performance custom built engines.

I have modified half a dozen of these chinese motors for my son and his friends. I tried several mods to find combinations that worked well. We have no dyno or other fancy tools or software. These are cheap chinese motors, but they do respond to specific mods. The motors that ran the best were as follows:
We modified the ports, head, intake, and the exhaust. The intakes are composed of V8 Breather filters from Checker Auto, Walbro 19mm carbs, and an adapter block made from phenolic. This adapter blends the 19mm diameter carb to the oval shape of the port and limits heat to the carb by being phenolic (previous versions were aluminum). The heads are slant heads. These heads have higher compression than the others to start with, so less machining is required and this retains their structural integrity. The heads are centered on the cylinders by putting machined alignment rods through the head/cylinders mounting holes. Two holes on either side of the bore are then drilled through the head into and through two of the cylinder fins. Roll pins are then pressed into the cylinders. The heads are re-drilled to clear the roll pins. This provides adequate alignment to keep the heads nearly concentric with the cylinders. The compression ratio is checked by sealing the piston/cylinder with grease, locking the piston at TDC, bolting on the head, and filling the head with oil to the bottom of the plug threads with a graduated 20cc syringe. The compression ratios (UCCR or CCR) can then be calculated. We machined our heads on the lathe (4-jaw chuck) for about 7cc combustion volume, or 10.4/1 UCCR, but raising it higher seems to be a good thing. The cylinders are ported. The exhausts are raised to 160 degrees duration (Open 100 degrees ATDC), and widened to a 1-1/4" oval. The transfers are only cleaned up NOT raised. Normally they are at about 114 degrees duration stock (open at about 123 degrees ATDC). This is about 23 degrees blow-down (123-100=23), which seems to make them "happy". The intake piston ports are lowered to provide about 130 degrees duration (Closes 65 degrees ATDC) and widened to 1-1/8", being careful not to get near the ring-end travel line. The port passages are opened up by cutting about 3/4" of the bottom of the cylinders and sharpening the bottom edges. This leaves about 3/4" of port passage wall left. The bottom passage side edge of the transfers are radiused by beveling the 90 degree corners slightly. This combination improved bottom/mid range torque while increasing top end over 7500 RPM. By the way, the RPM can be calculated by using the MPH and the motor/bike gearing and tire diameter. All edges of the ports were carefully filed to remove burrs and prevent ring hanging. The exhaust outlet was re-shaped to blend with the new port shape and polished. The same was done to the intake piston port without polishing. The exhaust header has an oval shape to match the exhaust port and is a 2" length of pipe to blend from this oval to a 1" round. The exhaust tubing is 1", and is connected to the rest of the exhaust by using 1" high-temp hose and clamps. The muffler is from a Banshee, cut almost in half and re-welded together (Banshee owners usually replace the original pipes/mufflers anyway). The ignition timing is verified by gluing a small degree wheel onto the flywheel, making a pointer from a small piece of safety wire under the nearby screw, and using a timing light. The timing is initially 20 degrees and reaches a max of 30 degrees at high RPM. The fuel we run is premium mixed with Klotz BeNol at 7oz per gallon which prevents bearing and piston damage. The compression ratio can be raised quite high on these 2-stroke motors unless you have a tuned pipe. The tuned pipe is a "sonic supercharger" capable of providing up to 5 to 7 lbs boost. As a result, the compression ratio will need to be low and the ignition timing will need retarding in the "boost region" (on-the-pipe) RPM. We have not balanced out motors as of yet, but plan to in the future. Here is a balancing we are proposing;

BALANCING YOUR BIKE MOTOR
by: DIYMark MBc Member (MotoredBikes.com: Motorized Bicycle Forum - Powered by vBulletin
edited by: JW

1) First decide on your balance percentage. The recommended is 55%.
2) Now you will need to weigh the total piston assembly - piston, rings, gudgeon pin, and record it.
3) Now weight each end of the rod with the corresponding bearing inserted into its race. Weight each end with the rod in a horizontal position. 2 accurate scales are ideal, but using one will work too and record it.
4) Add the piston assembly weight to the little end weight and times his amount by the balance percentage (keep in mined 55% equals 0.55) then add the big end weight to this number and you have balance mass.
BalanceMass = [( PistonAssym + RodLittleEnd) X 0.55 ] + RodBigEnd
5) Now make up a BalanceMass that weighs exactly as calculated above. You can make it from anything
such as nuts/bolts taped together or be fancy and machine a collar.
6) Inspect and re-machine the crankshaft counterbalances, if required, to obtain concentric components.
7) Fix the BalanceMass to the crank pin, press together, true, and mount your crank on 2 knife edge bearings that are level to the ground and parallel (2 steel rods will work).
8) You have to remove enough metal from the crank throws symmetrically (left/right) so that with the balance mass attached to the crank pin, you can turn the crank along the knife edges and no-matter what position you leave it at, it won't roll over to the heavier side. If the BalanceMass itself is too heavy, it will require removing an amount of metal from the BalanceMass and then removing amount/0.55 from the piston assembly. This requires careful thought. Although not necessary, if you want to be precise, use the density of steel/aluminum to calculate possible diameter holes and their depth to equal the desired weight to be drilled.
9) Once you are satisfied with the balance, dissemble the crank, clean and oil all components, press together, and true the crankshaft.

