76 replies to this topic

[sledgehammer]

.I like Tiger's idea of pre-lubricated needle rollers for primary gear.  Maybe a case-hardened sleeve with a wall thickness of 1 mm fitted over the crankshaft end with oil seals recessed in at each end to allow for the thrust washers. After all, wheel bearings are pre-lubricated and the grease doesn't normally get onto the brake discs. I'm sure the crankshaft tail diameter could go down a bit to allow for needle bearing diameter. There could be a bearing at each end and these could be quite long. Anyone fancy trying this.

I wonder if you would use high melting point grease - or oil ?

 

also with a seal at each end would it pressurise when the crank warms up ? - or could it be vented ? or the void is so small so not a problem ?

[Tamworthbay]

On current BMW's the timing chain is at the back of the engine, but the chains are said to last the life of the vehicle.But if you have, say, a 100,000 mile 7-year old BMW and the chain snaps, the cost of repairs is so high that the vehicle is scrap so, one might accept, the chain has lasted the life of the vehicle. Cynical, moi?!

This is becoming a major issue, as you say the cost of fixing it often outweighs the value of the car. The price of second hand BMWs are plummeting as a result, especially 6-8 year old ones at auction. Its a bit of Russian roulette but you can pick up some bargains.

[sledgehammer]

On current BMW's the timing chain is at the back of the engine, but the chains are said to last the life of the vehicle.
But if you have, say, a 100,000 mile 7-year old BMW and the chain snaps, the cost of repairs is so high that the vehicle is scrap so, one might accept, the chain has lasted the life of the vehicle. Cynical, moi?!

 

not cynical - honest - a disposable car

 

if the chain fails early - just out of warranty - a disaster for the owner

[Cooperman]

I believe the problem is caused by the 20,000 mile service intervals as they compete with Merc and Audi.

My 730d had done 100,000 miles and I change the oil every 7000 miles. It seems that the tensioner works on oil pressure and the high-mileage dirty oil causes the tensioner to fail, or to partly fail which then causes chain failure.

I would hate to have to take my engine out of my 7-series to change valves, repair the head and fit new chain and tensioner. But then I hear of 730d's doing over 300k miles with no problems at all.

 

With all chain driven stuff, chain stretch has always been the only real issue. Properly tensioned chains really don't fail so long as they are correctly sized in the first place.

[stretch tech]

Can I buy an Iwis pre-stretched duplex timing chain for a Mini? Please let us all know if they are available.

 

I like Tiger's idea of pre-lubricated needle rollers for primary gear.  Maybe a case-hardened sleeve with a wall thickness of 1 mm fitted over the crankshaft end with oil seals recessed in at each end to allow for the thrust washers. After all, wheel bearings are pre-lubricated and the grease doesn't normally get onto the brake discs. I'm sure the crankshaft tail diameter could go down a bit to allow for needle bearing diameter. There could be a bearing at each end and these could be quite long. Anyone fancy trying this.

 

it is something i have been thinking of. the mini supplier (i think MED) who has recently started using iwis for timing chain only offer simplex, purely because the strength and life time of simplex iwis elite brand chain is greater than other cheaper brand duplex chain so the added cost of duplex isn't worth it. but to answer your question, yes you can. i just need a length to ask for and the size of the timing sprockets. at an educated guess i'd say 3/8" inch pitch (06B-1 British standard)

 

i keep meaning to enquir about it at work but i'm either too busy or forget 

 

Rhys

Edited by stretch tech, 08 February 2014 - 06:49 PM.

[tiger99]

I am puzzled by the need to put a timing chain at the back of any engine! It can't have been easy, compared to having it at the front. I too am cynical....

 

You can't legally modify them now, in Germany (if I have understood the law correctly), so there is little hope of anyone introducing a front chain or belt conversion as a way of saving a potentially moderately valuable vehicle.

[sledgehammer]

Waaaaay of subject ...

 

the old renault 5 had a timing chain against the bulk head - and yes I have been ordered to cut the bulkhead 

 

to do the timing chain - & re-weld  - nasty car built backwards 

 

have also done it the proper way several times - not nice either way

 

I doubt you could make a kit for the BMW - to belt / chain drive from the front - but if you could - you would rich

 

http://www.bbc.co.uk...ngine-2007-2009

 

quote "Watchdog has heard from a driver affected by this same problem who only had 26,000 miles on the clock."

