Honda Odyssey and Pilot Forum
General Category => Pilot FL400R => Topic started by: lee1969gb on February 20, 2007, 01:52:29 PM
-
Can anyone please tell me what is the best piston to bore clearance to have on a pilot, I am getting bad scuffs on the front and rear of the piston and jaming the piston rings in the grooves.
When I used to do 250 gearbox karting and running a kawasaki kx engine we used to drill two small holes in the front of the piston to help lubricate the bore in a problem area, has anyone done this on a pilot or any other ideas, its costing me a fortune in pistons.
-
It depends on if you're running a Honda piston or Wiesco. I like to set them up a little loose, .006 for Wiesco. Wiesco says .004. I havent run a Honda piston for so long, I forget what they recommend. If your rings are sticking, it sounds as if your jetting is too lean, overheating the piston, and smearing it into the ring grooves. I'm no engine guru, so take this as just my 2 cents.
The Pilot doesn't have an exhaust bridge, so I've never heard of any cooling holes in it's piston.
-
.006" is nice and safe however short lived. .004" is better for top end life. The key is of course jetting. I can tell you that a piston seize between a 4 or 6 thousands bore is about 3 minutes. So why not take advantage of the extra 2 thousands. On a larger bore the cylinder port openings will tend to ware quicker and force you into a larger bore versus a simple piston change and cylinder honing.
-
Lee have you done WOT and midrange plug chops to check your jetting. This is so imporant on a 2 stroke motor. Also have you done a leak down test on the motor. If your going thru that many pistons than there is something wrong in one or both of these areas.
-
Are you talking about a Wiesco, Steve? I've tried .004 with them, and it didn't work for me. It would always scrape itself out to around .006, anyways. I'm not the most careful jetter around, though. My latest top end is on it's 3rd set of rings with the same size piston, so it has lasted good for me.
-
What is the life span of your set of rings(in hours). The number of sets really doesn't describe the longevity.
-
Does any one "high spot" there pistons. What you do is fit the piston run it in then strip the motor and clean up the piston, with wet and dry paper remove any high spots or areas that show signs of picking up then rebuild and thrash.
-
I don't log hours, but I have 2 seasons (icluding ice racing) on the last set. A few Silver Lake rides, mostly short motos, but always at maximum throttle.
My post was more to Steve's assertation that a looser bore will lead to needing to go to the next size piston sooner than a tight set up. I realize that is affected by the number of hours on an engine, as well. The rings weren't always worn out, just changed as long as it was apart. The amount of hours on this size piston has been as long as any bore in my Pilot history, where , when I set them up tight, the damage caused sticking the piston required going to the next larger bore right away.
Lee, I have never done what you describe. If you set them up tight, that might be a good idea.
-
Dave, Yes I was refering to a weisco piston. I have allways set mine up at .004" to .0045". Jetting is the key. Also the port champhering is as equaly important especially the horizont edges of the ports. If the edges are sharp they increase ware and can and will catch a ring. When the bore gets loose it allows the piston to slap and it wares the top and bottom of the intake and exhaust ports more than the rest of the cylinder. That in its self without a seizer will cause you to have to go to the next bore size. Thats why its good to cahnge the piston at least once a season. Just replacing the rings only gets your compresson back and does nothing to tighten the bore.
-
Thanks for your thoughts on this, Steve, and I hope Lee got the info he was looking for.
Hey, Lee, I never asked what clearance you had been using and which make of piston when you had your problems. Would you mind posting that?
-
I was using a wiesco piston both times this happened. I am mixing my 2 stroke oil 25 to 1.
-
I stripped my pilot engine today and found out why there is no compression. the piston rings are very badly worn near the exhaust port. These rings have only done about 20 hours. not sure what has caused this, possibly blocked exhaust?
-
Hi guys, I'm new here, just picked up a 89 pilot, took a
comp. test and I have 123lbs, runs and starts fine, just
wondering if that compression number is still ok to run it, and if
not, can I still get a stock piston and rings from Honda shop?
Thanks if someone can help me out.
-
May I add fuel to thought process related to piston clearence.
-
Sure go ahead
-
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)
-
sorry had to post as j- peg instead of bmp
-
Great stuff Adnoh. What kind of cranking compression will this yield? Also what octane fuel will you have to run?
Teach us!
-
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.
-
pics
-
more
-
more
-
#2 head
-
more #2 and stud tool
-
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.
