Porosity, a retrospective

[Lucky Phil]

On 1/28/2021 at 3:41 PM, docc said:

So, how big of a thing is this, actually, with our V11 heads in particular?

Not sure docc but the l/h head on my original engine was affected and a mates MK4 Le mans had porous crankcases around the r/h cylinder base. Plenty with Ducati's.

You'll know it if you've got it, an oil leak you just cant seem to fix is the clue.  

Ciao

[The Monkey]

Glyptol was the go to for the cases on old American bikes. Now with the scarcity of correct parts from the 20s -50s this practice has revealed its shortcomings.  Sealing against porosity locally makes more sense than overall as with time (30 yrs and on) the total sealing effect results in a dry aluminum or alloy that is difficult to work with being incredibly brittle. I'll throw this out here that any metal or combination of metals that can be fed (in our case oil aided with temperature change) should be fed.  A parallel is ceramic material, Think of the old set of cracking ceramic dishes that were never used. Ceramics need water and temperature change regularly to resist brittleness and cracking, its the same with your motor (oil not water obviously). A local point where oil makes it through is worth rectifying but only for that point. 

Isn't it the rate of cooling that dictates the imperfections of alloys.

it should not be a problem for the V11 as it is not a "busy" head. The 4 valve though (old and new) obviously should have had a better quality or smaller production supply to address the issue.

 

 

[Lucky Phil]

21 minutes ago, The Monkey said:

Glyptol was the go to for the cases on old American bikes. Now with the scarcity of correct parts from the 20s -50s this practice has revealed its shortcomings.  Sealing against porosity locally makes more sense than overall as with time (30 yrs and on) the total sealing effect results in a dry aluminum or alloy that is difficult to work with being incredibly brittle. I'll throw this out here that any metal or combination of metals that can be fed (in our case oil aided with temperature change) should be fed.  A parallel is ceramic material, Think of the old set of cracking ceramic dishes that were never used. Ceramics need water and temperature change regularly to resist brittleness and cracking, its the same with your motor (oil not water obviously). A local point where oil makes it through is worth rectifying but only for that point. 

Isn't it the rate of cooling that dictates the imperfections of alloys.

it should not be a problem for the V11 as it is not a "busy" head. The 4 valve though (old and new) obviously should have had a better quality or smaller production supply to address the issue.

 

 

Aluminium alloys dont become brittle because they are sealed from oil. They get brittle because they age. That's the nature of aluminium alloy it hardens with age.

Ciao 

[The Monkey]

We have to normalize or anneal hooks used for lifting. Ferrous material. this  temperature treatment (controlled cooling) ensures the molecules are aligned for the task (proof load)

does alloy not respond in like fashion? I was under the impression that the temperature fluctuation with the lubricant helped the material stay supple (relatively) 

am i mistaken?

[The Monkey]

Sorry poorly worded

Doesn't the alloy benefit from the expansion and contraction due to heating and cooling

and the lubricant in that process play a part regards longevity or stasis of the material?

[Chuck]

^^^^ I don't *think* so, although the only heat treatment I've been professionally involved in was in tool steels. As LP says, aluminum hardens with time. Take, for instance, aircraft "freezer" rivets. Once this alloy is annealed, they have to be kept in the freezer so they will be soft enough to drive. As they age, they get harder than...uh..Chinese algebra.

[Lucky Phil]

Yes Chuck that's a good example as well. Old race engines are generally RPM limited as well when the cases get to a certain age and it becomes impossible to find replacements. It's just the nature of the material. doesn't affect most people because old engines are generally used on old road bikes and aren't under enough stress to cause an issue so they are still over engineered for the application. Start hammering them in classic and post classic racing and things are a bit different.

Ciao