An Evo Stroker..... Pappy's Black Bagger

Many moons ago, the decision was made to rebuild the engine on this 1991 Bagger. The engine was strong but started going through a bit of oil and then later in the year, had to ride in the back of the pack because it smoked so much. When this fella originally purchased the bike, little was known about the recently rebuilt engine other than it was missing a carburetor. About five minutes later on EBay a carburetor was found and we set to get her running.

After the carb was on the test ride was impressive, the bagger had some balls. other than leaning out the carb a bit a month or so down the road, nothing was needed to be done. The owner road the hell out of it every chance he got. Late into the season it was smoking, nothing crazy but still an issue. Then it went to Tomahawk..... and it was all over, bike still ran, but now we are talking extreme oil burning. I was concerned it may have a holed piston it was so bad.

So finally the day came.....

Thankfully the liberation of the engine from her chassis was rather uneventful.... working at a strange to me shop had us chase a few forgotten must have tools, but other than that the tear down went well without any surprises.

Initially nothing was screaming total failure. When the jugs were removed it looked like a simple case of lost ring seal, common on an improperly honed Evo cylinder. The cylinder also has the typical 4 corner wear of a evo fired up and run hard without warm up, something that was confirmed by the owner. If you look and the pistons above you will notice first why she ran so hard.... high compression pistons, probably 10.5:1. But the other thing to notice is the carbon fouling on the pistons. Notice how the rear piston on the left is clean around the edge closest to the rings, and how the front cylinder has carbon all the way to the edge?

That rear piston had oil blowing up past the rings which is what kept that area around the piston clean. The front piston was getting most of it's oil from the top.. ie valve guides.

This shot gives you a good view of the piston domes... They did turn out to be 10.5:1 JE pistons, coupled with the Andrews EV-27 Cam, it was REAL perky.

As the tear down continued, the source of the top end oil on the front cylinder was revealed, a stuck valve had pulled the exhaust valve guide down and it was simply riding up and down in the head casting. At this point, the bottom end inspected out just fine, and I was going to simply rebuild the top end and be done with it. My friend really wanted to powder coat the cases, so I reluctantly tore the engine down the rest of the way.... glad we did!

The pinion race on the pinion shaft was heavily galled and then on further inspection of the pinion case race, there was indication that it was improperly lapped and the roller bearing were not making full contact. A full rebuild was now in order and decisions had to be made. Once the damage to the flywheels was discovered (previous builder used a cut off wheel or grinder to remove the race and damaged the pinion shaft), I threw out the idea of building a 89" Stroker.

My reasoning had several key points. First, we could lower the compression a bit for some added reliability, but maintain the torque levels via increased stroke and extra inertia provided by a set of Truett Osbourne "Heavy Flywheels". Because this engine wasn't going to be bouncing off the rev limiter all day, the extra stroke shouldn't contribute to much to added wear. The heads would get a basic clean up in the ports with some mild blending in the combustion chambers, and we would keep that torquey Andrews EV-27 cam.

Cosmetically, cases jugs and heads would be coated with TLTD thermal dispersant coating. The fin edges would be polished, and polished stainless hardware would replace the crusty stuff.....

Stay tuned for more fun and exciting wrench bending knuckle busting hyjinx.......