DIY Bolt-On-Pulley protective shield

[Hugabuga]

Hi guys
While rebuilding my 2 engines, reported in the NSX Builds section here:http://www.nsxprime.com/forum/showthread.php?t=157635, I came up with an idea for the harmonic balancer. I guess I got affected by the NSX comunity paranoia, this component can fail, and could lead to an engine destruction as many of you have experienced or reported here.

Here are a few pictures taken from a few threads, showing the failure of that harmonic balancer or cranckshaft pulley.

And ultimately an engine destruction

To prevent this to ever happen, I found 3 solutions on Prime:
- replace the pulley by a new OEM one while replacing the timing belt
- replace it by an aftermarket one (there are several available as I read)
or finally
- use a protective shield bolt-on-engine block to prevent the inner free part of a failed harmonic balancer to hit and destroy the TB cover

Having 2 engines to rebuild, and because even a new component can always fail I focussed on the last option: the protective shield

Even if the idea may work and effectively prevent the inner part to hit the plastic TB cover, my concern is how long will it last before the shield gets destroyed?

The surface of the inner ring is made of metal, it has a diameter of 100mm. The shield is fixed to the aluminium block only by 2 thin screws of 10mm. Imagine the impact, at 8000rpm, the tangential velocity would be

v=w.r, where w is the angular speed (8000rpm => w= 133.33 x 2 Pi / s )
with a ray of 50mm, the tangential velocity would be 41887,9 mm/s
v= 150 km/h @ 8000rpm (94MPH @ 8000rpm)

So my question is: for how long can the shield and its 2 bolts resist to such an impact? Imagine you are driving lets say a circle circuit at 94MPH, hitting over an over again with a 4kg harmonic balancer to the same small shield plate, fixed to the ground. How many laps would you need to destroy it??

Here in Europe, to get new OEM honda parts takes about 1 month, my personal usage of the NSX is mainly for long distances on weekends or holydays. So I was looking for a protective shield that would effectively protect me for a longer time, so I can still drive the car with a failed harmonic balancer, and do not have to call the toe truck right away and ruined my holidays

I know it may make no sense driving with a failed pulley, as the pulley is there to absorb the harmonic vibrations of the crankshaft preventing its own crack formation...but I don't believe it could happen in just 1 month or 1000kms...

So, I came up with a new solution: a bolt-on-pulley protective shield

I carefully took some measures, and ordered a 1.5mm stainless steel plate to fix on the back of pulley, at the same laser cutting company that makes the parts for the window kits

Here are the parts I got, all in stainless steel

I tapped the shield to the pulley to prevent it from spinning, and start to drill the pulley with a press driller

Then, I did the 5mm bolt pattern

I used 20mm long bolts, deep enough so it would hold the weight a failed inner part and not just the light shield...

And here is the shield bolt-on-the pulley

There is just enough gape for the inner part to freely vibrate

and finally fit on the engine, ready for the first test drive very soon

Now, the impacts would be contained between the shield and the pulley, with a much less speed diference, if any, between the free inner failed part and the the pulley or its shield

What do you think of my idea?
I absolutely do not pretend to critizise SOS or any other NSX performance company, this is just a different solution or approach to the problem

 

[Nefarious]

Very interesting. I curious how it works for you and if you see any wobbling at all from it. Keep us updated.

 

[Honcho]

Hugo, I think you might have a balancing issue, as you have added a mass to a balanced rotating unit. Maybe you should have the whole unit balanced to avoid any unwanted vibrations? Kind of like a new clutch/flywheel set.

 

[Hugabuga]

Honcho: yes, I also though of this, but the weight of the shield is only 150gr, simetrically distributed over the 4Kg of the pulley.

There is nothing like testing it, and if I feel any vibration I will have it calibrated yes, you are absolutely right this might be a problem.
The original balancing is made on the inner ring, by the 2 holes we can see on the pictures.

 

[scorp965]

Honcho: yes, I also though of this, but the weight of the shield is only 150gr, simetrically distributed over the 4Kg of the pulley.

There is nothing like testing it, and if I feel any vibration I will have it calibrated yes, you are absolutely right this might be a problem.
The original balancing is made on the inner ring, by the 2 holes we can see on the pictures.

I am conflicted about this for the reasons already mentioned, plus one more item for thought:

People often rail against aftermarket lightweight crank pulleys since they provide a dampening benefit to the crank, which can experience oscillations during operation. The crank pulley is often also referred to as a crank dampener for this reason, it's also a reason why it's taboo to run both a lightweight crank pulley, and a lightweight flywheel, even on engines where the crank pulley is frequently changed (since there is nothing to dampen oscillations).

Not only have you tagged a significant weight onto a balanced system, but it's in the absolute worst position, since it will now serve to exaggerate any oscillations.

