Author Topic: pilot piston/ bore clearance. (Read 9499 times)

Adnoh · « **Reply #15 on:** July 20, 2008, 07:52:52 PM »

One think to check is camp and barrel measurments. See attached chart of new honda stock piston. One think for sure is no matter what, it will swell and fill the cylinder. Weisco is diff from stock honda and requires a larger base clearence because of these measurment and the material there made of. special consideration should given to ring gap maintaining sealing levles. If the piston too tight the ring wear will be excessive. too loose and siezure can accure due to loose in sealing gases and ring flutter. the barrel and camp measurment can teel you how close or loose to run it as long as ring gap is with in spec. This is why weisco has a different camp measurment allowing for a loooseer base line clearence. A few other issuse need to be factored in as well. Fuel and Compression ratio's(Not cranking pressure)

Adnoh · « **Reply #16 on:** July 20, 2008, 07:58:58 PM »

sorry had to post as j- peg instead of bmp

PilotHawK · « **Reply #17 on:** July 20, 2008, 10:26:38 PM »

Great stuff Adnoh. What kind of cranking compression will this yield? Also what octane fuel will you have to run?

Teach us!

Adnoh · « **Reply #18 on:** July 23, 2008, 07:09:57 PM »

I'll post some head work for ya to llok at that goes with the #'s as well as a more readable j- peg. I cut two head with different cc's and both as pre set to 180lb's.

Adnoh · « **Reply #19 on:** July 23, 2008, 07:15:57 PM »

Adnoh · « **Reply #20 on:** July 23, 2008, 07:21:18 PM »

Adnoh · « **Reply #21 on:** July 23, 2008, 07:26:14 PM »

Adnoh · « **Reply #22 on:** July 23, 2008, 07:35:42 PM »

#2 head

Adnoh · « **Reply #23 on:** July 23, 2008, 07:43:25 PM »

more #2 and stud tool

Adnoh · « **Reply #24 on:** July 23, 2008, 08:54:46 PM »

I don't really now about teaching. Just a hacker here that will share what he has learned over the years. I will share some meaning behind the madness. As you see from the pictures the cranking #'s are close to the same for both heads. The third head used ( not shown, is the DCP head) is currently being used on my motor. I milled and cut so all three are close for Mrs. Adnoh's motor.

The Goal is to have the best CR ( compression ratio) to run pump gas with the ported motor and achieve the highest cranking pressure. The poting data on Her motor should be be listed on here motor post. The three heads show that just milling a head is not the only thing to consider.

What does this have to do with camp and barrell.

Compression levles change the burn rate ( flame front) on pump gas at a given cranking pressure. The burn rate has an effect on piston swell. The Squish clearences and area has an effect on thermal expansion of the crown in time with exhaust port.

Lets say the base line clearence on the honda has a greater camp than the wiesco a tighter barrell can be used as long as the ring cap is maintained. Now let look at a wiesco. the camp is less and the barrell clearence most be increased as long as the maxium ring cap is used. This is why ring changes is greater than honda. Remember the expansion rate from water cooled jug to air cool is less. So using max barrell bore will alow the piston to swell as the motor comes up to temp and swell up against the jug than the camp will start to swell because the barrell is now agaist the cylinder wall traping a thin layer of mix to lube wall. The camp will control siezures as long as sealing pressure is maintained. Note: ring material and thickness. The honda piston is made of a better material containng more silacone. To achieve a higher rate of sinacon in the material, the rate to which the material is cooled upon forging has a effect on the amount retained in the piston. higher silacon rate the better expansinon rates. This will alow a tighter barrell and effective sealing of the ring.

Back up a little. Calculating CR is important so you know what fuel to run and the effect on swell. I like to use V method knowing when your exhaust port close in degrees is the most import part to calculate corectly. An example of this would be lets say the you ccs is 200. and the exhaust port closes at 90 deg BDC ( back dead center) yu cc use in calculating would be 100 cc ( 1/2 th cc in degrees). Know your CR is 7:1 with a cranking compression of 180 lb. We all know this most likly would require fuel not pump gas.

How can we change this to run pump gas. Raise exhaut port, this would change CR by reducing cc in V calculating method. Increase squish clearenc and area. This changes cc on head used in V method of CR. Both will have an effect on thermal expansion of barrell and camp. Plus side to raising exhaust port if pipe is used higher RPM power curve. Increase in cranking pressure increasing power output. Lowering Cr stablizing thermal expansion on the piston increassing reliablity.

How. Cr has benn brought back to pump gas burn rae levles. The area of squish trapes more fuel in squish cooling edge of piston controling camp swell ( reducing heat transfer to bridge for 350's) The exhaust port changes time and duration of cylinder stuffing increassing intake charge supplying head chamber with a denser fuel charge that is burned.

I will touch base on the effect of intake charge next and the resonince effect. There is no magic # each motor must be degreedand cc'ed and each haed milled and cut for the porting spces and the power output levles at what RPM you want to run. This is why barrel and camp is important to know what clearence can safly be used.

Rember Not a motor builder or engineer just a hacker that burned a few pistons.

PilotHawK · « **Reply #25 on:** July 24, 2008, 05:15:29 PM »

Could you please define "CAMP" for the non engine builders of the world. I understand everything else except that.

