Harley Cylinder Boring Problems...

Life's a bitch...   Thank God there's Harleys...

Due to damage to the wall of the front cylinder of our 1973 Harley Davidson Ironhead Sportster engine we had to have the cylinders bored. This did not go without problems. Actually, one of the cylinders had to be replaced by a "new" one.

Read the story:

1 - Discovery of Cylinder Damage

Last year when we were stripping our Harley XLH Ironhead Sportster we discovered a wide and deep groove on the inside cylinder wall of the front cylinder. The groove was located on the side where we think the piston shaft retainer ring was forced in between the piston and the cylinder wall.

Shit happens - deal with it.   So we had our cylinders bored.

2 - Boring of the Damaged Front Cylinder

The damaged cylinder was bored to a diameter of 82.5 mm. Initially, because this was quite extensive damage, question was whether it would be possible to solve the problem by boring the cylinder. Boring takes away part of the cylinder wall, making the wall thinner. And there is only so far you can go.

But things went fine, nothing to report here...

3 - Boring of the Rear Cylinder

The rear cylinder of our Harley Ironhead engine had no damage, but had to be bored to the same diameter of 82.5 mm just like the front cylinder.

Things went fine, until a small problem was discovered:

As part of the Harley engine's closed oiling system, these Harley engines got these oil return lines that run vertically inside the cylinder wall.

At the photo below you can see how they run from the rocker box at the top of the cylinder to a small hole in the cylinder wall near the bottom of the cylinder.

After boring it was discovered that on our rear cylinder the longitudinal holes do not run exactly parallel to the axis of the cylinder. Actually they bend inwards towards the cylinder wall. And during boring of the cylinder, part of the side of the longitudinal hole was drilled open.

So in the end, the rear cylinder, the one which did not have any damage to begin with, had to be replaced.

4 - End Result

Here's an overview of the refurbished cylinders, new pistons, new piston rings, and new cylinder gaskets. The new oversize pistons are by Motorcycle Storehouse and are the largest size available in our local motorcycle shop. Piston rings by Hastings.

Click HERE to check out how the story continues...

OK. All's well that ends well !

April 2009