Mini Cooper Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
734 Posts
Discussion Starter · #1 ·
So everything says that only diesel engines are affected...

Does anyone know why the diesels are affected and the three cylinder petrols are not?

What's the difference?

Just curious...
 

·
Registered
Joined
·
1,169 Posts
Acoustic issues Mark

The diesels sound is much higher than BMW anticipated

Still don't understand that after what would have been a significant period of prior testing before launch - they must have had ear plugs on at that time then!

But the patrols have had problems too, specifically f56 copper petrol 1.5 - Mini UK said nothing but Mini USA released a statement about engine coolent leakage from the oil filter housing which stopped deliveries until problem was sorted - widely available to read on the internet.

Of course Mini have had paint issues as is widely known but as I'll write up later on my thread, all such problems to the car are over...
 

·
Registered
Joined
·
734 Posts
Discussion Starter · #3 ·
I think I understand that the need for a counterbalance bar is because it has three cylinders... so I thought the petrol engines must have a counterbalance bar too...

So what's different between the engines and bars such that the diesel engines have a problem and the petrol engines don't?
 

·
Registered
Joined
·
1,169 Posts
On the whole petrols are genuinely quiet and diesels suffer from the "rattle" especially lower cylinder ones - it's the way the two engines differentiate from one another when converting fuel into energy through a series of combustions - ultimately the combustions differ between the two. That's the only way I can put it.

Without going all too technical it would seem the rattle sound was probably too high for expectations - I can't really personally go technical into it personally I'm limited in the knowledge - but that's what BMW were trying to tome down - the acoustic sound from the Diesel engine when fired up.
 

·
Registered
Joined
·
340 Posts
I think I understand that the need for a counterbalance bar is because it has three cylinders... so I thought the petrol engines must have a counterbalance bar too...

So what's different between the engines and bars such that the diesel engines have a problem and the petrol engines don't?
The 3 cylinder engines do in fact have a counter balance bar, the Cooper S actually has 2.

If you remember years ago, before diesel engines became popular, they were noisy, slow, and had no torque.

Thanks to common rail injection and advances in technology, they managed to make them quiet and with lots of torque. For some reason, the engines in the new Mini were found to be too noisy, in comparison to other diesel engines on the market. I don't know why, or what BMW have done to address the issue, but hopefully it's sorted now
 

·
Registered
Joined
·
87 Posts
I think diesels have always had oodles of torque - well, at least as much as a comparable petrol engine. But the modern ones were less noisy and came with shed-loads of torque...normally demonstrated when zooming up hills.
 

·
Registered
Joined
·
508 Posts
The diesel has a much higher compression ratio, so the crankshaft and conrods are probably heavier than the petrol version, so that they can be stronger, which means the balance shaft will have more rotating mass to balance and so the weights on the shaft will be heavier. Maybe BMW did all the endurance/reliability testing on petrol engines and so didn't discover the diesel balance shaft problem until after the engine was released.
 

·
Registered
Joined
·
72 Posts
Word on the street is that the balance shaft on the diesel is causing a noise. This could be a bearing issue or oil pressure not getting to where it needs to be? Who knows, very little info has been released.. in true bmw style lol

while you can do all the bench testing in all the world, you must remember very little real world testing is ever done.

many development engines are put in dyno cells and fed fuel and air mixtures based on various altitudes and ambient temperatures.. with the right test cells this can be all done on the bench.

im sure mini did test the engine packaged up in the actual car.. but may have missed the noise due to many reasons. Development cars are not manufactured in the same way as a production vehicle... in the most part the production lines arent yet in place - so many assumptions are generally made at these early stages.

Therefore when the engine was loaded into the real production cars, engineers may have experienced (what we call in the game) excessive NVH - noise, vibrations & harshness...

There are many harmonics a diesel engine transmits, to the point that noise could be more apparent in the mini that what it might have been in the bmw 1 series... each package offers so many variables - some of these things get thru to the customer.

you can be sure anything safety related will not get thru in this way as those items are tested and tested again in simulated real world scenarios.

Back to the engine and why it needs a balance shaft...

in most cases engines, especially v engines, are typically smooth when running... this is taken care of by the crank design & the counter balance the crank would have built in - we call it the crank web.

we also use crank dampers pulleys to soften off NVH with the engine....

when you get inline engines you can only go so far with crank design and using damper pulleys... Thats when something like an I3 comes along.

An I3 engine is inherently out of balance due to its firing order... firing pulses has a tendency to induce an end-to end rocking motion... which makes the engine shake.

this shaking can be counteracted by using a balance shaft... a shaft driven by the crank with a weight attached. This zaps power from the engine and makes it less efficient than an engine not using a balance shaft...

take the ford eco-boot engine... now this I3 uses some pretty clever crank angles and an unbalanced flywheel to remove the need to use balancer shafts... cool eh!

To reduce noise the main timing chain / belt has been housed within a wet casing, which also helps to keep the noise down.


The major difference between diesel and petrol engines is the way these explosions happen. In a petrol engine, fuel is mixed with air, compressed by pistons and ignited by sparks from spark plugs. In a diesel engine, however, the air is compressed first, and then the fuel is injected. Because air heats up when it's compressed, the fuel ignites. The compression ratio is normally a lot higher in a diesel engine.

A high compression ratio is desirable because it allows an engine to extract more mechanical energy from a given mass of air-fuel mixture due to its higher thermal efficiency.

The side effect of this higher compression ratio is the noise.

Diesel engines have in the past always been fuel injected where petrol engines didnt... mechanical injectors were very noisy...

common rail injection is a common thing these days between petrol and diesel engines... and very good system for controlling emissions.

Conn-rods, crank, & block material dont normally play that much of a part when it comes to balancing out an engine... there are various reasons as to why certain materials are selected, generally longevity, strength and weight.

over the years ford has made engines from various mixtures of ali / cast iron / steel... all ali, or all cast iron blocks...etc...

these days we are driven to make engines as light weight as possible, so ail is the material normally used... however, the most recent I3 petrol engine used CGI... when normally it has been ali in recent years...

hope this post didnt go too deep and explains enough to understand the differences....

i work at ford, in powertrain, if you didnt gather that already lol
 

·
Registered
Joined
·
734 Posts
Discussion Starter · #9 ·
Thanks for some great answers!

So basically, three cylinders implies counterbalance bar (or other measures), so both engines will have this.

But diesel has higher compression leading to larger forces and more noise if the balancing is off.
 

·
Registered
Joined
·
12 Posts
hi

I just got my new 5 door 1.5L the engine I feel have excessive noise, vibrations & harshness... I can hear it inside the cabin. How can this be.

I am not sure this only effects the 5 doors model. The 3 door I tested it didn't have this noise.

I am going crazy. The dealer tells me is normal. Is actually louder then the music. How can this be.

pls chk

http://youtu.be/j-PE2xhXKCA
 

·
Registered
Joined
·
86 Posts
hi

I just got my new 5 door 1.5L the engine I feel have excessive noise, vibrations & harshness... I can hear it inside the cabin. How can this be.

I am not sure this only effects the 5 doors model. The 3 door I tested it didn't have this noise.

I am going crazy. The dealer tells me is normal. Is actually louder then the music. How can this be.

pls chk

http://youtu.be/j-PE2xhXKCA
I've not driven a petrol mini with the 3 cylinder, but I must admit your car sounds noisier than my cooper diesel which has covered nearly 6,000 miles in 2 months. I have driven 3 cylinder petrols in the past and they have always sounded a bit 'throaty' like a V6.
 
1 - 12 of 12 Posts
Top