Home » How A Tiny $1 Part Killed A $4000 Engine

How A Tiny $1 Part Killed A $4000 Engine

Bmw I3 Range Extender Fail Ts
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New York-based, 54-year-old welding inspector Tom Otto uses his white 2014 BMW i3 every day for his 96-mile round-trip commute. Because his car only gets about 65 miles of EV range (less in the winter), Tom relies on the gasoline “range extender” under his rear cargo floor to get him all the way home.

Unfortunately, in April, while on his way home, the engine just cut out, yielding a “drivetrain error” message on the screen. Trying to restart the engine led to a “horrendous noise coming from the rear of the car, and the engine shut down after about two or three seconds of runtime,” Otto told me. Yikes! So the handy wrencher decided to dig into the problem, ultimately finding that his engine ended up grenaded due to a tiny part probably worth only a buck.

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I noticed this post on one of the BMW i3 pages I frequent on Facebook. “I’m sure many of you saw where my Rex engine failed at 124,000 miles (1103 hours of runtime),” Otto begins. “While I admit this is quite a high number of hours, I was not pleased to find the failure point to be a $65 part.”

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“Upon disassembling the engine, I found the timing chain to have considerable slack in it,” he continued in the post. “This led me to believe that the chain tensioner failed. I disassembled the chain tensioner today, finding that there is a tension spring on the inside that is meant to apply constant pressure to the screw mechanism that keeps tension on the timing chain guide. The end of the tension spring failed where it engages with the screw. A $0.75 part (estimated) caused the failure of a $4000 unit (estimated).”

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To give a bit of background: On an internal combustion engine, the “timing” whatever — whether it’s a timing belt or chain or gears — is what mechanically couples the rotation of the camshaft (which sets the location of the valves at a given point in the combustion cycle) with the rotation of the crankshaft (which sets the location of the pistons at a given point in the combustion cycle). On some engines called “interference engines,” if the timing belt/chain/gears fail and the valves’ positions are no longer properly synched with the pistons’ positions, pistons can actually collide with the valves, causing major damage to the engine.

That’s precisely what happened with Otton’s BMW i3 range extender. The chain that goes over the camshaft/crankshaft sprockets came loose, and thus, the location of the pistons relative to the valves was no longer properly synchronized. The result? Well:

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It may not look like much, but you can see in the top photos that the exhaust valves have bent, and if you look at the bottom photo (particularly towards the bottom of the piston), you can see silver marks from where those exhaust valves hit the piston.

What caused this? Well, the actual chain itself didn’t break, it just got too much slack in it, causing the engine to “jump time,” which means it basically skipped a tooth or or two on one of the sprockets.

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If you look at the image directly above, you’ll see that the timing chain is tensioned via two plastic chain guides, one of which is pushed by a tensioner, which is marked part number 18 in the schematic below:

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Bmw Timing Diagram
Image: BMW

That tensioner, which you can buy for $65, looks like this:

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Image: Wolf Auto Parts (eBay)

But what frustrated Otto so much (and rightly so) is that the reason this tensioner failed, and thus allowed the timing chain to go slack, skipping teeth on sprockets, allowing exhaust valves to collide with a piston, is that a dirt-cheap part within the tensioner failed. This spring:

Failed Spring

 

“I had originally thought that the tensioner might have been a hydraulic unit like I have seen in other engines from other manufacturers,” Otto told me. “But, no, the timing chain tension relies solely upon a mechanical chain tensioner deriving its forces from a very small diameter tension spring.”

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“You can just barely see the coils of the spring within that gap [in the photo of the full tensioner],” he continued. “The top end of that coil spring engages in the body close to the plunger end, the other end terminates in a 90° angle and engages in a slot which is accessible under the 8 mm bolt that is on the end of the unit.”

Apparently getting to the tensioner is no easy job. “It is not conveniently located for easy change out either. The chain tensioner is bolted to the top end of the block on the timing chain side which resides on the end of the engine that is in close proximity to the electric motor,” Otto wrote to me over Facebook Messenger. “It’s also on the backside of the motor engine as you’re looking at it from the back of the car. Though it is only held in by 2 T30 screws and a gasket to maintain an oil tight seal of the engine.”

