The Basics, Port & Polish and Port Matching

[BarelyAWake]

re: The Basics, Port & Polish and Port Matching

One or two questions about port timing. I know this has been talked about before but I cant seem to find the information I am looking for. I have a spare jug that I want to try some mods on. Isin't it lower the intake and raise the exhaust port? I have already widened them some. Is this right? How much material should I take off? Raise and lower by 1/8"? More? Less? What performance differences can I expect. Guess I want this little china girl to run like my old Kaw. 500 2-stroke triple that I sold because I decided if I kept it I would kill myself on it!

This thread is essentially a basic primer regarding the cleaning and smoothing of the stock port size and shape and the attempt to match the stock intake and exhaust manifolds to their finished ports as well as possible - the finishing stages overlooked by the manufacturer in the interest of budget, it's also remarkably easy.

While obv removing material makes it larger, I'm not really getting into oversize porting (true porting) other than suggesting any modification is at the owner's discretion- not to alter it's overall shape and remember to leave enough for proper gasket seating.

There's simply too much experimentation and variables in application to give specifics beyond this basic "cleaning" (carb & manifold type, exhaust system, engine size & manufacture, etc.) - but feel free to do whatever you wish with your engine(s), remember to post any results you achieve or even create a performance thread!

TBH I see little point in widening/enlarging the ports much beyond what's outlined here, the intake and exhaust manifolds are simply far too small to gain any perceivable benefit. Even if you were to make custom manifolds - the stock port sizes will probably still exceed the manifold's ID by a significant amount. Worse yet, exceed stock size too much and you run the danger of hanging a ring - it's easy as pie to remove material... it's another story tryin' to put it back lol

Even altering the port timing is a similar story, as I've not seen any possible gained benefit from alteration & lots of potential for performance loss, I've left it be. This thread isn't an experimentation thread, it's a basic tutorial outlining some tried & true processes that all HT 2 strokes desperately need and with little to no risk of engine damage.

Do feel free to start another thread though - we've a couple-few members I'm sure would be willing to offer their opinions

 

[5446]

re: The Basics, Port & Polish and Port Matching

Ok Ive tryed everything posted here and I buffed the dome on the inside of the head. Is that something I should do? Hope to make the head a little cooler?

 

[GearNut]

re: The Basics, Port & Polish and Port Matching

Cooler, a little. Here's why: A polished surface is very much less prone to carbon build up.
Carbon build up will act as a blanket and trap some of the heat in.
We are not talking about a tremendous difference, just a little difference, and you will have cleaner engine internals as well.

 

[KCvale]

re: The Basics, Port & Polish and Port Matching

Quick question...
On the exhaust, what about that tiny final exit hole?
Is that in itself a port?
I haven't found the topic explain expansion chambers could you please point me?

 

[BarelyAWake]

re: The Basics, Port & Polish and Port Matching

Short explanation - the expansion chamber uses the exhaust's pressure wave reflected to act sort of like an exhaust valve on a four-stroke, increasing performance by reducing wasted fuel/air charge that would otherwise escape through the exhaust port;

Expansion chamber - Wikipedia, the free encyclopedia

As all two strokes need some back pressure to run properly - altering the stock exhaust system is... not as beneficial as it may seem as it's mostly an increase in noise & the placebo effect (louder = more power, right?). Not to say the stock system isn't unduly restrictive, but simply pulling the endcap doesn't earn enough of a gain to warrant the gawdawful noise, may perhaps harm your motor in the long run by causing a lean condition.

Expansion chambers for our 50-66cc two-strokes are fortunately commonplace with the only questions being how loud, cost, and appearance/routing technique. Many of our vendors sell them as well as members that have adapted low-cost pocket bike ones.

It's worth all effort and every penny, I consider an expansion chamber a vital component of any two-stroke, left out of our kits only as a cost-reducing measure


edit: If you've one of the newer style catalytic converter mufflers - then it's restrictive as heck and will only get more so as it loads up with carbon & oil over time, I'd recommend even the stock (but only baffled) kit pipe over that thing... but it's a bit of a moot point given the benefits of a proper expansion chamber design

 

[DanielMaia]

re: The Basics, Port & Polish and Port Matching

Anyone here have photos of transfer ports totally matched and polished?

