If you are interested in 2 stroke engines and bikes please follow this blog or check back regularly as I will continue to post information and projects as time goes on.

Sunday, March 11, 2018

Epoxy vs Ethanol Test

Been a while since posting anything or tackling projects. Between full time work and school followed by the cold winter weather its been slow here.

I did a test on a well known 2 part epoxy putty that was recommend on numerous sites for port modifications, especially among 4 stroke car guys.

The epoxy product is called A-788 Splash Zone Epoxy. It seems to mainly be aimed at the marine industry for boat hull repair.

Once equal parts are mixed the it becomes a very dark green, maybe similar to the "stuco verde" mentioned by Jan Thiel? It is very thick and can be somewhat hard to spread evenly but one trick that is shown in youtube videos of the product is using a bit of water to smooth it out and make it more pliable which helped a lot! I used some silicone tipped clay tools for this and it worked well.

Here are some photos of an old piston I used to later test holding strength. One area of the crown was prepped by light 120 grit sanding. The rest was simply cleaned with a bit of brake parts cleaner.






































You can see the one area on the piston skirt I smoothed with a bit of water.

The holding power of the epoxy was pretty amazing. The large globs on top I tried knocking off with a hammer and the actually epoxy broke and crumbled but never came unbonded from the metal. Same for the bit on the skirt, I purposely covered the piston window so I could pry on it from behind and it still never detached. So for holding power this stuff gets a 10 out of 10 for sure.

Next up came the important bit, the fuel test. I used regular gasoline with no alcohol/ethanol, gas with 15% ethanol and then some gas I had mixed up for riding which was 15% ethanol and some C16 leaded race gas with Klotz oil.



The pieces were fully submerged for 24hrs. As suspected the bits in the ethanol fuel showed softening on the outside, about .25mm-.5mm deep. This outer skin could be scrapped off with my nail with a bit of force. Not something I would feel comfortable running in an engine to be honest.

However, the non-alcohol/ethanol gas had no noticeable effect on the epoxy. It seemed exactly like the pieces that were never placed in fuel at all. So if non-ethanol fuel is used I think this epoxy would work great for any kind of porting projects.

Also, if you look there is a small bit of white urethane casting resin on the left. I also tested this as I was casting some small parts for a carburetor. I only tested it in the non-ethanol fuel and it also showed zero signs of being effected. So if you ever need a thin easily cast-able resin for making parts that will be in contact with fuel this product should work well.


I will update this topic later in the year as racing season starts and I run both products on some engines. 

Friday, February 3, 2017

An amazing and little known story


















I wanted to make a post about a book I recently was able to buy online. It has been out of print and not sure how many copies were ever made but some pop up time from time.

The book is about a New Zealander engineer and motorcycle racer named Kim Newcombe. I only know the main points of his story and am looking forward to reading this book and gaining more specific details on his life.

He grew up with a passion for motorcycle racing and was a gifted engineer. He came across a powerful and lightweight 2 stroke 500cc 4 cylinder engine made in Germany by a company named Konig. The engine was made for boat racing, mainly hydroplane racers. He got the idea of putting it in a bike and racing it. He reached out to Dieter Konig, the company owner and eventually moved with his family to Germany to build the bike and pursue racing it in the world championship.

He amazingly finished the 1973 500cc Grand Prix season in 2nd place. A truly titanic feat considering all the challenges he faced. He raced against the giants of the day like Agostini, Read, Findlay, Saarinen and their factory backed machines and much larger better funded outfits.

The Konig 500 motorcycle is a beautiful piece of machinery and in a way connects with "bucket" racing today. It was no finely polished factory engineered creation but a cleaver and utilitarian use of what was available to Kim and he executed his vision and it worked. I would love to know what the big factories thought when a boat powered motorcycle with minuscule development time behind it started beating them.
















Kim tragically died in August of 1973 at Silverstone during a non-championship event. One can only imagine what he could have done had he been able to continue developing the bike.

I have no doubt it will be a great read. If you're looking for a book about motorcycle racing from the past and like the story of an under dog this might be your ticket.

https://www.bookdepository.com/Kim-Tim-Hanna/9780473177461

Sunday, January 29, 2017

Comparing some 50-70cc port molds

I now have 3 transfer port molds made from 3 different cylinders. A Honda NSR50, Kawasaki KX60 and a Metrakit Pro Race cylinder for a Derbi.

