Bronze bush bearings

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fuelburner

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Hello,
Few months ago I finished my first engine after not been able to resist building one when got a lathe less than a year ago and its the Webster engine and runs well (Well would like to make a carb that can fuel correctly throughout the full rev range but that's for another day).

Anyways after 30 plus hours worth of running around 1000 rpm and random high rev bursts the bushes are wearing heavily.

I used SAE660 phosphor bronze bar with silver steel rod non hardened with a oil feed cup as per design and when completed there was about 0.02mm play between the bush and shaft barley noticeable and tight.

Now the crank pin and rod have lots play showing not far from now 0.1 mm play and the bush and shaft wearing evenly together. This one is lubricated with a grease cup.

The closest main bearing bush is showing signs of wear but no where near as much around 0.05mm play.

So basically my question is how can I make the bushes last longer and is this wear normal ?
Would a casehardened silver steel rod shaft and possibly pb102 bronze last twice as long or more?

Or for long hours of running am I better off using ball bearings?

Cheers for any ideas these was the first bushes I made and used a reamer for the bush and would like to sort these wear issues before building another engine.
 
Hi
A few points to check the oil used and an adequate amount of the right viscosity in the bearings at all times
The final finish on the Silver Steel shafts needs to be a mirror finish
The bursts of high RPM are not doing any good.
Ball bearings will give superior service but detract from the vintage look of the webster engine.
Needle rollers on a hardened shaft is an alternative compromise.

Eric
 
I switched to needle roller bearings on a Corliss, so much less friction. I will never ever wear out any bearing with it but I really like the needle bearings. I was able to completely cover them so no one will know without disassembly.
 
After some looking into it most likely more had 0.05 mm of play to start with which is way to much at a guess since a rough guide seems to be 0.025mm per inch diameter and I used a 8mm shaft so wants to be more 0.01mm of play ?

I guess this design uses hydrodynamic mode which will not happen with 0.05 mm play on a 8mm shaft.

I used full synthetic engine oil that had at time 10W 40 .
The shaft was a pre ground silver steel rod which looked to have a good finish possibly I could of polished it more . I used that rod measured at 7.98mm straight into a reamed bronze bush which making a new bush now with same tools and technique its measuring more at 8.02 to 8.03 mm.

Cheers for the ideas guys i wasn't to concerned with the look (Was happy enough with a running engine ! ) so bearings could be a option although would like to beable to make good bushes.
 
Fuelburner--one of the main causes of what you are seeing is the result of a crankshaft not being perfectly "true" between the main bearing surfaces. By that I mean perfectly concentric. It is almost impossible to machine a model crankshaft and not have some "run-out" from one end to the other. As a result of that, the crankshaft doesn't run perfectly true in the bushings. It will "squirm" a tiny bit as it rotates. Since the steel crankshaft is harder than the brass or bronze bushings, they will wear at a higher rate than you think they should. Bushings are very unforgiving when it comes to "linearity" of the shaft turning in them. Ball and even needle bearings are a bit more forgiving of this, as they allow a tiny bit of misalignment.---Brian
 
Hello,
Brian I have seen your webster build and good job I must say even used a design based on your crank throw dimensions ...

I made sure the bushes was as true as possible but yea they will not be perfect for sure.

Out of curiosity roughly how much has your engine run and what is the wear like on your bushes ?
 
My engine has ran about 5 to 8 hours. I can not detect any wear on the bushings, but then again, I haven't looked for it.---Brian
 
Okay Im going to remake my crank this time harden it and make a tighter fitting bush out of pb102 and hope it lasts longer.
 

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