Although you cannot balance a single cylinder, this might get you a little closer so it doesn't give yer mits "lawnmower" effect at 8500 RPM. I'll give it a shot soon.

Oh, yea, please make corrections or give feedback so others can use this or other balancing techniques to balance their motors. It might be a good idea to keep it at the "shade tree mechanic" level (because I'm one), to make it possible. If you can get a good balance, share the tech info with us as to where to drill holes, what epoxy you filled the holes with and so-on.


Tools we have used include a lathe, dial indicator with holding fixture, mini 90 degree 1/8" rotary pneumatic grinder, 1/4" grinder, 10" degree wheel, numerous files, graduated syringe, timing light, 6" steel rule, and magic marker.

Misterww225

Why the same exact post in two different threads?
I can understand 1 on each forum but you got 2 on this forum in 2 diff spots that are exactlly the same.

Maybe you could post a link to the TRANSFER PORT MODIFICATION thread instead of posting the whole read over again.

Don't be discouraged it sounds like you have done some interesting work.
Why not jump in and help out the team.

BTW
I still haven't seen any pics of your mods.

misterww225

The exhausts are raised to 160 degrees duration (Open 100 degrees ATDC), and widened to a 1-1/4" oval. The transfers are only cleaned up NOT raised. Normally they are at about 114 degrees stock.

Click to expand...

Sounds reasonable... What is the degrees ATDC that the transfer opens?
If it is the 114 you are refering to that would be a 14 degree blow down period.

The intake piston ports are lowered to provide about 130 degrees duration (Opens 115 degrees BTDC) and widened to 1-1/8", being careful not to get near the ring-end travel line. The port

Click to expand...

The duration sounds reasonable and being a 1 1/8" wide port it has to be the intake your talking about.

But i can assure you that port dose not open at 115 BTDC.
the transfer ports are close to that.
In fact you stated 114 BTDC " That would mean the bottom of your intake port is even with the top of the transfers??????

The intake port is opened by the bottom of the piston skirt at the bottom of the port on the upstroke around 60 degrees BTDC.


Please don't take offense i'm just trying to understand the mods you have done.
It is possible that the method of interpreting the port timing we use are different.

0 degrees = TDC
180 degrees = BDC
ATDC = 180 TO 360 DEGREE AREA ON WHEEL "downstroke"
BTDC = 0 TO 180 DEGREE AREA ON WHEEL "upstroke"

WHEEL ROTATION = CLOCKWISE

To be technically correct through 0 to 180 degrees we can read the wheel directly. BTDC

And through 180 to 360 one should take the wheel reading and subtract it from 360.
IE: if your wheel reads 260 degrees ( 360-260=100 ) that would be 100 deg ATDC.

Anyway thats what were here for.
To help each other out.

Look I am new here. I don't mean to offend anyone. I have "edited" the other post down to a small comment in an attempt to appease you, likewise, I have added a few pics. I feel I am "helping the team" by sharing my experiences. That I had become overexcited and posted the same information twice in an effort to insure as many as possible viewed this information, I apologise for- my bad.

Nice pics.
Looks good.
The head in the picture isn't a slant though.
And let me know what you think about the degree thing.
Maybe i'm not reading my wheel right ?

Yes understandable i drive my wife nuts working on posts.
I spend more time with my motor than i do with her.

Looks like you got a pretty decent setup there.

Really i don't mean to give you a hard time.

Just trying to verify that my thinking is correct.

Occasionally i have a Brain Fart if you know what i mean.

I have only modified the timing of the ports to a slight degree (no pun intended), and thus the timings are clear enough to understand by using the stock timings as a reference. Your thinking is, indeed, correct. That I am sharing my info means you can make sense out of it, clarify terms, and put it in a way so others can understand it (somehow I know you know what I mean't to say).

The head in the pic isn't a slant. Only two of the motors were. I didn't get a pic of all the motors and combinations we modified- just when it occured to me I should do it. Really, I was just too lazy to go get the camera and take a couple before I finished the motor and took it to the car to deliver it.

