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So this is another question about my Skoda Estelle engine rebuild project. Now it cranked and started, after a session of neither of those. To fix that problem I released the head bolts and retorqued them, and I also recalibrated the valves. It now can start but I hear loud clanking sounds, and I can't tell if it comes from the top or the bottom. It sounds like a piston hitting something. In one of the tries, after a few seconds, it kinda seized but it cranked again. If I take the rocker arma off, and the commanding rods, and the spark plugs, the engine cranks without making the sounds. Also, I don't see a bent rod. I didn't touch the timing, camshaft, chain, etc :)

UPDATE:

(Adding answers to @CcDd questions)

you sure the timing is aligned?

Well, I didn't touched anything regarding the timing, didn't even took the distributor off, nor removed the damper or took the timing chain out...

Was it banging before it seized?

Yes, it was doing the clank thing...since it could start, it is doing that

is it a bang that leaves through the exhaust port like a backfire?

No back fire, the clanking sound is inside the engine

when it had no spark plugs and you rotated it there was no weird sounds at all?

No sounds at all, without sparks and without the valves gear, i.e, naked head with only the valves and springs installed

Try starting it on 3 cylinders with 1 spark plug out then stop it replace the plug and go to the next cylinder. don't run it for long at all just long enough to hear the noise. see if one cylinder is louder than the rest or if the noise stops or changes when one is not firing.

Ok sir. I also was thinking on doing 3 cylinders at a time, for the "dead" one, remove its valve rods, so it reminds with valves closed and of course, no spark plug. That will tell us if there is a valve hitting the piston, or if the rods/followers are the problem?

Exhaust valves might be taller or shorter than intake but exhaust should be all the same and intake should be all the same. you don't have any that are too low allowing the pushrods to have too much play? one of those could be banging. Not sure how much play they should have for your engine.

The valves are almost all equal in height, only the 2 I changed seemed to be slightly taller. I will check. Should I grind off the tip of those taller than the rest?

I am assuming you are starting the engine outside of the car on a stand or something or is it in the car? if it is in the car you could pull it with another car with no spark plugs and listen but I would be simply connect the clutch at the right speed listen then push the clutch back in so you don't spin it much.

If you hear a bang without fuel such as towing the car or pulling a spark plug then the issue is mechanical where something is hitting something. It may have something to do with compression but this is less likely

The engine is in the car. I'm being assisted by another person who cranks it, then I can see things in the engine. I can't tow it, but perhaps I can jack it one side, put 4th gear and have someone spin the wheel, it will spin the engine without the starter noise and I would be able to pin point the issue?

if you do not hear a bang without fuel you may have some pre or post detonation going on.

If I crank the engine without fuel, and without spark plugs installed, I can't hear the noise...

One other thing to try is retard the spark as far as it will go while keeping the engine running. This may also stop the banging which would means its detonation. it will not make predetonation go away.

I tried that, but I was more scared than happy because the noise :( so I didn't tried for real

Was there any strange or severe vibrations coming from the engine? or was it pretty smooth? if so what were the vibrations like?

The engine was vibrating, I felt it when I was the one cranking, each banging could be felt in the body. It was really upset.

and did the exhaust sound normal or was there a strange lope or pop or anything?

No unusual noises in exhaust

and yes with compression the starter will go slower.

Yes

lastly you are getting oil pressure to all conrod bearings? nothing got plugged up while being worked on?

No that I know. I used your suggestion and super oiled everything when mounting the things back. I can't tell about oil pressure because the car doesn't have the gauge...

2

did a valve stick? when you take the valve cover off is there one that is stuck?

How did it seize up?

Is the sound a bang, a schlip, a ping, a clank. Is it sharp or long? Did you put all the conrod bearings back in?

In general which parts were replaced and refinished and what was reused?

Did all the reused parts go back exactly as they came out or are they in different locations or orientations? for example A piston backwards or a conrod that was flipped

My first guess is you have a bent valve do all the cylinders get compression or is one a little low?


you sure the timing is aligned?

Was it banging before it seized?

is it a bang that leaves through the exhaust port like a backfire?

when it had no spark plugs and you rotated it there was no weird sounds at all?

