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Stan,
Thanks for the input, seems like we have a small group of aviators here: you, me, Tony, Wisconsin Joe (and probably some others). From an aviation maintenance perspective, this makes perfect sense to me. Not that I'm discounting anything, but at this point I'm at borderline over what to do with this car. Do I fix it, part it out or sell as a project... I really don't have the time to deal with it right now, but ironically, I literally have all the parts on hand to fix it (I just cannibalize that parts from the Koenig motor - which is on a stand - but that's another story).
Dr Bob,
No offense taken at all, she's been a daily driver for 23 years and has served me very well. But as they say, some things in life tend to happen at the same time, and that's definitely me right now....so here I am debating what to do. Just can't bring myself to get rid of it, at least not yet. At the very least, my ex didn't get her way with the car so that's a plus
Back to topic, the pictures below show where the cam gears stopped when the T-belt teeth were stripped. The engine, of course, was cranked over many times with them in this position before we noticed the crank gear ate the teeth.
Do the compressed-air leak test if you can. It's pretty definitive, if your hearing is decent. There are "real" leakdown testers available pretty cheap, but the basic air in the cylinder test will do. Many local parts stores wil rent or free-rent (get your deposit back) things like compression gauges like the one I have, so you'll need a mating connector and a small air compressor with a pressure regulator on it. I'll grab a picture of the gauge fitting if it will help.
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Your compression numbers are low but pretty even, and probably consistent with the miles. A "real" compression test is done with engine warm, as a cold engine may not have the lifters pumped up and/or pistons expended to normal size in the holes. Bottom line is that I have more faith in your warmed-up numbers than the initial cold numbers, if that helps.
When we did the compression test on mine, I had good compression in all cylinders but 1. There was no readable compression on it. When I pulled the head, it was not obvious that the valves were bent. Just some areas where carbon was knocked off of the valve. I still have one of the valves on my desk. Very slight bend. Ended up replacing the two exhaust valves and was good to go.
Your compression numbers are low but pretty even, and probably consistent with the miles. A "real" compression test is done with engine warm, as a cold engine may not have the lifters pumped up and/or pistons expended to normal size in the holes. Bottom line is that I have more faith in your warmed-up numbers than the initial cold numbers, if that helps.
One more thing --
The protocol for a good compression test has a charger on the battery so all cylinders see cranking at the same speed. All the plugs are out. The engine is warm/hot. The throttle is propped wide open. Pull the EZK (ignition) fuse to kill spark and fuel flow at the same time for the testing if you are cranking the engine with the key in the ignition.
Having other plugs installed or the throttle not wide-open can easily give you false low readings.
Stan,
Thanks for the input, seems like we have a small group of aviators here: you, me, Tony, Wisconsin Joe (and probably some others). From an aviation maintenance perspective, this makes perfect sense to me. Not that I'm discounting anything, but at this point I'm at borderline over what to do with this car. Do I fix it, part it out or sell as a project... I really don't have the time to deal with it right now, but ironically, I literally have all the parts on hand to fix it (I just cannibalize that parts from the Koenig motor - which is on a stand - but that's another story).
Dr Bob,
No offense taken at all, she's been a daily driver for 23 years and has served me very well. But as they say, some things in life tend to happen at the same time, and that's definitely me right now....so here I am debating what to do. Just can't bring myself to get rid of it, at least not yet. At the very least, my ex didn't get her way with the car so that's a plus
Back to topic, the pictures below show where the cam gears stopped when the T-belt teeth were stripped. The engine, of course, was cranked over many times with them in this position before we noticed the crank gear ate the teeth.
Now, that's a WORN belt! Look at the gap between the cam gear and the teeth in the first picture. You got you money's worth from that one!
Your compression numbers after running the engine are....fricking amazing. It sounds like you knocked a bunch of carbon loose, generally pissed off the engine, but didn't bend any valves. (Bent valves are not going to "heal" themselves.) Go buy a lottery ticket!
I am, amazingly enough, really very conservative (except when it comes to engines that can not be replaced.) I only take things apart when there is a damn good reason.
Your cam gears do not look awful, from what I can see.
I'd make sure the oil pump gear is good, string a new belt gates/factory belt, and run it!
Check the compression again, in a few thousand miles. If as good as what you posted after running it for a short period of time....forget it ever happened and spend your time on something that needs it.
Now, that's a WORN belt! Look at the gap between the cam gear and the teeth in the first picture. You got you money's worth from that one!
Your compression numbers after running the engine are....fricking amazing. It sounds like you knocked a bunch of carbon loose, generally pissed off the engine, but didn't bend any valves. (Bent valves are not going to "heal" themselves.) Go buy a lottery ticket!
