alex30327

Ditto!

sixfive

Can one use that AF guage without much hassle - where do you get one - i imagine it plugs piggback into the MAF???

ct roadster

Wow, this is an ugly thread!

So let me ask two logical questions; first: are there any reliable reported cases of crank failure? Note: *CRANK* failure, not bearing failure, etc. Second: are there any reliable reported cases of belt derailment (belts hopping off the pulley)?

The VQ35 is a 60 degree V6; it is almost completely balanced through internals, with some residual vibration left to the engine mounts. You feel this residual vibration in the gearshift, which is a bit more active than in a straight six (BMW), or a flat six (Porsche). The front pulley on our VQ35's is *NOT* a harmonic balancer -- something used to achieve balance on 90 degree V8's of days gone by (before internal balance shafts).

Our VQ35 front pulley does incorporate a vibration damping ring; this damper is effective in reducing *TORSIONAL* vibration of the crankshaft.

Now, torsional vibration simply does not become a bending moment of the crank. Nor does it become a lateral nor longitudnal moment. And torsional vibration simply won't excite other modes of vibration, either.

What can happen if we remove the front pulley vibration damper and let this torsional vibration run amok? Will we encounter the dreaded "critical RPM's" and shake our engines to bits?

Well, if this was a problem, we would see two things happening:
1) cranks would fail from torsional vibration; we would see cranks shearing (typically at the first journal). Not bearing wear -- there's no bending moment -- just crank shear.

2) belts would hop off the pulley, as the belts would encounter a resonant frequency and jump off.

Thus, my two logical questions:
1) Are there any reliable reported cases of crank failure? Note: *CRANK* failure, not bearing failure, etc.
2) Are there any reliable reported cases of belt derailment (belts hopping off the pulley)?

(I've searched and searched for reports of these two sorts of failures and have yet to see any....)

-frank
Bone stock 2004ZR, but not for much longer

jpc350z

Good response. Perhaps a few questions need to be asked. What would likely be the source of any Torsional vibration and why do you think Nissan included the damping ring ?Does the damping ring isolate any torsional vibrations from coupling into the crank?..

ct roadster

Cause of torsional vibration: Although I'm no Dinan fan (and doubly not so after reading the linked Z8 butchering story), he had it right in his "whitepaper"; torsional vibration is a simple consequence of the cylinders firing. Nothing you can do about it; it's a fact of life.

Why the damping ring in the pulley: my background is in some race engine work, not designing road engines, so take this with a grain of salt -- my understanding is that the damping ring in the vibration damper is to make the belts quiet and ensure that they don't hop off. Without damping out the vibration from the crank, the belts will make more noise (they will act like plucked strings at their resonant frequencies) and may hop off if you are unlucky enough to hit the right conditions. The belt arangement on the VQ35 in the Z has short enough free lengths that I sincerely doubt belt derailment is a problem in these engines.

Source of vibrations: the source of the torsional vibration is the crank; the vibration damper is isolating the accessories from vibrations in the crank, not the other way around.

-frank

ct roadster

I should clarify one thing in my last post: when I wrote about the damping ring in the pulley being used to make the belts quiet, I mean this to apply to this particular situation, a 60-degree V6.

In other engines, particular longer engines like the BMW I6, the vibration damper is likely much more essential to preventing crank problems. V8's need both vibration damping *AND* a harmonic balancer; these are sometimes combined into a single unit, and othertimes the harmonic balance is provided by way of a balance shaft internal to the engine. I4's are similar to V8's in this regard.

It is the short overall length of the VQ35 that makes me believe that torsional vibration damping is not essential for these engines; further, if it were a problem, we would hear complaints of sheared crankshafts and derailed belts when running these lightweight undamped underdrive pulleys.

-frank

Z1 Performance

iTrader: (564)

you are confusing NISMO USA and NISMO Japan...the 2 firms have absolutely nothing in common

frank - excellent post...refreshing to see someone who understands the simple physics of the engine!

Adam

Jason@Performance

iTrader: (11)

So meeting today with Jackson Stewart from Unitech & Stewart Racing, we not only talked about new product from the race team and new things the race cars will be sporting but also....

You guessed it....

UR Crank Pulleys...

Lets look at the stock pulley...

