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Sudden total compression loss
05-19-2011, 09:27 PM
hey everyone i have a customer with a 93 scort with the 1.9L engine. He was driving one day and heard a loud bang. The water outlet hose to the radiator blew off. Then continued to drive home :screwy:. He had someone reconnect the hose and top of the fluids but then when going to restart, it has that distinct sound of no compression. Y'know the one. So i first run a compression test, not one pound of compression on any cylinder. I didnt bother with the wet test.
Timing belt was intact and all valves functioning freely. So i pulled the head and the cylinder walls are in great shape. Very smooth and i almost think i can still see cross hatching. The gasket doesn't appear blown. There is one spot where it looks thinned but its not even near anything important. I did however find two small cracks between the intake and exhaust valve. It appears to be seat to seat. But this is still in only 2 cylinders. There is nothing to explain compression loss in 1 and 4.
So Im thinking its gotta be in the timing. I wish i had thought of it before i pulled the head:banghead:.
So anybody have any other thoughts? I would appreciate any advice.
Also can anyone tell me about special tools to help with the timing tensioner? whats the best thing to pry it over with? Anyone have specs on the tensioner spring free height?
05-20-2011, 09:02 AM
Are you talking about the radiator hose that goes to the water pump? If so, then I'd say the antifreeze lubricated the timing belt causing it to slip and jump time.
Be careful with prying when you set the belt tension. It's easy to get it too tight. I've done it before. I think the book says to loosen the tensioner, rotate the crank shaft two complete turns and then tighten. The spring in the tensioner is supposed to adjust the tension and (theoretically) doesn't need any extra help. :2cents:
05-20-2011, 09:05 AM
no its the upper hose, the one on the opposite side of the block. Good theory though, anitfreeze can get a bit slippery.
OK so i verified the timing. Its lined up perfectly. Still no compression. So i removed 2 rocker arms effectively closing off both valves for the number 3 cylinder. Still no compression. After setting the timing it certainly sounds better. Not the way it was before. I even put a balled up napkin in the sparkplug recess (not past the threads mind you) and it was able to shoot it out. Next i opted for a wet test. I really gave it some oil because at this point im 95 percent sure the head will be back off anyway. No compression. I have recently tested my gauge on my car to eliminate the possibility of a faulty gauge and i got good numbers. '
So to recap:
No compression at any cylinder. Wet compression yielded same results.
Engine is timed.
All valves and rockers functioning.
Head gasket still in tact. No water in cylinders or in oil.
Cylinder walls are in great shape. No scores whatsoever.
Removing rockers had no change.
Eye balling head and deck appears flat. Obviously not conclusive by any means but if there was warpage bad enough to loose total compression on all cylinders, it should at least be something you can see.
Mechanic really stumped.
05-20-2011, 12:52 PM
Long shot but a completely blocked air intake might cause these symptoms.
05-20-2011, 01:06 PM
The intake manifold is completely disconnected from the head.
05-21-2011, 08:15 AM
Very interesting. If the timing is set and the valves are working then it seems it would be worn out piston rings. When you're cranking it over I wonder if there's any pressure coming up through the PCV valve? That would indicate excessive blow-by. Other than that this makes no sense :banghead:
05-22-2011, 08:07 AM
I agree its likely to be the compression rings got damaged/softened by the heat. What else could it be? I would wonder how long after he heard the bang before the engine was shut down. (like; how many seconds?) I would think driving even half a mile would be too long.
Its normal to still see the crosshatching on 1.9L blocks, even after 200,000 miles, except for the last 1/4" at the top of the 'sweep' of the rings; but be sure to rehone it before re-assembly, or the new piston rings wont seat for a long long time - and will use up a LOT of oil. I also find there is always a good bit of crud to scrape out of the bottom of each ring groove.
And if the compression rings got softened, I would make sure the pistons are still free to flop back and forth on the wrist pin. If the pistons were near melting temp, and changed shape, they might be binding on the wrist pin - and the rod will fail in the first couple of hundred miles.
Incidentally - to get that darned lower radiator hose back onto the water pump inlet, I do it with the accessory bracket -off- of the engine. I cant manage it any other way. Maybe Im just not strong enough (being 66). Also with the acces. bracket off and the other things not being in the way, I can get the OEM spring clamp back onto the lower rad. hose.
In my limited experience I have never had a spring clamp come loose, but have had such problems with the screw clamps. So with screw clamps I snug the screw, not trying to tighten it enough to destroy it. Than about 3 days later I resnug the clamp, and again after about 2 weeks. Each time the screw will be easy to snug up again - as the hose has relaxed from the heat and pressure. That way I can be sure the hose wont leak or come loose, for the next ten years.
