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Old 10-02-2000, 11:32 AM   #1
Subaman
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Post Flat-4 Power!!!

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Old 10-02-2000, 11:33 AM   #2
SCOOBYSHAG
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sweet!
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Old 10-02-2000, 01:03 PM   #3
markus
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Too Cool!!

Thanks Subaman!!! No wonder our engines don't need balance shafts.
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Old 10-02-2000, 01:07 PM   #4
MikeYOX
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Talking

This is cool:

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Old 10-02-2000, 01:59 PM   #5
Joel Gat, 1.8L
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Hello,

How so, Markus? Are you assuming that the opposing rods, pistons, and even crankshaft parts all weigh exactly the same? They don't. As long as they're close, the engine should be fairly well balanced. But unless they're identical, the engine will vibrate.

Joel

edit - didn't see "balance shafts" and assumed you were talking about harmonic dampeners. Oops

edit again - Jewbaru, sorry 'bout the mistake. What engines still use balance shafts?

[This message has been edited by Joel Gat, 1.8L (edited October 02, 2000).]
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Old 10-02-2000, 02:03 PM   #6
Jewbaru
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Joel, our engines don't have balance shafts. What does the engine vibrating have to do with his comment? He said they don't need balance shafts, and they don't.

Joel
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Old 10-02-2000, 03:15 PM   #7
bash555
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'71 914

Question

Well, I don't know about you guys, but in all of my VW expierence, Counter weights add rev potential and case/bearing longevity.

check out the VW cranks:



I have never built an Engine w/o a counter balanced crankshaft. It's such a difference it can't be explained.

In the pic above, the crank on the left is counterbalanced and the one on the right is stock. When not counterbalanced, the stock crank tends to actually flex at higher revs which causes the pistons to get "cocked" sideways in their bores. Massive scoring tends to occur at that point.

Hey Joel 1.8L (long time no see, 2 years now I think),

I believe some of the 911 enignes had balance shafts that were geared directly to the crank much like a VW camshaft.
Note: most late model 911 enignes have OHC.

Finally, Inline 6,12-cylinders and flat 6,12 cylinder engines are inherently balanced due to any given piston to be either 120 degrees away from each other(6cyl) or 60 degrees (12cyl).
Think of it this way.
120 x 3pistons = 360 degrees.
(double this for 6cyl)

60 x 6pistons = 360 degrees.
(double this for 12cyl)

Its basic geometry that the Egytptians figured out eons ago. 'member the pyramids??

It's all about the balance.

oh yeah, so why did Porsche need put in the balance shaft???
Well, they didn't need to, it was just a way of fine tuning the balance of the engine.

Notice that the M3 and the 911 have either of these 2 layouts. Porsche has run flat 12s in their racing program before.
They don't run them today because, (as Subaru found out in their flat 12 development for F1 a couple of years back) that for fitting and maintenance, the flat 12's would not sit as low in the chassis as a V engine would. Lower engine equates to lower CG , i.e. better handling which is half the game for roadracing.

Enough rambling out of my ass,

cheers,
DB

12sec 68 Ghia (in pieces at the moment)
Totaled 97 Probe GTS (too many pieces)RIP
71 Porsche 914 1.7L
(very tired engine, my daily)
69 Saab Sonnett 3 1.5L
(all fibreglass with a V4, now that is a "buzzy" engine)







[This message has been edited by bash555 (edited October 02, 2000).]
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Old 10-02-2000, 03:43 PM   #8
Yotsuya
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Don't forget the others:





[Edit - wrong link]

[This message has been edited by Yotsuya (edited October 02, 2000).]

[This message has been edited by Yotsuya (edited October 02, 2000).]
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Old 10-02-2000, 04:09 PM   #9
wolve80
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Joel,

I have no clue what engines use balance shafts now, last I saw them mentioned was in SCC I think. I just know ours don'w.

