WHERE'S JOHAN BORNMANN!!??

[Veloce]

JB, there's no time to take time off when there are hubbers out there with burning technical questions!!!

I need help, but i will first ask you about my bicycle problems :

 

1) I have a campy chorus chain that i took off another bike and now want to put it on my new bike. Is it safe to just link the chain with the existing half pressed out pin or should i rather put a power link?

 

2) I used to ride a 9 speed and had to put a spacer before fitting the cassette. I now have a 10 speed cassette, so i left off the spacer and only put the thin one that came with the new cassette but after tightening the lock ring, the sprockets are still loose. Do i have to find a different thickness spacer now???

 

3) Okay, off topic but here goes. I have a 1972 Alfa Romeo and the cast iron cam shafts run directly in contact with the aluminium head. There are no bearings at all. Why does the cast iron cam shaft wear out before the aluminium head?? Someone once told me that it is all to do with lubrication, and that lubricated aluminium will outlast anything when there is friction involved. 

 

  

[dirtrider]

And now we all know why a Alfa does not last !

[AndreZA]

And now we all know why a Alfa does not last !

 

Just because he fit a spacer to his 9spd cassette?

 

 

[Veloce]

Why???? The cam shafts only showed slight wear after 300 000kms and the head is still perfect. When a mechanic says Alfas are k@k he describes  his abilities more than the vehicle!!!!

[Tumbleweed]

i think he's in cape town, doing a maintenance course (that's according to the calendar i have)

[Wannabe]

How do you make a "Draadkar" leak oil?

 

Just put an Alfa badge on it!!!

 

OK, my first post in many weeks, and I go look for trouble, but I just could not resist this one.

[javadude]

The chorus cassette should have come with all required spacers. With mine i don't have to fit a spacer before the first sprocket goes on, so not sure what the problem is with yours.

[Sammajoor]

He can like to be playing wiff his yellow saddle

[bob_the_builder]

 

i think he's in cape town' date=' doing a maintenance course (that's according to the calendar i have)[/quote']

 

What are you his PA?

 

[Veloce]

Johan, sometimes we really under estimate the genius that you are. By keeping quite and not replying to my questions, you knew that the best way i would learn was to make mistakes and learn from them. Like a father showing a misguided son the light, little grasshopper is learning.

 

So, because of your sheer genius, i have answered the first two questions myself and am amazed at the simpicity and ease of maintainence of the Campagnolo design. You can still help me with the last one though because little grasshopper has run out of resources for this one.

[bobbie]

haha brilliant Grasshopper!! i mean Veloce!!

 

 

[Joe Low]

i think he's in cape town' date=' doing a maintenance course (that's according to the calendar i have)[/quote']

 

 

 

Doesn't he already know everything about the subject?

 

 

 

[Johan Bornman]

Johan' date=' sometimes we really under estimate the genius that you are. By keeping quite and not replying to my questions, you knew that the best way i would learn was to make mistakes and learn from them. Like a father showing a misguided son the light, little grasshopper is learning.

 

So, because of your sheer genius, i have answered the first two questions myself and am amazed at the simpicity and ease of maintainence of the Campagnolo design. You can still help me with the last one though because little grasshopper has run out of resources for this one.

[/quote']

 

I have to work sometimes, you know. Was doing classes this weekend and then I tend to stay away from the PC.

 

Anyway, glad to see you sorted your questions.

 

As for the Alfa head. I speak under correction but the wear part on that head is not aluminium but white metal, a soft metal that looks very similar. Sometimes it is placed as a lining on top of aluminium or a  cast iron part. White metal is an alloy of antimony, tin, lead, cadmium, bismuth and zinc - not necessary all of them. It makes for excellent bearings if they can be lubricated with filtered oil. They have a low co-efficient of friction and are ductile enough to reshape themselves and perfectly fit the profile of the harder material running on them. In a car through, the two surfaces don't rub against each other but run on a bed of oil that's pumped into the bearing by means of a hole. The oil pump supplies oil to the hole and it is ditributed through the bearing by way of a groove in the bearing. Note, the use of bearing does not denote ball bearing but a plain bearing or bush.

 

The reason the cast iron shaft wears before the soft bearing is because all is not what it seems in that soft metal. Although the white metal is soft enough to be cut with a penknife, the antimony in there forms hard crystals in the softer substrate and the shaft actually runs on that. The iron wears before the antimony. The other metal in that bearing wear away slightly, allowing the oil to circulate reasonably freely between the cast iron shaft and the white metal. Most wear happens when the car is labouring and the shaft distorts, overcomes oil pressure and pushes the oil away and of course on startup when there is not enough pressure yet and the surfaces run only on the residual oil.

 

This is an excellent bearing system and not even ball bearings have displaced plain bearings in engines and turbines. However, the oil must be absolutely clean otherwise Alfa things happen.

 

 

 

 

Johan Bornman2008-04-14 09:38:50

[Veloce]

Thank JB. This is fantastic information. Would you mind if I copied and pasted it into an article for our clubs newsletter???

 

Alfa things happen?......Hmmmmm. I'll leave that bit out though  

[Johan Bornman]

Thank JB. This is fantastic information. Would you mind if I copied and pasted it into an article for our clubs newsletter???

 

Alfa things happen?......Hmmmmm. I'll leave that bit out though  

 

You're welcome to use it, but it probably needs a bit of editing for clarity. I'm not always sure if my writing is too technical or if I attempt to over explain things. Something interesting I can add about white metal bearings is that their condition can be tested through oil analysis. By zapping a sample of the oil with a known hours or miles of use into a spectroscope, they can see how much of the bearing material (or in an Alfa's case, crankshaft material ) there is in the oil and make a reasonable judgement as to the bearing's condition.

 

I have an old Merc that I bought new in 1986 and put some high mileage on. All the way from 250 000 kms I used to take an oil sample after every 50 000 kms or so to the lab and ask for an analysis. Up to 500 000 kms they detected nothing usual. Eventually I had the engine redone because toher things started to fail and I lost faith in its immortality. When the mechanic measured the bearings there was nothing wrong with either the shafts or the bearings. We replaced the white metal bearings as a matter of course, just in case.

 

I stil remember cutting chunks of metal out of the old bearing with a pen knife, amazed at how this miracle metal works. That's when I discovered that it was invented some 100 years ago by a chap named Babbit.

 

Something else that I found interesting about big end bearings (those are the ones on the crank shaft) is that they are designed to leak oil. The oil pumped into them under pressure squirts out the sides and lubricates the inside of the cylinder behind the piston. Not only does it lubircate it, but it also cools it. Hot liquids rapidly cool when squirted out a nozzle under pressure.

 

There are lots of other interesting things that happen in there but this is a cycling forum and gratuitous tech will be flamed.

 

 

 

[R2S2]

In the case of modern aluminium heads, use is no longer always made of white metal, as the oxide layer that forms on exposed aluminium is crystalline in nature, and does exactly what Johann said about the crytals in white metal.  The crankshaft and block is another matter altogether, and there you will still find many white metal bearings.

In some high performance car engines (notably Porsche, who patented it) a material called Nikasil is plated onto aluminium wear parts to make them even more wear resitant.  Not on your Alfa though...