GX160 piston to bore clearance

K

knighty

Member
I'm in the middle of stripping 2 of my gx160 motors to have them properly honed out as the dyno performance implies they not in best health. I have not yet got any detailed bore or piston measurements, but have taken a look at the honda specs and it's saying a max clearance of 5 thou.

I will properly measure them up tomorrow.

Are there any advances on 5 thou clearance?...at what point should I say the piston is trashed and replace it?

Both engines have about 20 hours on each piston. One of the motors the honing is still visible, on the other the honing is rather polished out and I'm struggling to see it.

Boring out 0.25mm is forbidden in our rules.

A friend told me a steady pull on a 3 to 4 thou feeler gauge when shoved down the gap without rings fitted is another good condition check?

Are there any other piston measurements I should be wary of, perhaps the axial gaps between the rings in the pistons?

Any constructive help appreciated as always.
 
If the cylinder is round and not tapered, 90* to the pinat the skirt .003 to.005 is fine on a Honda. Put the piston in upside down hold thumb pressure against skirt 90* to pin and slide feeler guage in opposite side, check in several points in the cylinder.
 
Many thanks for both bits of information. If it's bigger that 5 thou after honing, is it time for a new piston?
 
With a stock piston you can get away with more clearance. Have to be careful with a short skirt piston and loose clearances. Sometime they try to turn around in the bore!!!
 
Many thanks. Just striped both motors and installed the piston in inverted as advised and I found 3 to 4 thou of clearance on the skirt at both the top and bottom of the bore. When I removed the pistons I could still see the horizontal machining marks on the skirt, through vertical wear patches, and the crowns are nicely carbon'd up for a higher CR, so I guess the pistons are ok.

Top ring gaps measured 14thou on one motor and 18 thou on the other when I put them back in the bore, which seems ok but I will replace with new.

Now it's off for honing and to have the blocks and heads skimmed down the the new regulations limits.
 
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