The weight of this plate is significant in terms of percentage, compared to the weight of the overall pulley, think of the effect a missing wheel-weight, which weighs only a few grams, compared to the weight of a rim and tire, which can easily weigh 50-60lbs - by upsetting the balance, the entire car can vibrate. You have done that on a much larger scale, to your engine's crank if you install this part.

Please also note, the NSX crank is one of the most-rare items for engine builders, since it's been discontinued for a huge level of time. Some people have even welded NSX's cranks back together as a result of the scarcity.

If you wanted peace of mind I think you have accomplished the opposite.

 

[Hugabuga]

I always enjoy this type of technical debates :biggrin:

Well, the wheel-weights are located at the edge of the wheel, this is why they only weight a few grams. You have to see my shield more as a wheel cover than a wheel weight, placed over a previously balanced wheel, especially if you consider its weight in relation to the pulley+cranckshaft+flywheel+clutch

Question is could my shield be unbalanced enough so it will affect the overall balancing of the engine?
The main reason would be to place it off-centered, as I believe we can consider the thickness and molecule distribution of the stainless steel sheet of the shield to be perfectly homogeneous.

I had the plate laser cut, precision is under 0,1mm here
The shield has an external diameter of 150mm, an internal one of 59 and a thickness of 1.5mm

But ok, let's say it would be 1mm off-centered.
To simplify, let´s calculate the weight of the off-centered material at its diagonal: 1 x (150 - 59) x 1.5 = 135.6mm3

Density of steel being 7,9g/cm3, that means 1.07g to be distributed on one side of the pulley, more than the other.

If we now consider the full rotary system, with the cranckshaft, flyweel, clutch, can 1.07gr (15 grains) located at maximum 75mm (3 inches) away from the center unbalance the engine??
My intuition is that it can't, but there is nothing like a test to verify my solution

PS: I am sorry to be using the metric system, but I really can't use your "standard" units
For us, 1Litre of water weights 1Kg, freezes as 0C, boils at 100C, at the atmospheric pressure of 1 Bar. That is the metric system

 

[Wavey1]

Hugo, I think you might have a balancing issue, as you have added a mass to a balanced rotating unit. Maybe you should have the whole unit balanced to avoid any unwanted vibrations? Kind of like a new clutch/flywheel set.

Agreed. You have to consider the attachment hardware too. Unless the placement of the holes is PERFECT, the weight of the material removed by drilling and tapping is EXACTLY the same for all holes, and the weights of the new bolts are EXACTLY the same, it will be out of balance.

 

[Hugabuga]

Correct, remember the shield has been laser cut, so holes location couldn´t be more perfect I guess

I did the holes with a press drill all with the same depth, the pulley removed material has then be replaced by the bolt part of the screws.

Added harware weight of bolt heads and washers is the same on 4 bolts, only way to unbalance it would be for them to be the 1mm off centered, then analysing only the off-centered material we would return to that 1gr I guess:wink:

But I am getting curious to get some real measures, so I will try to measure the balancing of the pulley prior and after my mod
I have only modified one of my 2 pulleys, I will measure the balancing of my 2nd one just to be sure

I just need to find a balancing shop that does this type of work

 

[pgilliam1]

I have never heard of an OEM crank pulley failure before 10 years or 100K miles (whichever comes first). It's easy to replace and cost only $250US. Add it to your maintenance replacement list and never worry again :wink:.

 

[Wavey1]

Not doubting your fabrication abilities, Hugabuga. I just wouldn't risk my crank especially when there's a perfectly good non-rotating solution.

pgilliam - agreed, we did the crank pulley last year @ 112K with the timing belt, cam seals, water pump etc. Easy preventative maintenance while you're in there.

 

[Larry Bastanza]

Just a point: The shield in the picture above is the old version. The new version has no holes and offers max protection in a non-rotating mass solution.

The above option which I think will certainly work effectively, is more complicated to fabricate, which means more cost, harder install. Frankly, tapping the pulley is way too much work for any DIY.

So, if you make them and decide on an exchange program as a marketing plan, it would be better, but still more complex of a sale, more mailing, deposits, $$, etc.

JMO,

Regards,
LarryB

 

[RYU]

Just a point: The shield in the picture above is the old version. The new version has no holes and offers max protection in a non-rotating mass solution.

The above option which I think will certainly work effectively, is more complicated to fabricate, which means more cost, harder install. Frankly, tapping the pulley is way too much work for any DIY.

So, if you make them and decide on an exchange program as a marketing plan, it would be better, but still more complex of a sale, more mailing, deposits, $$, etc.

JMO,

Regards,
LarryB

I pretty much agree with LarryB on this one Hugo. I think the bolt-on plate can be made to work but tapping is just one step too much for the DIY. If you get the bolt holes drilled even a little off center then you'll immediately unbalance the setup. My crappy drill press comes to mind...(which you have seen!)

