The extreme explosion was most likely the result of fuel and fuel vapors seeping into the engine itself and into the exhaust pipes at the exhaust manifold/exhaust couplings. Fuel vapors ignited within a contained area will be magnitudes more forceful and louder.

 

You mean outside the engine?, The only way I imagine inside the engine is fuel accumulating into the cylinders and being expelled through the exhaust valves to the escape.

 

You get a good vacuum reading yet?

 

Not yet, I will do it in the afternoon.

 

While you’re at it, if you have the correct fitting check your oil pressure.

 

Raul - I must leave for the remainder of the afternoon until later this evening.

Some guidance:
(1) Understandably you don't wish to compound an issue for which you have no resolution and cause further harm to your engine. You don't need to run the engine very long to take both the oil pressure test and the vacuum test. Use your better judgement - run the engine for a short duration. You have been running it with apparently no adverse effects thus far taking videos and troubleshooting flexpate/starter/converter. I think you'll be fine but be cautious and run the engine for a short duration.
(2) Regarding vacuum. One of the important considerations to look for is the vacuum gauge needle should NOT violently and erratically jump between 14" Hg - 17" Hg - look for a steady vacuum needle and record findings. Hopefully, you will have a steady vacuum of ~17" Hg - 22" Hg.
(3) Take the oil pressure reading directly from the oil sensor port on the engine. Remove the sensor, insert your pressure gauge and begin the recording IMMEDIATELY during the first crank of the engine. You should see the needle rapidly swing to a high reading and then swing back down to a much lower reading - generally about 10 psi is what we're looking for. At a minimum you need at least 5 psi during idle operation (hopefully higher). If you have NO oil pressure after one minute of operation, turn off the engine - you have an oil pressure issue and running the engine further can cause more serious damage. If you have a minimum of 5 psi or greater oil pressure at idle for one minute, it would be my suggestion you won't provide any further damage to the engine with regards to the ability to provide oil lubrication during further troubleshooting. At this point we'd like to know if you do, in fact, have oil pressure in the engine.

Best of luck.

 

Attached is the vacuum test, look stable around 15.5 and 16 inch. First thing of the day I raised the other wheel so know that car is leveled support by two stands. The surprise is that in this position the loud metallic noise becomes erratic, goes and comes!, but after some warm up the engine stopped with an awful sound like engaging something. If you happen to listen to the whole video of the vacuum test you will hear the original noise, maybe more metallic and not so loud, coming and going. Some runs I made today (all short duration) no more than one or two minutes where without the original noise, but most of them stopped abruptly with this engaging noise, like friction with something. How the inclination change the behavior or which is the origin and cause of the sudden stop with the engaging sound is beyond my knowledge, as always suggestions are more than welcome.

I did a final cleaning and inspection of the Flex Plate, all within the limitations of my position, and I couldn't saw any flaw or fracture at all. I couldn't record the wobble of the Flywheel but if someone can look at one of my first videos of the Flexplate, they are there, have no clue if that is acceptable behavior or the FlexPlate is deformed. I did not remove the Starter because after looking again closely there are no signs of contact within the starter and the tooth and the pinion when retracted is far away from the Flexplate, possibly half an inch.

BillK; I was trying to reconnect the converter to the FlexPlate and I am finding difficult to pull the converter to come in contact with the Flexplate!. What I can do is use the bolts to join the pieces, by hand adjusting all 3 of them, and then tight, lets say one turn, in order, until they match. I began carefully to do this but it looks the Flex is flexing but not the converter, is ok to do this? or else.

Thanks as always

 

Not really. You should be able to slide the torque converter forward fairly easily until it hits the flexplate. The flexplate should not be flexing. It sounds as though the front of the torque converter is not sliding into the back of the crankshaft easily like it should.

 

Where is the oil pressure test?
The vacuum needle is only slightly swinging within a 1" Hg - 2" Hg range which is OK. It should be spot-on rock steady. I suspect perhaps whatever line you used to take the test you didn't plug one side of the line and you're getting a slight swing perhaps. Generally, it's best to use a "T" in the line during a vacuum test.
The original sound is nearly negligible in the last vacuum video - it can barely be heard except in only a couple of places. It definitely is not as pronounced as in previous videos.
The flexplate should not be flexing at all - absolutely no flexing of the flexpate and in particular no flexing of the flexplate with the torque converter removed.
Without an oil pressure test you're risking knowing whether further engine damage might be occurring while running the engine - that's your decision.

