Bad Compression

DeadBunny · 01-05-2008, 12:24 PM

I need some opinions about whats going on with my car. I was changing the rubber ring for the distributer on my 86 NA and I didn't put the rotor back in at the right angle. I turned the car over, not realizing what I had done. I finally figured out that it wasn't starting because of the distributer position and set the rotor at the right angle, but it still wouldn't start. I checked the compression and the compression on the cylinder closest to the trans is only 90. it builds compression really slowly. What I want to know is, is there any way to tell if the this might be the valves or the rings. When the car was still running it used to stutter around 3000rpms. I think putting the rotor at the wrong angel advanced that problem. Im asking if its the valves because I have a built head sitting around that I could just slap on there.

what do you all think

MX450248 · 01-05-2008, 01:51 PM

you could have a local shop bore scope the cylinders. they will be able to see if you have a burnt valve. also, get a leak down test done at the same place.

tymr287 · 01-20-2008, 03:27 PM

Pull the spark plug and squirt some oil in the cylinder so that it gets and the rings and run another compression test on the cylinder. If compression goes up its the rings, if it stays the same its the valves.

DeadBunny · 01-20-2008, 05:20 PM

doesn't matter now. Iv already pulled the head and the valves seem to look "intact" and there is no scoring on the cylinder walls. However, there appears to be, by what I can tell, mechanical damage on the tops of the pistons and the flat spot on the head. But its weird because the number 4 cylinder has it too but that one fires. And when I say its weird, the mechanical damage doesn't look all that bad and it doesn't reach the valves nor does it look like it would effect compression. its like someone went in there with a letter punch and made little crosshatches. Also it looks like the piston and the head traded some metal... I'll have to take pictures and post them. Anyway Im thinking I should just buy a used 4age and pop that in. Use the old motor for parts.

Anyone in western NY selling a running 4age, let me know.

MX450248 · 01-20-2008, 05:26 PM

if the valves are leaking compression, sometimes its not that obvious. It could be just a hair bend or out of round

tymr287 · 01-20-2008, 09:01 PM

Since you have the head off put the spark plugs back in and turn it over. Fill the areas with the valves closed with water. That'll tell you if the valves are causing compression problems.

01-05-2008, 12:24 PM	#1 (permalink)
DeadBunny No Skills Join Date: May 2006 Posts: 85 Thanks: 1 Thanked 1 Time in 1 Post My Google Map iTrader Rating: (0/0% )	Bad Compression I need some opinions about whats going on with my car. I was changing the rubber ring for the distributer on my 86 NA and I didn't put the rotor back in at the right angle. I turned the car over, not realizing what I had done. I finally figured out that it wasn't starting because of the distributer position and set the rotor at the right angle, but it still wouldn't start. I checked the compression and the compression on the cylinder closest to the trans is only 90. it builds compression really slowly. What I want to know is, is there any way to tell if the this might be the valves or the rings. When the car was still running it used to stutter around 3000rpms. I think putting the rotor at the wrong angel advanced that problem. Im asking if its the valves because I have a built head sitting around that I could just slap on there. what do you all think

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01-05-2008, 01:51 PM	#2 (permalink)
MX450248 Your Resident Welder Join Date: Nov 2006 Location: Maumee, OH Posts: 530 Thanks: 22 Thanked 21 Times in 19 Posts My Google Map iTrader Rating: (1/100% )	you could have a local shop bore scope the cylinders. they will be able to see if you have a burnt valve. also, get a leak down test done at the same place.

01-20-2008, 03:27 PM	#3 (permalink)
tymr287 Some Skills Join Date: Jan 2008 Location: New Orleans Posts: 74 Thanks: 0 Thanked 7 Times in 5 Posts iTrader Rating: (0/0% )	Pull the spark plug and squirt some oil in the cylinder so that it gets and the rings and run another compression test on the cylinder. If compression goes up its the rings, if it stays the same its the valves.

01-20-2008, 05:20 PM	#4 (permalink)
DeadBunny No Skills Join Date: May 2006 Posts: 85 Thanks: 1 Thanked 1 Time in 1 Post My Google Map iTrader Rating: (0/0% )	doesn't matter now. Iv already pulled the head and the valves seem to look "intact" and there is no scoring on the cylinder walls. However, there appears to be, by what I can tell, mechanical damage on the tops of the pistons and the flat spot on the head. But its weird because the number 4 cylinder has it too but that one fires. And when I say its weird, the mechanical damage doesn't look all that bad and it doesn't reach the valves nor does it look like it would effect compression. its like someone went in there with a letter punch and made little crosshatches. Also it looks like the piston and the head traded some metal... I'll have to take pictures and post them. Anyway Im thinking I should just buy a used 4age and pop that in. Use the old motor for parts. Anyone in western NY selling a running 4age, let me know.

01-20-2008, 05:26 PM	#5 (permalink)
MX450248 Your Resident Welder Join Date: Nov 2006 Location: Maumee, OH Posts: 530 Thanks: 22 Thanked 21 Times in 19 Posts My Google Map iTrader Rating: (1/100% )	if the valves are leaking compression, sometimes its not that obvious. It could be just a hair bend or out of round

01-20-2008, 09:01 PM	#6 (permalink)
tymr287 Some Skills Join Date: Jan 2008 Location: New Orleans Posts: 74 Thanks: 0 Thanked 7 Times in 5 Posts iTrader Rating: (0/0% )	Since you have the head off put the spark plugs back in and turn it over. Fill the areas with the valves closed with water. That'll tell you if the valves are causing compression problems.