Spark knock

[sisdavid]

I hear a little banging around in my engine I hope it is not a bearing bounching around in there. I just put high octane fuel in it today, and it still was doing it, do these engines spark knock?

[Skyliner70cc]

no, at a 6.5:1 compression ratio, you could run kerosene and it still wouldn't knock.

What you have is a worn wrist pin bushing giving you notice it needs to be replaced. Do it sooner rather than later or you could really damage your engine.

[Bikeguy Joe]

At least take it apart and check it for play. Pop off the head and jug and check the piston for loseness up and down on the rod....I believe Norman can tell you exactly what it feels like or Ilikeabikea, since they worked on Normans bike awhile back and I remeber reading comments on the loose bushing.

[Skyliner70cc]

Remove the piston and then stick the wrist pin in directly into the bushing. Clearance should not exceed 1 RCH-rch is a military unit of measure and is a very small amount that is barely visible.

[Norman]

you might be getting piston slap)caused by piston too loose in cylinder) or the piston might be hiting the head (caused by the base or head gasket too thin or the head is not machined properly and tapping the head at the edge of the heads machined sealing ring)
I don't think you will hear preignition knock form these engines. I set the base gasket too thin on an engine and it will make a very strange sound when the piston taps the head and it will tap only when wound out.
burning anything but regular gas is a waste of your hard earned money in these engines.

[sisdavid]

Think my gaskets will stay intact, when I take the head off or will I need new ones, could I use some of that high temp RTV, also do I need a ring compressor to put it back together?

[Ilikeabikea]

On the gaskets you just don't know if they'll stay intact until you take them off. If they tear you can make new ones pretty easy. If don't think I'd use RTV. Aluminum paint works pretty good though to seal gaskets. And you won't need a ring compressor. There are only two rings. One word of caution. There are some little tits (for lack of a better word) that are in the ring groove. Be sure you get the ring gap around the tits. It keeps the rings from turning. If you try to put the cylinder on with the gaps somewhere else you won't like it. It's no big deal, just something to look for.........................

[deacon]

On the ring thing be very sure to look out for it tits he mentioned above the big thing is your ring will break if you try to but in over that little bump. Ask me I broke two before i found out.

You know what is good about this forum somebody told you about that without being asked because they know that is the most likely problem you will run into. I like that alot about this place. People actually try to look out for each other.

[Bikeguy Joe]

Heh heh...you guys both said "tits".

[Bikeguy Joe]

Those are "anti rotation pins"...I like the other one better.