Engine Knocking?

C

Cobrarul69

New Member
My engine seems to have a knock some times it stops then some times it starts banging almost? any ideas what it could be?
 
Give more details about your engine, size? How many miles on it, is the knock in rythme with rpm or eratic?
 
More erratic just starts usually during start up and when slowing down its an 80cc china girl maybe 20 miles on it checked every thing every things lubed up bearings are fine im stumped
 
How tight is the engine drive chain? You should have 1/2 to 3/4 inch free play as measured on the lower chain run, No more.
Less will work, but causes early failure of the chain, rear wheel and transmission bearings.
Also, is the chain rubbing anywhere on the engine case or sprocket cover?
 
My engine was knocking only at top speed and max RPM's. It had the Manic high compression head on it. I took it off and replaced it with the stock slant head and the knocking stopped. go figure.........
 
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Was your plug hitting? Try different gaps? You may have to gap the plug differently with higher compression.
 
magrider said:
very odd since I put the stock slant head back on the knocking stopped.
Click to expand...

I realize this an old thread from 2011 however I wanted to touch on something I figured out considering this was the first post that pops up on google when one searches knocking motor when hot but not when cold.!

I had the same problem after scratching my head for a week it all turned out to be a plugged jet in the carb .. I know it sounds far fetched but thats what it was I cleared out the obstruction re assembled the motor for the tenth time!!! That's how I eliminated an air leak theory i kept thinking was the cause.

This is a ported and polished motor , the connecting rod and crank have been drilled out .. they look like swiss cheese now, I am guessing the knocking was coming from expansion from the heat due to lack of oil getting to the motor I also noticed a great increase in mileage but I care not to junk my motor for the benefit of 180+ mpg
i cleared out the obstruction and the knocking stopped completely
 
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