Well about all i can figure is 180 - 115 = 65 degrees
So i guess it must be the way we intrpret the wheel.

Just started to get really deep in the timing thing myself.
Can become quite complex as simple as it seems.

And i don't want to destoy my new motor.

You were right about the timings so I edited the post above. Take a look and let me know if it's any better. I tend to be lazy and that makes it difficult to document things the way I should.

But what about the balancing procedure? Any thoughts? I would cram a Yamaha YZ80 crank/rod/piston in one of these if I thought I could make it work. Might not "rattle" at 8500 RPM like they do.

I am actually familiar with this post on motordbikes.
I'm not sure what Fabian ever concluded.
It is my opinion and that of some others that you cannot achieve true balance of a single cylinder motor.
Balancing like stated above only balances the crank at 90 degrees i believe.
Straight up and down.
And really only helps at a specific rpm.

I added a coupla things to that thread.
Look how they balance norton grinding wheels. "use google"
and there is a book on google called The theory of heat engines.
Has everything you could ever need to know if you have time for lots of math.
There is a chapter specifically on how to balance crankshafts.
But it is very math intensive.

So far i haven't experienced the excessive vibrating at high rpm.
I run my Grubee 6000 to 8000 rpm all day.

If you could machine the crank ends to the same as the HT why wouldn't it work.

And wouldn't that be very expensive?

The only major problems i see with these HT's are bearings and cylinder plating.

But it would be nice to have the availability to use racing pistons.
I'll have to compare the specs.
Stroke ect...
If the piston is for a 47mm bore and the stroke is 39.674mm or close.

Otherwise we would have to adjust the height of the jug for the stroke of the yz and then adjust the ports to the proper timing.

Anyway since were on the topic of performance engine building.......

Like i said the bearings aren't the best in the HT.
Most have a 13 roller caged needle bearing on the big end and a 9 roller caged needle bearing on the small end.

The big end bearing would be tough to change unless you want to take the crank apart and re true it later.

But the PB80-J that i got has a 23 roller crowded needle bearing in the bottom end.
The 23 roller is supposed to be much better.

My grubee has the caged type 13 roller and it is ready to croak.
I bet the rollers go all over the place when i finally dissassemble it.

As far as the top end we can fix that.

Now some pistons like my 48cc is designed for a 10mm wide bearing.
But you can file the wrist pin bosses to fit the 13mm wide bearing.
Make sure it has extra clearence in between the bosses the cage needs to rotate freely.

My PK80 had a 13mm bearing so i didn't have to mod it.

Here is some pictures of all three bearings.

The 10mm Broken Grubee bearing

The 13mm PK80 ( larger silver bearing )

The 13mm Sthil 028 chainsaw bearing ( large Copper Plated )
someone else originally found this bearing. " i followed there advice "
The sthil 028 chainsaw is rated at 13000 max RPM so it sould be plenty good in our HT.

You can see the Sthil part # on the sticker.


The two in my fingers are the PK80 bearing and the Grubee Bearing

After looking at the YZ80 bearing location, it would be harder than it seems.

Anyway, I found a straight and angled head to compare. Easy to see the volume difference in these.

Another shot of the cylinder to pulse tube for the Walbro. Other Walbro carbs had a tube for the pulse in the cover plate - this one had a hole in the flange.

Very nice
On the porting thread i have a side by side of the 48cc center fire and 80cc slant heads.
The slant and the 48 are close to the same size.

Are both of your heads 80cc?

Looks like even the center fire had a squish band.

Don't have that on my 48 cc grubee.

Misterww225

My question for you is about the shortening of the transfer port.
What is the reason for that?
Most tuning books say to leave the transfers alone unless you really know what your doing.
And it seems as pressure in the transfer is desirable.
I'm sure that reduced the pressure.

Have you noticed any bore distortion on these?
Also it increases the volume of the crankcase.

I know BMEP has alot to do with motor performance.

Not saying it's wrong just wondering the reason why?
And exactlly how it affects the performance.

Thanks
Rich

Well, my best GUESS is as follows, and mind this is a guess, nothing more.

From Yamaha testing it has been shown that the be best flow (direction and quantity) will occur when the path from the bottom of the cylinder to the actual port window is a large radius (inside/outside walls curved away from the cylinder and into the port window). This kinda makes sense because eddy currents (bad) form with sharp turns.

When the transfer ports "just open", the piston basically covers the cylinder section we removed, and forms a larger transfer port at the bottom that curves outward away from the cylinder, then into the port window (just like it's been "hogged out at the bottom").

Removing all the wall up to the port window (like with a hacksaw) seems to create an eddy current just below the transfer window and retards flow.

