Port Clean-up during rebuild (not really porting)

[BrianW]

A general question to all the experts out there - I've got a 94 RM 250 that I'm going to re-do the top end this winter. Is there any benefit to cleaning up casting flash and smoothing the ports while the cylinder is off? I'm not talking altering the port size/shape, but sinply cleaning the factory stuff up.

I know on all the car engines I build it's worth a few HP but on a single cylinder 2-stroke???

 

[RM_guy]

If you are just cleaning up the casting flaws, the biggest bang for the buck is in the exhaust port. It doesn’t have to be mirror smooth but any bumps or irregularities should be removed. Also make sure that the power valves all match an don’t interfere with the flow when they are fully opened. Even a 1/16” protrusion can make a difference.

Other things are making sure gaskets don’t block flow, removing any molding mismatches in the reed block, removing casting flaws in the intake passages. Matching the cylinder to the casings (transfer ports) isn't going to buy you a lot so I wouldn't spend time on that.

Stay away from the edge of the ports unless you know what your doing.

Have fun

 

[dirt bike dave]

On my old KDX250, there was some really ugly casting flash in the intake tract, and the bottom of the KIPS valve ports when open was about 2mm higher than the floor of the main exhaust port. By opening the KIPS valve up to make a smooth transition with the exhaust port the bike clearly picked up some revs and top end power, with no loss in bottom or mid.

To me, this kind of work is 'blueprinting' rather than porting. In my case, it was well worth the trouble.

 

[MikeT]

Go for it. Cleaning things up will always help. :D

 

[BrianW]

Well I thought I couldn't hurt but there's been some good info here - I was mainly hoping to see that it would be worth the effort and not simply a waste of time and sandpaper rolls.

Anyone else done this and gotten gains?

I guess I'd consider it simply a cleanup of the manufacturing process beyond what is cost effective for the item... It may not be cost effective to get that last HP from an hour of hand cleanup on the casting for the factory, but since I have a little time over the winter it might be worthwhile to me....

 

[Rich Rohrich]

Originally posted by BrianW
not simply a waste of time and sandpaper rolls.

Unfortunately that's really all it will be unless you alter the shapes of the ducts, the port timing, or the window discharge shape or angle. It's easier to do more harm than good in most cases.

 

[RM_guy]

Rich,
The only place I saw significant improvement was matching the power valves. They were off by almost an 1/8 of an inch. You sure are right about the rest of it though, unless you need something to do on the cold winter nights.:silly:

 

[SFO]

BLUEPRINTING?

It seems to me that calling optimization "blueprinting" is not exactly true.
It would require that you actually had a "blueprint" to match reality(the part in your hand) with the tolerances on the drawing.
It would appear that since it left the factory it actualy met the production tolerances that were set forth by the engineers.
I would love to erase the word "blueprinting" from the minds of people wishing to describe the kind of modifications they are doing.
Forgive me for my outburst.

 

[NC514]

Ports that i shouldn't touch?

I had a 2000 CR 125, it was a couple of winters ago and i messed with a little bit of sanding myself. Afterwards I asked a mechanic at a local shop if I had done anything wrong. It wasn't the exhaust port that i smoothed out, i believe it was the intake, on the base of the cylinder. the mechanic mentioned that i could've affected the air/gas mixture coagulation or something. Did I? For future reference can i take off the exhaust flange and smooth everything also? Any takers???

 

[spanky250]

Re: Ports that i shouldn't touch?

Originally posted by NC514
I had a 2000 CR 125, it was a couple of winters ago and i messed with a little bit of sanding myself. Afterwards I asked a mechanic at a local shop if I had done anything wrong. It wasn't the exhaust port that i smoothed out, i believe it was the intake, on the base of the cylinder. the mechanic mentioned that i could've affected the air/gas mixture coagulation or something. Did I? For future reference can i take off the exhaust flange and smooth everything also? Any takers???

The mechanic is wrong, but there is no benefit to smooth port finishes, either. Surface finish is irrelevant to flow or atomization. As for the exhaust ports, some people will say that polishing it will help reduce carbon buildup, but that isn't really true either. Even if you polish it to a mirror finish, when seen under magnification the surface will still be far from smooth, leaving a myriad of peaks and valleys for carbon to adhere to. You will have much better results reducing carbon buildup by jetting properly.

 

[Jaybird]

I've know car and harley tuners who rough up the intake hoping for better atomization. It's been argued a few times, but lets hear some more.

 

[Rich Rohrich]

Originally posted by Jaybird
I've know car and harley tuners who rough up the intake hoping for better atomization.

Most Harley "tuners" rely on an axe and a big stone to tune with so I wouldn't put too much stock in what they have to say.

 

[Jaybird]

Most of the Harley tuners I know have graduated to a BFH.
:)

 

[Rich Rohrich]

Originally posted by Jaybird
Most of the Harley tuners I know have graduated to a BFH.
:)

There is no stopping progress.

 

[SFO]

Harleys...

Rich, I can only imagine since you allow the harley word to be seen in print, unlike the Q***, four letter word you actualy like them?
I know every once in a while that you must hear one that sounds like it is really running right and not just another wheelbarrow running on two cylinders...
When you hear one that is running right it feels good:p

 

[Rich Rohrich]

Re: Harleys...

Originally posted by SFO
Rich, I can only imagine since you allow the harley word to be seen in print, unlike the Q***, four letter word you actualy like them?

Anything with wheels and a motor is OK in my book including qua ds. I just don't like idiots, and Harleys seem to attract more than their fair share of butchers masquerading as "tuner". Not unlike qua d tuners LMAO :)
I have nothing but respect for REAL tuners like Werner, but I'm guessing he wouldn't get sucked into silly polish vs. no-polish discussions, so he and the other DT and drag race super tuners are automatically excluded from this discussion.

I've done some Harley cylinder heads over the years and have helped put together some really enjoyable Harley combinations. Big inch motors with GOBS of torque are always fun regardless of what the tank badge says.

 

[BrianW]

Thanks guys for explaining how harley ports, hammers, and such relate to my question... :silly:

Oh well, guess I can 't get a straight answer to a real quiestion

 

[spanky250]

Originally posted by BrianW
Thanks guys for explaining how harley ports, hammers, and such relate to my question... :silly:

Oh well, guess I can 't get a straight answer to a real quiestion

If you actualy read any of the posts other than the Harley Humor ones, you would find a lot of infomation, and the answer to your question.

To make it simple enough for you to understand, unless you have some serious casting flaws that protrude into the ports and disturb the flow, there is no benefit to "cleaning up" the ports. Is that straight enough for you?

 

[RM_guy]

Thank you Spanky:)

 

[Titanium]

There is one non-performance benifit; it is much easier to clean the carbon off of the ports/head during routine maintanence, if they are polished.

 

[smilinicon]

SFO - the word 'blueprinting' has been used for bringing a motor up to the called for specs for a long time. You gonna be OK?

BrianW - that is how it works in here... you ask a question, get some helpful info here and there (bless those who actually take time to answer), but mostly you just start debates that lead to nowhere. A lot of members seem to think what they know is written in stone and there is never a shortage of posts telling you how wrong you are. You gotta just sift through it :)

I have a link that someone sent me that was helpful in answering the questions you posted. PM me if you would like it.