How long does stroked engines last without silent shafts

[ROCKETMAN]

Speaking with the engine builder today he didn't seem too happy about me rebuilding the engine without balancing shafts.

According to http://en.wikipedia.org/wiki/Balance_shaft there is nowhere that mentions running engines without shafts sacrifices their longevity.
The engineer explained the effects of engine harmonics and most of it was complex and hard to understand.

What do you all think?

[Junkers]

I'm not 100% on how much it cuts your engine life down by but it's nothing drastic, it's quite a common mod.

[ROCKETMAN]

^^^It's true I know staz owners running then without problems but will it be more of an issue since I will be stroking the engine?

[AB]

He might of mentioned it for liability reasons if he has had experience with angry customers coming back to him with broken balance shaftless engines. Weather there is actually a link between the engine breaking and the removal of balance shafts would be very hard to prove, but people have a tendency to latch onto any possible negative action being the cause of usually unrelated events, for example everyone has probably heard something like "a mate used oil X and two months later has engine blew up, therefore oil X must be the cause of the engine blowing up".

If it were me I would take the balance shafts out. Although after reading that wikipedia article it seems the vibrations will become worse with a stroked engine.

[tri26t]

Being harmonic and vibration are 2 differant fish
and that it is harmonics you would want to be rid of
then a TOTALLY balanced crank after shaft removal
must be the cure ?? NO ??
Cheers:Phi.

[DKshauno]

you'll have more problems leaving the balance shafts in then removing them. I've removed mine and had no problems

[NachoMan]

Same. I've had balance shafts removed on all of my motors, with no ill effects.
You gain a little extra power too.

[tri26t]

hey DKshauno you know how lyndon rev`s his stazza
and how many shafts he`s seazed
so I reckon leave them in and you`r sure to get SHAFTED
sooner or later, although Ive never had shafts fail

Cheers:Phil.

[kiwieurospec]

The only reason to remove shafts is for competition engines. They only sieze through poor maintainence, if you are reconditioning your engine why would you not expect them to last for another twenty years. Power gains is similar to a couple psi of boost.

[ROCKETMAN]

hey DKshauno you know how lyndon rev`s his stazza
and how many shafts he`s seazed
so I reckon leave them in and you`r sure to get SHAFTED
sooner or later, although Ive never had shafts fail

Cheers:Phil.

Could you please elaborate? How does a shaft seaze?

[RiceThief]

Having a totally balance crankshaft or engine assembly will not take out the vibrations, its the inherent nature of having long stroke motors. By increasing ur engine capacity by increasing the stroke may increase these vibrations, this is why porsche bought the rights from mitsubishi to use silent shafts in their 2.6 4 cyl.

The silent shaft can seize if you have oiling problems, they will go first because they spin twice as fast as the crankshaft.

[tri26t]

harmonics are indeed problematic with cruizing cars
say highway cars, but most stazza drivers that I know
are still on/off throttle and probably drive above or
below the harmonic positions (maybe by accident)
but I cant see how leaving a shaft in place would do
justice to an altered engine when (as stated b4)
most stazza engines are Stroked and/or over bored

So saying that, wouldnt this mean that balance shafts
would NOT be of the right harmonic frequency anyway ??

What RPM is a shaft spinning at anyway,FK:Engine RPM =6000 ??

SHAFTS OUT FOR ME
Cheers:Phil.

[RiceThief]

Actually i made a mistake when i said the vibrations are inherent to long stroke, second order vibrations are inherent in the inline 4 cyl design and is exerbated with increase stroke.

Second order vibrations have nothing to do with throttle position but engine rpm, on my engine without balance shafts its noticeable after 3000rpms. Balance (silent) shafts are there to reduce/eliminate these vibrations by spining in the (reverse?) direction at twice the speend of the engine, that is their "justice", if you dont care about nvh, and can deal with the vibrations by all means remove it.

As I said said they spin at twice the speed so if ur engine is spining at 6000rpms then they would be spining at 12000 rpms

[TWIMCAM BOY]

dont even think about puttin them in!!!! i had them in my vr4/starion engine and it spat out the bearing and cracked the block so i had too rebuild the engine that engine cost me big $$$ wasn t happy not too mention it was 3000kms old and still on run in tune! TAKE THEN OUT

[DKshauno]

I think the balance shafts actullly spin 4x the speed of the crank, because the oil pump gear is half the size of the crank gear, and it takes two rotation of the oil pump gear to line up the balance shaft, because the oil pump has two different size gears aswell.