I just completed a new build on my '84 Evo
(I'm sure folks are tired of hearing about it)

Mildly ported heads CC'd at 79.6
.030 head gaskets
.015 shaved from heads - new valves w/ 3 bevel cut
Cylinders bored out .030
KB domed 9 cc pistons and rings fitted to cylinders by machinist at Harley dealer.
170 psi compression approx 10:1 at 6000 ft elevation
New bearings and races in bottom end
Time-sert "Big Serts" installed in case for new cylinder stud strength
Woods W6 cam
2000i ignition
Mikuni HR 40 carb
Supertrapp 2-1

I was taking the maiden voyage and had about 60 miles on the bike when I stopped for a beverage. When taking off, I killed the engine. I went to fire it back up and it was very slow turning over, then spun right up and fired up. I headed back down the highway toward home and started hearing a little popping going on. At first I thought it might be detonation but then dedided it was a head gasket leaking. Before I could shut it down to check it out, I lost the back cylinder. I pulled over and spotted the back left head bolt hanging out between the tranny and linkage. Lucky it wasn't lost on the highway. I had my follow vehicle run back to the town where I turned around and pick up a 12 point 3/8 socket to see if I could torque the head bolt back down. Unfortunately it was stripped. I couldn't believe the cylinder stud had pulled with proper torque and the Big Sert inserts.

I trailered it home and tore it down. The piston on the back cylinder had blown a chunk out near the back stud that had pulled. It trashed the top half inch of the cylinder wall in the same area without doing damage to the cylinder below that. The rings have aluminum mashed into them making them a part of the piston. The head and valves look like they have been sand blasted with pebbles.

The front cylinder looks just fine.

WTF happened to me?
Would it be worth while to contact KB Pistons or are there too many changes to pin the problem on the pistons?

Thanks for any opinions or remarks.

Don

 

What a shame, the engine sure looked to be good.
Looks like the rings welded themselves to the wall of the cilender. Which tore the piston apart.

Two things
There is a chance the piston, and or, rings were fitted too tight. If this is the case the person doing the fitting. The piston and the rings are just what broke.

Break in. Did you do heat cycle breakin before you went on the first ride? Tremendous amount of heat at first at the rings. Can melt metal.

Good luck with this.

 

I took two easy three mile rides on the day I had her buttoned up. The next day I took a ten mile ride. Then on taking off for my 60 mile ride, I stopped in town about 15 miles from the house and had coffee. I then headed out for the maiden voyage which would have been 60 miles and then the 15 back home. I only made it 45 of the 60 b efore she died.

 

It would have to be ring fit or piston fit as the likely cause. Defect in the piston could do it too , but hard to prove now in it's mangled state. Damage could have occured right from the first startup, continued to the point of total failure.
That really sucks, and you must be feeling sick about it.
Ron

 

Well when you get things back together and are ready for breakin again check out the S&S site for their recommends. They are not the only ones but they have written it out well.

Everything you did above is good.
What they add is several very short startups, run 10-15 sec, shut down. Let cool, doesn't take long. Do again. This lets the rings and cilender wall meet and do their first kissing without getting too hot.

 

I've seen a leaking intake manifold cause a lean condition.

 

KB pistons require a larger gap for the top ring. You multiply .006 time the cylinder diameter to obtain the gap for the top ring. Use 3.530 x .006 = .021 for the top ring. Anything less will cause the gap to close and the rings seize to the cylinders

 

I was led to believe the Harley wrench in the SLC, UT dealership had done lots of these. He had the pistons when he bored the cylinders out .030 and said he had fitted them to the cylinders. Hopefully he had the formula.

 

He should have the formula, it comes with the piston kit.

I have built three EVO's running KB pistons and I have a set in my '82 shovelhead and haven't had any problems. The EVOs are two at 9.5:1 and one at 10.8:1 compression. You do have to have a proper tune to avoid lean conditions and preignition.

 

If anyone wants to look at pix (not too clear - taken with my phone camera) go to this link :
http://www.shutterfly.com/lightbox/v...4ab00f16ca9e1e

Use name of mcmeadow@dcdi.net and password Harley