: Zero compression in Cylinder 2



YueIBM
12-28-09, 02:10 PM
Hi Everyone,

I joined a few days ago because my 1999 Seville STS has a dead cylinder. The car has 226,000 miles. The previous owner said the head gasket had been replaced but there's so much build-up that it's hard to believe the valve cover has ever come off. No cloud of coolant out the tailpipe at all (just out the water pump seal)... no bubbles in expansion tank.

Now I've isolated it to a Cylinder 2 that has 0 psi compression. The compression gauge doesn't move at all. All other cylinders have fairly even compression.

I've moved the intake manifold to the side, and removed the front valve cover and all the valve buckets are moving up and down as they should. (Had to cut a piece of the radiator support and jack up the car an inch on the transmission pan to get enough clearance to remove the valve cover in-car.)

The intake valves should be OK since I can pour oil in the intake port with the valves closed, and it won't leak into the cylinder. I'm unable to fill the cylinder with oil at TDC - it all leaks out fairly quickly through the exhaust valve(s). One exhaust valve cam lobe shows significant wear but its lifter moves up and down freely with full travel.

Before pulling the head and having to do a Timesert job, does anyone know if valves on Northstars like to get bent? I hear that the pistons are forged so it would be less likely that the piston has a hole in it.

I attempted to do a leakdown test but with the valve cover already off, it's hard to tell if air is going in the crankcase, and my 2HP 3 gallon compressor doesn't seem to put out enough air to have it come out the tailpipes in detectable amounts.

Thanks in advance for any advice on how to proceed!

Happy Holidays!

Yuer has

Krashed989
12-28-09, 11:37 PM
It sounds like they did the headgasket and had the exhaust cam on the wrong timing for a couple revolutions. So the piston probably bent the exhaust valves... You might want to take it down to a mechanic with a small borescope to see if there are indentations/marks on the piston from the valves. If there are then you can be sure you have bent valves.

With your method using the oil the question is, is it at TDC compression or TDC exhaust? Try turning the engine until it reaches TDC again and then do the oil test again.

tateos
12-29-09, 01:30 PM
That's interesting using oil - why not use compressed air, introduced in the spark plug hole, and then listen to where the air is escaping from?

YueIBM
12-29-09, 10:05 PM
Thanks for the advice Krashed989 and Tateos!

I took a closer look and found an exhaust bucket worn all the way through!

Does anyone know how the valve is secured to the spring? I can't see the valve stem through the hole in the bucket... thinking maybe I dropped a valve in there!

I've ordered the repair manual on DVD from a member here ($15 shipped!) but thought that you guys would also have a lot to input.

Here's a picture of the surprising sight I got:
http://img.photobucket.com/albums/v343/yueibm/closeup.jpg
http://img.photobucket.com/albums/v343/yueibm/SNV30054.jpg
http://img.photobucket.com/albums/v343/yueibm/SNV30053.jpg


Thanks again, and happy holidays!

Yue

YueIBM
12-29-09, 10:06 PM
Thanks for the advice Krashed989 and Tateos!

I took a closer look and found an exhaust bucket worn all the way through!

Does anyone know how the valve is secured to the spring? I can't see the valve stem through the hole in the bucket... thinking maybe I dropped a valve in there!

I've ordered the repair manual on DVD from a member here ($15 shipped!) but thought that you guys would also have a lot to input.

Here's a picture of the surprising sight I got:
http://img.photobucket.com/albums/v343/yueibm/closeup.jpg
http://img.photobucket.com/albums/v343/yueibm/SNV30054.jpg
http://img.photobucket.com/albums/v343/yueibm/SNV30053.jpg


Thanks again, and happy holidays!

Yue

Krashed989
12-30-09, 05:47 PM
Wow, that is one worn lifter!... I think the hole you see is just the internals of that lifter. Regardless, you are going to need a new cam and set of hydrolic lifters (GM Part #21015025).

The valves are secured to the spring in the same way as most other engines, with the little 2 piece cone that goes around the top (the name slips my mind at the moment).

ejguillot
12-30-09, 09:23 PM
Krashed,

The name for the 2 piece cone is a valve keeper, or valve seat key. :bouncy:

Do be careful if you have to remove them, if you aren't careful the spring will launch the keeper into parts unknown. This happened to me... and I ended up paying $10 for a replacement.

