Piston mods and weight difference of pistons etc...

Here is a video I made today showing piston mods I did yesterday to the piston that will be going in my next Dax GenIV lower build, ( already together now by the way) excuse the jumping around in the video a bit and the length is just shy of 15 min. I cut the camera off a bit abruptly so the ending stinks but oh well, I pretty much got said what I had aimed to say and show.

If you're expecting to see some high end machine work, you'll be disappointed because there ain't none in it, just a DIY vid showing some improvements that can be done with a basic tool and the right bits and this tool being a Dremel type rotary tool. this video is unlisted so the only way to get to it is to have the link I listed here in this post.


http://youtu.be/ggfJVPQbzhI


Map

I've heard that theory before and I am thinking that there is likely something to it, I'm curious to know what the piston in the 48cc weighs compared to the pk80 and the grube type piston.

map

Greg58 said:

I had the grubee 48cc apart last month and ramped the piston and opened up the transfers, haven't put it on a bike yet so I'll look at it first and record the data then do the bgf engine when I take it off. I have three engines and right now only two bikes so one sits waiting its turn, I'm going to put the grubee back on the o/p cruiser and put the no name engine from it on the cranbrook, then do the mods on the bgf. We will have a base line of data to go by, I'll bet what will happen is we ( me anyway) will be even more confused !

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Sounds good and Yeah............LOL! you may be right on the confusion part for us but hey isnt it fun to find out a thing or two now and then and this may answer some of the same questions for others or maybe we're just doing what several others have done and known for a while.... either way we will have some more to think about anyway.

Map

Best I can tell using my calipers, the Grube type piston is measuring 25mm from bottom of piston skirt to center of wrist pin hole.

The PK80 type piston is measuring about 5mm less with only being about 20mm from bottom of piston skirt to center of wrist pin hole.

look at the pic I just took and you can easily see the pin location difference.

Map

2door said:

Shan, Keep us posted on your results.

I'm just a little concerned about strength loss in the piston due to the removal of so much material. Have you done the same piston mods before? Are you at all concerned about the structural integrity of the piston?

I'm interested but I'll let you be my guinie pig on this. Let us know how things go. I'm in the process of building a new engine for the black chopper. I'm not looking for more speed. It's way fast enough but it has always been a rough engine that takes away from comfortable riding. I'm looking for a smoother running engine. I'm going back to the old straight plug head and away from the slant, high compression that's on it now hoping that will make it a little softer.
I'll keep watching here for updates. Thanks.

Tom

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Well Tom I do have the thought in my mind about structural integrity being a bit less due to that much material being removed on the intake side of the piston, but these are such short stroke engines that I dont really think the piston not being strong enough is gonna be an issue, but then again...... the proof will be in the pudding....

As far as the straight plug head making an engine a little smoother.... I tried the same thing on one of mine, went from straight plug head to slant head, gained a little torque and it seemed to pull a little better overall, but I got to thinking that maybe the vibes increased a little so I went back to the straight plug head and wouldn't you know it..... same vibes at same speed/rpms, not saying this will be the case on all engines because I only did the comparison on the one, I actually like the looks of the straight plag heads the best and am seriously thinking I may pul the slant head off the engine I just built up today and put a straight plug head on it that has all of the "sealing ring" shaved off of it, thats one thing I like about the Puch 70cc hi hi heads, a good flat sealing surface and a nice small combustion chamber for increased compression or I can run two head gaskets and dial it down a bit.

I hollered and sang the praises of the Fred head last week but I have since discovered that my exhaist set up was the biggest factor in how welll the engine was running and that although the larger head may cool better, I jumped the gun on the added performance claim, no matter how I slice it it seems that a well tuned carb and an exhaust that flows correctly with a very small amount of restriction seems to always net me the best overall performance and as far as pipes goes I find that the expansion chamber exhaust I've used do a good job on the low end but always fall short for me on the top end compared to a. Ouple of the home grown set ups I've built, I like the sound of the expansion exhaust but I just cant get them to perform the way I want them to so far, im still tinkering and have some more trial and error to work through but in the end I may wind up right back where I started with my own set up that is a little louder than I'd prefer it to be but it performs best all the way around on my engines.... blah blah blah....lol!

Ill keep result posted as I have them, maybe if nothing happens to prevent it I may get this new engine mounted up and take it for a spin tomorrow, that is if I dont get over run with honey dooooooos......!

Map

Greg58 said:

I found the picture below on the piston bikes site, they show the two types as you have but only one for the 48cc. My grubee 48 is 15/16 from bottom of skirt to the top of the pin so the stroke should be the same as the pk.80 . my piston weighs 54.8 grams with both rings.

