GT380 Top end

[TLRam1]

The bike ran but was did not have the power off low end or top end. I checked compression they were 110, 105,110. Also had notable piston rattle.

Pulled the top end and here is what I have.

Scoring on middle piston. Is liquid suppose to be in the cavities in the crankcase around the pistons?



Heads, right being the cleaner side.



Bore is 54 mm stock and they all look like that with my inexpensive mic.







The top of the left piston has a protrusion on top with the center having an indention and the right having indention though less than the center. Is that the start of holing a piston??





This is the worst cylinder (center) the others look okay from a quick look. The center has some scoring.

Recommendations? Hone and new rings, bore and go oversize?

At what point do you know you have to go oversize and how far can you hone one Before having to go up?

[TLRam1]

The Center piston will pivot from side to side not slide but rock.

[TLRam1]

I failed to include the photo of the Center cylinder.

[Barry S.]

Looks like your ready for a rebore and new pistons. Check the wrist pin bearings, I rebuilt a 380 a few years ago and one of the wrist pins was worn WAY out, let the piston flop around a lot. Check to see if there is ANY up and down slop on the lower rod bearings. May could find another motor or a cylinder set on ebay, I think boring is about $50 a hole plus pistons and gaskets, would add up in a hurry.

[TLRam1]

Do you know the max clearance is between the piston and cylinder wall?

The Center cage bearings came out like this. Rod seems okay.

[Barry S.]

Mine looked like that but the wrist pin was really shot, look here for the specs.

http://www.3cyl.com/

[Suzukidave]

Do you know the max clearance is between the piston and cylinder wall?

The Center cage bearings came out like this. Rod seems okay.

http://kawtriple.com/tripleed/dalegt380/sm20.jpg

[TLRam1]

That's what I was looking for, thanks.