I saw these photos once, but i dont know where...

thnks

 

[KCvale]

re: The Basics, Port & Polish and Port Matching

I couldn't get perfectly matched, when I ground the other side of the flange flat for the washers I didn't have enough material left, but I got pretty close.

That $6 file from Ace Hardware made pretty short work of it.

What I wanted to use was this spiffy pneumatic file I found.

I bought it, a 100 PSI compressor with a 3 gallon tank, and the hose kit thinking I could get some use out them.

I got it all fired up and started and the file went back and forth about 5 times and that was it.
Turns out the file needs 90 PSI continuous to operate.
That little 3 gallon compressor can get up to 100 PSI, but it can only maintain about 15 hehehe.

I still think that file will be a handy tool, I will let you know when I have an air supply so I can try it out.

 

[BarelyAWake]

re: The Basics, Port & Polish and Port Matching

That is a spiffy lookin' tool man... now I wants one lol

...ya prolly know this but I'll sling it out there anyway jus' in case - you do not want to use a file of any sort on the cylinder's ports - while it's just fine for the intake & exhaust manifolds, with the softer aluminum of the cylinder you'll prolly gouge it excessively and end up distorting the port's shape, but far more importantly you'll stand a good chance of chipping/flaking off the chrome/naskil lining of the cylinder itself should you use a file.

 

[KCvale]

re: The Basics, Port & Polish and Port Matching

That is a spiffy lookin' tool man... now I wants one lol

Ya, I really wanted to see how it worked so I took a tailpipe and the file around the corner to Community Tire to use their air but they use a different coupler than my air kit had!

The tool uses 4 CFM @ 90 PSI, my compressor only puts out .6 CFM @ 90 PSI.
4 Cubic Feet, that's 30 gallons. You will need a pretty big compressor and tank to run the thing.

 

[mr.WFO]

re: The Basics, Port & Polish and Port Matching

awesome write-up.
thanks for that.

 

[sellouma]

I don't agree. I think something on porting for those who know nothing at all about these motors, but would like to learn is a good thing. If you already know all about it then there's no need to read it, but for the newbie to read some of these discussions of high speed stuff is like, well, "Chinese" or trying to read "Greek". And if a new person is not pretty sure of what to do, why to do it, how to go about it without wrecking a brand new motor then they aren't going to try. Imagine that you are explaining this to somebody who is a first time owner of a 2 stroke engine of any kind, or your 13 year old nephew who is really interested, but has little experience with things mechanical. I think this could be even more simple with more hand holding and more closeup photos. For example, the first time person doesn't know about what needs to be taken apart and how to do it. Are there any things to be extra careful about? Does this mean new gaskets? How tight should it be put back together? It is true that porting is not a new subject, but very often it was addressed on this forum without photos and if there were any they were often blurry. The person already in the know understood the discussion perfectly, but the newbie was left on the outside looking in and not much better off.
A how to for eighth graders is a good thing. A how to so absolutely clear that it is nearly impossible to screw up leads to success. Step one... here's your motor new out of the box. Step two... these are the tools you need to do this job. The one on the left is called a Dremel and the little attachment you see on it is... etc. No, this isn't going to be very helpful to those who already know how and is boring, but to the newbie it will be much appreciated, much studied and will lead to some happy mb campers who can say "I ported my motor and it runs lots better, heh".
And maybe instead of just the focus on greater speed the slant should be on cleaning up your motor so that it works more efficiently. I would guess that a ported engine just plain runs better. (By the way, some of those 13 year old eighth graders are retired and in their sixties... the baldies in the back row.)
Another way to approach this is to imagine that you are teaching seniors how to use a computer for the first time. These are smart people who are accomplished in many ways, but computers are new and daunting things for them. But they want to email their friends and send photos to relatives. Teach 'em how. As a former teacher I know that helping empower others is a great thing.
SB

Well said, Silverbar.
Thank you.

 

[MarkSumpter]

A couple of things I would like to interject into this very enlightening discussion about port matching. I am building my first China engine bike but I have been involved in small engine repair for over 30 years.

