honing, boring, etc

[xs650newb]

So I am taking the head, rockerbox, and jugs to a machine shop soon for a port/polish and bead blasting to clean everything up. The cylinder sleeves have some rust in them so most likely I will need to go up a size or two on the pistons.

What is the process here? Do I tell the guy the sizes of various pistons and he finds the smallest piston that will fit in the bored out sleeves? Does he bore out the sleeve before I give him the pistons, or does he need the pistons to properly bore the cylinder? Do large piston sizes mean more engine power because the displacement is larger?

Also, I am debating doing the port/polish myself with a dremel. My understanding is that you simply remove casting flaws, smooth the exhaust, and roughen up slightly the intake. I have 2 heads so if I mess one up, its not a game ender. Any thoughts?

Thanks,
Adam

 

[mouser]

if the pistons you have now are stock and rust is the issue generally first oversize will do the trick. Take the new pistons with you, as well as the clearance specs, to the machine shop. Then they are responsible for the fit. I had a bad experience doing it bass ackwards once that cost me a set of pistons and another rebore.

 

[retiredgentleman]

Have a read of this thread:
http://www.xs650.com/forum/showthread.php?t=2967

www.biker.net Read the Service Manual to understand piston/cylinder relationship

 

[littlebill31]

5twins post #11 in that thread breaks the numbers down very well. Also page #40 in the Haynes manual explains this.

 

[xs650newb]

Hey guys. So I think I am good to go with the honing/boring thanks to reading that post and calling a machine shop.

In regards to my question on porting, do you think removing casting flaws with a dremel is advisale for someone with no experience?

 

[littlebill31]

I was taught by a guy who told me to find the lowest points in the ports... and go no lower. Just get the high points off first with a tool, then do the rest by hand. You can mess shit up fast with a dremel. Use a slow speed if you do try it.

 

[Jack]

So I am taking the head, rockerbox, and jugs to a machine shop soon for a port/polish and bead blasting to clean everything up. The cylinder sleeves have some rust in them so most likely I will need to go up a size or two on the pistons.

What is the process here? Do I tell the guy the sizes of various pistons and he finds the smallest piston that will fit in the bored out sleeves? Does he bore out the sleeve before I give him the pistons, or does he need the pistons to properly bore the cylinder? Do large piston sizes mean more engine power because the displacement is larger?

Also, I am debating doing the port/polish myself with a dremel. My understanding is that you simply remove casting flaws, smooth the exhaust, and roughen up slightly the intake. I have 2 heads so if I mess one up, its not a game ender. Any thoughts?

Thanks,
Adam

You can remove the rough castings yourself but with a Dremel I have no experience as my experience has been with good air tools. You want to to smooth and roll the intake short side to the seat,just roll it over. Keep the cross sectional spigot area around 32MM to 34MM or port velocity will suffer somewhat if taken out larger. You can shift the flow around by reworking the guide boss but in your case just roll smooth,no feathering. For the exhaust unless you have a flow bench or experience knowing what areas need attention then I might suggest just shorting the guide length to match the intake guide length,as the mod will reduce resistance enough to increase port velocity and flow,smooth out the rough casting of the short side and roll it.
These ports respond favorably with volume reductions but that's another ball game

 

[pa-powerstroke]

Anyone have pictures?

 

[Paulrxs650]

Porting is often thought to be the process of smoothing out the existing inlet tract, however that is not strictly true. It is more to do with altering the shape of the tract to create a smoother and more efficient flow.
A rough surface allows fuel to evaporate more quickly, polishing the inlet tract will do very little to improve performance on anything but a highly tuned, performance engine, even then it will be minimal. Airflow at the wall of the tract is effectively 0, hence the minimal effect.