Few Q's about top end rebuild

[Swaie]

I locked up my motor the other day and decided to take the motor out. So I took off the left side exhaust and...metal shavings poured out. So I finally got the motor out and took the cool head off and come to see that the pistons were still together. The right cylinder seemed fine but the left seems like pretty bad at the top. I didn't take off the cylinders because I couldn't break the piston loose. So took it to the shop. It seems that the piston seized in the cylinder. I just hope the crank isn't broken. The guy that I bought the bike from said that the bore was .020. Is that a bore? The guy at the shop said that I could only bore one more time, is that true? I thought the bore last bore was .20. I wanted to get the HP wiseco piston kit to rebuild the top end. Are those the best piston or are there better ones? What type of piston do you guys run? In my cool head I run 20cc domes. If I go to let's say 19cc domes that should up my compression, right? Will that hurt anything? When I drained the oil I didn't find any metal flakes, so I guess that is a good thing. Thanks for any help

[CRAZY-SHEE!]

Im almost positive u can go bored over alot over .20 like up to .50 or something. Wiesco pistons are the best out there. and if its messed up, which im betting it is, ur gonna need new domes. 20,21,and 22 cc domes u can run primeum pump gas on.. however once you hit 19,18,17and 16 u need to start running high octane racing fuel and unless you have some heavyer mods that not a good idea. 19cc domes are more twards stroker bikes and drag bikes and serverly ported bikes. stick with your 20cc's.

[fastrthnu]

I locked up my motor the other day and decided to take the motor out. So I took off the left side exhaust and...metal shavings poured out. So I finally got the motor out and took the cool head off and come to see that the pistons were still together. The right cylinder seemed fine but the left seems like pretty bad at the top. I didn't take off the cylinders because I couldn't break the piston loose. So took it to the shop. It seems that the piston seized in the cylinder. I just hope the crank isn't broken. The guy that I bought the bike from said that the bore was .020. Is that a bore? The guy at the shop said that I could only bore one more time, is that true? I thought the bore last bore was .20. I wanted to get the HP wiseco piston kit to rebuild the top end. Are those the best piston or are there better ones? What type of piston do you guys run? In my cool head I run 20cc domes. If I go to let's say 19cc domes that should up my compression, right? Will that hurt anything? When I drained the oil I didn't find any metal flakes, so I guess that is a good thing. Thanks for any help

 

I use wisecos`s. .020 isnt a bore its 2/100 over. depending on what it takes to clean up the cylinder,. it might be your last. you could always get new ones though. your compression will be good with 20cc domes and a fresh top. Depending on what you plan on doing later or your altitude,. you might have to up a size on pump gas. If your builder is worth a crap,. they`ll know what to do.

[Bansh-eman]

Im almost positive u can go bored over alot over .20 like up to .50 or something. Wiesco pistons are the best out there. and if its messed up, which im betting it is, ur gonna need new domes. 20,21,and 22 cc domes u can run primeum pump gas on.. however once you hit 19,18,17and 16 u need to start running high octane racing fuel and unless you have some heavyer mods that not a good idea. 19cc domes are more twards stroker bikes and drag bikes and serverly ported bikes. stick with your 20cc's.

ok two problems with this statement... are you referring to(boring to .50) as the max bore size to stock jugs? if so this is incorrect... you can go double that...stock jugs can be taken out comfortably to 80 over... but they can handle 100 over being the very last stand on the sleeves...anything more and the metal is too thin....

 

know the statement that 20,21,22 domes u can run premium is too generalized of a statement... in most cases yes those can safely be ran... but without knowing his mods , squish , temps, altitude....and a few more factors you cant really say that those are fine...