It does Not have a harmonic Dampener. It is NOT Balanced. It is made of a cast iron... Those of You who know, when metals are poured into a casting the different cooling speeds in certain sections of the cast as well as any inconsistency's in the material can cause density inconsistency's as well as weight differences.

Lets look at the UR Crank Pulley's...

They are FORGED out of a Solid piece of Billet Aluminum. You cant get much more balanced than that. The material's that these pulley's are forged out of is the same consistency and density tthought the material. If it is cut perfectly symmetrical (which they are in the forging process) then they are going to be perfectly balanced. So, actually running the stock pulley, even though it doesn't matter your stock pulley is NOT BALANCED! So if anything. The stock pulley will cause all the problems before the UR Pulley would.

Good reading on UR's web site at this link...

http://unorthodoxracing.com/faq_pulleys.html

oh yeah... all pulley colors are in stock again on www.mynismo.com

jpc350z

Excellent discourse Frank. Nothing beats knowledge and experience. One or perhaps two questions however. I would think that "if" a big "IF" any deleterious effect was occurring to the crankshaft it probably would not would be evident for many many miles. Eventually fatigue caused by vibrations (cycles) within the crankshaft would reach a point where damage would become evident. The other question I have is do you think the rubber damper eliminates what could be described as a "ringing" sound much like the sound one hears when they run there finger around a wine glass..The rubber can only absorb energy due to sound waves within the pulley caused by the belts slipping on the pulley(s) Again great posts..

ct roadster

As to the first question, how long it would take for a problem to appear: it might surprise you, but this sort of problem is more serious at idle than at higher RPM. The reason is that torsional harmonics of the crankshaft and associated bits have a relatively low fundamental frequency (its a large-ish system), and directly exciting the fundamental frequency causes far more energy transfer into the resonance than by exciting the higher-order harmonics. So problems like this tend to show up very quickly!

As for your second question, about the ringing sound, I don't know. When belts slip and squeal, most of what you hear is actually coming from the belt, with the pulleys acting to some degree like a sounding board. Belts should not slip at all in operation (slip equals heat equals rapid wear, so definitely avoid it), so it's doubtful that the ring is there to prevent belt squeal from being overly loud. (In fact, it is in the manufacturer's best interest to make belt squeal really loud, so that you get it fixed ASAP.)

But a big round hunk of metal that is shaped somewhat like a bell -- the stock pulley -- may well be inclined to ring on its own, if its fundamental frequency gets excited. The bonded rubber ring would definitely put a stop to this aspect, so that is another potential explanation. Note that ringing is likely not going to be much of an issue with the aftermarket pulleys discussed here, as they are poked full of holes, swiss-cheese style. Further, if you compare the relative sizes of the belts versus the pulley, its pretty aparent that the belts have the larger area for emanating sound -- so I still think that the rubber ring would be more to keep the belts from singing. Then again, the free belt lengths on the VQ35 are so short that their fundamental frequencies are going to be very, very high (compare the lengths to that of a guitar -- different materials only change the timbre of the sound, not its fundamental pitch), and so the belts will likely only sing at high engine RPMs (when you have more high frequency vibration around to excite them).

And thus the above is what leads me to ask the two fundamental logic questions: 1) are there reliable reports of crank breakage related to these pulleys, and 2) are there reliable reports of belt derailment related to these pulleys? I've searched, and I've yet to read anything like that -- lots of (silly) supposition and the usual internet nonsense, but nothing logical.

-frank

PoWeRtRiP

man wheres an own3d pic when you need it

Z1 Performance

iTrader: (564)

Jason - the forging process is not what balances the UR pullies...its the CNC;ing they udergo (how the metal becomes "cut" into a pulley), followed by the shaving they do to make sure each one is balanced.

The onyl purpose the rubber ring in the stock pulley serves is noise reduction - that's it.

Jeff@Performance

And to answer another question.... yes, we do run these on our road race cars.... as well as mine.

hfm

iTrader: (1)

Nice reading Frank. You need to post more often.

UsafaRice

UsafaRice

Anyone have pictures of the red set installed? I've been putting off this mod pending the results here and Frank has me convinced!

Jason@Performance

iTrader: (11)

I will snap you a pic from Jeff's car tommorow...

UsafaRice

YES! You rule.

Jason@Performance

iTrader: (11)

Jeff will probably pop on early AM and get one online before me :P

Ill get it here tommorow though

Jeff@Performance

Not my best work.. kind of dark down there....