First the idea that the intake port be left slightly satin is correct as a highly polished surface allows the atomized fuel to re-condense to a fully liquid state more readily than a satin finish does. Another huge thing that causes atomized fuel to reform is a low pressure area where there is a marked drop off or restriction going from the intake tube to the jug. This is because the fuel swirls in and back on itself causing the fine mist droplets to collide with each other and become one. Stihl had this problem on the early version of their 024AV engines where the intake port did not match the carb properly. Their fix was a bakelite intake spacer that allowed a free transition from carb to port.

I see this as an issue of the same nature with these engines also so I am taking a piece of 1/4 inch aluminum (may have to go ti 3/8 inch to feather the difference in the 2 openings not sure yet) and am going to make an intake spacer to mate the intake tube to the jug without having any restrictions, drop offs or rides to cause the air fuel mixture to swirl on itself. then use a gasket on either sude of this spacer to seam the intake tube to the jug.

I am also thinking that this would be a good idea to do on the exhaust side also to the port to better meet the exhaust flange and reduce obstructions.

Barely Awake you mention to use a piece of better quality gasket material to make replacement gaskets but one issue I see is that if it is appreciably thicker and heavier then the thickness difference can cause a decrease in compression as the cylinder is not traveling quite as high to the head as it originally would be with the thinner gaskets. If you make a jug and head gasket you could well be reducing compression significantly.

Generally most 2 cycles that are of higher quality still have very thin gaskets. One of the issues is that the integrity of a 2 cycle engine has to be free of leaks to run properly (not to lean out) and sometimes these lighter gaskets can be difficult to get to seal well. I use a very thin coat of Indian Head shellac sealer on one side of the gasket tp ensure it sealing on the easiest surface to remove it from. Carb cleaner does a good job to soften the shellac when removing the old gasket.

These are just my thoughts though and I will post images of the carb and exhaust spacers when I have them made.

 

[MotorBicycleRacing]

This straight intake matches the intake port

 

[MarkSumpter]

This straight intake matches the intake port

I have the tube that is angled up. Does it also mate to the intake post? I haven't had mine off the engine so I am not sure. it just doesn't look like there is much meat on that flange allow it to mate well or even grind out.

 

[BarelyAWake]

A couple of things I would like to interject into this very enlightening discussion about port matching. I am building my first China engine bike but I have been involved in small engine repair for over 30 years.

First the idea that the intake port be left slightly satin is correct as a highly polished surface allows the atomized fuel to re-condense to a fully liquid state more readily than a satin finish does. Another huge thing that causes atomized fuel to reform is a low pressure area where there is a marked drop off or restriction going from the intake tube to the jug. This is because the fuel swirls in and back on itself causing the fine mist droplets to collide with each other and become one. Stihl had this problem on the early version of their 024AV engines where the intake port did not match the carb properly. Their fix was a bakelite intake spacer that allowed a free transition from carb to port.

I see this as an issue of the same nature with these engines also so I am taking a piece of 1/4 inch aluminum (may have to go ti 3/8 inch to feather the difference in the 2 openings not sure yet) and am going to make an intake spacer to mate the intake tube to the jug without having any restrictions, drop offs or rides to cause the air fuel mixture to swirl on itself. then use a gasket on either sude of this spacer to seam the intake tube to the jug.

I am also thinking that this would be a good idea to do on the exhaust side also to the port to better meet the exhaust flange and reduce obstructions.

Barely Awake you mention to use a piece of better quality gasket material to make replacement gaskets but one issue I see is that if it is appreciably thicker and heavier then the thickness difference can cause a decrease in compression as the cylinder is not traveling quite as high to the head as it originally would be with the thinner gaskets. If you make a jug and head gasket you could well be reducing compression significantly.

Generally most 2 cycles that are of higher quality still have very thin gaskets. One of the issues is that the integrity of a 2 cycle engine has to be free of leaks to run properly (not to lean out) and sometimes these lighter gaskets can be difficult to get to seal well. I use a very thin coat of Indian Head shellac sealer on one side of the gasket tp ensure it sealing on the easiest surface to remove it from. Carb cleaner does a good job to soften the shellac when removing the old gasket.

These are just my thoughts though and I will post images of the carb and exhaust spacers when I have them made.