The other Joel, AKA Jewbaru
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Old 10-02-2000, 04:09 PM   #10
ColinL
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Post

Actually the flat-4 is balanced every 720 degrees. You can see the difference between it and the inline 4 in the animated gifs linked right here. The flat four has pistons 1&2, 3&4 at TDC together, the inline four 1&4, 2&3.
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Old 10-02-2000, 05:40 PM   #11
XT6Wagon
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Flat 4's ARE balanced, or at least as far as people care about. They "wobble" which means they love to pitch up and down. Ever wonder why subaru seems quite anal about pitching stoppers?? Anyhoo, they don;t have those nasty vibrations, a inline 4 or unbalanced V8 ( external or internal) has.

Thats also why I want to build a 10K+ rpm ER-27 when I have a little cash. Its a flat 6, with a 2.62 inch stroke, and a 4.6xx inch connecting rod. That equates to dog slow piston speeds and forces at low rmps, and normal ones up high. Then factor in the natrual balance so I can make the whole rotating assembly very light and balanced.
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Old 10-02-2000, 09:53 PM   #12
markus
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Post

Bash555,

Thank you for your post, but with all due respect, me thinks you misunderstood me. I was talking about balance shafts not counter balancing a crankshaft.

Everything you said about the crank is absolutely correct, however, as I understand it, straight 4's have secondary motions (side-to-side IIRC) that create the traditional buziness/harshness that has been typically associated with 4cyl engines.

Awhile back some engineers decided that if they put a "balance shaft" in the engine that is on an eccentric it will offset/reduce these secondary motions of the traditional inline 4cyl engine. IIRC these balance shafts turned twice for each single rotation of the crankshaft.

Hope this makes sense.

Cheers,
MB
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Old 10-02-2000, 11:26 PM   #13
Joel Gat, 1.8L
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Hello,

Again, what engines use balance shafts? I could be wrong, but I haven't seen one or I missed it when taking apart a rustang 5.0, a civic D16, and a couple of subaru engines. Maybe I wasn't paying attention (quite possible since I wasn't looking for such a balance shaft), but I don't recall seeing anything like that...

If no common engines have that, then there's no point to that being an advantage of the boxer, right? So, do common inline 4s, V6s, or V8s use such shafts?

Joel - unsure of how such a shaft would be of any advantage over counterweighted crankshafts with harmonic dampeners, which would do more than such a shaft would do.
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Old 10-03-2000, 12:58 AM   #14
Tekken
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WRB

Talking

Oh my...
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Old 10-03-2000, 07:40 AM   #15
EricSC
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Don't Mitsubishi 2.0L turbo's use two balance shafts? I was under the impression that these were only for the benefit of passengers not feeling vibrations thought, I could be wrong though. Most racers take them out though.

-eric
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Old 10-03-2000, 10:41 AM   #16
markus
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Post

Balance shafts were only used for NVH reasons, certainly not for performance (why add the additional rotating mass).

From what I recall, balance shafts were only used in bigger 4cyl motors. Smaller displacment 4cyl don't have as long a stroke (thus causing not as large a side-to-side vibration - at least as I understand it). I believe that motors with 2.0+ litres were typically good candidates. Its been awhile since I checked it out, but I think Porsche (for 944s/968s, remember 3.0l 4cyl ), Honda (2.4litre in the older Accords...my memory?), and as as EricSC has already mentioned...some Mitsu's. Not everyone did this because not everyone had bigger 4cyl engines or chose not to do the R&D. I'm sure there are also a myramid of other reasons why manufacturers decided (or not) to go with balance shafts.

Thinking out loud..
Positives: Less NVH, others??
Negatives: Added rotational mass, additional wearing parts, expensive R&D, expensive to manufacture, etc., etc. etc.

I believe they are hardly used anymore because if NVH is a big factor for your target market group, they likely go with something like liquid filled engines mounts these days (read=much cheaper).

I would be surprised if someone is still making them.

Cheers,
MB



[This message has been edited by markus (edited October 03, 2000).]
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