Bore size???

[Leines]

Ok guys. Got my engine apart. I got a bore size of 67.2 I look on my manual and it says 66 something is the service limit. What's going on here??

 

[brandoz28]

thats the stock bore service limit. most of these things can be taken to 68mm

 

[royalt67]

How close of tolerance are you measuring? Could be a 67.00 overbore that is very worn or a 67.25 overbore.

 

[Leines]

Measured with micrometer it was 67.19 so I'd say really worn lower one. Looks like piston is screwed can't piston pin out. Piston measures 67mm

 

[royalt67]

So, that is a 67.00mm or +.040" overbore, altough it occurs to me that it could als be a +.050" or 67.125mm, they do make them. Most manufacturers stamp the top of the piston with either a part number or the overbore size. The good news is that you have several overbores left.

Try a sharp knife to remove any possible ridge in the piston pin hole, after removing the retaining circlip.

 

[Leines]

I tried to get the piston pin out..and it appears the bearings are shot..and its stuck in there... ive been out at my uncles shop trying to get a bit of work done... looks like im in need of a new piston... and i gotta try to find a place locally that can bore this cylinder....... im stuck right now at the flywheel.. uncle thought he had the puller and didnt... said he might be able to make one.. or ill ask around and see if there is anywhere i can borrow one....

another question is.. what is the stock front sprocket size??? mine is a 14tooth one.. is that stock?


Cheers

 

[Leines]

Ive been looking around for a piston... what brands should i consider...wiseco i believe is the big one.. looks to be about $100 for them.... And what should be my next bore size... 67.25mm or 67.5??? When you say i have a few bores left.. what incraments can you bore off at a time... If i do 67.5mm.. do i still have 67.75mm and 68mm???

Cheers

 

[dickymoe]

i believe w/ wiseco pistons the over sizes are in .5mm increments.your piston ring end gaps are a critical number to pay attention to when rebuilding your motor.if you dont bore the cylinder and get that end gap right you will wipe out the motor in less than 7 hrs run time.just happened to me unfortunately costing a brand new top end kit.

 

[x1rcr]

If you go 67.5 you actually have 3 more sizes above that. Wiseco makes a .090 over piston too. Let a shop mic your cylinder and tell you what size it will bore out to. And the stock size front sprocket is a 13 tooth. As for the wrist pin try heating the piston where it goes thru after you get the clips out.

 

[brandoz28]

wiseco makes a 67.25 piston, and if possible that's the size i'd go to

 

[Leines]

I talked to the engine shop and they told me to have the piston when i go there for the bore... so i think i have to order the piston first.... trying to decide if i should risk the smaller one.. or just go up to the next size to be sure its clean and fits properly...

 

[mmajay]

I would take the cylinder to the shop and have them tell you if they think they can clean it up with only going to the next size, then buy the right piston and take it back for the bore.

 

[royalt67]

Most shops want the piston in hand before boring, sure, but if they aren't willing to measure it first and tell you what size to get, then maybe you should find a diff shop.

My guy would never take a customer's word on bore size. "Wouldn't be Prudent!"

 

[sicivicdude]

The best person to ask if the next up (really close) bore size will work or you'll need to jump up past that one is the guy running the boring machine. He can take one look at it and tell you what you need to know...

 

[sheeblast]

^^^ true, owning many 2-strokes in my time, and working next to his shop, i became friends with my local machinist. he does good work.