Top end apart pics

[jake760]

Piston out of my bike. I bought it with unknown hours on it, it ran great when I tore it down. Tons of power, tons of compression, a little piston slap, and a bit rich on the main jet, it spooged quite a bit. I rode it for about a month and then decided to freshen it up. Experts, what do you think about my piston, why does it have the burnt mark on the bottom even though it's running a bit rich on the main?

 

[jdager]

I am by no means an expert... but do you have any pictures of the cylinder walls? it seems if you were having piston slap, with what looks like grooves in the piston, you might have a damaged cylinder wall as well that needs to be addressed, just something to think about, I may be totally wrong, and I am sure someone else will chime in

 

[_JOE_]

I, also, am no expert but it looks as though that piston was long overdue. Got pics of the cylinder?

 

[IndyMX]

No doubt.. Looks like you had a bit of sand in the cylinder!

 

[jake760]

The cylinder walls don't look too bad. They have some light scratches that are completely smooth to the touch, I am going to hone it with scotch brite.

 

[jake760]

No doubt.. Looks like you had a bit of sand in the cylinder!

The guy that had it before me used it in the sand dunes all the time. It had an old filter on it that wasn't sealed with grease. I bought a new filter and outerwear and I install it with grease.

 

[jake760]

Does anyone know why the bottom is burnt?

 

[_JOE_]

You might want to have someone measure that cylinder for out-of-round and bore size. If there's enough plating a good diamond hone would be a plus.

 

[_JOE_]

As far as the bottom of the piston, I'm pretty sure all the pistons I've seen have some carbon on the bottom.

 

[jake760]

Alright thanks everyone. I have a digital caliper, will that work?

 

[IndyMX]

Nope...

You need to get it checked with a Bore micrometer.

Take the cylinder off and take it to a machine shop or a good bike shop, they should have the right tools and knowledge to get it done.

 

[jdager]

someone else chime in..., but with a piston that looks like that, with a history of running in the sand dunes, I would do a top to bottom check of the bottom end before you spend a lot of money on the top and put it all together, just to find out the bottom had some crap in it as well

 

[jake760]

someone else chime in..., but with a piston that looks like that, with a history of running in the sand dunes, I would do a top to bottom check of the bottom end before you spend a lot of money on the top and put it all together, just to find out the bottom had some crap in it as well

The bottom end is in perfect condition. All bearings, seals, and crank check out ok. No sand.
While inspecting the bottom end and I noticed that the base gasket was sucked in! about 1" is sucked in and missing on the left side of the motor, transfer port area. I think that must be how the sand got in...
What causes a base gasket to get sucked in? The gasket surfaces are smooth.

 

[_JOE_]

Warpage or improper torque.

 

[whenfoxforks-ruled]

Expert? That is one abused piston. It has been drawing a lot of debris into the combustion chamber. The combustion has been blowing by the rings. The piston rubbing the debris against the cylinder, you have been honing it all along. I would double check the bottom end, this gritty fuel has been washing the bearings. Any up and down movement in the rod or at the crank ends, its shot. Measure the thrust washer clearance with a feeler gauge. You need to measure the bore, at different elevations and degrees around the bore, where the piston rides. A bore gauge, and inside micrometer are good. Heck, they probably can do it electronically! In a pinch, with a new piston, place it in the bore and measure the clearance at the skirt with a feeler gauge. The head is probably good. I think the carbon on the bottom of the piston is from the blow by. 300 to 450 dollars should cover the parts to freshen your top and bottom end. Re-plating, call Eric.

 

[2strokerfun]

What he said. Don't trust lower end bearings after sand has been in your engine.