensor is a PITA job and I have to wonder why it was removed and how long was it run without one. It all seems to be pointing to some event; missing knock sensor, low compression, new head gasket.


- Check the timing.
- Change the oil and pay attention to what color it is and how much gas is in it.
- Change the coolant and again pay real good attention to what color it is.

If the car runs; start it up with the radiator cap of and check for bubbles.

Leak down test will tell you for sure where the leaks are going.

 

[BogusSVO]

The knock sensor will not affect compression, unless the car was railed on for a bit and was in pre det and that started burning the pistons.

If he ran it very hot, the rings may have lost the tention in them so if that has happened, you would have bad blow by.

Get the leak down tester, that will tell you more and where to look.

 

[nickblackgsx]

Ok I totally forgot about the blow by problem. He said the dipstick comes out sometimes if he is hard on it. I haven't had it happen but I've been careful. The car is mostly stock except for an eBay front mount and a leaky(like crazy even at idle) eBay BOV vented to atmosphere (just swapped out to a greddy RS recirculated) and a 1g throttle body.

He said the knock sensor was just missing, like it fell out or something and he finally figured out what it was.

I changed the oil as soon as I got it but I need to check it out bc I didn't pay attention to it, but I still have it in my pan.

The car starts up and runs really well, it has a high idle sometimes but if I mess with the throttle body(turn the throttle plate closed more) then the idle will go back down.

I contacted the previous owner and he said the head was checked out and decked and was determined to be in good shape.

 

[BogusSVO]

Blue smoke out the tail pipe too?

 

[InfiniteGSX]

LoL My highest compression is lower than your Lowest.

 

[nickblackgsx]

Ok so I just went and checked the timing and I rotated the crank ###### 15 times trying to line up the camshaft marks. Well every time I put the crankshaft sprocket on it's mark on the timing cover the camshaft dowel pins would be at 10 o'clock and then 5 o'clock every other time. Does the oem crankshaft sprocket have the word china on it??

If the timing is that far off then how could the car run so well? Could that also cause excessive blow by?

 

[InfiniteGSX]

Then your timing is ####ed! Excuse my language. The Crank Pulley.... the one that has all the area's for the belts for Alternator, AC, PS. That has a timing mark on it. Its very small. But Both dowel pins should be at 12 and the 4 timing marks on the cam sprockets should be level. If not then your belt timing is way off.

And you don't need to turn the crank any amount of times. You just need to position the crank pulley to the proper TDC Mark. IF your not using the pulley and have everything torn apart, the crank sprocket has a timing mark on it also.