What I would love to see is a TiDave style plate that doesn't require having to take off the pulley itself. Not sure if that's possible but thought i'd throw it out there.

 

[d.n]

My first thought was also the balancing. Probably balancing after is the only sure way which is hopefully not super expensive? I'm not really in the know, but I want to say balancing a flywheel is in the $20 range. Would there be additional challenges to balancing a piece like this?

BUT! This fits his needs which are to be able to drive on it when the damper starts to separate which is very cool. I would love to be able to drive those extra miles to get the car home.

One thing I would worry about though is how will you know if the damper separates? Will it then make a less pronounced clunking? What will be the affect of driving with a separated damper? I assume the vibration will do bad things to the crank bearing(s)?

What about the idea of having the plate press against the damper . I guess that complicates the design, but wouldn't that prevent it from separating in the first place and hold it in place even if it did?

 

[Hugabuga]

Nice to see some familiar faces here :biggrin: how are you Larry? Regan?

I have no marketing plans, not all the DIY turns into a successful kit!
I am just sharing my alternative solution with you guys, risking the life of my 2 engines on this, so I am quite confident of results

In a near future, new OEM pulleys will probably get discontinued, and a new one may always be an old stock we never know. I am just trying to definitely fix the potential engine failure risk due to this component.

A failed harmonic balancer with my solution will probably just be noticeable by engine vibrations, as the free inner part won´t stay centered and will unbalance the crankshaft! But at least it would stay contained between the pulley and the shield, and couldn´t get jammed, melt by heat friction or destroy the fixed shield at high RPMs, at least that is the whole concept of my idea

I will bring the 2 pulleys, the OEM and the modified one to a calibrating shop to see the diferences in balancing and will let you know of results.

Tapping is not that difficult to my opinion, takes about 1 minute, we can even find some self-tapping bolts in the market. The press driller might be a little more complex to get your hands at, I agree on that...Removing the pulley is more complicated then fit the shield on it, as we have to raise the car, remove one wheel, fix the flywheel, and so on...
A plug & play solution, without any drilling, taping or pulley removing would be ideal of course, maybe we can think of something, this is the perfect place for this to happen :biggrin::biggrin:

Some super light carbon fiber pulley cover, made in 2 parts, partially fit on the pulley grooves perhaps??

Anyway, the last soltution of pressing the plate against the damper would also prevent it from vibrating, so the harmonic balancer wouldn´t be able to absorb the harmonic vibrations of the crankshaft anymore. That is exactly what we must avoid, and we will still get the same balancing issue to worry about of an aditional rotating mass

Larry, do you have a picture of the new model of that pulley shield? Is it fixed by the same 2 screws?

 

[d.n]

I had a feeling that was case about the damper needing to be able to move.

I believe I have one of the newer shields from Ti-Dave (bought in late '10 or early '11). It's the same overall outside shape and has the same attachment points. The swiss-cheese holes/moons are no longer removed

 

[Larry Bastanza]

Hi Hugo!,

The new shield is the same mounting and layout, just no holes. I typically install these during a timing belt change, so no worries about removing the pulley, it has to come off anyway.

Regards,
LarryB

 

[EdinKali]

What I would love to see is a TiDave style plate that doesn't require having to take off the pulley itself. Not sure if that's possible but thought i'd throw it out there.

I mentioned this to Dave a while back. He wasn't interested in producing one since one of the mounting bolts requires removal of the balancer anyway.

 

[EdinKali]

Huga, one thing you might want to do is red loctite those bolts. If one of those backed out due to vibration the damage would be just as severe if not worse than the rubber piece coming detached. Just a thought.

 

[Hugabuga]

EdinKali, yes red loctite is a very good idea, these bolts must absolutely stay in place!!
I used 2 self lock washers, one on each side of the plate for double protection, but red loctite is necessary yes.
Not under or over torquing them is also crucial, for 5mm bolts on steel I used 12NM with a dinamometric wrench.

I already have the contact for the balancing shop, I have the pulleys with me, I will try to go there tomorrow to compare the equilibrium of the original with the modified one

 

[Aurora]

One thing I would worry about though is how will you know if the damper separates? Will it then make a less pronounced clunking? What will be the affect of driving with a separated damper?

A failed harmonic balancer with my solution will probably just be noticeable by engine vibrations, as the free inner part won´t stay centered and will unbalance the crankshaft!

True, I had the damper fail on me (without chewing up the belt cover). If I recall correctly, the NSX 3.0 engine already vibrates a bit more around 1400 RPM. You will notice that in case of failure the engine vibrates much more around 1400 RPM and a few new resonances at different engine speeds will pop up. I guess this damper really does it's best to suppress that 1400 RPM vibration.