engine knock @ idle

[pitmaster]

iam after opinions from engine builders here,

is this excessive carbon build up?

iam chasing a engine knock (iam thinking ignition knock) at idle, when you first apply throttle it knocks,

ONLY WHEN FULLY HOT, soon as you stop for 15secs itll go away till you get it fully hot again,

ive checked so far:

piston pin (perfect fit)
rod bearing play (solid)
flywheel bearing play (solid)

its been run on PREMIUM since ive had the bike (700km its done on premium) and i found out today premium is a NO NO in low comp ratio engines, cause this be the result of using it????

[Maylands Performance]

Hi Pitmaster.
The piston shows some scuffing at the top of the piston above the ring lands.It shouldnt show any contact at those points.Also the carbon deposits that normally build up a piston can be Eroded away in spots if an engine is suffering detonation.
Can you take a pic looking down on top of the piston crown.
It sounds like you have a possible pre-ignition/detonation problem from what you have said.
Things to check !!!
Check your piston ring gaps.Worn rings allow a piston to rock excessively in the cylinder bore,allowing the piston to rattle !!!!!
Have you changed/advanced the ignition timing at all ??
Have you made any jetting changes ?

Premium fuel will not cause engine problems in a low comp engine it is purely just a waste of $ The only damage is caused to the hip pocket

Cheers Brian

[pitmaster]

Originally Posted by Maylands Performance

Hi Pitmaster.
The piston shows some scuffing at the top of the piston above the ring lands.It shouldnt show any contact at those points.Also the carbon deposits that normally build up a piston can be Eroded away in spots if an engine is suffering detonation.
Can you take a pic looking down on top of the piston crown.
It sounds like you have a possible pre-ignition/detonation problem from what you have said.
Things to check !!!
Check your piston ring gaps.Worn rings allow a piston to rock excessively in the cylinder bore,allowing the piston to rattle !!!!!
Have you changed/advanced the ignition timing at all ??
Have you made any jetting changes ?

Premium fuel will not cause engine problems in a low comp engine it is purely just a waste of $ The only damage is caused to the hip pocket

Cheers Brian

Howdy Brian,

i havent changed ignition timing or anything like that,

only thing i did since its started is:
change to Premium fuel every tank,
changed airfilter from the enclosed Z50 black box type, to a open air pod filter,

the sparkplug is a perfect coffee brown colour, no oil deposits etc, looks perfect,
before i pulled the engine down, i checked compresion, and it was right in the middle of the spec sheet,

how is the ignition timing adjusted on these engines? could i try retarding it just a bees dick?

heres the pic,

Cheers Paul

[Maylands Performance]

Hi Pitmaster.
The piston crown has an odd carbon pattern on the RHS.From the pic it almost looks as if the top of the piston has been coming in contact with the cylinder head or head gasket.In the pic there appears to be a ring of clean aluminium on the RHS outer.!!!???Is it possible you have previously been rough with the con rod ie:driven the gudgeon pin with a hammer and bent the conrod ?? Sorry dont be offended I have seen it done by customers previously !!..
If the conrod was bent the piston would float or shuttle sides ways in the bore causing a knocking sound. [But the noise would increase hugely under increased revs]
The easiest way to check if the con rod is bent is to re-assemble the piston and cylinder minus the cylinder head.If the rod is bent the piston crown will be tilted or cocked sideways slightly !!
Note :If the conrod was bent the very bases of the piston skirt would would have odd angled wear patterns.[The piston crown above the ring lands directly above the pin circlips on one side would also contact the cylinder bore !]

Check your ring gaps
Check your piston to bore clearance
If these are ok at least you can count them out of the equation !!

Ps .Perhaps the knocking sound is Clutch or Trans related

Cheers Brian

[kaneo]

Hello there, Im not a motor bike mechanic but i did build pro stock drag motors for a few years. Looks like you may be getting some oil blow by on that rh side of the piston. Maybe the rings have lost their tension. The oil getting into the cylinder would make it knock or ping at idle. Compression tests are useless if there is any oil present as it can seal faulty rings giving you good readings. Pressure leakage tests are the way to go. But thats a pros job to do. My thoughts but i could be wrong.

[themountain]

Originally Posted by kaneo

Hello there, Im not a motor bike mechanic but i did build pro stock drag motors for a few years. Looks like you may be getting some oil blow by on that rh side of the piston. Maybe the rings have lost their tension. The oil getting into the cylinder would make it knock or ping at idle. Compression tests are useless if there is any oil present as it can seal faulty rings giving you good readings. Pressure leakage tests are the way to go. But thats a pros job to do. My thoughts but i could be wrong.

..Iam with you on that...looks like a classical Blowby!!

[pitmaster]

thanks everyone,

what would be a way to comfirm your theory? is there another sympton blowby will cause, so i know for sure what iam dealing with...

would running 10/30 synthetic oil cause it not to seal properly?

i ran it on that oil for the past 500km, and when i was talking to a crf50 mechanic on sat, he said, NO synthetic and NO premuim fuel, thats what he reckons has caused this problem

[Maylands Performance]

Hey Pitmaster.
Here are some Ring blowby syptoms :
Excessive Oil consumption
Excessive crankcase pressure
Carbon build up and discolouration Below the Piston rings inc the piston skirt
Engine knock
Low compression
Loss of power
Crankcase/engine oil blackened/discoloured quickly
and so on ...........

I definately would not use synthetic oil in these Puppies !!!
Premium fuel will not cause the problem stated.

Ps. I have been re-conditioning/building race engines for 28 years and the Premium fuel argument is Crap !!!!!

Check/Replace your Piston rings etc as previously recommended by others here !!

Cheers brian

[pitmaster]

Excessive Oil consumption = NEVER NEEDED TO TOP IT UP.
Excessive crankcase pressure = HAVENT HAD ANY SIGNS OF THIS.
Carbon build up and discolouration Below the Piston rings inc the piston skirt = CARBON ON PISTON CROWN YES!! DEF NO DISCOLOURING ON PISTON THOUGH.
Engine knock = YES! ONLY AT VERY LOW REVS.
Low compression = NOT ACCORDING TO COMP TEST (I TAKE NOTE OF PREVIOUS REPLY ABOUT COMP VS LEAK TESTING).
Loss of power = DEF NOT, IF ANYTHING ITS GAINED POWER.
Crankcase/engine oil blackened/discoloured quickly = CHANGED EVERY 300KM AND STILL IS GOLDEN COLOUR.

i got yamalube 15/50 mineral today, and will use that and see how it goes,

thanks for the replys fellas, ive just finished putting new rings on, cleaned everything up, and put it all back together tonight, thats all the spare parts i have in the shed, so thats all ive done, and will see what happens when she gets fired up, and ridden maybe tonight if i can warm up enough to go back into the cold shed lol,

Cheers

[cass38a]

Is this your little z50 replica giving you problems, I am guessing this as you know the Klms so must have a speedo.
My solution to your problem would be adjust the idle up until the knock stops (no sound, no problem) LOL