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Discussion Starter #1
The victim - me and my 1985 GTV6. The case (simplified):
Feb 2019 I take it to the shop and diagnosed low compression to worn right bank camshaft and oil leak from belt tensioner. Told the shop to take engine out for easier work. Heads came off and headed to specialist shop in rebuilding heads. Able to source camshaft. Shop located a mechanical belt tensioner sourced as original upgrade by Alfa (I think for 164s). Ended up changing several things which took time.
Sep 2019 engine back and fired up perfectly. Compression excellent and consistent across cylinders. A couple of minor things to take care of (might as well at this point).
Oct 2019 shop calls and tells me the engine is making a rather loud knocking/slapping sound. I stop by the shop and hear it as well. Sound like something trashing around. Shops says they will look into next day Next day sound disappears and over the next several weeks in various conditions engine has no other visible issues.
Feb 2020, almost one year to the date, I have the GTV6 back to enjoy. Runs like a charm. Most noticeably it starts instantly almost like a quarter crank, an indication of excellent compression, fuel, and ignition setting. Use it for a couple of days and then the dreaded sound returns. I have the car lifted to the shop. Doesn't look(sound) good to me at all. After a couple of days shop calls and tells me that while running to source the sound, the engine stopped and would no longer turn over. They suspected a crankshaft bearing failure, but inspection from the bottom is limited as the rear cylinders are hidden. Not much of a choice but to pull the engine again. So they did and they decided to send the whole block to the specialist shop to determine failure.
Mar 2020 there was no doubt in my mind that the engine no longer turning could only mean a piston and valve failure. Indeed to valves were found bent and two pistons with kiss marks. The bent valves also had broken valve guides. No other damage was found. Pistons, bearing, crankshaft all in good condition.
May 2020 after Covid-19 lockdown I finally have it back (2nd time). Paid twice of course.

No doubt it runs fine, but I have no certainty to the root cause and it is cause of concern. So the question or the mystery is what happened? The shop believes the failure was induced by a valve guide failure. The specialist says that's impossible because they inspected and changed guides the first time around, and valve guides do not fail that way from normal valve movement which is basically up/down and this failure is a lateral force. If so, the other scenario is that a piston hitting a valve will cause it to bend and that has consequences to valve guides. Is this latter hypothesis the right one?
Clues that we have. The slapping noise. I'm not a mechanic by profession but am fairly knowledgeable. I have never heard that type of noise so I had no experience to place it. Also I have never had an engine fail on me in the past. My knowledge merely tells me that an engine failure where a piston and valve come into contact is due to a timing distribution failure, which normally assumes a belt breaking or a chain failure. Either way it is instantaneous. That's me. The shop mechanic that listened to the sound with was well experienced and knowledgeable. Is that really the case or merely my assumption. I'm quite sure that he has seen several engine failures due to piston and valves coming to contact although presumably after it occurred. He also had experience with rod bearing failures which give rise to various piston slapping sounds.
I have read over the years many experiences that all of you have shared and two aspects come to mind. The first is that setting the timing with a new belt on the GTV6 takes patience and there have been instances where the setting was off by one tooth. Apparently being off one tooth doesn't always correlate to an engine failure or perhaps even a piston coming into contact with a valve (maybe barely). Seems to be condition that can corrected without damage. There are also accounts where the timing is perfect but then changes subsequently and this can only happen when the belt tensioner is not performing its job properly. Having gone from the original hydraulic tensioner to the mechanical one introduces a possible suspect. Unfortunately neither myself or the mechanic considered inspecting the timing at the time of the first incident as that would have provided clear evidence of the condition (as I think he assumed being off meant the engine would have stopped, not continue to run).
If the tensioner is the suspect, the question to pose is - if the timing went off, is it possible that likewise the same tensioner behavior would allow it to shift again only in the opposite way and therefore correct the situation? Maybe it is a unique situation and there is no way to prove or disprove.
At the end of the day I don't know if there's still a killer on the loose. I only know that, if I'm really lucky, it might only shift one tooth and if there is the noise, I can inspect the timing before further damage is done.
 

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Timing belt jumped a tooth. Sound was piston hitting valve ... but that does not explain why the noise went away ...

Pete
 

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Having heard several instances of valve & piston contact I sympathize with your frustration. While a large percentage of 12 valve V6 owners never experience this issue, I suggest the root cause of the "Serial Killer" is the very insufficient wrap of the cam belt in the right hand cam drive; compounded by sometimes failure of the tensioner. Depending on personal experience these conditions could either be considered design defects or they contribute to the charm of ownership.

If you want to make your engine bulletproof, possibly consider a "Zat-style" locking adjustment mechanical tensioner along with adding an offset idler pulley between the camshafts to increase the belt wrap on the cam drives and eliminate slipping a tooth or more. There are pictures of this modification somewhere on the BB and it should allow the car to be parked on a hill when in gear.

My opinions only, with just a little tongue in cheek (y)
 

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Discussion Starter #4
Is jumping a tooth only possible in one direction and impossible in the other? Maybe the former when the engine is being cranked and the latter when the engine stops? Just trying to think if my condition could ever occur albeit rare, though technically possible.
 