The down side of this is that to be able to reach the screw on the clamp on that lower radiator hose - where it goes onto the water pump inlet, I have to remove the serpentine belt tensioner assembly. Of course this is easy for me to say, being a hobbyist, retired, and who needs the exercise anyway. A mechanic has a lot tougher situation to deal with. (the public).
Also, if the pistons got hot enough for the rings to soften, I think I would get a rebuilt head. A crack between the two valves isnt necessarily a head killer, but it is likely to eventually propagate to where it will open into the water jacket -- even if it passes a pressure test right now. A rebuilder would remove the valve seats, weld up the crack, re-machine the valve seat bores and install oversized ones, etc. I would be curious to know how much warpage there was on the bottom surface of this engine head. Did you use a straight edge to measure the 'hump'. I think the book says to mill it flat if there is more than .006" at the worst point - which is commonly between the #2 & #3 combustion chambers.
Before reassembling a head, I would personally make certain the rollers on the bottoms of the lifters are spinning freely, and well oil. The head cleaning gear at the machine shop can clean out the lube on those needle bearings, and a few days later they might be reluctant to turn.
I had to get one block milled .007". There was enough corrosion at a previous blown head gasket location, that even though this was a running engine, the replacement gasket was showing signs of failure. The engine probably sat for a few months or longer with the coolant still in the block.
I hope you will feed back any more info you find. Any problem with that Escort is one that could happen to one of mine someday. I have three 2nd gen. LX Escorts now, am looking for another 5-speed to buy and fix up. We get 41 mpg on the open road with our 94 5-speed wagon, & 37 mpg with the automatic trans in the 93 sedan.
05-22-2011, 06:38 PM
well in all honestly i hope the problem is the rings. I will get more hours out of this job that way. Fortunetly for my customers i work very cheaply lol. If the rings were bad then the wet compression test should show some improvement over the base CT (compression test). I will check that as soon as possible. Also, where exactly would I find the PCV? I dont have the car on hand to do a search. As soon as I get more info I will certainly be back to give updates.
denisond3 (http://www.automotiveforums.com/vbulletin/member.php?u=501512): very good info. I appreciate your input!
05-22-2011, 08:00 PM
The PCV valve is stuck into a grommet on the end of a metal tube item that is bolted to the front side of the block (behind the exh. manifold), and extends up diagonally to the right, being visible just to the right side of the exhaust manifold close to the head. From there it has a short piece of rubber hose on it (usually pretty wasted), and goes into a black plastic tube that runs up to the top of the throttle body. At least that is how they were manufactured. It has a right angle rubber fitting that feeds the crankcase vapors into the intake. The right angle rubber fitting is usually pretty well deteriorated too, sometimes replaced with a chunk of rubber hose.
The Ford dealerships used to sell the entire PCV plus the rubber hose, plastic tubing and rubber 90 degree fitting, as one part - for about $20. They didnt sell the pieces separately.
I thought of another thing to check; make sure the valves on the cylinders with very low compression are really closing. Maybe putting an adapter in the spark plug hole, and pressurizing the cylinder, to see where the air hisses out. I just thought it might be that there are a couple of valves that are not closing fully; either because if misbehaving lifters, or ?? Though if that is what happened, it might be the first time for an Escort 1.9L. I had a valve bend on the engine in my little airplane, a 46 Aeronca 11AC. I dont know why it bent, I dont think I ever overheated it - an exhaust valve just bent; so very low compression resulted.
In the last year there was a gent on the forums who had a camshaft snap in two. There wasnt any reason he could tell, or at least that he told us, and we couldnt understand it either. I believe it remains a totally unique failure. The Escort cams are hollow, for distribution oil to the lifters/rockers; but not known for breaking.
05-22-2011, 09:26 PM
I thought of another thing to check; make sure the valves on the cylinders with very low compression are really closing. Maybe putting an adapter in the spark plug hole, and pressurizing the cylinder, to see where the air hisses out. I just thought it might be that there are a couple of valves that are not closing fully; either because if misbehaving lifters, or ??
Maybe to test the exhaust valves, I will remove only the exhaust rockers. This way the intake will still open and let air in. If the ex valves arent closing fully due to the lifters or cam related then I may get a diagnosis there. I will try this tomorow after my real job.
Unfortunetly, I dont have access to an air compressor. So while that would certainly help, I will just have to use the pistons to help show me where the air is escaping.
05-26-2011, 03:56 AM
Hmm... seems you would have found it by now, but is it possible there is a leak around the spark plugs?
Are you certain the starter is engaging the flywheel?
Have you already confirmed correct timing?
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