3mm crank question

[BlasterCrazy]

I have a 3mm crank and it seems to be knockin at the bottom end at idle i dont know if it does all time i cant really hear it the well when i get goin but is this normal for 3mm cranks

 

[OConnor Racing]

The +3 mm crank needs to have clearance at the crankcase. Could also be the crank bearings or the big end bearing.

 

[BlasterCrazy]

when you mean clearance do you mean the spacer plate cause I have that in I also replace all the bearings

 

[BLASTER HP]

turn the engine over by hand on the flywheel and see if you feel or hear it then.

 

[BLASTER HP]

because the casting varies year to year some of the cases need to be releaved, just in the path of the rod on the back half of the cases and usually only a few mm's. could be done with a hand file if you dont have a dremel. always mock assembly a new crank and make sure you in the clear

 

[BlasterCrazy]

I thought that It would be but if i dont have the clearance wat will it do to the motor

 

[OConnor Racing]

Do what HP said to do and see if you can feel it drag or hear it knock. Did you change the bearings when you changed the crank? Not sure what it will do to the engine by I bet it won't be a happy ending if the rod is hitting the case every rotation.

 

[BlasterCrazy]

Yes I did change all the bearings

 

[brandoz28]

Do what HP said to do and see if you can feel it drag or hear it knock. Did you change the bearings when you changed the crank? Not sure what it will do to the engine by I bet it won't be a happy ending if the rod is hitting the case every rotation.

wise words, who know's what'll happen...........but it's probably going to end very badly for you

 

[BlasterCrazy]

Ok so I turned the crank over with the stator and couldnt hear anything so wat could it be know

 

[sicivicdude]

piston slap, detonation knock, loose case bolt, gear lash on the primary drive gear to clutch outer gear.

Take your pick.

 

[BlasterCrazy]

Ok so its def in the top end so if a piston slap wat do i do

 

[sicivicdude]

IF is is piston slap you; measure current bore size, order an overbore piston, take the assembly to a machine shop and have them bore to the piston size, chamfer the ports, and hone the assembly. Reinstall...ride happy.

There are a few more things you need to check before you go buying a new piston already. The first thing you need to do it make sure you don't have any loose nuts. base nuts or head nuts. Anything loose on that top end can cause bad things to happen and even worse noises to form.

The next thing you can do is remove your headpipe and see if there is something stuck inside of it. You'd be surprised what can pass straight through a 2 smoker without harming anything but can drive you to fits with noises being made.

While the headpipe is off you can use a compact mirror to look back up the exhaust port and see if the piston is gouged. If those things look ok, take the carb, intake, and reed cage off and see if anything is wrong with the intake side of the piston. If there is nothing apparent on either side of the cylinder and you are SURE it's coming from the top end, pull the jug off and have a look see inside

Some things that can cause knock from the top end: bad wrist pin bearing, excessive piston clearance, broken piston skirt, slipped wrist pin retainer clip, gouges in the bore, or a snagged ring.

Some of those will require replacing/having worked on most of the top end components and almost all would say don't put the top end back down without replacing everything just to stave off any disasters later on. If anything in there looks real nasty, better off to do a complete top end rebuild while you have it off.

 

[BlasterCrazy]

Ok I will do that but could It be that there to much oil