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We got rid of the last of our three V6 Alfas in 2003, so some people better informed may have an answer to your question.

Is jumping a tooth only possible in one direction and impossible in the other? Maybe the former when the engine is being cranked and the latter when the engine stops? Just trying to think if my condition could ever occur albeit rare, though technically possible.
 

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The one that got me 10k miles after a rebuild... The early valves are to be paired with bronze guides, the later valves with the steel guides. If you pair the early valves with the later steel guides, they can stick, which causes all sorts of damage. If you have bronze guides installed, your are likely OK, assuming the clearances are to spec.
 

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Belts don’t skip back and forth. I would definitely find a different shop/garage to do your work. Maybe your new belt tensioner has a broken spring, did the tensioner get removed and inspected after broken engine and before reassembly? Is your belt currently tight between cam pulleys? You should be able to get a finger past the covers to push.
 

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Discussion Starter #9
So, let's say the 99% the sound first heard was that of piston contacting valves and since prior everything was perfect in terms of measured compression, idle, etc, the belt must have slipped subsequently. We are then back to the question that throws it into question - how on earth could the noise disappear if no one knows of condition for this to occur? I have a '85 GTV6 and from what I could see the original guides were steel. How about a valve not lifting properly? Is that something to consider? Maybe if it were binding, but then I would think the noise would be rather inconsistent as the condition changes constantly.
 

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If so, the other scenario is that a piston hitting a valve will cause it to bend and that has consequences to valve guides. Is this latter hypothesis the right one?
Yes

Many elements of this story are mysterious to me, mainly the noise that came and went, I can't think of any explanation for that.

This I will say. I have a very low regard for the timing belt tensioner, the "Mechanical" kind that is currently installed in your car. I have two Alfa 75's (they are called Milano in the USA) with the V6 engine, neither have the "Mechanical" tensioner, and I would not have that tensioner on any V6 Alfa that I own.

Your GTV6 was originally equipped with a "Hydraulic" tensioner. When the shop rebuilt the engine they changed to the "Mechanical" kind. This is a common practice, and it is recommended by Alfa Romeo. So it is hard to fault the shop for doing that, however it is not what I would have done. You might ask them if they still have your old "Hydraulic" tensioner. If the bearing is still good, the tensioner can be resealed and reinstalled.

If you read the thread below it discusses the various timing belt tensioner for the V6 engine, and the pro's & cons of each. Both of my cars have a "Zat" tensioner. There are two problems with the "Zat" tensioner. The first is that it is no longer produced, so you have to find a used one. The second is that it uses the same bearing as the original "Hydraulic" tensioner. That bearing is both hard to find & expensive.

Recently the USA company Centerline International, began producing a improved version of the "Zat" tensioner. I will have this tensioner on my next V6 Alfa. I do not have any personal experience with the Centerline tensioner yet, but I think highly of the company.


Hope this was helpful to you.
 

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Discussion Starter #11
I've always kept my tensioners, actually have the original that was the factory install besides a later replacement. The mechanical one was most certainly an Alfa decision for economical reason rather than just technical (prone to leaks). In the scheme of things though, there were literally tens of thousands of the same engine 12V in the 164 and none for the worst for the mechanical tensioner. I would have expected stories to abound for the 164 running into issues, but apparently not. Could be that the V6 12V in the 164 has something else that is slightly different but enough to help the tensioner with any defect (in design) that it may have. Kind of nags as a logical thought.

I went through the link material some time ago, even a couple of years, as I researched various aspects. The reality is that if i had the space to work on my car, I would do so. I just have no practical way to have garage and bay areas. On my own and can take all the time, make all the musings, and keep questioning. Obliged to have a shop do work is the only practical option in my case, and to mitigate I try to have one where I can have a strong relationship with the key guy. The compounded tragedy in my case is that I did so over a year's time and was getting to the point to making headway on this problem as distribution consequence when the guy passed away in tragic circumstances, leaving me with folks who did not know the intricacies of what we were discussing.

Yes, the result of all this was also a financial impact that most would have simply junked the car, but for me a GTV6 is still a she (having owned her for more than 30 years) and as in this coronavirus time we save lives rather than letting go because it's going to cost too much.
 

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One reason for the noise going away was the shop realized what was happening, didn’t want to say anything. Reset cam timing after just to kick the car out the shop. Clearly something wasn’t right with how they did it the second time.
Who knows, belts don’t unskip and those noises don’t just go away. Especially considering what the end result was.
 

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Unfortunately on the 2 valve Busso v6, belts do just skip teeth (but I do not know why). While I have never owned one, I have had to reset the distributor timing on one that just one day decided to jump a tooth. Luckily the camshafts were not involved in this drama, just the distributor timing. Reset the timing, car drove perfectly and off into the sunset

Pete
 

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Discussion Starter #14
Well, that the belt would jump can only done with human hands...not impossible, not improbable. Certainly paints a desolating picture and means assuming everyone in bad faith. Guess I tend to see with glass half full. If that were the intention to reset timing, wonder why the head mechanic had me come in to hear the noise? Wouldn't it have been easier for him to take care and me none the wiser? As he didn't work on the engine directly, just supervising, maybe it's the other mechanic and we were both duped. This is possible.
 
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