Balance shafts, Mazda 6.

[Silk]

I don't get to see inside engines much these days, the car is either too costly to repair and goes to scrap, or we fit a used engine as I did here. We wouldn't normally pull them apart, but we had a kid on work experience, so got him to pull the sump to see if we could find the knock. I didn't expect to see these balance shafts, most have an external belt, chain or gear drive, this is a bit different. I did split the case and it has a couple of gear driven shafts. We suspect a collapsed piston.

 

[Shannow]

Wow, that's an expensive way of doing it...they mus be targetting some other orders of vibration also to be such a high speed set-up.

Do they destroy the oil with the high speed gear mesh ?

 

[Silk]

It'd done 40,000km since it's last oilchange, and then developed a bad knock not long after....but it looks pretty clean in there. The balance shaft housing holds about 200ml of oil that'd never be changed, and what came out looked black and thick. That large gear is a crankshaft web. I guess with an alloy block the bearing cradle is a must.

 

[hpb]

That's an interesting setup alright, quite ingenious really! A big improvement over, say, the old Astron 2.6 Mitsubishi engines, with their rattly chain driven balance shafts.

 

[d00df00d]

Originally Posted By: Shannow
Wow, that's an expensive way of doing it...they mus be targetting some other orders of vibration also to be such a high speed set-up.

Do they destroy the oil with the high speed gear mesh ?

An inline-4 will have second-order up-down vibration; hence, twin counter-rotating shafts rotating at twice the crank speed.

According to this: http://www.autozine.org/technical_school/engine/smooth2.htm

 

[Shannow]

Originally Posted By: d00df00d
Originally Posted By: Shannow
Wow, that's an expensive way of doing it...they mus be targetting some other orders of vibration also to be such a high speed set-up.

Do they destroy the oil with the high speed gear mesh ?

An inline-4 will have second-order up-down vibration; hence, twin counter-rotating shafts rotating at twice the crank speed.

According to this: http://www.autozine.org/technical_school/engine/smooth2.htm


Yeah, I'm all over that.

But look at the diameter of the bull gear (crank web turned into a gear), versus those it's meshing with...D/d, theres a lot more than 2:1 ratio in there.

 

[Vern_in_IL]

This is nothing new. We had a 1988 Oldsmobile Ciera 4 cyl. with these balancing shafts.....except they integrated the oil pump into the unit as well...

The Iron Duke engines, usually called Tech4's.

 

[edwardh1]

some camry 4 cylinders run smoothly, and most hondas ,
the olds 84 ciera we had, had terrible midrange vibrations.

we had a 4 cyl camry with balance shifts that ran well and smoothly, think it had a single? balance shaft

 

[HerrStig]

How long is the oil trapped in the balance shaft drive going to lubricate properly? "Black and thick" you said.

 

[Papa Bear]

Originally Posted By: Silk
It'd done 40,000km since it's last oilchange,


How often are you supposed to change the oil in that vehicle?

 

[Silk]

Originally Posted By: HerrStig
How long is the oil trapped in the balance shaft drive going to lubricate properly? "Black and thick" you said.


The shafts are on plain bearings, pressure fed. But there is no drain in the housing. As Shannow points out, it looks more than 2:1, but I'd have to count teeth to work that out, and that's not going to happen.

 

[Jetronic]

you can just measure diameter aswell.

looks about right to me, the bigger gear in the balance shaft housing takes up about half the width of the pan or block...

 

[Kiwi_ME]

No matter how it looks the ratio must be 2 times crank speed. Just about every modern inline four over 2 liters is going to have second-order balance shafts of a similar design. BMW puts them on their 2.0 fours as well.

 

[Shannow]

Agreed,...there must be a reduction set in there somewhere at the lumpy end.

Want to go digging ?

A paper on design, and why they don't chain drive them

http://www.researchgate.net/publication/...d_Diesel_Engine

 

[Kiwi_ME]

A pic of the other side is here:

http://i142.photobucket.com/albums/r86/C...alanceShaft.jpg

 

[asand1]

Seems to me this would only mask vibrations, wouldn't reduce stress on the crankshaft, would shear oil, and would use some HP. If I was driving a vehicle with these, they would likely get removed the first time I had reason to pull the pan.

 

[Jetronic]

true, but you'd get vibrations...

a 2.0 can do without with ease, but 2.4 and above they'll be missed. Petrol engines then...