Thanks for your experience Mark, you've made some good points

I don't think I suggested using thicker material for the head or base gaskets... in fact while I've toyed with the idea of making a thinner head gasket to increase compression slightly, TBH I've been too lazy to bother w/it heh - as well as there's been some concern that any significant increase in compression takes it's toll on the somewhat questionable bearings in these kits - but, again as I've not delved into that I'm not sure *shrug* In any case, the stock head gaskets seem to be fine provided the head is torqued properly - the base gasket is a bit cheesy (literally, it's about the same consistency heh) but you're absolutely correct, it's thickness is crucial - particularly for port timing.

The gasket I most heartily recommend replacing is the intake gasket due to the stock one being so poor - and again you're absolutely correct, it's thickness (and overall length of the intake manifold) does indeed have an effect on performance... still, a few thou over with that particular gasket I don't think as important as a good fit and seal... and actually, I've been known to cheat and use a bit of leather work glove as it's actually thinner than stock, seals really well, easy to make - and best yet, free (provided yer buddy doesn't notice he's now missing a glove)

Insofar as the "beveled intake spacer" I think that's a great idea! When I wrote this thread the difference between the port, the intake manifold and the carb venturi while significant - wasn't quite enough to bother with beyond beveling the manifold. While making a custom manifold would also be a solution, as it's limited by the carb it also didn't seem quite worth it. The newer engines have far larger ports however and what with the newer carbs allowing for a larger manifold as well - your solution and/or making a better manifold is defo something to be considered.

Another factor contributing to some of the oversights in this thread (which I hope you'll forgive me for) was it's intent - which was a "quick down & dirty" tutorial focusing mainly on the gawdawful castings & terrible welds & how with a little time and no investment even the most inexperienced could easily clean 'em up to get a far smoother running engine - while it's far from professional, so am I lol

Still, I'm quite glad you've taken the time to clarify and offer your experience - thanks for that & I hope you'll include some pics of your work if ya get the chance

 

[foureasy]

The ONLY reason to leave the intake rough is to support a boundary layer. A boudary layer is formed on golf balls because of the dimples to help the air slip over the surface. Slippery intakes are not smooth. You will flow more air with a cnc'd finish than polished. My friend brett from racers edge, my free dyno, did a test on his flow bench with a 450r Honda head. The cncd finish was worth 4-5 cfm over the polished. So, everybody start banging die grinders around in there!

 

[MarkSumpter]

Hey BarelyAwake sorry if I sounded contentious and for erroneously attributing the comment about gaskets to you. I guess I might have interpreted the "Make your own gaskets from a better material" phrase as meaning thicker. It is something for people new to making their own gaskets to keep in mind though when buying material.

I did get into my engine today simply for the fact I was dying to hear it run so I hooked up the CDI and chain and gave it a drink and started it up. I didn't take the time to clean up the ports because I wanted to see if there would be a difference in the ease of starting between a set of ports that were matched and ones that were factor fresh.

The machine started relatively easily without porting it out and after a little fiddling with the mix and idle speed I was able to ride it down the street.

It ran pretty well for about 15 minutes then the RPMs surged up a little and the tell tale sound of a lean engine shortened my maiden ride. I got it shut down and pushed it home.

I checked all of the easy things I have seen here on this forum for air leaks (IE: head stud and nut tightness, gap at carb clamp, intake tube tightness etc.) but everything looked OK.

So I decided what the heck I might as well pull the engine off and look a little deeper look into the lean condition.

The sad thing is that I loaned my digital camera to a friend and it hasn't come home yet so I can't document the steps I went through to find the leaks but I will try to describe my procedure and post some image later in another thread.

After pulling the covers, coil etc. I made 2 - 3/16" plate block offs out of aluminum that fit over the intake and exhaust ports along with some rubber gaskets for both out of an old tire and tightened them over the intake and exhaust ports to seal them off.

My next step was to take the new plug that came with the kit and break off the porcelain cap and and punch out the anode from the middle and grind off the spark tang. I then took a 1/4" NPT steel nipple and with a little judicious grinding was able to get it to fit into the top of the plug I just destroyed well enough to be able to braze it up so it didn't leak.

So then I put a small O ring over the threads into the place where the sealing washer had been and screwed it into the jug about a quarter turn past seating.