Adnoh · « **Reply #26 on:** July 26, 2008, 12:33:00 PM »

Camp is the pin side cam mesurement.

All piston are not round but oval and thinner at its crown.

cam, is the measurement skirt to crown.

barrell, is the cam measurmetn on the skirt side

camp is the cam measurment on the pin side 90 deg fro skirt vertical to pin.

These measument are important when having the cylinder bored, clearenc is efected by the following.
The CR compression raito: V1 + v2 / v2
CR corrected is degrees of exhaust close in degrees v1c
The BEMP cranking pressure
The BHP brake horsepower: P L A N
Plan=P= pressure, L =stroke in feet, A=ares in sq inches, RPM

The G-max: piston accerlation: Gmax N L A
Gmax : is piston accel in feet per second squared
N: crank rpm
L is stroke in inches
A ratio of rod between centers of stroke

The squish: distance between piston crown and head
The squish area: the presentage of bore area used to form squish

I wil leave other out for know.

The ones lised above are most of the main ones wich effect swell rates. These eeffect the rings is feet per sec squared. That controls pressures gases.

Notice that both head posted have same BEMP 180 lb (cranking rpressure). Also notice the diff in area of squish and squish. # 1 has a CR of 6.64 to 1 and #2 has a CR or 7.40 to 1. Which one at this state will require a high octane of fuel. By the wat stock 6.2 to 1. wil BEMP at 150.

Head #2 will require a greater clearence than #1.
The greater clearence for #2 will increse swell rate and sealing pressure.
The sealing pressure on the greater clearenced cylinder for #2 will create more stress on the rings require them to be change sooner. as the ring stress increases it will have an effect of the warpege of the ring that expands against the ring gap on piston which leads to flutter. Once flutter has begun the seal presuure now starts to work on the second rings ( note on second ring this help the first ring seal more effectly)allowing gases to start down the piston burning up the thin layer of protection( two stroke oil) between the wall and piston. Rember you had to use a greater clearence for head #2 which allows the flame front to reach further down the cylinder( piston scuffing) cause loose in lubracation.

Also note the squish clearences and area of the two heads. One will trap more mix and reduce thermal loding on the piston crown it self. As the flame front reaches out the the squish clearence holding the traped gases will not enight. As the piston travle down on power stroke the hot exhaust gases mix with the cooler trpaped gase removing heat fromthe piston edge. Less heat less swell. Now the exhaust port height in degrees comes in to play. Sooner the heat is pushed out and the sooner its replaced with a high denesity intake chagre the more effective the power stroke will be.

I will touch base on Cr effects power stroke in RPM next. Ask your self just what your rpms are when your running. I run form 6300 to 7600 on the power stroke for the DCP motor. Thats only a 1300 rpm power stroke. Try that on a non CVT bike and the CR has even a greater effect. You will notice that I figured piston speed on her motor before I started.

Tobey piston 3-08       measured at   OD   min   max         150   168   6800

Piston OD      10 mm up from skirt   79.925   0.080   0.092   80.005   80.017

Piston crown      17 mm down fron crown   79.516         79.596   79.608


Swell factor tolerence         0.409   19.56%   22.49%

Race
185   psi
7700   rpm
86.99068224   bhp
60.89347757   m-bhp

Max crank speed 7700

Adnoh · « **Reply #27 on:** July 26, 2008, 12:37:35 PM »

On a lighter side how many ever herd your engine builder say What your plan. Know you know what they mean P L A N. Most of us just say I want to beat my buddie. The problem is my buddie is my engine builder. Thats why I hack. It's me against me. I always win even when I loose.

PilotHawK · « **Reply #28 on:** July 27, 2008, 08:13:31 AM »

Great post. You are truly a very knowledgeable person when it comes to 2-strokes. I played around with one of my pilot motors and calculated out some of the stuff you are doing, but never got too worried about ring pressures or clearances (I was using a wiseco piston and clearanced it to .0045" and never had an issue). I was able to calculate the CCR on mine and with the static compression at 165, I was able to keep the CCR low enough to run pump gas using a cool head and 47cc dome from K-fab. Beyond that though, I never got too far into engine modifications since I don't have the money, tools, or knowledge I needed to play around too much. Maybe I lucked out with the last pilot motor I built, but it sure ran strong.

Keep it coming! Even though I am working on transplanting an 07 phazer engine into my pilot now, I have a couple of chainsaws, and a weedeater to play with

To answer your question about which of your engines will need a higher octane I will "guess" engine #1. I base this on the fact that squish is so much tighter with a smaller profile towards the edge of the piston, making the likelihood of detonation much higher with lower octane fuel even though head #2 has a smaller chamber volume and higher CR.

Adnoh · « **Reply #29 on:** July 27, 2008, 12:51:28 PM »

Thanks for the kind words. I thru in your #'s and came up with 46 BHP and a CR of 5.5 to 1 using a 70% effency. Not knowing your porting and squish, carb ect. The low Cr will definitly give you a wide power stroke and a more usfull carb single in the mid. I checked out you conversion page and will moniter. This is intreging to me I have never does anything like that. Please keep us up to date. Do you know what cylinder angle was used with that twin in relation to driven angle alignment. I like learning new things. What is luck anyway. Is that the application of ones knowledge and a little extra. If interested, I will contuine on the effect on in intake.