 

and you can certainly run smaller domes 18cc on a stock motor .... only draw back is that you will need to run race gas and it would be VERY smart to have your crank welded if its not already... size of domes isn

Edited April 11, 2007 by Bansh-eman

[yamaha04]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 

listen to this guy he knows what hes talking about. definatly dont go any lower then 20cc domes if you dont want to run race fuel. 20 is right on the edge of 50/50 mix race/pump fuel depending on compression of course. and yes if you really f$#@ed a cyilender it may take acouple bores to get it round and true again so you very well could be on your last bore. but i find it hard to beleive you could mess one up that bad. i would take it to another shop just to see what they say. maybe even the dealer since they would know the piston sizes and how big you can go off hand. lol dont quote me on that sometimes the dealer dont know shit lol. oh yeah and also my buddy took his cyilender to get them bored on time and this builder he took it to send them out and they went from stock to max bore. so definatly take it to somewhere who knows the sizes.

Edited April 11, 2007 by yamaha04

[Swaie]

I don't mind running race fuel but am I going to get a hp increase worth the hassle. My cylinder is bored to .020 right now. They were saying the next size up from where I am now is .20. Basicly they were saying that the .020 was a mistake. I suppose it would be on the piston but I couldn't read it.

[Bansh-eman]

smaller domes might squeeze a few hp but nothing thats worth it imo... for the cost of the fuel your going to have to run id stick with premium unless you get a heavly modded motor and then you need to run race gas...

 

smaller domes will help your revs quicker... so you can launch out of the hole a little better..but 6 or 7 bucks a gallon to launch a small amount better... not worth it in my book unless your racing and not just riding for fun..

[Moddoo]

Hey guys,

Glad to see experienced guys helping out when others have questions.

 

I can tell that YOU know what you mean to say.

 

I just want to make sure that a rookie doesn't get the wrong idea from reading threads like this.

 

It looks like a couple guys are missing a decimal point in there posts.

 

.50" over is a half inch, I believe what you are trying to say is that you can take a jug to .050" over or "fifty over" That is generally understood as fifty thousandths of an inch.

 

Same goes for .20 over comments.

 

Some manufacturers use metric numbers for overbores too.

 

.5mm over and 1mm over are common sizes. Some sell pistons in .25mm increments.

 

1mm is about .040"

 

Just want to help clear it up for guys new to rebuilds.

[fastrthnu]

.50" over is a half inch, I believe what you are trying to say is that you can take a jug to .050" over or "fifty over" That is generally understood as fifty thousandths of an inch.

 

 

.05 is 5 one hundredths of an inch. .005 would be thousandths. thanks for clearing all that up for us retards. If your cylinders are already .020 over and they go another .020 over you still have about .040 to go, which could vary from 1-3 more builds.

[Screaming Yellow Zonker]

I agree take it to someone else that knows banshee engines a little better. I took my jugs to Vito's and said true it up and he did so with out any other add ons. Also Vito's is 3 miles from my house. And they have all the parts right there on the shelf to match to your engine.

[Swaie]

Okay so I'm not in need of any cylinders yet. Is it the general consensus that the 20cc dome is about lowest I should go?

[Swaie]

So will the decrease in dome size give me worth while increase in hp or should I wait and put on the adjustable timing plate?

[yamaha04]

So will the decrease in dome size give me worth while increase in hp or should I wait and put on the adjustable timing plate?

 

take your cyilender to someone how knows. and yes get a timeing plate. i dont think i would be a good idea to go any lower until you have your stock crank welded. i would just stick with 20's if you go lower there is a higher chance your crank will come apart and i dont think it will be much of a gain in hp. it may give you abit more low end but probably not noticable.

[.]

64 mm is stock bore

 

Take the cylinders to a machine shop and find out what its gonna need to be bored out to. Order your piston kit (rings, wristpin, bearings, and gaskets) out of the dirtwheels catalog for 160 to your door.

 

Take the cylinders back to the machinist with the pistons so he can bore the cylinders to the exact pistons (pistons come .020 over, .030 over etc. and they can actually be .023 over or .026 over or .019 over. He should be able to bore to the thousandths.

 

Keep the 20 cc domes and adjust your new plate to +4 and you should be good to go. The higher compression with race gas will give you some more torque on the bottom. But I wouldnt go there until you weld the crank.

 

If you dont already, get some dual stage reeds or some vforce's. They'll give you unbelievable throttle response compared to stock and are worth every penny.