Deburr BBK?

[crabjoe]

Years ago, I had a friend's dad tell me one should deburr edges when building an engine.  My question is, how many people actually deburr the edges when installing a BBK?  If people aren't doing this, might this be one of the reason we hear about engines failing after a BBK is installed?

Thanks!

[Zino]

If he means chamfer ports which means knock the edges of the ports so you dont catch a ring .
That is a best practice .

[Petro]

Jun 7, 2020 19:48:32 GMT -5 crabjoe said:

Years ago, I had a friend's dad tell me one should deburr edges when building an engine.  My question is, how many people actually deburr the edges when installing a BBK?  If people aren't doing this, might this be one of the reason we hear about engines failing after a BBK is installed?

Thanks!

That should be done at the factory, at the last inspection station. How ever, that station doesn't seems to exist when it comes to cheap motor parts for cheap scooters...
Yes, I always go through my hardware before installation, even today when I buy good brands only.
It's more a pleasant thing to do these days over a cup of coffee, no scraping and filing, no sandpaper, no porting or getting cut on the sharp edges...

[GrumpyUnk]

The 4T engines don't have much to deburr. If you install a new piston, rings and cylinder, you may inspect the edges for sharp burrs, but there aren't many spots where a burr would normally occur.
The ports cast into the cylinder walls of a 2T will likely have sharp edges as the cutting edge approaches and departs over a 'void' such as the port. It doesn't lift up as it leaves to go over blank spot, nor as it approaches the edge. Burrs can form there, and be enough to catch a piston ring as it goes up and down. In general the edges that need deburring most would be the 'horizontal' edges where the ring approaches dead on, rather than the edges where the ring kind of slides by, such as the sides of the ports.
The top of the cylinder could develop burrs, but most I have seen(all, actually) seem to have been deburred.
If you have new cases, crankshafts, then it might pay to check all bored holes and edges. A seam in the mold can leave a bit of flashing on the part, which can lead to stress fractures developing, but I expect that happens more in race engines operating at the limits or close during most of their (short)life. A sharp edge in a connecting rod journal, or main, where the machined surface meets the cast surface, can develop cracks, and should be rounded when machined. A sharp departure between one surface and another somehow lets cracks develop.
If you inspect cast connecting rods, most have a casting flash along the long side of the rod, which has been ground close to the cast surface, leaving only evidence that there was casting flash there previously. I think that is done to relieve any stress points. Why? Not a metallurgist nor engineer. But, do know that performance rods seem 'polished' in general.
tom