That worn lifter is a good advertisement for pre 2000 Northstar owners to run an oil with as much ZDDP as possible.

stoveguyy
01-01-10, 07:30 PM
a different lifter and maybe a used cam and your good to go. or pull the head? either way, you need to take off the cam sprocket/chain. very hard in a car but folks have done it.

YueIBM
01-02-10, 01:55 PM
Thanks everyone!!! And I hope your new year is heading off to a great start!

I've ordered a webcam board out of an HP laptop on eBay to put inside the cylinder to see if there's piston or cylinder wall damage. (will need to solder on a USB cable for it since it's just a webcam on a circuit board) Here's the webcam: cgi.ebay.com/HP-Pavillion-DV9000-Internal-Web-cam-for-Notebooks_W0QQitemZ230418640959QQcmdZViewItemQQptZ PCA_Video_Conferencing_Webcams?hash=item35a605703f

I think either way the head will have to come off because while I'm not sure, it seems unlikely that replacing the worn lifter and cam would solve the zero compression issue. I'm hoping a valve is burned, or a valve guide is bad, but the webcam will hopefully take some clear pictures of the inside of the cylinder.

I did a little searching and think that doing the head should be possible in-car since my garage isn't very tall or long and my driveway is on a pretty steep incline (would hate for the car to roll down while on a hoist, haha). Also hoping that it had been time-serted before since it's a 1999 with over 200,000 miles and no head gasket problem.

Here are the threads I've been reading up on regarding head replacement in-car. Most of the details are for a 99 Deville but from what I read, the engine bay dimensions are very very similar:

www.cadillacforums.com/forums/northstar-performance-technical-discussion/160216-hg-timesert-car.***html

www.cadillacforums.com/forums/northstar-performance-technical-discussion/168640-check-out-my-headgasket-job-car-4.***html

Thanks again everyone! I'll post an update and pictures when I get the webcam inside the cylinder! It could be a good alternative to an expensive borescope if it works!

-Yue

P.S. sorry about not using real links, I need a few more posts to be able to insert them. Remove the *** from the end of the URL and copy+paste.

97EldoCoupe
01-04-10, 10:50 PM
I consider them valve locks. "Keepers" is another term often used. I've seen a lifter that far gone before, that engine must have had quite a bit of top-end noise... at least at some point. The bad part is that all the metal from those lifters is now travelling through the oil system. Who knows what's all began to wear as a result. I hope the oil filter you have on there caught most of it. The factory lifters are hardened to 60 RC (Rockwell Hardness) which is a hardness similar to tool steel. It can take a long time for them to wear out but once the wear is started, it slowly starts a wear pattern and progressively gets worse. I can see the exhaust lifter next to it on the #4 cylinder has started to wear as well. You'll definitely want to change them all.

What these engines need is more oil flowing over the exhaust lifters and possibly harder cam lobes. This is all too common. With the right baffling under the cam cover I'm sure this could be achieved.

Good luck with the project, and yes I would be leaning toward bent valves or possibly incorrect exhaust valve timing. I'd have to look into it but it may be possible for the timing to be a tooth or two off and have 0 compression on #2 but full compression on 4,6, and 8. What are the pressures on 4, 6, and 8?

YueIBM
01-08-10, 03:02 AM
Thanks 97EldoCoupe!

The compression test that I ran after taking the intake off resulted in right around 140PSI for all cylinders except for cylinder 2. 1,3,5,7,4,6,8 had right around 140PSI. This was with spark plugs off, engine cold and 4 seconds on starter at 11.8V (key on voltage).

I finally figured out how to get somewhat decent pictures from my webcam board / lightbulb borescope. Attached are a few of the pictures.

It looks like the cylinder and piston are A-OK and all 4 valves are present.

One valve is hanging a little lower than the other 3. (intake cams were right on the round end of the lobe, while exhaust cams were on their sides (between round and point) I can't bump the engine anymore until I figure out how to retrieve a lightbulb that dropped inside yesterday.

The guys on this forum are right - the cylinder honing pattern is still clearly visible at over 200,000 miles!

If anyone sees anything interesting in these pics, I'd really appreciate a pointer. THANKS!!! -Yue

P.S. In pic 63, the liquid pooled up on the piston is oil - I dumped it in to test to see if the piston had a hole... and in the oil is a light bulb I dropped in.