Dash01

Exactly how bad is the vibration when the 951 engine is run without the balance shaft belt? After all, most inline 4 cylinder cars don't even have balance shafts or the belts that run them, with no ill effects. Granted, most inline 4 cylinder engines have smaller displacement and pistons than the 951, but how big a deal is this?

What are the pros and cons of simply removing the balance shaft belt?

Is it quieter? More fuel efficient?

Voith

There are no pros. Factory would delete it in a heartbeat if it was anywhere near acceptable.

If anything it can get more oil efficient

Van

A friend of mine had his belt on wrong... in one track event, it broke the dipstick tube and power steering pump bracket...

Go ahead - YMMV!

Dubai944

I broke two alternator tension rods and pickuptube just running without a harmonic balancer...

reno808

HAHA you guys are funny, because its true

kev951

street car, forget about it . Race engine with profesionally balanced and lighter internals ok.

Oddjob

I was told you gain about 5-6hp w/o them, but there are associated risks as noted above.

Fuel rails are also vulnerable to higher vibration - know of those cracking too w/o the balance shafts running.

reno808

search dude

Dash01

OK, thanks for sharing.

I was curious because some years ago on this forum, some folks went on about deletion of the balance shafts and belt. Some had installed plates to cover the holes left when the balance shaft housings were removed, to reduce engine weight.

This had me wondering, so I raised the question once again to gain fresh perspective.

fortysixandtwo

You guys are making is sound like the engine will self destruct, in short order, if the balance shafts are not used. There is not enough reliable data to support claims of broken parts either way.
If the reciprocating masses are going to remain stock and the car is primarily for street use, there is no point in disabling the balance shafts.
If you're going to be installing lighter pistons / rods, and looking to shed as much weight as possible, removing the balance shafts becomes a more viable option.

edredas

The engine vibrates the same with or without the shafts... all the shafts do is keep that harmonic from reaching the occupants in the cabin.

gruhsy

Google 4 cylinder balance shaft for more info. Below is the first paragraph

Balance shafts are most common in inline four-cylinder engines, which, due to their design asymmetry, have an inherent second order vibration (vibrating at twice the engine RPM) that cannot be eliminated no matter how well the internal components are balanced. This vibration is generated because the movement of the connecting rods in an even-firing four-cylinder inline engine is not symmetrical throughout the crankshaft rotation; thus during a given period of crankshaft rotation, the descending and ascending pistons are not always completely opposed in their acceleration, giving rise to a net vertical inertial force twice in each revolution whose intensity increases quadratically with RPM, no matter how closely the components are matched for weight.[2]

refresh951

This is not accurate. The balance shafts cancel much of the the vibration caused by differences in piston acceleration. This cancellation most definitely reduces the vibration load on the engine components.

edredas

The mass rotating inside the engine is very heavy, the shafts only cancel the harmonic that is emitted. They in no way are heavy or forceful enough to counteract the weight being thrown around inside, nor are they meant to.

Voith

rotating mass does not vibrate since it is balanced. reciprocating mass does. 951 has +/- 5kg of reciprocating mass.

balancing shafts are designed to counteract vibration of those 5kg and they acomplish that task brilliantly. because they are meant to.