Motorcycle Repair: Possible Problems 83 Lowrider, piston slap, rear cylinder

Question
Hi Mike, Thanks for the prompt response. Maybe preignition was the wrong word. Maybe piston slap was the worng description too.It just did not sound like it should. It seemed to start fine but idled rough. Do you think the massive leak could be the cause of the poor idle and what i described as piston slap. It actually sounded like clanging on deceleration, I don't know how else to describe it.
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Followup To
Question -
Hi Mike, I'm looking at purchasing a used 59,000 miles 83 lowrider 1340. The bike has a major leak at the cylinder to crankcase base only on the rear cylinder on the left side. It also sounds like it has preignition when it is idling. I noticed it has an s&s carb but everything else looks pretty much stock. The seller told me he did a gasket job, crankcase up, on it less than 1000 miles ago. Judging by the condition and cleanliness of the rest of the motor, this looks to be true. The  other thing I noticed when the seller drove the bike was a clanking sound during deceleration, sounding kind of like my old 2 stroke dirt bike piston slap. It didn't sound too bad when it was reving through the gears. I'm not a mechanic but have the technical capabilities to figure out and repair problems, and I've rebuilt other types of engines so I'm not completely clueless. I would like to know if you think these symptoms could be from a single problem or a multitude of problems. A couple of my ideas of what it might be are: bad connecting rod? bad crank bearings? obvious one might be timing alone? Could bad timing blow a new gasket? Just remembered, it does have electronic ignition, no points. Thank you in advance.
Answer -
As with any motor you always have to wonder if the seller really know what he was doing. You also have to be careful of the clean motor. Degreaser is cheap and make a motor look good.
On the preignition at idle. I have never heard a harley preignite at idle. That is somthing that only happens under a load. Piston slap also happens under a load not deceleration. From what you have described is almost sounds like a rod bearing is going out which would be the worst case. In this event you would have to rebuild the motor. So if you still looking to buy the bike, it would be in your best interest to take into consideration the cost of a motor rebuild.
Good luck
Mike


Answer
The leak at the bottom of the cylinder will not cause a noise. It is just a bad base gasket. The noise you are hearing might be a bad piston or a rod bearing like I said before. the only way to be sure is to remove the top end and do some investagating.
Good luck and happy riding
Mike