Otto managed to find a new BMW i3 range extender with starter/generator built in for just $1,500 plus shipping. I took him — someone who has “always been active with Auto repair, small engine repair, wood boat restoration, vintage outboard restoration etc.” (Otto wrote to me that “people often wonder how I came to know all of the things I do about repairing cars, it’s because I never had the expendable income nor time to pay someone else to do something that I could do myself.”) — five days to do the job. Total cost of the repair was $3,000 — significantly cheaper than what BMW charges for a complete new engine.

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Could Otto have saved those $3000 by pursuing the i3’s humongous 15 year, 150,000 mile warranty in CARB states like New York? Perhaps. But, Otto told me, he’s never taken a car to a dealership, he needed the car to get to work, and he didn’t want to waste the time.

It’s possible that the tensioner has been revised after 2014, and that later i3s won’t have this issue. I’m hoping so. Regardless, Otto concluded by telling me: “My posts are more of a cautionary tale, to hopefully help others not experiencing a catastrophic failure.”

A failure caused by a dirt-cheap spring. How absurd! But it’s yet another example of how, while a well-designed timing chain system is much better than a typical timing belt system, a poorly designed timing chain system is just the worst of all words.

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Slow Joe Crow
Slow Joe Crow
41 minutes ago

Stuff like this is making me reconsider a modern BMW motorcycle. The R1200RT was magic on a demo ride but unknown 10 years down the road while my Airhead is over 45 years old and has only one major repair due to design. The shift cams in the transmission were replaced in 1991 as part of a recall

Scoutdude
Scoutdude
2 hours ago

1,000 hrs is not a lot, for an average ICE vehicle with an average driver that is 30-35,000 miles.

I’m not seeing a destroyed engine. Valves kissing pistons because of a timing failure usually doesn’t damage the piston to the point where it can’t just drive on. In this case I see no damage that would indicate engine/piston replacement is required. I lost count of all the Hondas that came in on the hook with a broken timing belt that also needed valves replaced. At least a couple of those I know kept running since the customers kept bringing the car back to me for various things for several more years.

Another reason that EREVs aren’t a great idea. The engine gets stuck some place that isn’t accessable and also at least in some cases not very durable “since it won’t see that much use”.

I’m also wondering how a $1500 engine ends up costing $1500 to install DIY. I guessing there were some shipping charges on top of that but that shouldn’t have been more than $500, if it came from somewhere in the US. A couple of hundred for fluids and other might as well why I’m in here still leaves ~$750 unaccounted for.

Cheap Bastard
Cheap Bastard
3 hours ago

This really isn’t selling me on the i3…

Cryptoenologist
Cryptoenologist
4 hours ago

Hmm. Taking the car in under warranty is the best thing about these cars. Free repair, and a loaner to use while it sits in the shop waiting for the dealer to get around to working on it.

Bonus is you might get an i4 or i5 as a loaner.

Cal67
Cal67
5 hours ago

Rookies. We had several failures where an $0.83 part took out a $250K drive assembly. We did a redesign to remove the $0.83 part – no more failures (at least from that root cause).

Shooting Brake
Shooting Brake
5 hours ago

I don’t understand why the Germans can’t seem to build a decent timing chain system after however many decade of trying…

Fix It Again Tony
Fix It Again Tony
5 hours ago

It’s possible that the tensioner has been revised after 2014, and that later i3s won’t have this issue. I’m hoping so.

So like the AC thing, you have to do another preventive maintenance and change out the tensioner every 1000 hours.

Last edited 5 hours ago by Fix It Again Tony
S0crates82
S0crates82
5 hours ago

I’d do it every 750. We don’t know where on the bell curve that instance sits.

Alexander Moore
Alexander Moore
6 hours ago

Before I came to this site I loved the BMW i3 and figured I’d own one someday. Now I still like it, but I’d absolutely never own one.

Dinklesmith
Dinklesmith
5 hours ago

That seems like pretty good advice for just about any BMW

Last edited 5 hours ago by Dinklesmith
Cryptoenologist
Cryptoenologist
4 hours ago

If you live in a CARB state it has an absurd warranty. And BMW is pretty good about giving loaners for warranty work.

