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Whelp, I pulled the head on my recently assembled 750 engine to repair threads that stripped in the cylinder block when re-torquing the head (another story).  Upon inspection, I found that all 4 cylinders have visible score lines present.  This is a brand new bore for 810cc pistons.  I can just barely feel them with my fingernail. The engine was run for maybe 15 minutes, first idle then slow break in cruise around the neighborhood.  Am I correct in assuming that this engine is F’ed?  Any idea what might have caused it?  I guess at the very least it will need a re-hone, but if I don’t know what caused it that will be throwing good money after bad.  Thanks for any advice.

PLEASE, edit your post, and click "insert all" with your photos.  They will show up in high resolution then, instead of tiny thumbnails.

Thanks in advance...

Sorry for this trouble.  I'm not sure what could have happened, but letting the bike idle may have deprived the cylinders of needed splash lubrication on the cylinder walls.  

Did you oil the piston skirt before install?  What kind of oil are you using?  

When I assembled the engine, I wiped down the bore with a light coating of non-synthetic 30 weight.  I don’t think that I lubricated the pistons separately.  I’m using some inexpensive 10w-40 dino oil in the engine for break in.

Does this amount of movement/clearance seem normal?

Did you check and adjust ring end gap? 

Ring gaps were measured, all were on the loose side.  I read somewhere “if your end gaps are too loose, only you will know.  If they are too tight everyone will know”.  This is what I measured:

That looks like the result of a "dry start" using such a light oil probably means that most of it had run off before first start. If the scuffs are only visible but you can't feel them with your finger nail chances are you will be OK. I always use "assembly paste" as it doesn't run off so does it's job until the oil is circulating enough to wash the paste out.

 

Wookie58

How much and when do you apply the Graphogen paste to the piston skirts?

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daveo wrote:

Wookie58

How much and when do you apply the Graphogen paste to the piston skirts?

Expect to pay around $40 for a 125g tube (there is also a 50g tube) I wipe it onto cam bearings, crank bearings, cam Lobes etc. With my finger and use a paint brush to apply it to pistons prior to installing them in the block. If you are putting "the block onto the pistons" (I put them in the block first as working alone I find it easier without damaging rings) paint the graphogen in the bores rather than on the pistons.

The Graphogen must then coat everything as it dissolves and circulates through the motor...

Are certain oil change procedures recommended during and after engine break in?

daveo wrote:

The Graphogen must then coat everything as it dissolves and circulates through the motor...

Are certain oil change procedures recommended during and after engine break in?

I will leave that one for the guys much more familiar with these motors