The IT175 thread reminded me of my YZ125 experience. The transfer ports were so mismatched, left vs. right that bike had no power, at all. Porting was what let the big boys run away from y'all. Here's the scene, a lowly engineer says this will work great. We'll leave the Suzukis in the dust with this. The factory was unable to reproduce the engineer dream, failure often ensued. Get out your rattail files, ease transitions, balance right and left, then get into the mind of the designer. This is when my buddies take their cylinders away from me. Go solo, figure it out. Was the designer going for a Schnurle effect or stopping the incoming transfer ports to each other, a Honda innovation. Resist the urge to hog it out. Velocity is more important than volume.
Smartass, I'm preaching to the proletariat here. You have ignored the wisdom I am imparting to the unwashed masses, it is so simple. Were you the guy that roosted me at Washougal?
would agree, port maching and smoothing is easy cheap power. I'll be doing an RT1 soon and plan on just a cleanup of the ports.
i am very interested in diy porting....i have shitloads of bultaco and ossa cylinders to experiment on.....hopefully some secrets will be imparted... mike
Clean your cylinder of carbon first. Flat-blade screwdrivers work well. Look it over carefully for sharp edges. Sharp edges cause problems with flow. No tools yet, we're looking it over. Does the intake tract flow smoothly downward to the crankcase? This is a good time to gain an understanding of 2-stroke theory. The intake flows to the crankcase, it is compressed by the downward piston movement, and pushed out the transfer ports to the cylinder. The exhaust scavenges the burnt gases, but not too much. Now, let's look at those sharp edges, starting with the intake tract. The intake should flow decidedly downward, and a sharp edge at the bottom edge of the intake is disruptive. However, hogging out the intake will rob bottom-end power and your goal should be to maximize low-mid power. Often, the intake port will require a smear of jb-weld to smooth it out and ease the transition. The precursor to jb-weld is a clean metal surface to apply. You don't want it coming loose, ever. Removing an intake port edge by grinding often removes too much metal at the cylinder port, increasing intake timing and hurting bottom-end power. Next, the transfer ports. Use your fingers as gauges to determine if the ports are the same size. A smooth, rounded flow is the object here. Most cylinders have a blunt edge at the base of the transfer ports, on the inner (piston) side. For the best flow, this blunt edge should be rounded, not knife-edged. Flow, not volume, is important here. The YZ125 I mentioned before was so bad it required the outer side of the transfer ports and the crankcase to be opened up on one side to match the other. I used sealer on the base gasket so it didn't leak. Fingers as gauges, use them. The top and side edge of transfer ports at the cylinder really matter. A chamfer with 80-grit emery cloth is a start. Now, the exhaust port. Watch out here, you can alter the powerband adversely by hogging it out. Sharp edges should be removed, but watch out, usually a chamfer job is all that's required. I do this with rat-tail files and 80-grit emery cloth from a roll. I spent 40+ hours on a Maico 490 jug and it was magic. Be very cautious with power tools, they tend to get away from a guy. If you take no metal off, it cannot be worse than when you started.
Don't waste out of production cylinders on poorly advised exercises. And unless you are sure of the end result pay someone else to port you smoker. A good pipe and correcting the squish is cheaper and easier.
Yeah, this advice is only meant for single-cylinder owners. We're gonna use the pipe we have and you'd hafta show how we could adjust squish. Don't touch the cylinder, yet, maybe never. Notice the transfer port flow includes the bottom of the crankcase ports. Right vs. left is a common imbalance. Use your fingers and a base gasket as gauges.
My intent was to save some hard to find 'taco and Ossa parts from doorstop duty. I do have a little idea what goes on inside a smoker.
Let em grind ! The value of rare cylinders will go up another 20 % next month ! Cant tell you how many scrap metal cylinders we have tossed over the decades from home brew "Tuners" thinking they couldnt go wrong !!!!! The factory has a bit of a clue on how to do porting.......especially with production MX bikes !
