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Discussion in 'Heads and Cylinders' started by BlueSmoker, Jun 27, 2016.
How often do you need to change piston rings and the piston?
In my experience, it's always been the cylinder that needs replacing due to wear. Any times I've needed to replace a piston or set of rings was when the cylinder-wall deteriorated and caused damage to the rings/piston. I've had to replace upper-ends on the average of once every 6-months. On the rare occasion, a needle-bearing will fail and a needle will get sucked into the chamber causing damage. I've had pistons with defective index-pins that loosen up over time, and slowly gouge the cylinder-wall (compression will gradually diminish until the chrome-shell flakes off). One really bad jug I had a few months back just started shedding its chrome like a dog with mange after a couple of weeks' use. So, if it ain't broken, don't fix it.
I changed mine everytime I blew up a motor. These motors rarely last long enough to worry about piston ring service intervals, and will usually seize up unexpectedly when a ring snaps, retaining pin pops out, bearing fails, or gremlin eats it.
And when they do fail, usually takes out the whole motor, as all the broken parts grind around inside like a cement mixer.
Then, piston and ring replacement is easy. It's already assembled inside a new motor.
Fix it if it is broke. I've never replaced a piston as regular maintenance but whenever I put in a new jug I would put on new rings to set into that specific jug.
Okay, how many miles have you ridden your bike then without piston change? I just don't like to worry about the engine all the time.
My bike is more performance oriented and doesn't get ridden often, but when it does it's hard miles usually. I probably have over a thousand miles on this piston. My original performance build went over 2000 miles. That is until I revamped everything.
Rough estimate of about 2000-miles to a top-end & 6000-miles to a bottom-end for me.
It's a crap shoot. Had one motor last five blocks, then the main bearing blew, and another that lasted 3 years as my main transportation.
That one had no chrome left in the cylinder, piston was totally scuffed up, and still was fast and worked fine, til the chain broke, whipped around and cracked the case.
Thousands of miles on several different engines. I've never replaced a piston, cylinder, rings, or had any reason to. I don't abuse my engines but I don't baby them either.
What am I doing wrong?
Tom, if you want to blow one up, try racing them and squeezing 10+hp out of it to try to keep up with guys that have more money than you.
If that doesn't work, forget everything you've ever learned about these motors, assemble it according to the instructions on a huffy, and think it's as reliable as a 1977 italian moped.
So, all this talk about piston lifespan seems to have jinxed me; thanks guys!
As I was tooling down the highway yesterday and coming to a light, I let off the throttle and pulled the clutch. My engine purred down and suddenly I hear a single CLUNK, and my engine made sounds no more. I was about a mile from home, so I locked the clutch-lever, and pedaled on. Once home, this is what I found:
The durned nut on my carb's choke-lever fell off, and the washer got sucked into the intake. It took some doing to work the piston back-and-forth to first clear the obstruction and THEN do a little dental-work with the dremel to get the raised damage down for the piston to clear the cylinder-skirt. The piston is toast; the washer caused a large fracture in its side, but the cylinder MIGHT be reusable after some grinding. There was no damage in the combustion-chamber area, and the rings were unscathed as well. Pity. It only had probably 150-miles on it, and it had just broken in so beautifully. I really could have avoided this too. This carb's choke-lever was maddeningly loose to begin with, and I'd tried to tighten it adequately in the past (it had a tendency to engage at speed and would flood the engine). I tried unscrewing the nut early on, but the bolt it's on is designed with a slight peen to keep it on there no mater what...and to prevent exactly what happened to me. I've never needed the choke, but rigged up a linkage to engage and stabilize it anyway. Well, if I HADN'T done that, I'd have probably either replaced the carb, or ripped out the choke assembly before it came to this. ANOTHER lesson learned. New cylinder and piston already installed with the old rings. Time to break it in again...and order a spare upper!
Never seen that before! I would had assumed it was a wrist pin clip, but dang! I still stand behind my replace it when it's broke mentality!