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You need to do a lot of reading before attempting any porting. I totally agree with reading the 2 stroke porting book by A. Graham Bell. I read it twice then decided to just but the Race Logic porting templates. The templates make it easy to port a stoke stroke motor, and it helps teach you what a correct port window should look like. In fact these templates will help setup your exhaust and intake ports for a 4mil bike. By the way, if you are going to bother buiding a 4mil bike you need to get a cool head with recessed domes. You are better off with the stock crank that using the lame ass spacer plate. I know from experience. The transfer ports are a pain in the ass because you do not have the proper tools to port them properly. I just finished my 4mil bike with my home porting, so I wont totally discourage you from going at it yourself. I should know in a couple weeks whether or not it runs well or not. Here is some reading for you that I have come across, there is tons more out there.... Try to resist the urge to post questions before searching for a few hours on what you are trying to learn. I assume you likely need to do a little reading on degree wheels in order to understand some of the details in these posts. http://bansheehq.com/forums/index.php?showtopic=136007&st=30 http://bansheehq.com/forums/index.php?showtopic=132925 http://bansheehq.com/forums/index.php?showtopic=140120

Well I got a crank and new pistons slapped everything together, check the squish to be .042", and took her out. She runs like a beast. I have overheated a couple times with the 170 / 50 setup. Now I am running 185 mains and 50 pilots. I still think it is a little lean though. But the power is incredible... Thanks for everyones help. Now time to hit the dunes for some fine tuning on the jets... I am sure +4 swingarm and new cpi pipes will be in my future...

Thanks, I already sent you a millon emails. I'll definately call Monday...

Dave, you are the man... Thanks for sticking it out. The casting in the intake shows 58. Wow, wish I would have known that before... HAHAHA. I am kinda excited now to build the 421 setup since I have basically built the 392 at least twice by now. I think I will go ahead and go with a the 4mm crank and long 115 rods so I can use the normal 573 weisco piston. The additional cost of the pistons wont break the bank. I should be able to sell the "used" pistons and my crank to help offset the new stroker crank cost. Another learning experience of this was that the cub NEEDS to have a "clean up" port job to fix casting flaws. I just used my dremel again to cut out the casting imperfections. It is very easy to do so for other DIYers go ahead and do a clean up port yourself. The transfers were really bad on my cylinder. One of the transfer ports was probably blocked by about 50% with left over casting flaws. Also the smaller left and right intake ports needed to be cleaned up. I did a minimal clean up on the edges here but the excess casting is obvious. Sorry I did not get any pictures before the clean up, but google has a lot of information with pictures on clean up port jobs... Hopefully this thread helps someone else in the future. I imagine there are not many people out there that try to build a 392cc engine with a 421 cub, but my mama always said I was special. :biggrin:

Yea, I probably should have bought all the parts from one location. Luckily this is a hobby and is a fun learning experience. I know what not to do next time... Thanks for the thoughts on the 110 rod and piston. I will check the casting tomorrow, I think the puzzle is getting closer to being solved.

Well let me reply to myself on this one. If my best measurement shows the cylinder as being .07" larger but infact it is .08" higher, then this would be the extra 2mm needed to be a cub for a 4mil stroke crank. It is diffilcult to guess use my previous squish measurement compared to what is would be if I had the 4mil crank, because the pistons are different. Is there any other thoughts on how to verify the cylinder?

I just measured my stock cylinder from the base to head, it is about 4.04" my best measurement show the cub from base to head at 4.11. This is an additonal .07" overall... VERY STRANGE!!! I am not sure what to do now. I definitely need to verify the cylinders to be correct. Hmmm..... That would be great to have 421 setup. It doesn't look like next weekend will be an option for riding....

Well guys I just installed the .018 base gasket in preparation for the new head domes, but I am still a little worried that something is not correct. Below are a couple pictures showing TDC and BDC. Should there be such a large step between the head surface and the piston edge? I also took a picture of the Bottom Dead Center for the other piston and you can see that the transfer ports and exhaust port do not sit exactly level with the piston top. Does this seem correct? I also took a picture of the step on the dome. The dome step is approximately at .041" and the step between the head deck and the piston is slightly larger but was a little difficult to measure... After seeing the piston not reaching the head deck it seems like I may have another issue. Does anyone have any good idea's?

I have a caliper and used it for measuring the squish. I just put the ruler in the picture for some scale. After measuring the squish it is pretty safe to assume the domes are not correct. I am going to check the squish on the other banshee tomorrow so it should give me a decent baseline for what I am looking for. Thanks for everyones support and troubleshooting help. I will report back after installing the domes, hopefully they will get here fast enough to go riding next weekend.

I cobbled the parts together for a number of different places, include the ever popular e-bay. I bought the pistons through Andy, mmatv, so I am sure they are correct. I have the boxes for the pistons, so I know they are fine. I tried to save as much money as possible for the setup, but I guess a few mistake will cut into some of my savings.

