Cause of blown motors?
 

Thought people should read this before putting light weight crank pulley's on their engine. I wonder if their is a correlation between the blown motors and guys that are boosting and/or changing their pullies out. Food for thought. It could be causing the bearings to wipe themselves due to vibrations in the crank if they aren't properly cancelled out, yes it's a flat engine but their is still deflection in the crank, and especially if your boosted.

"To help us understand more about harmonic balancing, we spoke to our engine builder, Jeff Gerner, of FRP. "A balancer works through a process called ‘phase cancellation'. Additionally, balancers add mass to the front end of the crank to help with damping. In other words, all balancers are at least two-piece assemblies, which work by taking a reaction and using it to lessen the next ‘action'. This process is known as phase cancellation."

"What actually increases on modified engines is the torsional deflection in the crankshaft, which is attributable to increased brake mean effective pressure. This is the result of increased turbo boost cramming in more air and fuel. To put it simply, when the piston and rod assembly exert force on the crank throw, the crank twists on its axis and then snaps back to shape as the power stroke is completed."

"This action is what's responsible for breaking oil pumps and causing bearing failure in more extreme cases. Aftermarket balancers are engineered to better cope with the torsional deflections and the attendant vibration produced," says Gerner."

http://www.motoiq.com/MagazineArticl...ibrations.aspx

Crank pulley. Blown engine? I think not.

Did you even read the article? You can't argue physics. I thought I would post the article and you can come to your own conclusions, but if the OEMs put a harmonic balancer on the engine, and race guys that build professional engines include one, don't you think that they may know more than you? By all means do what you want but I was only posting it to enlighten the uneducated in automotive terminology, and design. I myself have come to the conclusion after many years of denial that yes OEMs are smarter than me....and so I don't bother with modifying anymore. I just enjoy driving without worry and completely covered by warranty. Case in point my dad has a completely stock 2003 Yamaha R1 with 60k km, including track time. That to me is justification enough to not mess with harmonics of the engine.

We dont' have harmonic balacers on our cars. Boxer engines are self-balancing :iono:

Yup I read the article.

I have read dozens of articles on other Subaru forums that seem to resurrect this every couple of years. Subaru confirmed that it isn't there as a harmonic/damper balancer, it's just a crank pulley. This thread resurfaces every couple of years on NASIOC since 2003. I installed my Perrin LWP nearly 2 years and 63,000 kms ago and have not had any problems. Here are my two favorite posts.

http://forums.nasioc.com/forums/showthread.php?t=444518

http://forums.nasioc.com/forums/showthread.php?t=437237

I read those threads and Fwiw my trucks harmonic balancer was only a piece of rubber sandwiched between two metal discs as I recently had to replace it as the rubber disintegrated. So to say that rubber is there to account for manufacturing deficiencies seems a bit far fetched. It's there to for vibration damping, and the longevity of the oil pump, crank bearings, rod bearings, wrist pin, and pistons. If you read the motoiq article, you would've noticed that their is a properly engineered race harmonic balancer that INCREASED the HP for their 2JZ build. That to me suggests there is more to it than "it's lighter to it's better for the engine" thought process. I'm not attacking anyone, was only questioning if their is a correlation between blown engines and certain mods like turbocharging and light weight crank pulley's. That's all.

And sure, there is probably a lot people running LWP with no problems for lots of miles, but that doesn't mean it couldn't be related to other peoples failures. All depends of tolerance stack ups, and minuscule manufacturing deficiencies.

Stock pulley has a bonded rubber part, meaning it is indeed a harmonic dampener.

Do as you wish, but one of those pulleys is NEVER going on my engine.


Also, ATI makes an SFI rated dampener for this car if you want to replace the stocker...

http://www.atiracing.com/products/da...mper_dinan.htm

Subaru BRZ/FRS harmonic balancer

http://www.atiracing.com/products/da...dam-subaru.htm

Did you even read what the OP said? :bonk:

Harmonic balancers, balance AXIAL (torque), not transverse vibrations. Transverse vibrations on inline, and V-engines are mostly balanced with weighted crank shafts, and secondary balancing shafts. Boxers don't need those.

But ALL engines suffer torsional vibrations of the crankshaft which as the OP said have to do with the pulses of torque from the firing pistons.

http://www.strand7.com/html/archive/...ive/cranka.gif
http://www.vibratechtvd.com/images-n..._peakstart.gif

In engineering, Mode 1 is always the most probable and dominant vibration with the largest deflections. Typically Mode 1 will cause the most damage, but it's possible that secondary modes cause force that are acting on parts that are not specifically reinforced for vibration.... but I digress.

Absolutly get it. Lightweight pulleys have been run for lots of miles with no adverse effect, including cars that are raced. I get what he's saying, but a couple blown motors here or there does not an epidemic make.

This mass hysteria that people try to create (not talking about the OP here, so please don't be offended OP) is always funny to me. It's like the DI seals.

Our car does not come with a balancing component from the factory. I get that it has some weight to it, but torsional vibrations are probably happening anyways.

As @Apoc pointed out, SUBARU states that there is no balancer on this car, and I actually agree with @Gords_zenith here when he states that "OEM's are smarter" than us. If he needed it, it would be added from the facotory.

Just because a SOA customer relations guy said it doesn't have one doesn't mean he's right. He could be mistaken and be thinking of a different type of damper. But this is from ATI's website. I'm inclined to think that there is one based on what he said and how others have described the one that is on our car.

"For years, major manufacturers have used the elastomer-type damper design. These conventional, single-strip elastomer dampers have proven very effective on OEM applications operated at low RPM's. They were also surprisingly effective at high RPM's. Many engineering studies have shown that elastomer style dampers to be the far superior to the friction type and markedly better than the viscous type in controlling vibrations over a wide range.

Conventional single strip elastomer dampers are not re-buildable. The main problem with this type of damper is a loss of certain controls inherent in the manufacturing process. An inertia weight pressed with a rubber insulator to the crank hub allows the possibility of the ring to move in its relation to the keyway. It is also impossible to maintain the concentricity of the inertia ring during manufacturing. The ring must be machined after it's pressed to the hub, and then balanced after machining. When it works loose with age or from multiple cycles, the ring will move, and the damper will be out of balance."

http://www.atiracing.com/products/da...amper_tech.htm

It doesn't make any sense for an OEM to NOT have some form of vibration damper. Further more, I'm not trying to create hysteria. I was only questioning if there is a relation between the blown engines that people are posting about and LWPs. If you think your right than mathematically prove it. I will admit that I can't prove it mathematically, so I'm inclined to take the OEMs word for it.

Of course. The dual-mass damper is there to keep the vibes better controlled over a broader rpm range.

I would feel better about a lighter dual-mass damper than a simple single-mass part.

The point about dual-mass damper with rubber being somehow cheaper to produce is absurd. You can't throw two parts with bigger tolerances together with a piece of rubber and magically get the necessary tolerances met! The two mass part will require tighter tolerances, and it's two metal parts with rubber. Definitely MORE expensive than a simple one-piece pulley. They do it for a reason, and it's not to save money...

Harmonic DAMPENER.


The engine is internally balanced. If someone asked if it needed a balancing pulley, of course the OEM is going to say no because you asked the wrong question.