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Broken Timing Chain

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roscoe

Jedi Knight
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So today was the Almond festival in the Capay Valley near where we live. Beautiful almond orchards in bloom and food, vast numbers of motorcycles, custom and antique cars up and down about 17 miles of countryside. My wife and I had a great time and when we were about 5 miles from home there was a brief scraping/ rattling noise, sounded like something might have been caught under the car and rpms went to zero and I coasted to the side. The engine cranked fine, perhaps a bit faster than normal but not a hint of firing.

Long story short, as I suspected the timing chain broke. No valve train motion when cranking. Given that there were no horrible noises, I'm guessing that in our 4 cylinder cars, the valves do not ever touch the pistons when the cam becomes disconnected from the crank gear. Does anyone know this to be correct? Im just wondering what I'll find when I get everything taken apart. I guess it depends on where the valves were when the chain broke but I'm assuming some valves were depressed fully or partially. No unusual sounds when cranking after I got it home. I'm figuring on at least a new cam gear, crank gear and a chain, perhaps a new cover if there is damage.
 
FWIW (but it did mention a timing 'belt'). Not so for the 6-cyl engines, unfortunately. I'll be interested in what you find, like did the rubber 'tensioner' degrade and fall apart?

Interference.JPG
 
Thanks. That was my guess but who thinks their timing chain will ever brake. I should have added that for a while I've noticed an intermittant " tick" at idle which I assumed was excessive play in the chain. I really was going to get around to addressing it. Could have been worse. Close to home was kind of nice.
 
Jon--

So sorry to hear of your difficulty. and I hope you have no further damage than what first appeared.

A couple of years ago while changing the oil I saw what appeared to be a lot of hard plastic bits in the drain pan. When I dropped the sump I saw that in fact they were the remains of the timing chain tensioner which had broken and made their way down into the sump--which explained the unusual rattling noise I had been trying to identify for a couple of thousand miles!

Installing the new chain and tensioner with the engine in situ was not easy as getting the front pulley onto the end of the crank with the woodruff key started into the slot seemed at first an impossibility, but after a number of attempts it just happened, and from there on the job was pretty simple. I took the opportunity to install the front cover stifener sold by BCS.

Good luck and keep us posted.
 
Should you decide to replace the gears--crank or cam, or both--be advised the original cam gear had a metal plate riveted to the gear (I've heard it called a 'slinger,' Moss calls it an 'oil catcher'). To my knowledge, none of the suppliers have this type of gear, they just offer a gear without the slinger. Moss says they supply the rivets with which to transfer the slinger. I installed mine without the slinger with, so far, no adverse effects, but I only have a few hundred miles on the engine.
 

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Thanks to all. I'll be replacing both gears, tensioner, chain and some other bits. As has been asked and answered, the 4 cylinder engine is not an interference design so valve damage is not likley. I have everything off but the timing cover and I'll get to that tomorrow. I'll do a differential compression check when I adjust the valves prior to running. The hardest part so far was getting the lock washer unfolded off the crank nut. I kind of overdid that all those years ago thinking I'd never have to un do it.
Thanks for the reminder about the riveted slinger. I can handle removing the old one, assuming it is intact, and I'll install it on a new gear. Pictures and further details tomorrow. Don't ignore timing chain noises.
 
Here are the pertinent images of my timing chain failure. All pieces accounted for. Crank gear shows some tooth damage and some gouging is shown on the bottom of the timing chain cover. I think it is useable, I'll probably replace the seal and hammer out what I can. The cam gear looks good but I'll replace it as I'm pretty sure it is original and likley worn.
 

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One more photo. On looking at the cam gear off the engine, there is some damage and excessive wear visible. 8k miles ago it looked good enough for me to use.
 

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I have a completely rebuilt engine. About 800 miles on it now. 02.18.25 I was driving to a British mechanic to work on the tranny/OD. 88 miles into the 200 mile drive, engine made some studdering, no loud noises. I pulled off the freeway. On the side of the freeway, Engine would turn over, wouldn't start. With the mechanic on the phone, spent about two hours trying things. Ended up getting towed to mechanics place. Next morning, finds out timing chain related damage. Lots of broken parts. Mechanic has been speaking with the machinist trying to figure out what happened.
 

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AUSMHLY said:
I have a completely rebuilt engine. About 800 miles on it now. 02.18.25 I was driving to a British mechanic to work on the tranny/OD. 88 miles into the 200 mile drive, engine made some studdering, no loud noises. I pulled off the freeway. On the side of the freeway, Engine would turn over, wouldn't start. With the mechanic on the phone, spent about two hours trying things. Ended up getting towed to mechanics place. Next morning, finds out timing chain related damage. Lots of broken parts. Mechanic has been speaking with the machinist trying to figure out what happened.
Click to expand...
The cam locating plate (Moss 031-210) is obviously broken and the tensioner (Moss 011-139) looks doubtful (the spring). If the cam locating plate broke, the cam can move fore and aft, which would put a side load on the timing chain and may cause the tensioner to come apart. When the tensioners come apart, everything else gets trashed. The tensioners have the reputation of being the weak link in the timing chain system.
 
I replaced my timing chain a few years ago, with the engine in the car. The worst part was trying to get a new tensioner installed - once the tensioner was installed, it was nigh near impossible to get the timing chain installed. The advice from several folks at that point was to forget the tensioner and run without since its such a weak link. . . which I did. There was no tensioner when I took things apart. Any updated thoughts on deleting the tensioner?
 
I have a tensioner ring installed, and it was actually in pretty good shape when the chain gave up the ghost; not hardened and intact. Looking back years ago, I think by the time I got the big bits back from the machine shop I went into money-saving mode and reused the gears and chain AND tensioner. If it serves to snug up the chain just a wee bit I would think it does some good, which could be undone as with all the folks who have found bits of it broken up.

I will be installing one when it goes back together. Hopefully it will outlast me. I'll give the engineers who felt it was a good idea some credit, but who really knows without some hard data, which I expect is non existent. As they like to say in the US, "The proof is in the pudding," which should really be, "The proof of the pudding is in the eating," and I don't think anyone has tasted the pudding ( data) on that question.

Perhaps it should remain a Heaey mystery for all to ponder. I mean it's not like one would lose concours points if it is left off.
 
Speaking of tensioners, Moss offers two.
011-139 $14.59
460-561 $219.99
I under stand you want to use the good stuff, but this is quite the price difference.
Thoughts on that?
 
The tensioner for the BN4 and beyond is the expensive one. The BN1/2 4 cylinder cars use a remarkably heavy " rubber band" that fits between the rows of gear teeth and gives the chain a little cushion, or so the theory goes. If it fails it is unlikley to cause any real damage, whereas if the expensive set up fails you are in for some cost. Very different set up for the 6 cylinder cars.
 
As listed on Moss's site, both tensioners are for BN4-BJ8
What would make the expensive one worth the price for the BJ8?
 
AUSMHLY said:
As listed on Moss's site, both tensioners are for BN4-BJ8
What would make the expensive one worth the price for the BJ8?
Click to expand...
It's made in France. AH Spares also has an upgraded one that is less than the French one. It looks the same as the DWM one.
Also, the camshaft locating plates were originally sintered and were a weak spot. I don't know about the Moss one, but the AH Spares one is steel and supposed to be stronger.
 
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