TOPIC:

Just seen your post, ART pistons are Kawasaki, the factory fitted early engines had no stamp on the crown, the one with a stamp may have been replaced, carefully take off the top two rings and check them in the bore see what the gap is, check the manual, if the rings are worn that's your smoke, the pistons are okay unless pitted, I have the z 250 twin had the same thing. Take care not to brake the rings.

+1 your ring gaps are critical, you can enlarge them but not reduce them - depending upon the measurement/wear on your bores.

I checked my end gaps with my current rings which have about 1500 km's on them, the top two are in the good part of the table, right at the low end of the standard gap. I wasn't quite sure how to check the oil ring as it's 3 parts. The corrugated ring just falls through so it's not that one so I checked one of the thin rings and that was within the service limit also. So that would indicate that the bores are ok and hopefully my brand new Wiseco pistons and rings will do the job with a coarse hone of the barrels. The fsm recommends checking the piston to cylinder clearances so I'm thinking I might take them to an engine reconditioning shop just to do the measurements for me.

That or get a rough estimate using a piston top, middle, bottom with a feeler gauge and the piston upside down.
Steve

So that would indicate that the bores are ok and hopefully my brand new Wiseco pistons and rings will do the job with a coarse hone

No, if you used the original rings then it indicates that the top two gaps were in spec. For the bottom 3 piece oil scraper just measure the two thin rings - ignore the wire spacer. Test it in several places up and down the bore.

Really a block should be bored to each individual (numbered) piston, then the ring gaps set. Also your forged wisecos runs slightly larger clearances to the factory cast pistons. This is quite precise so as a minimum you need to check the clearance with feeler gauges, and preferably micrometers.

swest wrote: That or get a rough estimate using a piston top, middle, bottom with a feeler gauge and the piston upside down.
Steve

If you've never done this before what Steve means is to carefully place the ring into the bore near the top. Then use the piston, upside down to push the ring down a little. That insures that you have the ring properly seated and square to the bore. Then measure your gap with feeler gauges. You do this near the top of the bore, middle and about an inch from the bottom. We do this because after a few thousand miles the bore will actually be wider at the bottom than at the top. Do this for both compression rings and both oil scraper rings and per cylinder. In other words. you keep the piston and rings with the cylinder so keep them separate.

Are you putting new pistons in a cylinder that was not bored/honed for that piston?
If yes, you should take the cyl block with all the pistons to a machine shop that does this work.... or you might end up doing it all over again in a few hundred miles with a .5mm overbore.

jdvorchak wrote:

swest wrote: That or get a rough estimate using a piston top, middle, bottom with a feeler gauge and the piston upside down.
Steve

If you've never done this before what Steve means is to carefully place the ring into the bore near the top. Then use the piston, upside down to push the ring down a little. That insures that you have the ring properly seated and square to the bore. Then measure your gap with feeler gauges. You do this near the top of the bore, middle and about an inch from the bottom. We do this because after a few thousand miles the bore will actually be wider at the bottom than at the top. Do this for both compression rings and both oil scraper rings and per cylinder. In other words. you keep the piston and rings with the cylinder so keep them separate.

Not quite. That is the way to size the end gaps of the rings. My suggestion was to use the piston in the bores they will go into and measure the space between the piston and bore in the three places. That will give you an idea how uneven the bores are. It's rough but workable.
I got a low mile block from eBay and checked this way. I was also able to match which piston fit each bore the best.
Steve

Tyrell Corp wrote: So that would indicate that the bores are ok and hopefully my brand new Wiseco pistons and rings will do the job with a coarse hone

No, if you used the original rings then it indicates that the top two gaps were in spec. For the bottom 3 piece oil scraper just measure the two thin rings - ignore the wire spacer. Test it in several places up and down the bore.

Really a block should be bored to each individual (numbered) piston, then the ring gaps set. Also your forged wisecos runs slightly larger clearances to the factory cast pistons. This is quite precise so as a minimum you need to check the clearance with feeler gauges, and preferably micrometers.

I'm definitely going to get the cylinders and pistons measured by some pros. Tyrell Corp, you mentioned that the clearances should be slightly larger. Is that the piston/cylinder clearance? How do I find out what Wiseco recommend for this, there was nothing specific on their FAQ? Also the FSM is not totally clear on this for the 305. All the numbers are there for the 250, it gives the standard cylinder size and standard piston size and the clearance (0.030-0.057mm), when I do the maths it easy to see where they get the clearance numbers. It's not as specific for the 305.
It says:
'Cylinder Inside Diameter
Should be less than 61.10mm and 0.05mm difference between any two measurements.' I guess these are the key numbers for the measurements. If I'm over that then I'm probably still going to have a smokey bike! I'll still go down the coarse hone route though and fingers crossed that should be enough.
Also I just noticed on the Wiseco page is says the stroke is 52.59mm stock is 52.4mm is this where the higher compression comes from? Would this be enough to cause issues with the valves?
Thanks to everyone who has chimed in on this, I'm learning a lot!

Do you know if those Wiseco pistons are cam ground?
If you do not know or you do not know what that even means or how and where to measure piston clearances correctly, spend the small amount of money to an engine shop to do this for you.
Each piston will be a slightly different size! The thing you change is the bore diameter to fit a singular piston.
For some reason, could just be financial, ....I'm thinking you are ignoring the solid advice from some of us.
The comment about hoping for the best with a rough hone is really a bad idea for a novice builder.

I'm not ignoring any of this advise.? I said I was going to take the stuff to the engine shop for all the measurements. The problem is I don't know what the clearance should be. I'm still building my knowledge up on this. If you think that going for a coarse hone and hoping for the best is a bad idea then I'll take that on board too. I'll have a talk to the guys at the engine shop to find out what they need. My pistons are probably 2 weeks away yet so in the meantime I'm all ears!

Sorry. I didn't mean to sound like I was scolding.
When a young man in the early 70's, I spent 6 straight semesters in college with automotive engineering and a few machine shop classes ...giving me a big leg up but I've still made plenty of mistakes over the many years of backyard repairs and rebuilds. Those that ended up costing me more then I expected.
Wishing I had someone to put a bug in my ear a few times! Lol