Silent shaft/balance shaft belt

[ccautos]

I had a customer pose a question to me recently and I am trying to get a general feeling from mechanics on their opinion.

If a balance shaft belt was to break, unknown to the owner for approx 10,000km would it cause any potential long term engine damage and if so what would that damage be ??
Also what could cause that belt to break if it has been replaced along with the tensioner.
I have already put forward my ideas but would like independant opinions from others to pass on to the customer.

Thanks, Glen

[jessef]

The balance shaft belt can take out the timing belt and we all know what happens when the timing belt goes.

[ccautos]

Anything else it might damage ?? If both the balance shafts are not turning ?? Timing belt is still turning and engine is still running.
I am a licensed mechanic and I am fully aware of the correct answer here, just trying to achieve a second opinion.

[Mephisto]

Not to say it is correct in any way, but for both the 4G63 and 4G54 engines (of which the latter is nearly identical to our 4D56 block) there are many balance shaft eliminator kits available. I don't know specifically about our engine, but the 4G54 eliminator kit comes with a shorter chain (obviously chain drive rather than belt) to run the oil pump, so if the belt broke there would be no oil pressure = dead engine. As I said I don't know the specifics for the 4D56, so I can't say whether the oil pump is on the balance shaft belt. I also agree that it would be unlikely for the balance shaft belt to go without taking out the timing belt. The general concensus in the performance gasser field is that if you have your reciprocating mass balanced it's ok to eliminate the balance shafts that is of course as long as your oil pump is still being turned, lol. Just remember a person building a performance engine is not looking for longevity.

[ccautos]

It is not common that the balance shaft belt breaks and causes the timing belt to fail also. The belt normally breaks and just lays in the bottom of the engine(but the possibility is there). I have seen many Delicas with failed balance belts that apart from noticeable shaking do not have any running issue. My customers concern is that if an engine were driven for an extended period of time without that belt turning the two shafts would it cause any potential long term engine damage. The main engine oil pump is driven from the crankshaft and so general engine lurication is maintained but the lower balance shaft doubles as a small oil pump. The upper balance shaft is exactly that a balance shaft and does not create any issues. I have explained to the customer what I think could potentially happen with this engine and I am looking for a second opinion from another mechanic that has Delica specific knowledge.

[Modsqwad]

I'm wondering if the added vibration could cause cracking in things like the manifolds (weight of the turbo package) How severe is
the vibration with the shaft not turning?
Andy Wilson

[RaddCruisers]

I have seen a couple of balance shaft belt failures, and they have taken out the timing belt with them. Once the timing belt breaks, there's the not too much concern of damage related to the balance shaft belt breakage since everything grinds (crunches) to a halt pretty quickly.

The balance shaft oil pump would appear to supply oil to the piston bottom oil cooling system. If this system was to fail, I can't see there being any long term problems if not repaired immediately. Over the long haul, there may be some issues with reliability... Having the engine running without the balance shafts operating may lead to some longer term problems, but my impression is that most balance shafts are in place to make small diesels (and some gas engines) appear to run more smoothly than they otherwise would without doing other things, like adding a much heavier flywheel (reduces economy, makes the engine less responsive to revving).



A few pictures for your viewing pleasure....

Some of the types of belt breakage I have seen:

Belts (new or old) which are too loose - and the flapping of the belt exceeds its tensile strength and the belt breaks. The breakage is usually straight across with a few strands pulled out. Evidence is often noise (belt hitting covers) and then the uneasy silence of your newly dead engine...

Belts that are clearly very old and are still in use. Mileage is NOT a good indicator of the need to change a belt. I always make a point of noting that if the service history is unknown, the belts must get changed at the first opportunity. Belts (2) along with the tensioners (2) must be replaced at least every 5 years or 100,000km whichever comes first. Belts that are really old can often be easily torn by hand, the breaks are of all types, but straight across with few (if any) strands sticking out seems to be the common one.

Contaminated belts - oil, coolant etc... causes the belts to degrade and fail prematurely. Usually the cause of the breakage is apparent due to the saturated nature of the belt and fibres in the belt. The teeth appear flattened at times.

Tensioner pulley failures - the pulleys must be replaced along with the belts... The belts are often torn in really creative ways with lots of fibres and rubber bits all over the place.