Pedro Soto
Pedro Soto
4 hours ago

Owning BMW in warranty is almost always sound advice. When they fall out is when the crazy bills begin.

As others have said, Otto probably could have taken it to the dealer to have this fixed and gotten a free loaner for the time it took. So he likely would have been out less time unless the dealer was backed up in terms of scheduling (which is definitely a possibility)
The hard part is that the dealer during their “courtesy checks would have almost certainly found $$$ of “recommended services” that he would have had to suffer through and say no to a thousand times before getting this fixed.

Davey
Davey
4 hours ago

Take it from any previous BMW owner, great in theory, never in execution/ownership. They’re like boats, better to just enjoy the one your friend has.

Double Wide Harvey Park
Double Wide Harvey Park
43 minutes ago

The EIC has one for sale for an unbeatable price, though.

Urban Runabout
Urban Runabout
6 hours ago

Sounds about BMW.

Al Camino
Al Camino
6 hours ago

I was wondering earlier today when this week’s i3 article would be posted.

Rad Barchetta
Rad Barchetta
7 hours ago

Would it make anyone feel better if it was a $1000 part that failed and trashed the engine?

Saul Goodman
Saul Goodman
4 hours ago
Reply to  Rad Barchetta

I’d rather pistons fly out the engine. If it’s gonna go down, it better go down in a blazing, awesome, fiery and flaming ball of glory! (/s)

Last edited 4 hours ago by Saul Goodman
Cheap Bastard
Cheap Bastard
3 hours ago
Reply to  Rad Barchetta

I’d feel better if the rebuild cost less than $1000.

NosrednaNod
NosrednaNod
7 hours ago

Yikes! So the handy wrencher decided to dig into the problem, ultimately finding that his engine ended up grenaded due to a tiny part probably worth only a buck.

Is there literally any part on a BMW that only costs $1?

Mr. Fusion
Mr. Fusion
7 hours ago

After the great debate about belts vs. chains, maybe the real problem has never been the timing mechanism, but rather the entire concept of interference engines.

JT Eastwood
JT Eastwood
6 hours ago
Reply to  Mr. Fusion

Agree. Back in the olden days, my wife snapped the timing belt on her Cabriolet. Threw the toolbox in the car and replaced the belt in the parking lot while she worked. Piece of cake!

Pedro Soto
Pedro Soto
4 hours ago
Reply to  Mr. Fusion

It’s all about chasing those really high compression ratios in the name of efficiency. The problem is that the Germans inevitably under engineer some component in the name of cost savings which sets the time bomb ticking. I had an X5 with bent valve stem guides which, before someone engineered an easier fix, required $20k shop visit and dropping the engine out of the vehicle.
I ended up just trading it in for a Honda Fit.

StupidAmericanPig
StupidAmericanPig
7 hours ago

David- when are you going to admit that maybe the i3 is not the amazing vehicle that you want it to be. Barely Mechanically Worthy vehicles are great for 3 years or 30k miles. No matter the model. To this day the only vehicle that grenaded an engine while I was driving was a BMW. 70mph on the highway and boom. Just to make sure that it really tried to kill me it spewed oil all over the windshield in an attempt to blind me while I coasted to the side of the road.

NosrednaNod
NosrednaNod
7 hours ago

David- when are you going to admit that maybe the i3 any BMW is not the amazing vehicle that you want it to be. #ftfy

StupidAmericanPig
StupidAmericanPig
7 hours ago
Reply to  NosrednaNod

I knew something was off about that sentence. Thanks.

Angel "the Cobra" Martin
Angel "the Cobra" Martin
7 hours ago

The best part is no part. That’s why I like EVs so much. One moving part. Granted, there are a million failure points in the battery pack, but I hope that chemistry beats mechanical as far as service life goes.

Alexander Moore
Alexander Moore
6 hours ago

Luckily BMW figured out how to make the battery pack shitcan itself too!

Angel "the Cobra" Martin
Angel "the Cobra" Martin
5 hours ago

BMW at its mot BMWist.

