Chipped barrel skirt

[Dave L]

Here is a pic of my Forza barrel skirt that I have just dropped! Is it usable in this condition?http://www.motoscrubs.com/forum/download/file.php?mode=view&id=5101

[Duccout]

As long as the piston skirt does not travel that far, and there is definitely no evidence of further cracks, then I would grind the rough edges off and use it. What do others think?

[double diamond]

The piston is tapered with the largest diameter at the bottom of the piston. By running a broken liner, it effectively increases the piston clearance at the bottom of the stroke just as the piston is changing direction. It will also tend to cock the piston in the bore, introducing all sorts of unwelcome effects. I suspect your piston wouldn’t last long.

Matt

[ducwiz]

I'm afraid you are partially wrong.
Pistons have special contours, with their largest diameter in the wrist pin area:
https://www.researchgate.net/figure/Description-of-the-axial-profile-of-the-piston-The-real-profile-of-the-skirt-was_fig1_320954592

Hans

[Duccout]

I would say that it all depends on how far the piston skirt travels down the barrel - if the bottom of the skirt is well above the missing barrel piece, then it is of no consequence. I once replaced barrel liners in my 750 with pattern ones that were around an inch shorter than originals, but there was still plenty of liner below the piston skirts.

[ecurbruce]

Hi Dave,
A couple of things come to mind ,
Is the bore of your liner still round, or did the fall bend in that side as well as breaking off the pieces? May be worth checking.

I don't know what piston you have, my Wössner piston has shorter skirts than the original stock piston, and also is lighter than the original,
could you shorten the skirt on the piston you have?

Bruce

[Jordan]

The slots for conrod clearance have square corners - stress risers that are weak points, possibly why this one broke when dropped.
I have a liner where a crack has started from one of them, just in normal use, found in a low-mileage engine.
On a new replacement liner, I filed a semi-circle so that both slots are now arched-shaped, doing away with the corners.

[double diamond]

Hans, the article you reference addresses supercharged Diesel engines. Russian supercharged Diesel engines probably operating at temperatures -100 degrees C. The physics do not apply to naturally aspirated air cooled gasoline motorcycle engines. One can not operate a motorcycle at -100 degree C, the Elephant Ralley aside. Perhaps barrel profile pistons would work well in motorcycles at the Elephant Ralley but that is a limited market.Your analogy is incorrect.

Matt

[Dave L]

I have lined up the piston in the barrel, marking where it sits at the very bottom of its stroke. There is a small part of the piston that protrudes past the broken part of the barrel skirt, 10mm at its max point. There is no sign of any other damage, cracks etc. I'll carry on...

[Dave L]

Actually more like 5 mm