Sir, you are one of the most knowledgeable fellows on this site. I want to pass on the knowledge I have gained through years of DIY porting. I ruined my share of cylinders before I figured it out. First, do not trust this job to a paid professional. They work too quickly, and they usually "hog it out". The plan is to match right-to-left, ease transitions and get the best cylinder scavenging while removing only a small amount of metal. With that in mind, power tools are off-limits. Use an assortment of files and 80-grit emery cloth. No grinding. This is a labor of love, it's yours, right?
Its really very silly for those who dont know how to waste time trying to "port" a 2T cylinder, when in most cases the squish clearance is going to be way out, and exhaust and intake systems are likely to be a very long way from ideal.
I learned how to port back in the early 70's from the late great EC Birt when I worked for him at Precision Cycles. Later I did all of the porting for Donny Emler when he opened Uncle Donny's Flying Machine Factory (now known as FMF). Carbide burrs in die grinders are the tools of choice, with many custom bits and angle attachments also used extensively. Files are only used to champher the edges of the ports after you've finished so the rings don't catch. Only the exhaust port is polished to prevent carbon build up, intake and transfer ports are left rough sanded. The single biggest issue with porting is port timing. 2 stroke port timing is laid out similar to 4 stroke cam timing. Port timing laid out in degrees from TDC. How many degrees after TDC the exhaust opens and then how many degrees later the transfers open dictate where your top end an bottom end power will be. Ever since the introduction of reed valves, intake timing is WFO with the reeds controlling the action. Recent (newer) 2 stroke race bikes benefit more from a quality pipe than playing with port timing and simply cleaning up your stock ports rarely yields significant increases in HP.
Squish clearance can only be way out in one way...too much, too little and you will be banging the piston on the head. Too little and your compression will be lacking. A stock bike's squish clearance is usually "in the hunt" and total compression is more of a concern than simple squish clearance. IMO that is.
In my experience Yamaha squish tends to be around 1.7MM from the factory. They really benefit from correction.
My friend Mean Dean Travis had both a fully tricked out FMF RM80 and a fully tricked out DG RM80. I thought they were both too pipey for their own good but it's damn hard to soup up a 80 and not make them too pipey. I agree that most people should leave their ports alone for just F'ing them up but then there are some of us that can actually port. Cleaning up ports does make a difference IMO but it really depends on what you start with. Back in the seventies, a lot of them came out of the crate looking like crap! Without changing the timing at all you could often get things flowing a lot better. The trick with the tranfers is to keep their "aim" right. I think a mirror polish on the exhaust does more than keep carbon from building up. It helps them FLOW. I use to get mine like a mirror and then every couple of tanks put the piston on TDC and clean them back up real quick for big payoffs! A friend of mine's dad use to polish the inside of his pipes with a frayed auto emergency brake cable. He said it made a noticeable difference and from my experience with exhaust ports, I don't doubt it although I have never tried it. I know exactly what willis is saying about velocity over volume. I could look up the tried and true formula that proves this. More tuners should keep velocity in mind over volume but they don't. I grew up around short track races and I have seen SO many strokers tuned to a stand still for trumping volume over velocity. Most often by hogging out exhaust port height but . . . . High RPM power? First you have to GET to high RPM!!
In most cases correcting factory squish clearance (which is generally way off!) and paying careful attention to intake and exhaust systems, will make far more difference than any porting job, most of which will make bikes run worse, unless riding WOT at all times is intended.
A good pipe will increase flow far more than "port matching" ever will. After spending a decade (uhm.....two) with a (sometimes wet) Superflow 600 screaming in my ears I found finish does nothing to foster increased flow. As long as it has a smooth clean profile there's nothing more you can do. The boundary layer is up to 1 mm thick and cancels anything more than a smooth finish. You should see what a pitot tube does to flow.And that my friends is empirical not anecdotal evidence.
