pinging sound on a fresh top end rebuild

[smacky]

ok, i just rebuilt the top end,402 new piston 10:1 wiseco, new in & ex valves with a 3 angle valve job,450r timing chain i run 93 octane my problem is the bike runs fine when i first start riding but the longer i ride and the hotter it gets it start getting this pinging sound about half throttle under load can anybody help me figure this out thanks :confused:

I didnt know they made a 402? anyways 10:1 should be fine on 93 octane. what oil are you running and were you running low? did you change to a colder plug? are you running lean?

[smacky]

for oil i'm running mobil 1 10/40 stock plug and stock jets in carb but i do have some bigger jets 402 was the listing when i bought the piston i did have the cylinder bored

[ae13291]

change up the jets man. play around with the octane, and do u have the 6 degree sparks timing key? and are the valves adjusted?

[F-16Guy]

Engines run a little hotter when they're new and tight. By increasing displacement and raising the compression ratio without re-jetting, it's probably running very hot, which will promote pre-ignition (pinging). Richen the main jet to about 160-165 and install a 42 pilot jet. Don't start it again until you get the jetting changed because that pinging can quickly damage the piston, head, and other expensive parts. Don't grenade your rebuild for $10 worth of jets.

[smacky]

thanks for the info,do yall think a colder plug would help?

[F-16Guy]

Changing the temperature range of the plug has minimal effect on combustion chamber temps. Different plug heat ranges are meant to keep the plug itself at the optimum temperature to stay free of carbon, while not so hot that it gets damaged. You run a colder plug with engine mods because the mods (such as a high compression piston, cam, etc.) raise the combustion chamber temps because of the stronger combustion, which in turn heats up the plug more and necessitates a plug that can shed the extra heat.

To reduce temps in your case, proper jetting is the answer. The majority of combustion chamber cooling is the result of the cool fuel mist entering the cylinder and cooling the top of the piston and other components. Too little fuel, and things start heating up until the fuel mixture gets so hot that it spontaneously ignites as it begins to compress (gasses heat when compressed and cool when they expand). In some very high compression engines, even though the fuel mixture is correct, the compression ratio is so high that regular fuel heats up and explodes before it can be fully compressed and ignited by the spark plug. In those cases, a higher octane fuel is used because it resists detonation and can be fully compressed and ignited by the spark plug at the right time. Engine design, the type of cooling (air vs. water), proper jetting, etc., can affect the octane requirements of an engine. Though roughly 11:1 is the general threshold for the 400ex, that can vary slightly depending on a number of variables. If you're properly jetted, you should have no problems running premium pump fuel with a 10:1 CR.

[smacky]

i will change jets and see what happens.thanks again