Help please - strange noise EC 300-2019
 

Today I heard a strange noise, that only appears when the engine is hot. When cruising in any gear as soon as I close the throttle I hear a knock. It is one single knock.
The bike is stock, except that I installed a GP head with 1,8mm squish (instead of 2mm of the stock head) GG says use 98 octane fuel but I only could get 95. And it never did ping/knock before with 95 octane gas.

The knock is only audible when I ride with low rpm's in any*gear and it is only audible the moment I close the throttle. It is pretty loud. I checked a lot of things but I fear it comes from inside the motor.

I called a GG dealer and friend in Germany and he says the GP head has too much compression for the EC 300. But to be honest that's hard to believe as piston and cylinder of both engines are identical. I measured 2mm of squish with the standard head and 1.8 with the GP head. But he says the squish aint the problem, its the combustion chamber which raises the compression too much.

My OEM head has been on the lathe and 0,5mm been taken off, creating higher compression and 1,55 squish. So I took off 0.25mm of the squish band and also took a little bit off the combustion chamber. I will try this head and check if the capacity of the chambers off both heads differ.

If it is not a typical ping, what else could it be? And why would the engine knock/ping only once in exactly the moment I close the throttle. Bike runs fine, has good fuel consumption and rips like an animal...

(will crosspost to TT)

The only sound like that I have heard is "knacking" in the pipe when unburned fuel ignites. It's usually from rich jetting. Otherwise perhaps your crankshaft pinion nut is loose?

If your compression was too high, I'd expect knocking/pre-ignition under load.

Appreciate your answer Neil.

But why would it do it only once and only when I shut the throttle? I have changed the right crank nut (GG re-call) and can remember that I torqued it plus I used Loctite.

It does not knock under load, it knocks when I shut the throttle when cruising with very low rpm's...

Check the rotor bolt, mine was drowned in loctite and would not moved but was not tight against the rotor. Remove clean and retorque. Mine was knocking on a closed throttle as well.

[QUOTE=Doc Brown;195930]
The bike is stock, except that I installed a GP head with 1,8mm squish (instead of 2mm of the stock head) GG says use 98 octane fuel but I only could get 95.
I called a GG dealer and friend in Germany and he says the GP head has too much compression for the EC 300. But to be honest that's hard to believe as piston and cylinder of both engines are identical. I measured 2mm of squish with the standard head and 1.8 with the GP head. But he says the squish aint the problem, its the combustion chamber which raises the compression too much. [QUOTE]

I can confirm your findings regarding heads as my GP300 was knocking when I dropped the base gasket from 0.5mm std to 0.15mm to get 1.45mm squish.

I then had the GP head machined by TSP who also dropped the compression & went back to the std base gasket & the bike was better as it smoothed out the mid-range hit allowing a more even spread of power & rev into the top-end. TSP remarked that they could not drop the compression enough due to the limited amount of material to machine in the GP head.

Finally I bought a complete RKTek head, currently set-up with 1.35mm squish & the performance is better again with more off-idle grunt pulling strongly into the mid range & top-end making the bike easier to ride.

Thank you guys. Gasser Nate, yes will do. Easy things first.

EC Rider, yes the OEM heads are both very thin and do not allow to take off enough material when the squish gets below 1.65mm. Unfortunately getting parts from the US (RK Tech) is a pain but I have the S3 head in mind that I could test with the standard head insert.

We'll see. My plan is to use my altered standard head where I took off 0.5mm from the sealing surface and 0.25mm from the squish band to come back to 1.8mm of squish. I also machined the chamber but only very slightly. So the plan is to measure the capacity...and compare with the GP head. If it is more I will try it, if it is less I'll try something else.

@Neil E. : in the other forum two guys had a similar problem and said it was/is simply pipe bang....

Worth checking the flywheel nut. I need to do mine too!

Pipe bang from a bit of extra fuel on the pilot. If I coast in gear downhill my bike will knack or ignite unburnt fuel in about every 5-10 seconds. Still not as often as I've seen some other brands of bikes do it either.

Usually becomes more noticable the higher you try and set the idle.

A little reading: http://www.powercdi.com/manual/combu..._bangs/en.html

Ok, today I took off the skid plate, corrected chain tension, checked fly wheel and its mounting bolt and changed the exhaust pipe o-rings.

I just wanted to be sure that nothing else caused the knocking noise. I rode almost 2 hours on a parking site but only could hear the noise twice and not as loud as on the playground.

Whatever it is, it is not pinging/knocking. An engine that is pinging/knocking sounds different and: it does not ping/knock once, it does it over a longer period of time. Nevertheless I will use 98 or 100 octane gas whatever I can get. I also checked the spark plug and it looked good, a bit dark but that's due to riding around in third with low revs. Decided to put a new one in, but only had a BR8ES instead of the BR8EG. ES is the one with standard electrode but the heat range is the same and I always used them on all my Gassers.... Compression is also fine and the bike really rips. It is the strongest 300 I had so far.

Now the bad news. I never have seen a piston like this one. Holy shit! That damn thing has 23 hours of an easy life, was always fed with Motul 710 always warmed up carefully.... I cant believe what I see..... The strange dots can not be felt with finger nails. They do not worry me much, they are just strange. What makes me anxious is all the shit between the piston rings. Never had this on any other bike, at least not after 23 hours.

https://up.picr.de/39077995ls.jpg


https://up.picr.de/39077993os.jpg


https://up.picr.de/39077994aa.jpg

Jakobi, I am far from saying I understood everything Fabio wrote in that brilliant article. Additionally I am not a native, but this link opened my eyes. I am now pretty sure it is a pipe bang I hear as - like Fabio described - I always could feel a slight forward movement when it banged. That is exactly what Fabio describes, a fast increase of torque caused by that bang.

Thank you for the link. I will share it with some others on TT.

that first pic seems like showing a crack in the piston skirt :eek: