Serious About Porting

[210061741]

Yes it is time for a serious porting thread.
I have been buisy working on this PK80-J.

Came up with a way to determine where the porting is at.
Timing / Duration.

Once i get the data i need i will run it through some software to find the best tweeks.

I'll break the process down a little as i go.

#1 Create a Port map. " a rubbing of the cylinder walls"

We will use this to calculate the volume of each port and will also need to take note of any angles to the ports.

#2 Buy or make a degree wheel so we can measure port timing and duration in degrees of crankshaft rotation.

#3 Mount you engine and setup a dial indicator or piston stop to find TDC.

#4 Adjust your degree wheel to 0 degrees at TDC.

#5 Take your measurements.

So far i have ground the transfer area of the crankcases nice and smoothe.
Also skimmed the exhaust and intake ports removing only enough material to clean the ports up nice and smoothe.

The software will tell us what to cut and where later.

The top of the Intake port is slightly blocked by the bottom of the piston skirt.
Maybe by about .030 of an inch.

But the duration of degrees at that position is so short it may not effect much.

It will be a balance between milling the piston skirt and lowering the Intake Port.

Just remember if your ports are too big the rings could bulge out and get hung up in there.

So cutting in the right places and shapes is very important.

I made this degree wheel on a CNC Laser.
The etching isn't real deep but it is there.
I bolted a steel plate to my workbench and mounted the motor to it.
The indicator is attached to another steel plate.

 

[210061741]

Completed So Far

So far here's what i did to the PK80.
Ground and polished the crankcase halves.
See the before and after.
Thinned out the transfer webbing on the cylinder side.
Matched the crankcase to the jug transfers.
The smoother and more step free = less resistance to flow.

I posted a pic of the grubee crankcase halves.
Notice how the transfer isn't ground out at the factory.

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A few other things.
When you do this seal up the bearings.
Mill all the gasket surfaces only enough to clean up nice on the sandpaper and glass.
Grit in your bearings is not fun.

Very important.

before i assemble the bottom end i check everything for good fit and resurface all the mating surfaces. where i can.

For this step we need only the jug and the head and crankcase halves.
Were not putting anything in there yet.

Assemble the empty crankcase halves.

Tighten all the crankcase screws pretty good but not like final torquing.
Insert the cylinder studs into the crankcase.
Then loosen the crankcase screws a couple of turns out.
We want all 8 screws to be very loose.

The circular bored portion of the crankcase halves fit together.
One half has a little counterbore and the other half has a raised step to fit into that counterbore.
This helps locate the Mainbearings and Crankshaft but dosen't do much for the JUG.

The reason we need the screws loose. "locate The Jug"

Next i put the jug on and head on without the piston in place.
Tighten the jug down pretty good.
Now tighten up the 8 crankcase screws good and tight but remember it is coming apart again..

I know this sequence is a PITA but it pulls the Crankcase Halves into alignment with the sealing surface of the jug.

How else you gonna do it?

Now remove the jug and head and head studs.
Mill the crankcase base gasket area on sandpaper and glass.

Remember after it's done it has to come apart again to put the internals in.
But if you assemble it in the same sequence you should have the best match to the base gasket sealing area.

If that base gasket leaks too bad the motor will just stop running.

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On a side note:

I would like to encourage all the other members to get involved here and add any data or insight they may have.

Exact specifications of the HT motors aren't easy to come across.
So any of that stuff would fit good here.
It will be needed to port different motors correctly.

I also am aware there are some engine builders around here who's input would be very welcomed.

I am not perfect and do make mistakes sometimes.

As a Team we could create an outstanding thread here.
Lets just stay on topic and use real factual data....." no guestimates "

In the end we will all benifit from this work.

Especially if the HT goes extinct and we have to machine our own.

 

[210061741]

Grubee Transfers.

forgot to add the pic.
Here they are... notice the big step.

 

[210061741]

The first set of data.

Few things to note befor we get too deep here.

This data is derrived from the PK80-J slant head and alltough the numbers may be very close to another PK80-J thay will slightly vary due to varience in stroke length.

The only safe thing to do is make a degree wheel yourself and find your timing.
Especially if you have a different motor.

There is a few sites that have a printable degree wheel that you can glue to a CD and attach to the magneto magnet shaft.

The first oops i made was putting my degree wheel on the sprocket.
It is geared 4.1:1 so that's no good.

I moved the wheel to the magneto.


This may seem like alot of data and were just getting started.
We will need to know all of this for any motor we want to port.
There will be more added later but i need to lay out the port map in CAD and crunch the numbers i have so far.

But for thoose who cant wait........


PK80-J PORT TIMING AND DURATION.
--------------------------------
A nice informative page.
A two-stroke

TDC= Top Dead Center
BDC= Bottom Dead Center
BTDC= Before top dead center
ATDC= After Top Dead Center

Degree wheel mounted on the magneto magnet and rotated clockwise.
Wheel incremented 360 degrees.

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The intake port opens on the upward stroke from the bottom of the piston skirt
and the bottom of the port.
It then closes after the piston reaches TDC and travels back down, when the
bottom of the piston skirt closes the port completly.

The intake port opens at 60 degrees BTDC.

The intake port closes at 59 degrees ATDC. "= 301 degree mark on wheel"
360 degrees - 301 degrees = 59 degrees.

60 degrees + 59 degrees = 119 degree intake duration.
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The exhaust port opens on the downward stroke.
When the top of the piston opens the top of the port.
Then travels to BDC and closes at the top of the Port
on its way back to TDC.

The Exhaust port opens at 253 degrees ATDC.

The exhaust port Closes at 108 degrees BTDC.

253 degrees - 108 degrees = 145 degree Exhaust duration.
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The transfer ports
The transfer port opens on the downward stroke.
When the top of the piston opens the top of the port.
Then travels to BDC and closes at the top of the Port
on its way back to TDC.

The ports open at 236 degrees ATDC.

The ports close at 125 degrees BTDC.

236 degrees - 125 degrees = 111 degree duration.
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BLOW DOWN "The time we have to get rid of the exhaust before the transfer opens"

Exhaust port open 253 degrees ATDC
Transfer port open 236 degrees ATDC
253 degrees - 236 degrees = 17 degree blow down duration.
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OTHER IMPORTANT DATA.

Bore diameter is 47mm "measured"

Displacement = 68.8605 cc "calculated"

Distance of piston crown above the Deck @ TDC
.141 inches / 3.58mm "measured"
The edge of the piston is below the deck by (estimated .100 inches / 2.54mm)

Distance from TDC to Exhaust port open.
1.129 inches / 28.68mm "this is the length of the power stroke"

Distance from top of exhaust to top of barrel.
.988 inches / 25.10mm

Stroke Length
1.562 inches / 39.67mm "measured"

Con Rod Center to Center
2 x Stroke = 3.124 inches / 79.34mm "calculated"

Center of Crankshaft to center of con rod big end.
stroke / 2 = .781 inches / 19.835mm "calculated"

 

[210061741]

Here are the approximate port areas.
Now we have enough data to start doin something.

Port areas.

Port areas.

Exhaust = .4413 sq.in. / 2.8471 sq. cm. / 284.7091 sq mm

Intake = .3463 sq. in. / 2.2342 sq. cm. / 223.4189 sq. mm.

Transfers = .2779 sq. in. / 1.7929 sq. cm. / 179.2899 sq. mm (EACH)

 

[210061741]

you guys want more or what?
Been too darn quiet around here.

 

[michelevit]

i'm still listening

very interested with your porting project.

 

[give me vtec]

ohhh yes... quite intrigued.

Please keep going... I want to see how the story ends.

 

[roddy4477]

Yes i am extremely interested in what you are doing. Good hard data that we all can use. thanks a lot.

 

[210061741]

Sorry i havent posted too much here.

Got quite a bit done here.

http://motorbicycling.com/f13/porting-time-get-serious-13396.html

More folks got involved and it gets time consuming creating all these posts.
I'll have to transfer the info here as well.

That was my original plan.