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Wow that is a lot lighter than the PK80 66cc piston, and thanks for the SAE measurements on the pin position, I've always seen it measured in milimeters and never even thought to see how it would measure with a ruler.... just had me a DUH.......... moment...LOL!

I just weighed the PK80 66cc piston along with rings and it weighs 84 grams....!

and was with the piston that has already had some weight removed by notching the skirt a little on intake and exhaust side, starting to see why the cranks are so unbalanced for the larger and much heavier 66cc pistons 30+ grams difference in weigh is a lot.

hmmmm......? so I have things floating in my head now...!

I just weighed a crank and rod assembly that is one of the cranks that has the holes drilled through it, one on each side of rod journal, this crank with rod weighs 1438 grams, I'm wondering if I drilled just to the outside of the existing holes just enough to remove about 10 grams with each of the 4 holes I drill if that might help the balance on the 66cc rotating assembly, that would be a total of 40 grams removed on what is the heavy side on the crank when the piston is attached..... I have this engine all new and in pieces just sitting here in a box and begging to be reassembled, I may have to give this a try and see what it does to the amount of vibes that engine will have at higher rpm, it can only do one of two things I would think, either help or make it worse....LOL!

What say you bro.

Map

Well, fellas I have some results to report, the bike you see in the included pix is the old 1963 Western Flyer that until a couple hours ago had an old china girl on it that had been laying in the shop floor for a couple of years, it is a strong running engine but on this bike could only achieve 36-37mph and would cruise at around 30mph fairly comfortable.

I put my old tried and true home grown exhaust that you see in the pix on today to see if this engine would gain any MPH from it vs the expansion pipe that was on it and yes it picked p a couple MPH on the top end.

Now onto the actual purpose of this post.... I pulled that engine off and put the newly built up Dax GenIV lower that I completed yesterday with the extremely lightened piston and with the transfers enlarged and I'm using two base gaskets between jug and case, I went ahead and left the Dax Slany head that I shaved down to the point yesterday until "raised sealing ring" was only about 0.006-0.007" high, exhaust and intake port only slightly enlarged mainly from cleaning them up, I did take a very small amount of extra material from the bottom of intake port and about the same from top of exhaust port but very little.

Ok on to the good stuff... every item I put externally on the new engine came directly off of the old beater engine that was on the bike, same exhaust, same intake, same RT Carb, same HD Lightening Ignition and coil, same spark plug and of course same rear sprocket and chain.

After I removed clutch cover and installed a flower nut retaining screw that someone forgot to install at either dax or the china factory, I fired the new engine off and took it for a 10.17 mile ride, GPS running the whole time, and I can tell you that the lighter piston made a huge vibration (reducing) difference at low, medium and high RPM, now at medium-high RPM which on this bike is @ 29-31mph with the 30T rear on the 24" wheel, it has a vibration and a shaky feel and then as the MPH and RPMs increase up to about 33MPH and beyond it just gets smoother and smoother and never has that hard vibe feel again, and at 28MPH and below this thing runs BUTTER SMOOTH... like crazy smooth... and this engine has torque and power out the wazzoo... from about 15MPH to WOT top speed, some of you may cringe but I break my engines in hard and fast, I break them in like I plan to run them, I don't maintain long periods of WOT at top speed but Im gonna find out what she's got early on within or just after about 5 miles of checking things out and listening for possible problems.

Now, I don't know what this bike is gonna do on flat ground when it does get loosened up a bit but I put a top speed of 45.8 MPH on the GPS after only having about 10 miles on it, I was on a slight declining part of the dirt road, so this would not be the flat ground top speed at this time, but it was singing like a cricket mating with a bumble bee.....LOL! wound up pretty tight but darn smooth, so time will tell what the flat land speed will end up being but if it in the 42-43MPH range I'll be happy.

So to sum all of this up, the piston work I did has paid off good so far on the low end being butter smooth to 28MPH having the unbalanced feel from 29-31MPH and then from that point on it just gets smoother and smoother, it's kinda weird actually, its like it has a vibe switch and at that certain rpm range it clicks on and as soon as the rpm increases a couple hundred more it switches back off, I think this engine hooked to a 36T on a 26" wheel would be the berries...... but it may get the 28T I made up on the 24" wheel is what I'm thinking.