It was very interesting to see the major differences in the transfer designs. I was looking at these with the optimal transfer design being based on the RSA 125 cylinder and the comments made by Frits and Jan in their posts on the Pit-Lane and KiwiBiker boards along with Frits article on transfers I posted.














The first difference to note is the size of the A&B transfer port inlet against the size of the port window where the charge exits into the cylinder. The Honda and Kawasaki use the old widely held idea of forcing the charge through a narrowing duct to increase velocity. The port size is cut in half from entry to exit. The Metrakit however shrinks by about 15-20%, focusing on the principle of "mass transportation" rather than velocity.














Next up is the inner radius of the transfer ducts. The Kawasaki had the ideal design with the largest radius you could fit. This optimizes flow and I have also read that it helps oil transfer to the piston as it can attach itself to the wall and gradually flow up to the port exit and the piston skirt increasing lubrication and reliability. The MK and Honda both have less than ideal shapes, especially the MK. I believe these 2 cylinders are limited by having full length cylinder studs the run through the cylinder that obstruct the port shape from being optimal.














The Metrakit cylinder and its "A" transfer port was the only one to have any upward angle. This is done to effect the central column of fresh charge by impacting it higher to keep it from flowing out the exhaust port. This is all explained in Frits' article on the leaning tower of Pisa and transfer theory that is posted here. I did finally get a large bubble at the bottom of the Kawasaki port. It might not look like it but it has no upward angle.














Lastly is the way in which the inlet charge is orientated when it leaves the duct. The MK most closely mimics the RSA cylinder here as well.

Very interesting to see the differences in designs from one manufacturer to the next. As 2 stroke R&D peaked and then went the way of the dinosaur some companies adopted certain RSA traits while others never did.

Here are some photos and specs of the RSA cylinder to compare with.




Sunday, January 15, 2017

HRC piston and ring prep info

This is some information on piston and ring preparation for the Honda RS125/RS250. These steps can be used on any high RPM 2 stroke used for racing. Small detailed tedious things like this can be the difference between failure and reliable use. HRC knows a thing or two about building GP 2 stroke engines. This is mainly used to prevent rings sticking, catching in ext port, and ring stopper pin damage. 

Cylinder
With increased power, the 2001 model year RS125R and RS250R have cylinder bore shape and timing similar to the manufacturer's kit engine.
Accordingly, cylinder maintenance has become more important than before.
Basically, it is recommended that the items described in the manual be followed. In particular, mentioned below is the description on the necessity for chamfering.
Picture
The chamfer on the upper surface of the exhaust port may be glittering when obliquely viewed from the skirt side of the cylinder taken from engines which have travelled to some degree.

The figure above shows a magnified view of the cross section of the port chamfer. The piston ring slightly protrudes into the exhaust port when the piston goes up and down.
This chamfer again rests in the bore surface. If there is, however, an angular (even obtuse-angle) section at the cylinder chamfer interface section, the piston ring movement gradually becomes bad, resulting in strengthened contact by the ring on chamfers.
For this reason, chamfer should be made. When chamfering is made for upper and lower ports, wet abrasive papers will be applied to the interface of the bore surface and the port chamfer at small angles (10 to 15 degrees) to make the interface round.
Chamfer maintenance would avoid stuck rings or peeled plate at the cylinder port.
Piston
•Piston contact
Piston contact should not usually be removed. Severe contact with the cylinder is attributed to some other reasons. Pistons have special profile (out of round), which is designed to produce heat emission, providing proper contact when pistons and cylinders are subject to deformation.
Accordingly, careless piston modifications in profile will degrade the ideal profile, resulting in more contact with other portions.
Ring sticking
With the increase of service engine speeds year after year, even if keystone rings are used, sticking may result.
If rings and pistons are new, ring groove modifications are not required against sticking. However, if stuck rings are found at the time of maintenance, the modifications must be done. Stuck rings may cause engine troubles as well as a significant power drop.
Stuck rings can be identified by signs of a failure exhibited at the engine start, such as unwillingness to start engines or abnormal engine noise emitted from the silencer. 
Piston rings
The abutment of piston rings should be chamfered at the gap using a round file. This is intended to prevent stopper pins from being cut by rotational force generated when pistons are moving up and down.
Picture 

All this info and more can be found at
http://www.sp125racing.com/rs125r--rs250r-notes-on-engine-maintenance.html

Tuesday, January 10, 2017

Want to build a custom expansion chamber? Here's the best place to start.