-
Could you please define "CAMP" for the non engine builders of the world. I understand everything else except that.
-
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
-
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.
-
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.
-
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.
-
Please continue. I love the opportunity to learn.
As far as the twin I'm using goes, I have no idea about the angle. The output shaft on the twin is driven off the crank, and tops out somewhere in the 8000 RPM neighborhood while the engine itself red lines around 13000 RPM.
I am waiting on a new input shaft for the pilot tranny now, and I'm trying to work some numbers so I can calculate what kind of helix I will need to use in the new driven clutch to get the most out of this motor. I am on my 6 day stretch at work now, and on my next off cycle I'll be calling team to see what they can come up with. I don't see any real progress happening on my pilot for at least 3-4 weeks yet.
By the way...did I answer the engine question correctly? Which one will require the higher octane fuel?
-
Good guess, however I faid to mention some info for you to consider. Due to my miss information I may have lead you a stray. The ansawer is #2 will require a higher octane fuel. Whne I do work the motor is bench tested. This means the engine has no pipe, reeds,carb, intake tract ect. The system is full open set on bench and cranked. What I do is use a fogging oil on the itake side to prevent siezures while testing. This will cut down the friction and protect all surfaces and seals and supplies the motor with dence charge. After all testing is done the motor gets air check for insurances. As Items on the intake are bolted up the #,s change. First on the intake side. Reeds and then reeds and spacer. Logging numbers for future refrence and effect. Then stock and larger carbs, once carbs hooked up Iuse gravity fuel set up for charging. Then intrake tact tube , then filter set up. Once I get best #,s I bolt up stock and after market pipes to see which works best. I do this because I set exhaust port to a lt ( lt is a tuned lenght of pipe)measurement. By switching pipes I found this is a good check for exhaut port. Once this is done the #s change. Final cranking # is 172 with full system bolt up. My target cranking # was 168 so I had to recut head a little to dial in. This was preformend by increasing the 2 cc,s in the combustion chamber and increasing the first squish angle .5 degrees. This did effect the CR however in my favor. It added 300 rpm in the power range and increased the top speed by 3 mph. See the corlationin rpm and mph. I started with the pramators with a cranking pressure 168 and max rpm of 6800 using stock pipe with a cr of 6.84:1. I ended up with 160 cp at 7200 rpm and a cr of 6.5:1. I will share the ex port height in degrres for stock pipe.
New cylinder port in degrees
Ex Port atdc bdtc
Start to open 93
Full open 180
Full open 0
Full close 93
Duration 174
The area and intake#'s I will keep secert for know. This will give you a idea on how the intake and ares cann be set. Look for the corlation in the exhaust #,s for clue. Rember this is using stock pipe. This is also why the head had to be milled and cut. get back to head question #1 will require lower ocatne due to the lower cr #s. the more fuel trapped in the tighter squish and increasing combustion chamber denesity this will reduce thermal load on piston and decrese the chance of pinging( rember I raised the exhaust port). The amount of squish gase mixing with the enginted gases help cool down exhaust gase temp and the thermal load on piston. the enlarged combustion chamber and tighter and larger squish allows for a longer flame front and a longer duration of the burn (decresing flash HP). this will give a longer power stroke. This is why I like the dual stage squish.
The other key is using the proper heat range as not to wash cylinder or cause over heating. Too cold or hot of plug will cause you to wash cylinder reducing power and causing you to jet down and running motor lean. One key is to wick as much heat as you can tru the head decresing thermal load. An example of this on this motor the plug of choice is a 7 heat rage( I use 7 for he ngk guys, I use champion). The 39mm crab used came with 175 which I emeditly changed to a 215 for jetting. To make a long story short the 8 used a 185main and plug showed signs of being to cold. The 7 required a 195 and showed signed of being spot on.
The motor went from a ok bottom end to a wheel standing bottom end this is with running 14 disc the the drive. The proper heat range is a key to power with this set up. I will post some dyno #s when I can get it on there. The target # is 43.6022 rear wheel hp with a power curve of 3510.568 rpm peaking at 6900. If I get 38 rhp I be happy after alll it the wifes bike.
Sorry for the late and long post I have been work on new suspion for pilot.
P.S. Using head #2 with pump gas will produce less power and burn up piston. I was showing that you can achieve 180 psi and how to keep it alive with out 111 fuel. PSI is just one step in the process. Mill and do notheing eles is do at your own risk.