Engine Bushings

[gregwils]

I sourced all of the bearings for my planned 160 rebuild, but not so on some of the bushings. I don't have the equipment to make them myself, and have not found a source with the correct sizes. What is the most common way to get these bushings if you need them - have them made or does someone sell the correct sizes? thanks.

[Paddy]

You dont say where you are but most bearing suppliers will supply oilite bushes

http://www.bearingboys.co.uk/Oilite__Be ... tAod6zQAMA

[gregwils]

Thanks for the link. I did find bushings of similar sizes. Let me be more specific by way of example. There is a bushing listed for the points/pump cover in the parts manual for the 160 and the 250 as # 40049263 with the size of 15 x17x18. I am interpreting that size as 15mm ID x 17mm OD x 18mm L/W. Assuming my interpretation is correct - all the bushings and bearings have their sizes listed in the manual, but I can't find a matching size anywhere. The webstore you provided has the same Oilite sizes as the others I have found. Am I missing something? What do others do?

PS - I added my location to my signature - good suggestion.

[Jordan]

You don't want to get a lathe?
They're great for making bushes and spacers, but you'll need to spend some time learning how to do it. Another hobby!
A low spec lathe would be adequate.
Idea: Try to find a hobby machinist in your area, who might be willing to turn up the odd bush for you.

Jordan

[Paddy]

These people do 15x17x 50 so you just need to cut to length. and they are your side of the pond
#
http://asbbearingsonline.com/index.php? ... 20a&page=5

[gregwils]

You don't want to get a lathe?
They're great for making bushes and spacers, but you'll need to spend some time learning how to do it. Another hobby!
A low spec lathe would be adequate. Jordan

Actually, I would love to own a lathe. I just don't have the time for another hobby, I am having a hard enough time making my weld beads look half-way decent.

[graeme]

Try Phil at Road and Race in Australia.
But most standard size bushes won't fit that well and will need reaming or may be too sloppy.
Best to get them made locally to your exact size.
Most engineering shops can make and fit them for you

Graeme

[Eldert]

why do you need new bushings ? they dont need to be tight . all bearings are hydrostatic that means they ride on a oil film
to tight means no room for a oil film . i rebuilt many engines and the only bushings i ever replaced are the
oilfeed bushing to the crankshaft in the timing cover and the bushing in the selectorbox where the splined
shaft goes thru and only when this was real sloppy

Eldert

[gregwils]

Why do I need new bushings? Good question, just being prepared and wanting to do a thorough job. I will examine each bushing before I make a decision. I have read many of your posts, so respect your opinion.

[StewartD]

Eldert,

I disagree with your statement:
"they dont need to be tight . all bearings are hydrostatic that means they ride on a oil film
to tight means no room for a oil film"

First, I think you mean 'Hydrodynamic', that is the shaft self-centralizes due to the oil pressure that is created when the shaft is rotating. This oil pressure is higher at the side of the bearing where the clearance is smaller, the oil present is pressurised due to the shaft rotation trying to drag the oil through this 'choke' point. If clearance is not too small or not too large then this oil pressure forces the shaft away from the 'choke' point and tends to centralize the shaft. It will never fully self centralize, if it did then the difference in clearance would cease to exist, and the pressure would not be created.

For the shaft to float in this manner the clearance must be within tight tolerances. If a bearing is running in this way there will be no wear. However on start up, before the hydrodynamic situation is established. there will be metal to metal contact and wear will occur. Also where there are shock loads, wear will occur, due to momentary contact between shaft and bushing.

The bushings that might aspire to this ‘wear free utopia’ will have a continuous pressure feed of clean oil. This sort of situation is sort after by engineers. The plain bearings in automotive crank bearings (big ends and mains), are designed for the hydrodynamic ideal of no metal to metal contact. The clearances are critical. No automotive fitter would fit crank bearings with the attitude of "they don't need to be tight". They fit them to very close tolerances.

The problems of metal to metal contact on start up and due to shock loads require the bushings or bearing shells to be made of a material such as bronze, that have an inherent ability to withstand metal to metal rubbing. Also the bushing must tolerate impurities in the oil.

The ideal of hydrodynamic bearing lubrication is not likely to occur in the Ducati engine. The only bush that has a pressure feed is the oil feed bushing of the crankshaft. For this bearing to establish the hydrodynamic condition the shaft to bush clearances would have to absolutely perfect. The crankshaft would have to be running absolutely ‘true’. If there was any runout, then the higher pressure would not have time to become established

The task of this bush is not to support the crankshaft however. It is only to provide a seal so oil is fed to the big end bearing. As the big end is a roller bearing there is very little back pressure and this feed bush does not need to seal very well.

The other bearings in the Ducati all benefit from fitting to correct clearances. If a bush is fitted with too much clearance, then the contact between bush and shaft becomes very small. Without some distortion of the bush it would approach a ‘line contact’ only situation. 'Line contact only' equals zero bearing area; zero bearing area means infinitely high metal to metal contact forces and destruction of the softer metal.

Cheers,

Stewart D