Wow, measuring the squish is basically the easiest thing I have ever done. Mine is totally wrong. I bought some .062 solder and .125 solder. It turns out the .062 stuff would not squish. I had to use the .125 to get a reading. At the tip it is just under .1", so this is way off. With the small base gasket I expecting too tight a squish. SO.... Either I have the wrong pistons or wrong domes. I am pretty confident the pistons are correct and at least I know which pistons I have; I am thinking that the e-bay domes were not correct. So now the question I am confused about is what domes to buy. It sounds like I want to get standard blaster cut domes, and I think I will go with 20cc for the hell of it. Does that sound correct?

I have the stock 110mm rod. I will check the squish today. Does anyone know how to verify the domes are correct. In any case I am ready to go buy some "correct" style 20cc domes as a test to see if it corrects the power and compression issues. I will post the pictures of the rod tonight... And yes the pistons were in correctly, I wish I had forgotten something that simple.

Yes on the WOT for the compression test. I kicked a good 30 kicks and watched the needle top out on the tester. I will check the squish and double check the compression with a different gauge. I am still hoping that it is only a jetting problem. Maybe I am too lean with the 38mm carbs, as these jet sizes are usually used by those with 35mm setups. I am still a little worried about the compression not being correct though. Hopefully it is only the gauge. Thanks...

The setup is a 68mm bore and 54mm stroke. I used the .012 base gasket and the 9768M06800 Wiseco Piston. I forgot to include that I had installed dual 38mm PWKs for the engine. The price on the crank included a used crank. Thanks for all the feedback. I ordered the domes on e-bay, and specified a 68mm bore for use with a cub motor and blaster piston. I did do any checks on the domes that I installed other than they were 21cc's. Smaller domes might be needed but I was trying to stay away from having to run race gas. I was thinking of going towards some CPI inframe pipes but this will be later in the year if needed. For measuring the squish does the solder need to extend all the way to the cylinder wall to get the correct reading? I do not want to damage anything. But it sounds like I had ordered the wrong gasket. That sucks.

Over the past month I have been swapping out my ported cylinders to build a 392 cub motor on my 89 shee. For those of you without ported cylinders I highly recommend having them ported, it is well worth the money and makes a night and day difference in the seat of your pants. My other shee only has pipes and a filter, the ported bike will do circles around it. I ported the cylinders myself with a dremel and the race logic template setup. Some patience and a do-it-yourselfer will not have any issues porting the intake and exhaust ports. Back to the Cub project. I used this forum for all my research, thanks much... I typically ride dunes and of course love to hit comp. hill and the strip while in the sand. So I figured the Cub motor would be a great new upgrade. I already had the stock crank trued and welded so the cost of building a 421 motor was a little more than I wanted to dish out. Other prior mods are a timing plate at +4, T5 pipes, and a trinity 2to1 35PWK. I traded my milled head for a new cool head setup and 21cc domes to continue to run pump gas safely. I also needed new to me 38PWK's for the cub. Approx. Costs: 600 Cub 392cc 150 Carbs 50 jets 200 head 200 pistons and gaskets, STUD EXTENDERS 50 K&N Filter Also needed: 250 Crank True and Weld 75 Gaskets/Bushings 100 New chain and sprokets (stock sizes) - I tried a 15T up front and do not recomend this, it robs power big time. Tons of Brake and Carb Cleaner to get all the years of grime off the case/frame/carbs/hands. Unless you religiously clean your bike... I did not know I needed the stud extender until I had already stuck the cylinders onto the case... Remember to purchase the stud extenders or make sure that you have them before going too far. So the engine build was relatively easy, and my jetting is at 48, DEK 3rd, and a 162 for the main. I have no clue rich or lean as it sits. I have only taken a handful of passes up and down the block. I was not impressed with the power thus far, although I am hoping this is simply a jetting problem. The power comes on way way way way late in the rpms, and doesn't really hold as long as I had expected. As it stands the ported stock motor would walk on this build without a problem. With my POS compression tester I got 110PSI after 30-40 kicks and WOT. This was true of both cylinders, I may get another tester or gauge to check if the readings are accurate. I am basically at sea level in Cali. OC, so I had expected to see higher compression readings. But I have to confess that this is the first time I have ever bothered to check the compression on anything. It has been a fun project I still need to get the bike out in the dirt and get the jetting dialed in. It still feels to me the long wait for the power band should kick a little sooner, the bike seems to hesitate just prior to getting on the pipe... I need to figure out if the long hesitiation is due to a lean condition or possibly the bike is loading up in the lower RPMS... Not sure yet. I bought pistons and gaskets at the website below, they have some good deals on various other parts, service was great as well: https://www.mmatvonline.com I ordered all my jets a while back from www.jetsrus.com. I am not sure if they have the best deals but the shipping was fast, and waiting for parts always sucks. I did not measure the "SQUISH". Basically because I do not know how. I found a few threads that talked about this measurement, but within the thread there were some recommendations on the base gasket thickness to be .012, so I just ran with this size. One gripe about the project was tightening the nuts to hold the Cub cylinder to the case. The cylinder is too close to the nuts so you can not fit any type of wrech around the nut... Extremely annoying. I ended up grinding one of the cheap 12mm wrenches down to fit in the limited space. I am not sure if there are other nuts that people use or if everyone has this problem, but I am dreading changing pistons simply because it was a PITA. I have a few pictures of the setup I will post in a few days. But I just wanted to thank all of you for the information I have been able to find in the forum thus far...