This is the FOS exhaust formula/design. Developed by Frits Overmars. This man has probably forgotten more about 2 stroke exhaust systems then most people can hope to learn. He shared his calculations and design online that he recommends as a starting point. There is no magic way to get the perfect design the first time but these numbers will get you well within the ballpark and probably outperform most stock and older aftermarket designs.



Underdogs racing has developed an easy online calculator that will spit out the design for you.

http://www.underdogsracing.com/fospipe/

Ezin Hobeki also has a program you can download as a demo that can create a FOS design chamber.

http://ypvsbox.free.fr/?cat=10&lang=en_us

Remember to include the "restrictor" at the end of the rear cone. Below is a drawing for the design to use. These can be made interchangeable and used to manipulate the powerband for specific tracks. It also has the added benefit of making the tailpipe length irrelevant which can make fitment and fabrication much easier on yourself.

If you then need turn the measurements into actual cones there are several online cone layout programs that can create templates for manual metal cutting or fit up with card stock, or export files for laser/water jets to cut. They can also help with turning right circular cones into oblique circular cones to help with clearance and fitment on certain bikes.

Cone Layout 2.0 is a good option for doing this.

https://www.conelayout.com/

Sunday, January 8, 2017

2 of the best internet threads for 2 stroke information.

Posted below are 2 threads on the internet for arguably the best information on 2 stroke engine design and modification. Numerous people contribute and ask questions with most of them directed at Frits Overmars, Jan Thiel and "Wobbly". All three of which are probably the most experienced 2 stroke tuners around. They have had their hands on championship winning engines for 30+ years and you cant get better information anywhere.

Pit-lane.biz has over 4 threads about the Aprilia RSA 125 GP bike that Frits and Jan were involved with. The most successful 125 GP bike and CC for CC the most powerful 2 stroke around. Tons of specs, drawings and info are shared in these threads, along with numerous common misconceptions about making more power with 2 stroke engines.

This is just the 1st thread, 4 more are on the board in the 125GP section. The thread starts in French but quickly changes to posts in English so dont be discouraged when you start reading.

http://www.pit-lane.biz/t117-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked

The other thread is on a New Zealand motorcycle racing forum. It began as a thread about "Bucket racing" and 2 stroke engine building. Overtime the 3 people mentioned about started to regularly contribute and there are 20,000+ pages of info to read through. Just like the thread above, you cant get better info from more experienced people on how to make your 2 stroke bike go faster!

https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner

Transfer Theory by Frits Overmars aka The leaning tower of Pisa

Here is a great piece written by one of the best 2 stroke tuners, Frits Overmars. He and Jans Thiel both worked at Aprilia(along with many others) and helped develop what is arguably the best pound for pound 2 stroke racing engine in the 2 stroke GP era, the RSA 125. Their knowledge is backed up by thousands of dyno tests, hundreds of GP trophies and several world championships. It doesn't get any better than that.

The leaning tower of Pisa


Transfer theory part 1

the central column
We want ample angle.area for our transfer ports while at the same time keeping their height within limits, so we need all the transfer area we can get; we want to use as much as possible of the cylinder circumference.
The best way to utilize the available real estate would be to aim all transfers radially inward; that way the cross section widths of all ports would be equal to their chord widths and you can't get any better than that. All transfer streams would meet in the center of the cylinder, slow each other down and form a central column with only one direction to go: upwards, in the direction of the cylinder head.
But since you can't have a transfer port at the exhaust side of the cylinder, an imbalance would occur and that central column would be inclined (sic) to topple over towards the exhaust side of the cylinder. You don't want that because too much of the fresh charge would take the escape route into the exhaust duct without first scavenging the cylinder.

How do you prevent that central column from leaning towards the exhaust side? If you omit the transfer ports directly opposite the exhaust, you would restore the scavenging balance, but you would sacrifice too much valuable port area. There is a solution, but let me address some other scavenging aspects first.

