piston surprise

[gwcrim]

The trip to Hatfield McCoy went off pretty well after getting the clutch sorted out, thank you very much.  I was ticked at my boy for not getting started sooner on the clutch, causing the last minute SNAFU.

He was complaining about poor power and hard starting.  The bike is 10 years old and I don't think the top end has ever been off so......  in addition to a missing chunk or reed, I found this:



Wrist pin and big end bearings seem OK.  Any cause for concern?

[gwcrim]

Is a 265 or 301 kit worth the money?

[sandblaster]

We recently built a 265.
http://www.kxriders.com/forums/index.php/topic,10300.0.html
Just rebuilding it stock would have netted a few ponies over the worn engine.
The extra bore size made a nice performance gain and didn't cause any difficulties.
Since the cylinder was already sleeved, a 265 was a no brainer.
Checking out your piston I would go with a new one.
Hows your cylinder look?
Have you checked the size?

[Motorrad]

Yes picture of bore  and piston crown will tell us alot of helpfull info

[gwcrim]

The cylinder bore looks very nice for its age.   Cant imagine it needs bored. Piston crown has some carbon in the center but no  worse than others Ive seen.  Ill post a pic tonight.

[gwcrim]

The crown:

[DoldGuy]

The bike will be a Turd with a broken reed and a PITA to start. That piston looks good for 10 years, but shows a lot of blow by. I'd run a hone thru the cylinder, install a new piston, rings and bearing with a good set of reeds.
DoldGuy

[Motorrad]

just noticed... is that a big crack in the piston?

[ramblnman]

wow!..you caught that just in the nick of time! could of made a expensive mess for sure

[gwcrim]

I do consider myself lucky.  It was a ticking time bomb.   The bike got new Pro Action suspension this summer, a new clutch and basket, and a Warp 9 18" rear wheel.  I woulda hated to see the thing explode. 

Probably sending it off to Kustom Kraft tomorrow.  Standard bore?  265? 295? 301?  My 15 yr old hoss rides it.  He started off at age 4 and likes to  a hare scramble now and them.  Oh, he goes about 250 lbs. 

Suggestions?

[sandblaster]

With the size of the rider considered, bigger is better as long as he is a competent rider.
Here is something else to consider, I assume that crank has 10 years on it as well.
If this is the case you really need to carefully inspect the crank.
I don't mean wiggling on the wrist pin end and saying "Oh that's good".
Find out what the side play is with a feeler gauge and check against the specs.
If you go with a big bore, you will be exerting more torque on your crank.
If it's marginal it won't last long which is why my 250+ lb employee smoked his crank....
Thankfully it didn't explode on him and blow the cases or it would have been parted out 

[gwcrim]

Just check side play?  I thought I needed to look at vertical play.  I have no instrument for that.

[sandblaster]

Yes, there is also a spec for vertical play but it's harder to measure accurately compared to the side play.
Most of the cranks I have checked on usually call out a vertical play of something like .0004"-.0005"
However, if you can feel any vertical play just by moving the crank up and down it's time for a new one.
You can measure side play with a feeler gauge.
Most people have a feeler gauge to measure spark plug gaps if nothing else.

[gwcrim]

OK, so I've decided to remain at standard bore because the bottom end is so old and I've already sunk too much money into this bike.  Just going to send the jug to US Chrome and be done with it.

[gwcrim]

So here's the end result and proud pilot.  After all the bucks that went into it this year, I decided to go the extra mile and spring for new plastic.  It was in need.