hole in my piston

[dalknob]

I somehow manged to burn a hole through my #3 piston on my 78 gs550e...thinking about rebuilding it, but OEM parts are too expensive. So, does anyone out there have a donor motor for cheap, if not, I will be forced to part her out.
Pretty much everything on it is in good shape except the speedo cover & stator cover.
Any help would be greatly appreciated.

[rapidray]

What happened to lean out that cylinder to CAUSE the piston to hole? is what I would like to know! Ray.

[Guest]

Did it look like this?

[49er]

Did it look like this?

Hey Bill, that's what nightmares are made of! I don't see a hole through the middle though.

[SqDancerLynn1]

Someone here probably has a used piston

[dalknob]

shouldn't I replace the whole set?

[trippivot]

detonation is a hole in the middle of the piston

pre-ignition is damage at the edges of the piston.

you had a problem for thousands of miles.


too hot of spark plug. improper ignition timing too low of octane fuel partially plugged pilot jets/lean needle circuit.

remedy the cause or your next engine will do the same thing.

[dalknob]

I gues sthe problem was detonation then, plugs were OEM, always used high octane/premium fuel, had it professionally tuned & carbs professionally cleaned & rebuilt...........maybe I need a new mechanic

[TheBigRed]

Someone here probably has a used piston

Or several for that matter.. Send me a PM, I've got parts from several 550 engines sitting in my garage (LONG Story, search for posts by me to see some of it).

Amos

[TheCafeKid]

I gues sthe problem was detonation then, plugs were OEM, always used high octane/premium fuel, had it professionally tuned & carbs professionally cleaned & rebuilt...........maybe I need a new mechanic

Premium/high octane gasoline will CAUSE detonation in relatively low CR motors. You should be using 87. Period. Don't believe me? Do some research. High octane fuel will preignite/detonate in a stock GS motor. You never noticed it pinging?

[dalknob]

I believe you now!

[Billy Ricks]

Carbon in the combustion chamber or too hot of a plug may have caused this pre-ignition problem.

[Nessism]

Rebuilding the top end with used, but good, parts is fine but you need to figure out what caused the detonation or the same thing will happen to the new engine.

Was the bike stock or did you change the intake and/or exhaust system? Was the bike running well before this happened? A lean mixture will cause the engine to run hot, such as if the intake boot O-rings were leaking, and a lean mixture can cause detonation. I've never heard about Cafe's claim that high octane fuel will cause detonation, and I seriously doubt that was the cause.

[Turtleface]

Premium/high octane gasoline will CAUSE detonation in relatively low CR motors. You should be using 87. Period. Don't believe me? Do some research. High octane fuel will preignite/detonate in a stock GS motor. You never noticed it pinging?

How's that? I thought the flame front propagation was slower with higher octane, resulting in less chance of preignition/detonation. I found this with a quick Google search:

http://www.nitrous.info/nitrous-historic/fuels_detonation_preignition.htm

6.16 What happens if I use the wrong octane fuel?

If you use a fuel with an octane rating below the requirement of the engine,
the management system may move the engine settings into an area of less
efficient combustion, resulting in reduced power and reduced fuel economy.
You will be losing both money and driveability. If you use a fuel with an
octane rating higher than what the engine can use, you are just wasting
money by paying for octane that you can not utilise. The additive packages
are matched to the engines using the fuel, for example intake valve deposit
control additive concentrations may be increased in the premium octane grade.
If your vehicle does not have a knock sensor, then using a fuel with an
octane rating significantly below the octane requirement of the engine means
that the little men with hammers will gleefully pummel your engine to pieces.

[Billy Ricks]

Higher octane causing pre-ignition or detonation is a new one on me too. If anything it would lessen the chances. This guy's problem was caused by more than octane rating.