Now comes the fun part. I have a Mikuni Pressure Tester (like this one only lots older)

After hooking it to the 1/4" NPT nipple I pressurized the engine to 5 LBS and then sprayed around the mating surfaces of the Head, Jug, Crankcase half gaskets and seals with a soap and water solution to find any leaks (Some people will simply dunk an engine in a wash tub of water but I didnt want to get the clutch wet).

I found a leak at the head and lower Jug gasket as well as on the bottom of the crankcase.

2 of the crank case bolts were only finger tight so breaking them all loose and cross torquing them all to 120 inch/pounds solved the crankcase leak easily enough. (BTW is there a torque specification table anywhere for these engines? I hate to guess...)

As I said the head bolts seemed tight when I checked so after pulling the head I found out that there was no head gasket on the engine. I had already read in a previous thread the Chinese are terrible on QC so it didn't surprise me too much.

Now seemed like a great time to port the engine intake and exhaust a little so I followed the steps in this tutorial and things went swimmingly well. I still think I will make a spacer for the angled intake tube and maybe one for the exhaust but right now all I wanted to do is get the machine running again.

After a couple of attempts I got a decent head and jug gasket made and after re-torquing the head to 120 inch / pounds the engine was leak free and held the pressure for about 15 minutes while I had a cold beverage and a break.

After about an hour more work I had the engine back together and on the bike ready for a test run.

I happened to not have had the clutch lever locked into the neutral position while pushing it out of the garage and to my suprise it fired and almost got away from me (about 3-4 cylinder cycles is all it popped before firing). The difference between the initial start and this one was amazing and if it starts this easy new I cant wait to see when it gets broken in.

If anyone has any doubts that cleaning the ports up and doing some minor tuning on you bike will not make it perform better then they are foolish. Also being able to recognize a problem like a bike running lean and understanding the steps to find and repair an air leak helps alot. I guess the moral is not to take anything for granted even on a new out of the box engine.

Thanks again BarelyAwake for the tutorial and other info it is good for new builders and experienced people alike to find out some of the pitfalls others have experienced.

 

[mr.charlie]

Hey BarelyAwake sorry if I sounded contentious and for erroneously attributing the comment about gaskets to you. I guess I might have interpreted the "Make your own gaskets from a better material" phrase as meaning thicker. It is something for people new to making their own gaskets to keep in mind though when buying material.

I did get into my engine today simply for the fact I was dying to hear it run so I hooked up the CDI and chain and gave it a drink and started it up. I didn't take the time to clean up the ports because I wanted to see if there would be a difference in the ease of starting between a set of ports that were matched and ones that were factor fresh.

The machine started relatively easily without porting it out and after a little fiddling with the mix and idle speed I was able to ride it down the street.

It ran pretty well for about 15 minutes then the RPMs surged up a little and the tell tale sound of a lean engine shortened my maiden ride. I got it shut down and pushed it home.

I checked all of the easy things I have seen here on this forum for air leaks (IE: head stud and nut tightness, gap at carb clamp, intake tube tightness etc.) but everything looked OK.

So I decided what the heck I might as well pull the engine off and look a little deeper look into the lean condition.

The sad thing is that I loaned my digital camera to a friend and it hasn't come home yet so I can't document the steps I went through to find the leaks but I will try to describe my procedure and post some image later in another thread.

After pulling the covers, coil etc. I made 2 - 3/16" plate block offs out of aluminum that fit over the intake and exhaust ports along with some rubber gaskets for both out of an old tire and tightened them over the intake and exhaust ports to seal them off.

My next step was to take the new plug that came with the kit and break off the porcelain cap and and punch out the anode from the middle and grind off the spark tang. I then took a 1/4" NPT steel nipple and with a little judicious grinding was able to get it to fit into the top of the plug I just destroyed well enough to be able to braze it up so it didn't leak.

So then I put a small O ring over the threads into the place where the sealing washer had been and screwed it into the jug about a quarter turn past seating.

Now comes the fun part. I have a Mikuni Pressure Tester (like this one only lots older)

After hooking it to the 1/4" NPT nipple I pressurized the engine to 5 LBS and then sprayed around the mating surfaces of the Head, Jug, Crankcase half gaskets and seals with a soap and water solution to find any leaks (Some people will simply dunk an engine in a wash tub of water but I didnt want to get the clutch wet).

