350 kmt piston question

[moturbopar]

Hi all! I need to rebuild a 1987 350mxc. The problem I have found is there are 2 differnt part #s for the 350 piston. The first is-
55530007000/I
second is
55530007000/II
Does anyone here know what the difference is in these pistons? Is the II an oversized piston or is it for some kind of factory machining differnce? There is about a $75 difference in the price of these pistons.

The other question is that I noticed the later model 360s have the same bore size with a 1mm longer stroke. Do you think this piston could be used with a 1mm thicker base gasket? If so i could use a wiseco. I guess it depends on rod length.

And finally can the lower rod bearing be replaced, or do I have to replace the rod as well? If so does anyone have the bearing part #?

Thank for any help!

 

[2smoke]

I thought I seen this one a few weeks ago. Look on top of your old piston it should have a 1 or 2 stamped on it. As far as I know it signifies whether your bike was production run 1 or production run 2. There's usually a slight difference in the tolerences for the two runs hence different pistons.

 

[moturbopar]

Thats what I was thinking. Do you think the difference would be anything major? Could the II piston be run in a I bore and vise versa? maybe with some honing? Unfortunatly I cant look for any marks since the top of the piston is beat to crap!
Thanks for the help

 

[agitt73]

WHAT THE HECK IS A KMT :flame:

 

[moturbopar]

Oops! KTM, Sniffing to much parts cleaner today, maybe i should open a window!
Sorry I will be more carefull :-)

 

[marcusgunby]

chances are a 87 bore will accept a bigger piston but its a risk.When you replace a lower rod bearing you get a rod kit that comes with a rod and all the parts.On the changine of the stroke a call to eric gorr would be a good idea as he will know better than most if it can be done.A 1mm longer stroke will only need a 0.5mm gasket.

 

[2smoke]

Measure your old piston with a vernier (apologise if spelling is incorrect) caliper and get your friendly KTM parts man to do the same. That should narrow the choice down to the right piston.

 

[Bish]

Go with the larger #2. I believe it's .001" wider. At this point, the cylinder is worn enough that the #2 will fit just like new. I've done this on 3 KTM's (starting with an '88 350exc) after the first two seasons (ring after 1 season, piston after 2) with good results.