Boring stock jugs

[deuce217]

Hey guys,

I was curious if anybody has bored the stock jug to 47mm and ordered a new piston and rings to make a BBK? I was thinking, my new mill has 5'' of quill travel, maybe I could give this a shot and then try to port the stock jug a bit. What do you think?

[Johnniespeed]

I have had CRF 50's, CR80's, Spree's, Aero's, and Gyro's bored. I have a local motorcycle shop that bores, sets piston clearance, chamfers the ports and does a machine finish hone, all for $45. They usually have a two day turnaround. My vertical mill and hones are gathering dust.
If you try this, make sure you don't overbore, leave material so you can hone to get a .0015" or .002" piston to wall clearance.
Too tight and you soft sieze, too loose and it clatters cold.

[Red Eft Performance]

In my opinion its just not worth it. the ports are just too mild. Yes you can port it but you would have a very hard time increasing the size of the side transfer ports. You just cant get inside them and open them up. A decent piston and rings and gasket set is going to cost you as well. Then you would still be left with stock head. would need to open it up and cut proper squish ect.

You can get a Malossi cast kit for 165$ shipped that would be a very good bore to put some time into porting. I would say its the most underrated bore. Its cheap and high quality and responds very well to porting.

Either way I have some Malossi and Polini pistons in stock if you want to use one for the stock bore.


Keith

[deuce217]

Johnnie,

Thats a great deal

Thanks Keith,

Dou you think that the MHR porting would be the best way to port on the cast? Maybe I could do that. The deal is, I have spend a ton of money on porting abrasives and tools and would like to put them to work. I even have the little 90 degree micro die grinder to get inside of the jugs.

[Red Eft Performance]

Johnnie,

Thats a great deal

Thanks Keith,

Dou you think that the MHR porting would be the best way to port on the cast? Maybe I could do that. The deal is, I have spend a ton of money on porting abrasives and tools and would like to put them to work. I even have the little 90 degree micro die grinder to get inside of the jugs.

Yes That would be a good start. Pending on what you are going for even the MHR(as all bores) could be improved on.

[deuce217]

Johnnie,

Thats a great deal

Thanks Keith,

Dou you think that the MHR porting would be the best way to port on the cast? Maybe I could do that. The deal is, I have spend a ton of money on porting abrasives and tools and would like to put them to work. I even have the little 90 degree micro die grinder to get inside of the jugs.

Yes That would be a good start. Pending on what you are going for even the MHR(as all bores) could be improved on.

Man,

That would be something. To know how to port them to whatever you want and understand it all. I read that A Bell. Book on 2 stroke tuning. That was a good read.

[JDOBBS86]

I have had CRF 50's, CR80's, Spree's, Aero's, and Gyro's bored. I have a local motorcycle shop that bores, sets piston clearance, chamfers the ports and does a machine finish hone, all for $45. They usually have a two day turnaround. My vertical mill and hones are gathering dust.
If you try this, make sure you don't overbore, leave material so you can hone to get a .0015" or .002" piston to wall clearance.
Too tight and you soft sieze, too loose and it clatters cold.

Johnnie,

That really is a decent deal do you think they take cylinders by mail? I'm only a little ways east of you. The only place i can find (online) around me would do it for about $70.00 - $80.00.

[Johnniespeed]

Give them a call, the worst they can say is no. http://www.metricmotorsports.biz/showroom/
I added the link to their website, and here is their phone number. 231 739 1111
You should ask the price, just in case my cost was some type of special deal.
I was just a walk in customer at first, now I bring a lot of jugs there. Sometimes they do same day service , sometimes it's next day service, the longest was two day service. They will ask what piston to cylinder clearance you want, so look up your specifications first. I usually do .0015" but sometimes I use .002" for high RPM motors ( over 11k rpm)