I found a leak at the head and lower Jug gasket as well as on the bottom of the crankcase.

2 of the crank case bolts were only finger tight so breaking them all loose and cross torquing them all to 120 inch/pounds solved the crankcase leak easily enough. (BTW is there a torque specification table anywhere for these engines? I hate to guess...)

As I said the head bolts seemed tight when I checked so after pulling the head I found out that there was no head gasket on the engine. I had already read in a previous thread the Chinese are terrible on QC so it didn't surprise me too much.

Now seemed like a great time to port the engine intake and exhaust a little so I followed the steps in this tutorial and things went swimmingly well. I still think I will make a spacer for the angled intake tube and maybe one for the exhaust but right now all I wanted to do is get the machine running again.

After a couple of attempts I got a decent head and jug gasket made and after re-torquing the head to 120 inch / pounds the engine was leak free and held the pressure for about 15 minutes while I had a cold beverage and a break.

After about an hour more work I had the engine back together and on the bike ready for a test run.

I happened to not have had the clutch lever locked into the neutral position while pushing it out of the garage and to my suprise it fired and almost got away from me (about 3-4 cylinder cycles is all it popped before firing). The difference between the initial start and this one was amazing and if it starts this easy new I cant wait to see when it gets broken in.

If anyone has any doubts that cleaning the ports up and doing some minor tuning on you bike will not make it perform better then they are foolish. Also being able to recognize a problem like a bike running lean and understanding the steps to find and repair an air leak helps alot. I guess the moral is not to take anything for granted even on a new out of the box engine.

Thanks again BarelyAwake for the tutorial and other info it is good for new builders and experienced people alike to find out some of the pitfalls others have experienced.

"BANG!.SHUFFLE CLANGGG!...ahem....excuse me M R .S U M P T E R !...that was just me fallin off my bar stool at my terminal in the shop as i freeze my a$$ off in "non sunny Florida" this late afternoon.....YOUR ACTUALLY A BONA-FIDE GEARHEAD!....UUUUHHHH YOU SCWUWIE WABBIT YOU!.....here i was thinkin you were just a keyboard crackin such an such.....and you turn out to be a "friggin gearhead"........"momma can i have another servin of that crow please?..."ya'all shaw can mr chuckie".............i tip a long-neck to ya........truce?....comon now Bubbles.....(pink bike)...lol....

 

[MarkSumpter]

"BANG!.SHUFFLE CLANGGG!...ahem....excuse me M R .S U M P T E R !...that was just me fallin off my bar stool at my terminal in the shop as i freeze my a$$ off in "non sunny Florida" this late afternoon.....YOUR ACTUALLY A BONA-FIDE GEARHEAD!....UUUUHHHH YOU SCWUWIE WABBIT YOU!.....here i was thinkin you were just a keyboard crackin such an such.....and you turn out to be a "friggin gearhead"........"momma can i have another servin of that crow please?..."ya'all shaw can mr chuckie".............i tip a long-neck to ya........truce?....comon now Bubbles.....(pink bike)...lol....

I will take that as a compliment Charlie. Yea I have twisted one or two wrenches over the last 30+ years as a mechanic and I also have an IAM Journeyman Machinist card, Government Certified Aeorspace Composite Bonding and Fabricator card and an ASE master machinist patch to boot (edit) with a wall full of school certs. including Briggs and Stratton Master Mechanics program.

Truce works for me.

 

[BarelyAWake]

Good ta hear it worked out so well for ya Mark, no worries - I didn't think ya sounded "contentious" BTW, there's was just some inevitable ambiguity in my ramblings is all and your questions & observations no doubt helped others that may have been unclear on the specifics

 

[mr.charlie]

I will take that as a compliment Charlie. Yea I have twisted one or two wrenches over the last 30+ years as a mechanic and I also have an IAM Journeyman Machinist card, Government Certified Aeorspace Composite Bonding and Fabricator card and an ASE master machinist patch to boot (edit) with a wall full of school certs. including Briggs and Stratton Master Mechanics program.

Truce works for me.

oh it was nothing but..serious....believe me i can truely appreciate and admire that list ^.....you take "BUBBLE"S" out for a spin today??????