Try starting it on 3 cylinders with 1 spark plug out then stop it replace the plug and go to the next cylinder. don't run it for long at all just long enough to hear the noise. see if one cylinder is louder than the rest or if the noise stops or changes when one is not firing.

Exhaust valves might be taller or shorter than intake but exhaust should be all the same and intake should be all the same. you don't have any that are too low allowing the pushrods to have too much play? one of those could be banging. Not sure how much play they should have for your engine.

The starter tells a few things but its not going to be spinning the engine fast enough to tell everything.

I am assuming you are starting the engine outside of the car on a stand or something or is it in the car? if it is in the car you could pull it with another car with no spark plugs and listen but I would be simply connect the clutch at the right speed listen then push the clutch back in so you don't spin it much.

If you hear a bang without fuel such as towing the car or pulling a spark plug then the issue is mechanical where something is hitting something. It may have something to do with compression but this is less likely

if you do not hear a bang without fuel you may have some pre or post detonation going on.

One other thing to try is retard the spark as far as it will go while keeping the engine running. This may also stop the banging which would means its detonation. it will not make predetonation go away.

Was there any strange or severe vibrations coming from the engine? or was it pretty smooth? if so what were the vibrations like?

and did the exhaust sound normal or was there a strange lope or pop or anything?

and yes with compression the starter will go slower.

lastly you are getting oil pressure to all conrod bearings? nothing got plugged up while being worked on?


the reason for towing is you want the engine to spin at a higher rpm than the starter or someone spinning a tire would be able to do. I think even with the plugs out and the car in first gear someone would have a hard time spinning it. This will tell you if it's something not associated with compression or combustion.

running on 3 cylinders with the push rods removed is also something to try it would eliminate the bang from a valve strike. To expand on running it on 3 cylinders I would:

  1. start with what you suggested removing the pushrods and the spark plug and listening. if you find the cylinder and it is quite then:
  2. leave the spark plug out but replace one push rod. still quiet:
  3. replace the other push rod. still quiet:
  4. put the spark plug back in but leave the cable off. still quiet:
  5. retard the distributor till the engine cannot run as you probably have detonation. retarding should make the bang stop if it does not then you have pre ignition.

The longer valves are a bit concerning. is all the valve gaps checking out ok? none are riding on the cam or too large? if the valve gaps are ok you can probably leave it if it's not striking the piston head.

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    No stick valves, they open and close ok. Seize was "progressive", i.e, revving down, progressive "hum" sound :) and then stopped. It did that once only, tho. The noise is a clank or bang sound, like if when the engine is out of timing and you suddenly gas it, clank clank clank. like if you hit a filled up oil sump with a metal rod. I double checked pistons/rods/parts placement when assembling, I think all is in place. Compression is ok, blown my homemade compression tester hose :). – Aram Alvarez Nov 18 '16 at 1:15
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    Replaced: rings, liners, 2 valves (originals were burnt). I noticed: some valves are slightly tall over the springs (4mm or so), would that be? I can grind that off... – Aram Alvarez Nov 18 '16 at 1:15
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    Also: when i leave the head naked, torqued, with valves and springs only, and no spark plugs, the engine cranks ferociously :) and without the clanking sound. As soon as I add the rockers, the commanding rods, etc and the sparks, it cranks much more slowly. That's ok, we are adding load to the crank...right? – Aram Alvarez Nov 18 '16 at 1:19
  • @AramAlvarez edited my answer with lots of things to try and some questions about what the results are. – Cc Dd Nov 18 '16 at 2:30
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    So...mystery solved: the oil pump linkage somehow jumped off, the pump wasn't pumping oil, the parts didn't got lubricated, therefore noise and seized. Thanks for your suggestion to check oil pressure, I just noticed no oil in the rockers arm...then filter was dry. The noise: big end bearings got more play than a Las Vegas casino :) So I will do you other suggestion: full revamp. The crankshaft needs to be rectified, new big end bearings, I will rectify the liners for another piston set and new "black" rings. – Aram Alvarez Nov 19 '16 at 3:53

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