Interesting notes about Wiseco pistons

[ttyR2]

I assume this is by the real Harry Klemm. I guess he's running another business related to vintage bikes. They have an interesting writeup on engine break-in and talk about Wiseco piston kits a bit.

http://www.klemmvintage.com/breakin.htm

[hoodlum]

That is interesting....I will say this...There is no way I would leave .0035 clearance on a 350 or any other air cooled 2 stroke...Been there done that,and the outcome wasn't very pretty....I have also seen pilots sieze running the wisecos at factory spec...We rebuilt one at Durhamtown on a picnic table about 3 years ago due to the piston siezing after being bored to the wiseco specs....It rubbed on all 4 corners....We sanded the roughed aluminum off the piston with sandpaper and borrowed a flex hone from their shop (you take drastic measures wher you're 8 hrs from home) and cleaned up the cylinder...Didn't have any measureing equipment,but just guessing,we probably ended up with .006 clearance....That thing is still running strong....
I had a 350 several years ago that was on it's last bore...After cleaning up the cylinder,I had .009 clearance left....I always let it warm up really well before hammering it,but it ran for 4 years with that much clearance and never had a problem...I checked it after 2 seasons for piston/cylinder wear,and there was minor wear on the skirt,but nothing that would warrant changeing the piston....
I always run .005 on my pilots,and have never had a problem with piston wear...I actually had one ni-com plated 3 years ago,and stated I needed .005 clearance....They took it on themselves to give it factory spec,and it lasted about 10 minutes before the piston got tight enough to break off part of the coating....After they had to pay for shipping both ways and do a rush job because of an up-coming ride,they decided to honor my request on clearance....It is still running strong....
I know many people have their own ideas about this issue,and has been discussed in great length...I say do what works for you....I do believe that .0015 can make the difference between sieze and no sieze,but will not make a large difference in skirt wear due to piston slap....In fact,I have never had piston slap on any of my pilots,or excessive skirt wear....
Hoodlum

[LiveWire]

It is always good to read up on what someone else is doing when they have done analysis of what has worked on not worked for them. You have to always factor in though if it applies to your own machine. On the 350, factory spec is .004 and the Wiseco rings are setup for .003. While Wiseco change their suggested clearance from .003 to .004, the rings are still the same part number. So the ring end gap is not tight. I set them up to .005 making the end gap even larger. If you bore a 350 to .003, you will very likely have the ring end gaps touch if you broke it in hard. You will also have the piston smearing itself on the bore, likely the first time it is run.

I used to let my engines run a long time at high idle. I would at least do it in several short runs though to heat cycle it. There are very experienced people who said this was bad because it would wear the sharp edges off the cross hatch without removing much off the rings. The claim was it would extend full break in because once you started putting a load on it, the rings would not get cut to shape quickly.

I currently do run the engine a few times without load, but not as long at that article suggests. I also still do it in several short runs bringing the engine up to temp then shutting down to cool. I start the engine as soon as I am able without the seat and several other things installed.

I do assemble dry, but put oil in the bottom end as that article suggests.

[ttyR2]

If you take the time to verify and open the piston ring end-clearance before assembling the engine, you'd be able to run 0.0035 piston clearances, no?

[LiveWire]

No, the piston would stick. I found it odd that the article said the gap was tight on Wiseco rings anyway. I have never had to size them. They were always sized right for .003" piston to wall clearance. I did have to size Honda rings.

It may be possible to run the tighter clearance with a windowed piston. A window on the intake side of the piston improves circulation of the intake charge inside the piston to do a better job cooling it. I have been running a windowed piston a couple years now. I used to only arc the bottom of the intake skirt and thought the window was just an alternate way of improving intake flow. The arc also prevents the skirt from snagging the bottom edge of the intake port so I stuck with that until realizing about the cooling effect from the window. Now I do both. I have continued to run .005" clearance. I will shrink it down to .0045 on the next top end.