With a tuned pipe this may be different because the pipe creates a negative (suction wave) that forces flow even with a bad port path and compensates somewhat, but without the pipe we have to rely on crankcase pressure to create flow, which is not nearly as powerful and dependent upon piston displacement and diminishing pressure during flow.

It would seem then we need a "nozzle" (read:transfer port) with 1) low resistance to flow 2) directional flow. The "tapered nozzle" formed by the larger opening tapered to a smaller opening (port window) creates high velocity at the window opening.

Of course, I've seen all kinds of theories that confound and confuse. My REAL opinion is that it's all magic, and if we modified 100 cylinders in different ways and tested them on a dyno, we would still be left scratchin' our noodles.

Both heads off 66cc motors, yup.

Yea, the volume of crankcase is slightly increased. I notice there is some space either side of the crankshaft around the bearings that could be filled with epoxy that would likely more than make up for the volume increase. Initially, only for testing this theory, if we put some "play dough" behind the crank and pressed it into place we would see a significant space to fill with epoxy, if you think it would help with the crankcase C/R.

Misterww225

That is just plain wonderful.
It's nice to meet someone that thinks like i do.

Even though we kinda stole this thread........

We are pretty on topic.

I say we continue on this path.

Maybe this thread will become a sticky as well.
On building the high performance HT.

This is turning into an awsem thread.

YOU ARE CORRECT

From Yamaha testing it has been shown that the be best flow (direction and quantity) will occur when the path from the bottom of the cylinder to the actual port window is a large radius (inside/outside walls curved away from the cylinder and into the port window). This kinda makes sense because eddy currents (bad) form with sharp turns.

Click to expand...

especiall in the exhaust and intake ports.
In fact you want the manifold and intake to match the angle of the ports if possible.

The less resistance to flow the more power.

With a tuned pipe this may be different because the pipe creates a negative (suction wave) that forces flow even with a bad port path and compensates somewhat, but without the pipe we have to rely on crankcase pressure to create flow, which is not nearly as powerful and dependent upon piston displacement and diminishing pressure during flow.

Click to expand...

Yes there is a preszsure wave to suck out the gases but it is also a lot less restrictive to flow.
The key thing with the tuned pipe is.....
The wave that travels back to the port and slams the fresh fule mix that escaped into the exhaust back in.
This packs more in the cylinder head and increases compression as well.

I'll tell you from experience that the SBP pipe rocks.
If your porting and all that get a chamber it is worth it.

So as far as the transfers go i have an analagy.
If you make a hallway bigger you can still only get so much air through the door.

I am curious about this mod.
Might even try it.
But i did read somewhere about putting epoxy in the transfer port to increase the pressure.
Any way that could be because of an excessive area.

So i will try to find out about and verify with math the effects.

Like i said lets keep building this thread

This is awsem.

Riding Rich said:

The key thing with the tuned pipe is.....

The wave that travels back to the port and slams the fresh fule mix that escaped into the exhaust back in. This packs more in the cylinder head and increases compression as well.

I'll tell you from experience that the SBP pipe rocks.

Click to expand...

I've never heard it put so well. I love my SBP pipe too.

Now things get a little difficult.

The question is does this belong in the porting thread or here.
You see we are currently discussing the transfer port timing.

Making the transfer port shorter actually would require less time to complete the cycle.
Shorter passage length = less time required to pass through the port.

= lower timimg duration or lower volume of the transfer is required for balance.

so here's the interesting bit from Gordon Jennings.

An increase in the transfer-open duration of only 4- to 6-degrees would probably broaden the effective power band enough to make the machine very much easier to ride, reducing maximum power by perhaps two bhp and adding about three or four bhp at the lower limit of the present range. The same applies to all two-stroke engines: increases in transfer port time-area tend to depress the power peak, but add to the power curve at lower engine speeds.

Click to expand...

Now to effect the time it takes to complete the transfer without affecting the transfer duration could be a positive effect.

Shorter passage = shorter time to pass = broader power band " needed with single speed gear"
= less reduction in maximum power and positive increase in low end power.

In theory i think this would have the same effect as increasing the transfer duration.
Without changing the timing.

The only catch is the pressure in the crankcase is constant up thru the transfer passages.
Increasing the volume of the crankcase and transfer passage will reduce the pressure.

If you packed the extra bearing area with epoxy you could offset this.
But lubrication of these bearings would suffer.

Now if we used high quality 6202 hybred ceramic bearings shielded and sealed on both sides the epoxy may not be bad at all.

I have thought about usind a double shielded bearing for the main bearings.

What do you guys think?

Got the PK80 running.
Roars like a lion.

I cant wait to build the next one.