As Bill stated the torque converter should easily slide into the flexplate. Since you removed the torque converter from the flexplate the only video you have recorded is the last video where you measured vacuum and in this video you can barely hear the knocking jack hammer noise. My guess is the issue resides with alignment of the transmission to the engine: (1) The engine motor mounts are mounted into the incorrect mounting holes and possibly the motor mounts are located on the incorrect sides (2) The motor mount on one side is located in a back frame mounting hole while the motor mount on the other side is located in a different mounting hole (I believe there are three holes?); (3) The engine did shift at some point in time and your alignment of engine to transmission is misaligned. It might have been misaligned from the very beginning; and unlike what Bill suggested in a previous post where he suggested he would find it difficult to believe it just happened all of a sudden, I tend to disagree. The motor to transmission was so misaligned that for a period of time when you were running the engine you got no noise - but, as time moved forward that flexplate could not withstand the continual misalignment of the engine to the transmission and something had to break and it did - the flexplate broke or something in that area broke, or became terribly pinched and I don't know what. But at this point, with no torque converter attached, the fact you can't align the torque converter to easily slide into the flexplate and you can barely hear the jack hammer noise except in a couple places my suspicion is you have a misalignment of the engine to the transmission and you've had that misalignment for some time and something placed enough stressed on this misalignment until it finally "gave up".

 

If I were to make a wager (and expect to win), I'd bet you have not a cracked flexplate, but instead a broken flexplate. Regardless of whether you can't see it - that flexplate needs to be removed and evaluated.

 

Here's what a worst case scenario broken flex plate looks like. You're most likely somewhere between the worst case scenario and a not (yet) worst case scenario. Read Post #72 by gs72 the crack (or complete break) might very well reside around the crank circle of the flexplate (which you probably cannot visualize unless you remove the flexplate). Once you determine if in fact the flexplate is cracked and/or broken, you need to address how it became cracked/broken. Sorry, but my bet is still on the flexplate itself.

 

Vintage Chief:

Oil pressure test was not done because I do not have the fitting, as soon as I get it I will do it.
You guessed wrong, the vacuum test was through a direct, single hose connection to the intake manifold. The fluctuations are in no case more than 1 inch. I will say .5 inch around 16 inch. This result, along with the compression test, which was uniform on all cylinders at 150 psi, will be for the moment enough indication to rule out the valve train?

Not sure why you are saying the Flexplate should not flex, if this is because of my comment to BillK regarding my issue connecting the converter, then the Flexplate is NOT flexing. I meant it flex because while beginning tightening the bolts to the converter the converter won't move but the flex plate approach the converter by flexing. The only behavior the Flex plate has a wobble which once again I do not know if that is acceptable or not. The flex plate is in NO WAY BROKEN as the video you send showed, also not visibly by eye fractured. I spent an hour today cleaning and inspecting all the Flexplate and couldn't find a glitch, I have plenty of photographs i am not sending. Distorted : Possibly, Broken : Definitively Not, Fractured : Very unlikely.

Engine and Tranny are joined by the bell housing so I do not see any possibility of misalignment between them because of the motor mounts (BTW you are guessing I switched them but its very unlikely). I did not remove or even touch the bell housing bolts ever except the only one which is used to hold the fluid level pipe. If they are misaligned they were already misaligned previous all my work. At this moment of time the tranny is decoupled from the engine and things look pretty bad (I will elaborate later) so for the moment neither the tranny nor the misalignment can be a cause. The only thing left aside the engine is the wobble of the Flexplate alone. Please feel free anyone to correct me if I am wrong here.

All:

With the tranny out of the picture I wasn't able to run the engine steadily for more than one or at most, in one case, two minutes. The hammering noise comes and goes and then the engine suddenly stops with an awful grave sound, like engaging with something.

One thing i did yesterday was check the timing because I felt it was wrong and I saw a behavior which I believe is not correct, With the vacuum advance off and blocked i measured 7.5 degrees which was my setting based on the CSM but when i connect the vacuum it comes to 0 degrees. I believe this is not correct at all. I was expecting the vacuum advance to increase the advance not to decrease it. Can someone elaborate?. My distributor is not the stock one but a Mallory Unilite.