I am, amazingly enough, really very conservative (except when it comes to engines that can not be replaced.) I only take things apart when there is a damn good reason.
Your cam gears do not look awful, from what I can see.
I'd make sure the oil pump gear is good, string a new belt gates/factory belt, and run it!
Check the compression again, in a few thousand miles. If as good as what you posted after running it for a short period of time....forget it ever happened and spend your time on something that needs it.
Thanks Greg, I appreciate it!
What do you think about the slight wobble with the driver side cam? (was not there previously)
See video:
look at the tip of the rotor it appears to also be rubbing on something,
the snout of the cam is definitely bent . so either someone has been prying on the cam gear to remove the pulley,
or its snapped and the bolt is still holding it in position for it to run.
At the very least I would remove the pulley and and bolt to investigate if the snout comes off with the bolt
the pulleys being worn are part of the reason the belt looks the way it does and the wobble of the cam pulley will also wear the belt .
The scratch marks on the rotors were from a scotchbrite pad when we were cleaning and troubleshooting, it wasn't rubbing, but everything was caked in a real fine black dust - which was the t-belt. They're gonna get replaced anyways.
I've got a good set of used s4 cams I can transplant in... (then I can finally break out the gt cams I've had forever for the other motor)
At the risk of going pear shaped with advice again, but having the similar failure mode, I think you need to find out why the cam gear is wobbling. Cams are so very brittle. It's hard to believe one could bend at the snout and not break entirely, or at least have fretting at the cam gear mating edge. Maybe put a different cam gear on and see what it looks like? Since you have cams, and it's not a hard job to do, repl the cams and new gears.
I think you have somehow avoided the dreaded bent valve. I know I avoided it when my cam broke by sheer luck as the lifters were not pumped up, and the cam stopped in a very special position. New belt path parts, and away you go!
As for having 300k miles, these engines operate typically at around 20-25% of rated power most of the time. If taken care of well with good oil and not overheated, a half million miles or more on an S4 engine is no trouble at all. 300k miles is 'broken in' for the S4.
PP-ASEL, ASES, IR, TW, CPLX, HP, Acro. ~2400TT. Currently motoring a Bonanza D35 around the blue for fun and profit.
I agree with Stan: too much cam gear wobble. But, I also agree that cams don’t bend. So... problem with the gear, bolt, or the ‘spider” behind the gear.
Inspection of the original belt damage tells us that the teeth on the belt sheared around the crank sprocket and then there was no drive for the cams or the oil pump. The $64 million question is what caused the failure? Did the belt fail because it was well past its sell by date or did it fail because of some force acting on it? I know from practical experience that if the belt fails whilst the engine is running down [or more likely is at idle speed] then at least two valves will fail on the 32 valve interference motors [mine fubarred two exhaust valves on No 7 cylinder after my late S4 crash and they subsequently would not support any test pressure at all.
This set me thinking as to how or why this S4 motor seemingly has dodged such a bullet. Could it have failed whilst cranking? Now we see the cam sprocket is clearly a bit wonky so what could have caused this to happen? One would expect the valves to deform before anything else threw in the towel.
The only scenario I could think of was if something somewhere jammed the belt onto either the oil pump sprocket or one of the cam sprockets causing resistance that in turn sheared the teeth on the belt. Given we have a wobbly cam sprocket perhaps a closer inspection of the item and the point of contact with the belt might reveal something interesting?
Yes it failed while cranking. I remember turning the key over to start it, but for whatever reason I didn't engage the starter long enough (which is unusual for me). So I hit the starter a second time and it never fired up, have no doubt that's when the crank ate the teeth at that point. Perhaps there was a bit more pressure/tension/whatever on that driver cam after the missed start, combined with other missing teeth it's possible the timing could have been slightly off, and when the engine 'hiccuped" on the missed start it bent the cam snout, I don't know. I gotta dig more into it.
There was nothing jammed or obstructing the t-belt circuit, but based on what I saw on teardown, I think the sharp edges on the cam and oil gears shortened the t-belt's life rapidly. You can almost cut your finger running it across the gear ridges. Looking closely at the remaining t-belt teeth, almost all of them are at some stage of being cut off. Scary.
I think you should consider the belt damage prior to the teeth shearing.
looking at the belt side view its clear that the teeth have all been worn down and this process will take a while to reach this level,
the teeth dont fill the belt hole on the pulley,
thus their is an extra force being added to the belt run.
Its quite possible the gears in the belt run are also quite worn and or the wobbling cam pulley could also be part of the reason.
NOTE by finding the area with the most belt dust the area just prior to this will be the area of the belt run thats been causing the belt to wear
03-26-2019, 12:50 AM