We want as much transfer port area as possible, so it would make sense to have all transfer ducts enter the cylinder perpendicularly, right? Nope.
To begin with, most pistons are domed, so transfer flow entering the cylinder would collide with the dome. Aiming the transfer ducts axially at about the same angle as the piston dome, usually about 10°, will not cost any effective cross section area and it will noticeably improve the flow coefficient. Larger-than-zero axial angles at the port floors will also enable you to fit larger inner radii in the transfer ducts, another benefit for the flow.

Second: those transfer streams entering the cylinder and colliding in the center will convert kinetic energy into potential energy. In English: their flow velocities will slow each other down in the collision process and the static pressure in the middle of the resulting central column will be higher than the pressure in the transfer ducts.
That static pressure in the central column is a good thing: it will provide for a higher density of the fresh charge in the column and that helps to expel the hot, thin burnt gases from the previous combustion cycle. Think of it as using a jet of water to chase away smoke: that will work a lot better than the other way around (using smoke to chase away the water).

But the static pressure at the foot of the central column can also have adverse effects. Too high a static pressure will impair the flow, because the higher this pressure is, the smaller will be the pressure differential that accelerates the charge through the transfer ducts. Aiming the transfer ducts axially a little will improve the flow, just like it did because of the domed piston. Slightly axially-aimed transfer streams will provide for a less violent, not completely head-on collision. The central pressure can be controlled this way, and the transfer streams will keep the axial component of their velocity, so the central column does not need to begin its journey to the cylinder head with zero velocity. So the axial column speed can be controlled as well by the axial transfer angles.



Transfer theory part 2

positional & directional scavenging angles
Most two-stroke people define radial scavenging directions by quoting the distances where the ports would intersect the center line (the leading distance and trailing distance in the drawing below left). Gordon Blair used that notation in his publications, and 95% of us followed suit.
But there is a better, more universally applicable way.
I will explain with an example, not of scavenging directions but of port timing: I might say that a transfer port height of 13 mm is perfect for a racing engine. That may be true for a 125 cc engine but it would be nonsense for a 50 cc or a 500 cc.
But if I say that a transfer port timing of 130° is perfect for a racing engine, then that is valid for any engine, regardless of its cubic capacity. Absolute distance values (millimeters, inches etc.) are not suitable for universal guidelines. Degrees are, as are percentages of bore or stroke. Rpm values are not; mean piston velocities are.

I express transfer duct directions in degrees. Each duct has a leading flank and a trailing flank. Each flank intersects the bore at a point which I can define with a positional angle. And each flank hits the fore-aft center line of the bore with an included angle which I call the directional angle. The drawing below left may clarify what I mean. And the drawing on the right is an example of an existing cylinder.
Now we can express the radial characteristics of the transfer ports with positional and directional angles, regardless of bore and stroke.
And we can express the ports' axial characteristics with axial angles, but that only gives a 'universal value' for engines with identical bore/stroke-ratios.
We may quote a height H in the cylinder where the transfer port's roof would hit the opposite cylinder wall. But we need to express H as a percentage of the stroke. Then we will have a truly universal value.
Then we will also see that short-stroke engines require smaller axial angles.





Transfer theory part 3
the tower of Pisa
As we are on the subject of scavenging angles, now would be a good time to say something about the axial angles of the A-transfers.
Surely a duct with an axial angle of over 20° offers a smaller cross-section to the flow than a duct that enters the cylinder perpendicularly?
Yes it does. But there are two good reasons to angle it upward anyway.

First, perpendicular mixture streams coming from the A-ports would collide and slow one another right down. The axial angles provide for less velocity losses and less pressure losses, so despite their smaller cross-section, upward ports may flow as much, if not more, than perpendicular ports.
(Now you may well ask why the B-ports do not get the same treatment. It is because the central scavenging column, resulting from all incoming scavenging streams together, must not have too much axial velocity, or the loop scavenging will result in a loop-loss into the exhaust).

Second, there is a thing called scavenging balance (I invented the word for my personal use, so this may well be the first time you ever saw it).
If you looked closely at the scavenging picture of the MB-cylinder I posted above, you may have noticed that the 'radial scavenging directional resultant' had a value of 101,045°.
90° would have meant 'straight up'; more than 90° indicates that the central scavenging column is leaning towards the exhaust side of the cylinder.
But we don't want that; it is bad for the scavenging of the rear part of the cylinder, and it is risky because it may provoke scavenging losses straight into the exhaust.