 

BMW was always the boring uncle of the motor industry - always power full , £xpensive , reliable & boring --- but now without the reliable 

 

anyway back to idler replacement ...

[Dan]

.I like Tiger's idea of pre-lubricated needle rollers for primary gear.  Maybe a case-hardened sleeve with a wall thickness of 1 mm fitted over the crankshaft end with oil seals recessed in at each end to allow for the thrust washers. After all, wheel bearings are pre-lubricated and the grease doesn't normally get onto the brake discs. I'm sure the crankshaft tail diameter could go down a bit to allow for needle bearing diameter. There could be a bearing at each end and these could be quite long. Anyone fancy trying this.

I wonder if you would use high melting point grease - or oil ?
 
also with a seal at each end would it pressurise when the crank warms up ? - or could it be vented ? or the void is so small so not a problem ?

There may be a way to run roller bearings dry and have them last a lifetime, at least in this sort of on-and-of intermittent service kind of application, but it's a proprietary treatment heavily patented and not cheap. It's used in motion picture camera movements from a certain manufacturer who managed to completely eliminate lubrication from their machines, while other makes require oiling every 10,000' or so of stock run through the gate. This can mean a camera will be out for oiling up to twice per day which is costly and obviously you don't really want oil near the film, so although expensive it has been extensively developed. It's similar to impregnation methods used in other industries such as semi conductor production. You heat the steel to a specific point which opens its grain structure and then rapidly expose it to total vacuum. At this point the steel is quite weak and vulnerable I understand so there is a fairly high failure rate in manufacture. Then you have to bath it in a plasma of whatever lubricant is required for the task. The open grain free of any atmosphere just drinks the plasma in and then you cool it, trapping the lubricant in place. It's amazing, the steel parts of these cameras film paths feel slippery to the touch. So much so that it's hard to actually get hold of them. But they are completely dry and the lubricant cannot wear off, ever. Obviously thermal management is a nightmare, holding the plasma is a nightmare, having a machine capable of doing all this in a sealed environment is a nightmare. And it costs loads. Still, very cool.

Edited by Dan, 09 February 2014 - 12:21 AM.

[Mr Joshua]

One other point about big bike power being delivered through chains they only last about 12000 careful miles! Now, who on here is willing to have their engine out every two years to be stripped to change chain and sprockets hands up, and if you can't do it your self who would be willing to stump up the bill to have someone do it for them.

Now before offence is taken, let's think of this from a manufactures view. The abuse the chain would be subjected to due to poor maintenance by lazy tight arsed owners could have caused all manner of warranty nightmares which could lead to catastrophic product reviews.

In today's market not an issue for the conscientious mini owner but the drop gear has modification in depth to see off radical component change such as fitting chains.

[Pete649]

One other point about big bike power being delivered through chains they only last about 12000 careful miles!

 

Wouldn't they be under a lot more strain though?

[Mr Joshua]

You would have to look at the torque and how it's delivered. How much torque can a 500bhp Busa actually utilise in a 3.1 second 0-60 pass? Also a bike weighs what 150kg. I would imagine if you dumped 500kg on the the rear axle that chain would not last long. You also have to take into account the smaller you go with the sprockets the chain path around the sprocket moves away from a circular path and becomes more segmented thus causing the chain to ride up and down the teeth of the sprocket.

Like I said if only life were that simple.

[tiger99]

Yes, and I have been known to do well over 30k miles in one year in a Mini, so if I am in a position to do that again, I would hope for at least 100k miles, roughly similar to the life of a diff or well set-up idler gears. I have never worn out the main part of a gearbox, although one failed spectacularly due to manufacturing problems, so I don't know how long the complete transmission would last, but on a 998 engine it must be over 200k miles, with regular changes of Castrol GTX, so that would be a better design aim. Half that for a 1275 would be acceptable.

 

Not going to be easy!

[jimmyjjohn]

Didn't the Princess gearbox have a chain driven input gear in the same arrangement as the Mini drop gears? Good place to start looking.

[69k1100]

Dubious relevance but the 60-70's Cadillacs were front engined front wheel drive with a chain output.

[Ethel]

You'd have to consider the the reaction forces right along mainshaft. The bulk of the webs carrying the bearings is underneath. Considering the idler was used to reduce inertia, how would a chain compare? It could be lighter but it'll certainly have a larger radius of rotation.

 

Potential for keeping the reaction force in the drive chain, and saving the primary gear bush?