Regards

Raul

 

Forgot to mention timing on the previous message was measured at around 600 rpm. When I set the timing initially i do it at 850 rpm according CSM.

 

Raul,
This should not be happening. You should be able to easily push the converter up to hit the flexplate. You should not have to pull it up with the bolts. If you cannot push the converter all the way to the flexplate by hand then something is wrong.

By the way, it is very rare for a stock flexplate to run absolutely true. They almost always have a little bit of "wobble" to them. This is especially true for flexplates with a weight welded to them like an Oldsmobile.

 

Norm,
Engine mounts and transmission mounts have absolutely nothing to do with the alignment of the engine and transmission. The engine block has two large solid dowel pins that go into holes in the front of the transmission case to align the two. Unless the dowel pins are missing for some reason it is hard for the engine and trans not to be aligned properly. Only thing else would be if maybe something got caught between the two and is not allowing them to bolt together solidly.

 

Tx BillK, i was aware of your concern, I will leave this issue till we found where the problem is, I do not need to reconnect the tranny anytime soon. Regards. Raul

 

With the original

 

Bill - Understand regarding the dowel pins - if they're in there.

 

 

What part of your 1966 425 has never been touched?

 

Raul - It is not my intention to become vindictive or spiteful with you, but I am afraid it is has become difficult for me to continue to assist you since I'm growing apprehensive in my abilities to make useful suggestions to further assist you. Your statement "Original, never touched 1966 425" is not true. Someone has worked on this car and I continue to read more and more interjections regarding previous work which counters your statements regarding "original, never touched 1966 425". I have become very confused and I do not wish for this to become a fight about who said and what was said. Therefore, I'll take ownership for my actions by calling you out on the statements you have made which demonstrate there is more to the spoken word than resides in the statement "original, never touched". I don't know where your issue resides, and I sincerely wish you the absolute best of fortune in finding resolution. I believe you're most likely a good person, but I've lost faith in my own abilities to assist you and it's going to wear on the both of us.

La mejor suerte para ti mi amigo.

 

Norm:

Wow!, you are decidedly right, my initial statement was inaccurate, I stand corrected: "Mostly Original, never overhauled 1966 425 Engine". My sincere apologies to anyone mislead by my statement, it was probably a consequence of the excitement of the hour, my native Spanish speaking influence and my initial abduction of the hypothesis it is a major fault of which I am pretty sure nothing significant has been made to the engine. Always the intention was to qualify the engine and not the entire car since it is pretty obvious a lot of work is being done by me on it. Please understand it doesn't make sense for me to hide anything, it is my best and only interest to solve the problem, Which will be my gain hiding info?.
I do tend to notice your diagnostic approach was usually biased first to what I may have done wrong, which is under-stable to a point but not to the extent to become fixated on a cause even the facts, the logic and the observations point to the contrary.
I do thank you so much for all your effort and again you are right about in wishing good luck!.

On another note, I will thankfully be silent for a couple of days, since I have remove the distributor and carburetor, I will probably replace the distributor with the original since I have lost confidence in it, the carb needs inspection also. I am ruling all the things I know so i can start fresh with the engine.

Best Regards to everybody, happy Weekend. Raul.

 

Gents: Just an update for all of you still interested on this issue. The Unilite distributor was working just fine and since the OEM has the vacuum break broken I did not replace it. I do check the carburetor and found a couple of issues: Tip of needle all metal no rubber and power piston broken in four pieces, replace both items, adjusted the float and put new gaskets in place. It took a while to adjust everything but finally I had it running again, timing is +7.5 without vacuum and around +17 with vacuum at 800 rpm. I am attaching a video. You can hear the loud knocking engine is so far gone but doesn't run stable for too much long, it sputters sometimes and it is somewhat rough, I am finally going to take out the tank, clean it, inspect and repair the gas sending unit which it is stuck at full and add again new fuel in order to rule out another source of trouble. I have one valve cover off, and I noticed oil coming from the rods is uneven between them, some of them even sputter oil beyond the cover and others look dry, all of this after no more than 5/7 minutes of running. I have not being able to get the fitting for oil measurement. Also please notice the screeching noise the engine has when starting or accelerating, I thought initially it was the only belt still in place, I tighten it but the noise is still there. Any comments will be as always highly appreciated. Please note the car is still running with both front wheels on the air. After finishing with the tank I will run it again with and without both wheels in the air and post the findings. Best Regards. Raul.