EmotionalSupportBMW
EmotionalSupportBMW
7 hours ago

You could make a weekly article about BMW’s minor parts failures that somehow end in catastrophic failure. Is there a BMW that doesn’t have some odd Achille’s heel? Maybe the Isetta?

Mr. Fusion
Mr. Fusion
7 hours ago

A car would have to be mechanically sound to earn Steve Urkel’s trust.

Pedro Soto
Pedro Soto
4 hours ago

This would be a great weekly article! While BMW would feature prominently there are many other automakers who under designed or cheaped out on a component which could destroy your car.

The series could be called “$5 Part of Doom”

A. Barth
A. Barth
7 hours ago

A new, complete REx engine for about $4400?? It would be tempting to keep a couple on the shelf, just in case.

Pedro Soto
Pedro Soto
4 hours ago
Reply to  A. Barth

I love the thought of putting these into a self contained trailer and plugging them into an EV for road trips.

Double Wide Harvey Park
Double Wide Harvey Park
42 minutes ago
Reply to  A. Barth

They’ll probably fail on the shelf.

Kalieaire
Kalieaire
8 hours ago

The infamous IMS Bearing in 9×6 an 9×7.1 Porsches is yet another great example.

Jdoubledub
Jdoubledub
8 hours ago

Suck it timing chain stans! Moderately easier to change and inspect belts (and belt tensioners) for me.

1978fiatspyderfan
1978fiatspyderfan
8 hours ago

I had a 1987 Chevy Spectrum, my 1st new car, had the timing chain break and bent valves problem. It mystifies me how auto manufacturers will continue to you such a failed design and plastic parts and just shrug their shoulders when this happens to most of their line. I wonder how many cars would go from failed to success or crap to caviar with less than $100 extra spent on construction or parts.

John Beef
John Beef
8 hours ago

Excuse me, your ideas will infringe on quarterly profits, the single most important metric for any endeavor, ever, in the history of humanity.

Hondaimpbmw 12
Hondaimpbmw 12
7 hours ago

I’m willing to bet that a better (rolling element) tensioner would cost less than $10 more than the plastic on metal guides in common usage. Perhaps I am not accounting for chain slap if a roller like that used for cam belts were used to tension a chain. But as noted below, it would reduce profits by some small margin, thus making it unacceptable.

Jatkat
Jatkat
8 hours ago

The more time (heh) I work with and learn about the various timing systems employed in cars, the more and more convinced I am that Toyota had it right in the 3FE engine. Big ol’ gears. No chains, no belts, no tensioners.

Goblin
Goblin
7 hours ago
Reply to  Jatkat

Well, weren’t most Toyota engines non-interference ones till not that long ago, anyway ?

Hondaimpbmw 12
Hondaimpbmw 12
6 hours ago
Reply to  Jatkat

The 3FE is an overhead valve, not overhead cam engine kinda copied from/based on the old Chevy stovebolt 6. The Chevy and the similar Ford use timing gears (with a plastic coating on the cam gear teeth). The only OHC engines I’m aware of w/ gear drive are racing motorcycle engines (vertical bevel gear drive shaft or spur gears in the middle of the cam & crank) the VW V10 TDI (look it up, insanely complex gear train), and possibly a Cummins OHC 6 cyl Diesel (a quick search did not reveal any pictures of the cam drive). Oh, the Crosley CoBra engine had a bevel gear drive OHC.

American Locomotive
American Locomotive
5 hours ago
Reply to  Hondaimpbmw 12

Pretty much all of the big over the road truck engine are OHC or at least “high cam” engines. They just have a big stack of gears going all the way up the top.

Hondaimpbmw 12
Hondaimpbmw 12
5 hours ago

Pretty much what I expected. The diesels where I worked had gear drives for the air compressor, so I expected similar for the cam. I knew the v type engines had gear drives for the cam, but was unaware that there were very many OHC Diesels. Nowadays, all I see are 12 valve Cummins in relative’s Dodge 2500s. 😉

At the Auburn Truck Museum, I saw an early Cummins DOHC prototype that was impressive… and RED.

Last edited 5 hours ago by Hondaimpbmw 12
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