~John

[Golf Cart]

Glen,

Wouldn't the majority of vibtration be taken up by the motor mounts causing premature motor mount failure? I can't see any internal damage being done. Could you have a problem with bolt ons , such as starter bolts coming loose. Possible IP pump working loose, or water pump bolts. Enlarging the threads creating leaks ? Electrical connections working loose ?

[ccautos]

My concern was not for the excessive vibration but for the lower balance shaft not turning and there seems to be some confusion over what the lower balance shaft actually does other than balance the engine. When ordering the seal for the lower balance shaft it is described by Mitsubishi as the "oil pump seal" and we are trying to establish whether that is because the shaft passes through the oil pump housing or whether it drives an auxilary oil pump. Examining the engine it appears that the lower balance shaft does turn another smaller shaft inside the engine that comes into the back of the oil pump housing. What we are trying to establish is what this is driving and whether it would cause any long term engine damage by not spinning. We did earlier today remove the oil filter housing adapter from an old engine to examine this but did not have time to remove the oil pump to expose this additional shaft. Will post any findings to clarify what this is and what it does. Thanks, Glen

[RaddCruisers]

Glen,

Wouldn't the majority of vibtration be taken up by the motor mounts causing premature motor mount failure? I can't see any internal damage being done. Could you have a problem with bolt ons , such as starter bolts coming loose. Possible IP pump working loose, or water pump bolts. Enlarging the threads creating leaks ? Electrical connections working loose ?

Most of the "vibration" would be in rhythm with the engine, and would not affect fastener tightness, but more the driver's impression of how smooth the engine is. The shafts move quite slowly in the scheme of things, and offset the natural motion of the engine's rotating assembly. Some engines are, by nature of their design, more balanced than others. 6 cylinder in-line diesels are naturally quite smooth, as are 5 cylinder engines. 4 cylinder engines tend to be less balanced, and hence the shafts.

Glen can add to this as he finds time.

[RaddCruisers]

Here are some photos of a block and the front cover removed.

You can see that the balance belt drives an oil pump, that goes up through the pump gears and in turn drives the lower balance shaft. The oil passages go from the oil cooler/oil cover on the right side of the engine to the oil pump on the front housing.

The oil passages from the balance shaft/oil pump go to the piston skirt nozzles.

~John

Edit: I should add that the primary oil pump is driven by the crankshaft and is the reason for the splined section on the front of the crank (not visible in my pictures). The secondary oil pump is driven by the balance belt. I haven't fully followed the oil passages through the secondary oil pump to see where they go, but it appears that they only supply the piston bottom nozzles. I could dig into this further if there is any interest.

[marsgal42]

Most of the "vibration" would be in rhythm with the engine, and would not affect fastener tightness, but more the driver's impression of how smooth the engine is. The shafts move quite slowly in the scheme of things, and offset the natural motion of the engine's rotating assembly. Some engines are, by nature of their design, more balanced than others. 6 cylinder in-line diesels are naturally quite smooth, as are 5 cylinder engines. 4 cylinder engines tend to be less balanced, and hence the shafts.

Have a look at http://www.autozine.org/technical_schoo ... mooth1.htm.

The balance shafts in our 4D56Ts run at twice crankshaft speed - the masses are balanced, but the accelerations are not. A 5 cylinder engine has an intrinsic end-to-end vibration, balanced out by a shaft running at crankshaft speed. So do inline 3s, V6s and V10s. Inline 6s are balanced, as are V12s and cross-plane V8s. But not flat-plane V8s. And so on.

...laura

[Golf Cart]

And all this time I thought the reason was 4 doesnt go into 720

[MieRo]

While replacing my engine head, I noticed the belt of my top balance shaft is gone. The shaft itself is stuck and the pulley is loose, I don't know which happened first, the belt coming off or the shaft getting stuck.

I would rather not replace the shaft, considering the cost and effort.
> Is this a bad idea? Obviously I don't mind the engine vibrating a little more since I only noticed now.

[Yokohama]

Considering that the balance shaft belts turn both the shafts and the secondary oil pump, I would consider finding out what is wrong with the upper shaft. It could be that the upper shaft bearings have seized for some reason.

Not having the piston skirt oilers working will not be good for the engine, but how much additional wear/issues it will have is unknown.