But how can we prevent a scavenging column from toppling over to the exhaust side like the leaning tower of Pisa? Not by pushing against its basis, but by pushing higher up. Hence the axial angle of the A-ports. The pictures will tell the story. (If only the Pisa architect had known a bit more about two-stroke scavenging....)




Transfer theory part 4
vectors
Let us assume that all transfer ports are of the same height. Let's also assume that a port with twice the cross-sectional width will give twice as strong an impulse (that is already doubtful; it presumes equal densities and equal flow velocities in all ducts, and as duct contents can have different inertias, their accelerations may differ, as will their flow velocities at any given moment).

If you accept these assumptions, you can resolve each transfer stream into an axial component, a fore-aft component over the piston, and a left-to-right component over the piston. The axial components all work in the same direction: towards the cylinder head. The left-to-right components will cancel each other out (if they don't the scavenging is asymmetric) while contributing to the pressure creation at the root of the central column (which in turn will accelerate the axial flow and thus enhance the axial vector), and the fore-aft components will result in a vector that may either point towards the rear side of the cylinder, be zero, or point towards the exhaust side.
This fore-aft vector together with the axial vector will give a resultant that will lean towards the rear of the cylinder, or point straight up towards the head, or lean towards the exhaust side.

What we want to achieve, is an axial column that clings to the rear of the cylinder, so it can wash away the spent gases with as little turbulence as possible. Turbulence will result in mixing of fresh charge and burnt gases, and we don't need that. And mixing will heat up the fresh charge, bringing it nearer to the detonation treshold. And we certainly don't need that!

I realize this is a crude way of describing a complicated flow dynamics event, but hopefully it will help you form a mental picture (no pun intended).


Saturday, January 7, 2017

Port Molds with Composimold

Just had my first go at making a transfer port mold on a stock NSR50 cylinder. The product I used is called Composimold. It is a reusable material that can be melted in the microwave and then poured for molding.
I wanted to do this to get an idea of how the stock ports were aimed and also take measurements that would otherwise be a pain to get with tiny measuring tools.

I used petroleum jelly and a small brush to put a light coating on the walls of the ports.
Next I made a small wall out of cardstock so I could stand the molding up and have the 2 connected. I should have put some jelly on the paper but forgot and it did tear some off when I removed it so don't forget to do that. I also used masking tape to tape off the port windows in the cylinder.

Next I took a small chuck and put it in the microwave for 40 seconds. It was melted and bubbling when done, I stirred it up, let it settle for about 60 seconds and then poured.
I then tossed it in the freezer for 10-15 minutes and once it was set I easily pulled the mold out.
          
All in all it turned out nice. No bubble issues like some people have mentioned. The detail is pretty good since I can clearly see the petroleum jelly brush marks on the flat turned surface on the cylinder base. Also, it was removed very easily and holds is shape well. Seems to be a good product for this job and is not too pricey!

Cheers,

Links:
This is where I bought the material. It is available all over the web if you Google it.
http://www.ebay.com/itm/ComposiMold-Reusable-Molding-Material-20-Ounces-Food-Molds-783583657570-/152348946146?hash=item2378b46ee2:g:62AAAOSw5cNYSaB1

NSR50 project. The never ending learning experiment

NSR50 Mini GP Bike-
This at the moment is my main project, among about 4-5 other 2 stroke bikes. Raced in a few races last year. Could never dial in the engine setup perfectly. Tried changing too many things at once and was always rushed by the next race while in school and working. No one to blame but myself on that note :)

Here is the bike shortly after I bought it. Fairings are off, removed the previous owners decals, painted the tail, etc.
The modifications by the previous owner: Jemco pipe, pretty lean jetting, Racetech front fork setup and some crash protection.

My current incarnation is running a KTM 50 single ring Vertex piston, custom machined head, Polini PWK 24mm carb and HPI inner rotor programmable ignition. I was never able to dial in the jetting and ignition settings perfectly. Would love to spend some time on a dyno figuring that issue out but that is a project for later this year.

Here are some pictures of the bike during my first race. It was a last minute effort, didn't have time to sort out the fairings or jetting and didn't have time to order number decals. A real hodgepodge affair that day but it was fun none the less.


Here is another photo of the bike a few rounds later with some actual fairings and hardware store address numbers on it.


Racing this bike on the local kart tracks is a blast. Much cheaper to maintain than a big track bike and most importantly, when you go down the repair costs and risk of injury is exponentially lower.