Engine Rebuild

[The_Steve_Man]

So now that I have to rebuild my motor, I have a few questions.
First I am going to put a stock motor together for time being.
Second, this motor will go in my race bike. I will use the cylinder I have so I can race in vintage class. I like the porting for racing but hate it everywhere else. So I am going to build a dedicated race bike.

1. Is there any noticable difference in power going to a 261 or 265? I am at 66.25 now and going to have to bore it anyway.
2. Pro X vs Wiseco piston. The piston that broke is a Wiseco and only been together for a little over a year and only run hard for the last 6 months. If I used the Pro x what is the best interval to change it? I want to use the Pro x becouse of cost. I dont mind changing it to avoid what just happened.

[udontknowme]

wisecos normally dont just break without good reason. in all my years i could count the broken ones ive seen on 1 hand, although none of my personal engines have broke a piston and im using wisecos in about 4 different bikes at the moment. wether that engine was just setup wrong from the get go, or a bad piston design by wiseco, i cant say for sure. cast pistons normally work fine if everything is setup correct and you dont run it past the service limit. other wise youll end up with a big train wreck similar or worse that what just happened. its nearly impossible to say what the service limit is however without disassembly, inspection and measuring but at that point you may as well just drop a new piston in since its tore down anyways.  never hurts to use plenty of oil either but still theres people who are convinced 60:1 amsoil is sufficient :rofl:.

[rsss396]

It is strange you broke the wiseco skirt so quickly, IMO for this to happen, the piston to bore tolerance was probably very high and if you would have ran any piston the results would have been the same.
 Cast pistons run tighter tolerances and many times make more power than the looser fitting forged wiseco/wossner pistons but cast pistons tend to break skirts much easier than the softer forged alum pistons

[The_Steve_Man]

It was a low hour cylinder that I sent to Eric Gorr to port. He sent it back ported bored and with that piston.
I had two cranks. One that was good and one I got rebuilt becuse it came out of a motor that the stock piston broke. I put the rebuilt one in. I replaced the rings once because it felt like the compression was down a some and put a cr head gasket on it. Check everything then and it all seemed fine.

[udontknowme]

you may never know for sure but eric gorr may not have bored it properly. since it did fail rather quickly i would almost take a guess that the machine work might not of been right. personally i wouldnt send anything to eric goor but thats just me.  pickup a used mitytoya bore gauge and micrometer off ebay so you can be sure what you got when assembling engines next time. thats what i did and it will reduce machine work related failures down to basically zero.

[The_Steve_Man]

You could be right. I used him because a friend of mine uses him for his sons mx bikes and he has been very happy with his work. Any future work will be sent one you guys on this site.
Anyway it happened so now I looking into the future.

[udontknowme]

most average joes dont have a clue what good or bad machine work looks like. and with the naked eye youll never be able to tell if theres .002" or .006" clearance. thats why its important to get your own meauring tools or send the parts to somebody that will do the job right the first time.  many failures can be traced right back to bad machine work. its unfortunate but any monkey with a few bucks can pickup a used boring machine and open up shop without a clue what hes doing. shops with higher volume like eric gorr may be letting high school trainees do some of the work which isnt a good scenario