Technical Information Sheet for the Restoration of the BMW R75 and Zündapp KS 750.
Monthly available on our website.
H - P Hommes
© 2011 h-p hommes
There are several ways to break off a cylinder
The left cylinder you can break off out of stupidity, but this is usually quite painful for the left foot. So it is best to avoid this option if possible.
For the BMW R75 we have quite often the case that the cylinder has got a new bushing but after a short time this proved to be not useful.
When the cylinder has reached the maximum size of 79 mm, it should not be enlarged anymore, since this leads to the distortion of the raceway and weakens the entire cylinder.
In the simplest case it leads to piston squeezings. These are then solved by honing the bushing again been honed and a new piston is inserted.
Then we have, after further weakening of the cylinder wall, even faster the possibility of piston squeezings and consequently the demolition of the cylinder sooner or later.
Rebushing the cylinders is not recommended, because then the remaining connection of the cylinder base towards the cylinder head is too weak.
It is possible that the rebushed cylinder breaks off while driving and has happened often enough.
Can be cylinders, pistons, connecting rods, exhaust, bumpers, and more.
Then you still have the option to remove the cylinder hydraulically from the housing.
Also known as water hammer.
The water hammer
It is well known fact that water cannot compress. If there is a large amount of water sucked into the engine and it is abruptly stopped, then considerable engine damage can result. The connecting rods can bend or the cylinders can be torn off the housing.
This can happen but not necessarily because with some caution this can be avoided.
If you drive slowly using a small revolution speed into the river and the engine sucks a bit of water, it can stop without damage.
The better knowing man can do it differently.
But if the driver takes a real run, drives with a high revolution speed into the river and the engine sucks in water then there can be a great bang and some other ugly noises. After that, apart from the driver swearing, you can only hear the rippling sound of the river. Almost a romantic situation, but not environment-friendly because oil can escape. Unfortunately, this silence of the engine can only be cured with a lot of work and the cost of material.
First the damage looks not that bad, but then you notice that the cylinders are approx. 2-3 cm protruding to the outside. The exhaust has also deformed accordingly. The worst, however, is: Man is still stuck in the river with his bike; woman is sitting in the sidecar having a whinge and noticing that the water is slowly rising in the boat. But the boat is not a real boat because it does not float.
It is not the high engine revolution speed that creates the damage. It is also the thrust of the bike that tries to turn the engine over by the momentum of the wheels. But this condition is not possible because water in the combustion chamber hampers any further rotation. Then the engine is disrupted at its weakest point. Such damage brings very good sales figures for the spare part suppliers but I do not begrudge it to anyone.
So be careful when crossing rivers!
Important is getting through it and this i soften better to use manpower than treating your bike very hard, and as a result the destruction of valuable material.
By the way how was the problem solved between river, cylinder, man and woman?
They still live together. He is driving again. She is sitting in the sidecar again with a new iphone. She is a lot on the phone and he does not cross rivers any more.
H-P Hommes Ersatzteil-Dienst
Ersatzteile + Instandsetzungen
repairing + restoring
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