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RB26Dett lightweight Font Pulley experiment

rev210

By rev210,
in Engines & Forced Induction

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rev210 Grand Master

rev210

Posted
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I've decided to use my GTR's engine as a guinea pig for a light weight alloy front pulley.

In a few months a mate is going to have two Rb26 long motors from which we will use the front pulley to have a copy made in lightweight alloy.

It is my belief that the 'harmonic' issue people have suggested is not an issue at all for an engine that will see less than 8,000rpm , is a street motor with less than 600hp , and will only ever occasionally see a drag strip appart from regular road driving. To date the only evidence given of a front pulley having conection with harmonic block cracking is the reports from the early group A days when the front balancer was re-designed. My optimistic take on this is that the regular factory rb26 crank needs work in the counterweight area to address the sustained high rpm use. Seems there are a few factorys making upgraded cranks for this reason. Attempting to externally balance the engine is a bandaid.

Since my engine is over 230,000kms old if there are any 'harmonic' issues I expect it will show up rather quickly.

Anyway I'm happy to continue the debate and provide a real working example.

Fitzpatrick Speed Works Mentor

Fitzpatrick Speed Works

Posted
Posted

the harmonic balancer is balanced in con-junction with you crank... its weight is vital to your crank shaft being balanced over the main journals and big ends having a lighter one will throw this out and probably throw a rod through the block as well!!!! THere are no harmonic imbalances in a rb26!!! The haromonic balancer is also a dampner and the reason it is often steel is due to its better resenence frequency as opposed to alloy!!! You cannot internally balance a crank on its own as there will always be the flywheel and clutch hanging off one end. the balancer also is there to counterweight these!!! I would talk to an engine builder not just a mechanic before you decide to do this!!! Hope this sheads some light on the problems associated with this!!!

Cheers, Daniel.

rev210 Grand Master

rev210

Posted
  • Author
Posted
the harmonic balancer is balanced in con-junction with you crank... its weight is vital to your crank shaft being balanced over the main journals and big ends having a lighter one will throw this out and probably throw a rod through the block as well!!!! THere are no harmonic imbalances in a rb26!!! The haromonic balancer is also a dampner and the reason it is often steel is due to its better resenence frequency as opposed to alloy!!! You cannot internally balance a crank on its own as there will always be the flywheel and clutch hanging off one end. the balancer also is there to counterweight these!!! I would talk to an engine builder not just a mechanic before you decide to do this!!! Hope this sheads some light on the problems associated with this!!!

Cheers, Daniel.

daniel,

It's not a harmonic balancer. It has a tortional vibration function not a balancing function, very different things. your on the wrong track.

Look at the description of the crank pulley in the GTR manual. There is a fair bit covered in a previous thread on this issue.

http://www.skylinesaustralia.com/forums/sh...ighlight=pulley

Thanks for your input none the less.

Did I say 230,000kms?

I meant 237,000kms. Engine runs very well for a grandpa and thats testimony to a good service history. Oh, it has had a full life too with track days and hill climbs and things.

Fitzpatrick Speed Works Mentor

Fitzpatrick Speed Works

Posted
Posted

rev i have been led to believe that the so called balancer issues in the early group a's were to do with no.1 cank main journal issues on a batch of n1 engines!!!

I cant get that thread to open, can everybody else if not maybe Prank can see if its bugged!!! I believe you can reduce the mass by a degree but i would be scared of cutting the weight in half and using a very non conductive and non acoustic metal such as alloy!!! Also the stock harmonic balancer isnt just a chunk of metal it is actually cleverly designed, i know i shouldnt say the factory wouldnt have done it like this if they could do it better cause that is such an unrelated comment for so many other things but the harmonics of a crank is a very detailed thing.. an un-related example you jsut dont change the main journal size cause you think it can be done different or better, these are the areas where all the research hours go when creating an engine...and its the same for dampening they spend many hours trying to get the engine smooth and vibration free through r&d on thinks like the balancer(Sorry to call it that even though the crank is what is balanced) But again you have your reasons i have mine just adding to the discussion!!!!

rev210 Grand Master

rev210

Posted
  • Author
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rev i have been led to believe that the  so called balancer issues in the early group a's were to do with no.1 cank main journal issues on a batch of n1 engines!!!

I cant get that thread to open, can everybody else if not maybe Prank can see if its bugged!!! I believe you can reduce the mass by a degree but i would be scared of cutting the weight in half and using a very non conductive and non acoustic metal such as alloy!!! Also the stock harmonic balancer isnt just a chunk of metal it is actually cleverly designed, i know i shouldnt say the factory wouldnt have done it like this if they could do it better cause that is such an unrelated comment for so many other things but the harmonics of a crank is a very detailed thing.. an un-related example you jsut dont change the main journal size cause you think it can be done different or better, these are the areas where all the research hours go when creating an engine...and its the same for dampening they spend many hours trying to get the engine smooth and vibration free through r&d on thinks like the balancer(Sorry to call it that even though the crank is what is balanced) But again you have your reasons i have mine just adding to the discussion!!!!

It's all good I'm very happy to have the input. And of course I need plenty of people to say 'I told you so' when it doesn't work :)

rev210 Grand Master

rev210

Posted
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Posted

Something from the thread I mentioned for those who can't open it...

I think we are getting the pulleys confused with the harmonic dampers found on some V6 / V8 engines. "Harmonic Balancer" is a term that is used loosely in the automotive industry. Technically, this type of device does not exist. The "balancer" part comes from engines that are externally balanced and have a counterweight cast into the damper, hence the merging of the two terms. None of the applications that we are talking about utilize a counterweight as part of the pulley as these engines are internally balanced.

The pulleys on most of the new import and smaller domestic engines have an elastomer (rubber ring) incorporated into the pulley that looks similar to a harmonic damper. The elastomer in the OEM pulley serves as an isolator, which is there to suppress natural vibration and noise from the engine itself, the A/C compressor, P/S pump, and alternator. This is what the manufacturers call NVH (Noise Vibration & Harshness) when referring to noticeable noise and vibration in the passenger compartment. It is important to note that in these applications, this elastomer is somewhat inadequate in size, as well as life span, to act as an effective torsional damper. If you look at the pulleys on some of the imports there is no rubber to be found at all. Most who have installed and driven a vehicle with pulleys will notice the engine actually feels smoother. This is a natural result of replacing the heavy steel crank pulley with a CNC-machined aluminum pulley. NVH is variable and unique to every car. NVH will increase with the installation of an aftermarket intake and/or exhaust, for example. Think of OEM intake systems in newer cars, they use baffles and resonators in the intake to quiet all the intake noise. Aftermarket intakes eliminate these resonators and create dramatic increases in engine noise from the throttle opening and closing. So to most tuners, certain types of NVH can make the driving experience more enjoyable.

The purpose of a traditional harmonic damper is to protect against crank failure from torsional movement. This is not necessary in most modern engines because of the many advances in engine design and materials. Factors such as stroke, displacement, inline, V configurations, power output, etc., do determine when and how these harmonics and torsional movements occur.

Again, there is a lot of internet hearsay about the pulleys. When motor failures occur, too often people are quick to blame the pulley first, rather than taking the time to look logically into why there was a problem.

Here's a few examples of successful front pulley change overs on 6 cyl:

BMW M series , 5 series, Audi A6 ,Toyota the whole range of 6's found in supras including NA's and turbo's. This is a small sample of the straight 6's that can live without the harmonic balancer. All have had the front pulley replacement and none have had premature bearing failure as a direct result.

Food for thought.

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