Anyway, initial report on the new Dax Lower build with the piston with lots of material removed is a good one, engine runs great, looking like this may be my best one yet, we will see in time, but I have another new Dax lower inching for being built so I think I will do this same mod pak to it and it will likely be on the Huffy Karaoke Bike when its done and hopefully it will yield the same results as this last one has so far, the haters can say what they want, but these "GenIV and GenV" lowers are excellent platforms for building a strong and much smoother running china girl, this is the second one for me and its a good smoother runner just like the first one, already gonna have to replace clutch pucks in this one, clutch adjusted good and it slips the pucks when I ram the throttle hard at about 25+MPH.

Map

Greg58 said:

Good deal map, I'm going to put the 48 back on the o/p after all the mods and see how it runs. I did a lot of work on the transfers and ramped the piston and widened the ports. Since this engine runs smooth I didn't want to take much off the piston skirt but made it totally clear the intake port. If it ever quits raining here I'll give it a try.

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Sounds good and I'll be expecting to hear a report on what the mods have done for your 48, since it runs so smooth already Id be doing just what you did and leave the piston alone other than the ramping for a slight timing change.

Best wishes and hope it runs a hole in the wind for ya.

map

2door said:

Thanks for the progress report, Shan. I'll keep watching. Sounds promising so far.

Yesterday I was installing the piston on my new engine and the inevitable happened. The wrist pin snap ring popped out of my needle nose pliers and I heard it hit in a pile of junk. Took me an hour but...I found it. The funny part was before I found the snap ring I found two tiny dead centipedes that looked exactly like the snap ring. Twice I thought I'd found it before I actually found the little devil.

Got the engine buttoned up but I have to go to Easter dinner tomorrow so I won't get to try the new engine until maybe Monday or Tuesday.
Keep your reports coming.

Tom

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Yes sir Tom, I lost two of the snap rings yesterday myself, I heard the dang thing hit something but I never found either of them.... I need to make me a set of needle nose pliers specifically for use of putting the snap rings in, just a slight groove dremeled across the very end of the bird beak ends of the pliers and that would secure the snap ring from slipping and flying out, after the loss of two of them yesterday I plan to take an old pair of my needle nose and do that little trick to them before I build the next engine up.

I'm wondering if maybe I removed a little to much material on the piston is why i'm getting the vibes at upper mid RPMs, maybe on the next build I'll only do the ramping, cut the skirt on intake side and only drill 4 or 6 total 3/16" holes instead of 12, just thinking I might find a happier medium...???


Looks like I'll be pulling the new engine off the Western Flyer and putting it on another bike soon, I broke the seat post off of the western flyer and it is rusted solid into the frame, I've tried a pipe wrench and it was soaked for days with PB Blaster and it is solid and now broke off almost even with bike frame, so I guess I'll be stripping it down and using the parts on another frame this next week, I've got an old 24" Western Flyer BMX frame that will need some modifying for the engine to fit but I might just do it up on that frame, or make on of the other 26" frames I have into a 24" wheeled bike.... no biggy, I sure like the old 63 Western Flyer frame but I think the only way I can use it would be to weld a solid rod of steel inside the seat post and then slide another piece of seat post over that and then weld it all together for a permanent fix, that may be the route I go, since I'm kinda talking myself into it as I type this part of the post...LOL!

Happy Easter Tom and to all who read this post, have a blessed day and enjoy being with friends and/or family.

Peace, Shan

GearNut said:

Subscribing to this thread with interest!
Does anyone supply a better piston at a reasonable cost that is not prone to loosing the locating dowels?

mapbike, that frame is awesome!
If you can, weld a piece of steel to the seat post stub that will allow you to pull on it again. If you can incorporate into using a slide hammer, all the better. Heat the whole seat post frame tube evenly in the area where the stub is stuck with a heat gun or propane torch and let it cool. Do this a few times to break up the rust lock effect. Try pulling the stub out on the last heating cycle while it is still hot.
If you want to use penetrating oil, get yourself a can of Kroil, it is much more effective than PB Blaster.

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Funny you should mention slide hammer, was thinking wbout that last night, may make me one up using a stick of. 5/16" allthread with grade 8 nut on the end of it ground down to a good flat edge so that I can slide the rod and nut down through inside of seat post tube and then as I slide an old heavy window weight up the allthread the edge of that nut will cat h on bottom of thenpost and hopefully Ill be able to bust it loose, yes heat to expand the seat post tube will be a must I have an acetylene cutting torch so I can get it as hot as needed in a jiffy, just need to pull the fuel tank off so no chance of creating a big..... problem.....!

Raining here today but I think Im headed to the shop to devise a slide hammer and see if I can drive that tube outta there...

Map