forumsearcher Posted January 8, 2008 Report Posted January 8, 2008 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... Quote
[email protected] Posted January 8, 2008 Report Posted January 8, 2008 whats ure timing and ure pipes ure running. Quote
bada450r Posted January 8, 2008 Report Posted January 8, 2008 thats how the power band on a cub is basicaly no buttom end with everything up top, but it shuold pull on top pretty dam hard.also i would suggest that you go to dual carbs if you want to get the most out of your cylinders, with your size set up i'd say at least 34'rs this cylinders love gas.also even with 21 cc domes you should be getting i say atleast 145 on your compression tester.if you pull your head out i would put 20 or 19 cc domes and run half race/half pump gas.imo Quote
sheerider1026 Posted January 8, 2008 Report Posted January 8, 2008 (edited) i would ditch the t5's and get cpi inframes or shearers.. put dual carbs ( i am running 33's on mine) and hold on, i am running a 48 pilot, and a 148 main, and it is strong.. the late powerband is the nature of the beast, but the good part is when the motor starts to pull and pull and pull.. that single carb and t5's are whats holding your cub back, the motors love to breathe , and they like fuel a lot also.. hope this helps. Edited January 8, 2008 by sheerider1026 Quote
dajogejr Posted January 8, 2008 Report Posted January 8, 2008 Whomever charged you 250 to true and weld the crank should've included a bottle of lube with it, that's outrageous... Even if they put a TZ bearing on the PTO and Igntion side, that's still HIGH AS HELL.... Other than that...you got some parts used on there, or at least posted used parts pricing, good for you...way to save a few bucks... Quote
No Limit Powersports Posted January 8, 2008 Report Posted January 8, 2008 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... Thanks for the props we do what we can!! Is your motor a long rod motor or a short rod motor??? Im guessing you have a 68x54 cause u said 392cc. The base gasket needs to be a .012 if its a 115 rod (using the 573m06800 piston) and .022 if its a 110 rod (using the 9768M06800 piston) either way you should be setting bout .018 in the hole with that combination of gaskets, rods and pistons. With that said your dome should have about .020-.024 step in it to get the squish right. As for the bolts we sell and highly recommend an arp bolt that has a 12pt 10mm head on it that makes it real easy to tighten down. Give me a call if you want some or ill have them up on the site probably later today... Andy M&M ATV Quote
dajogejr Posted January 8, 2008 Report Posted January 8, 2008 Grinding down a 12 point 12 or 13mm wrench is how we ALL tighten the base nuts on a cub motor down.... Checking squish is easy...get some .090 solder with a flux core (it flattens easier), bend it into the spark plug hole, make sure the solder is parallel with the wrist pin, and kick the motor over by hand. Measure the "flattened" portion of the solder with a caliper mic, and post it up. You have to make sure the solder is parallel with the wrist pin, if you measure it front to back (intake to exhaust) the piston rocks just a hair in the cylinder, but enough to throw off the squish measurement.... ON smaller cubs I like to shoot for .040 to .050... Quote
Dave I. Posted January 8, 2008 Report Posted January 8, 2008 Looks like Andy pretty much said everything I was going to. You really need to check your squish. Depending what pistons you used you might have some serious issues. If you got blaster pistons and have stock rod length its not right. The pistons you need are sort of custom and can be ordered through trinity. Base gasket should be .022 like Andy said. Make sure you have the correct domes also. Get dual carbs, 35 pwk are good. thats what I run mine on gas. The t5 are not perfect but they will work. Get some race gas, smaller domes and up the timing. Where at in California are you? Quote
dajogejr Posted January 8, 2008 Report Posted January 8, 2008 What bore/stroke combo are you using? Normally, you can get just about any piston you need right from Wiseco, whether it's a banshee OEM type, 795 series or blaster piston... However, as many of you know, the domes on those pistons are different, so...the domes for the head need to be cut accordingly.... Quote
Dave I. Posted January 8, 2008 Report Posted January 8, 2008 What bore/stroke combo are you using? I have 68x54 (392) with stock rod lenght. This is what calvin had to say about the pistons in this bore/stroke/rod combo. Basically what he said is they designed a special piston for stock stroke/stock rod length 68 bore so that they could use off the shelf 68mm cub domes and you wouldnt need a special cut dome. You can have a dome cut for any combo I guess but then you are stuck getting a custom dome cut every time you want to switch domes. For some people thats the only way they would do it anyway, for others if they saw a cheap set of domes for a 68mm cub they would buy them and could use them. """""CPI-6854 68mm bore by 54mm, (stock stroke)???392cc When using stock rod crankshaft (110mm rod X 54mm stroke) Cylinder is setup to use a Wiseco 9768M06800 Piston Kit available through Trinity Racing Should use stock thickness Base gasket , (.020-.022) Head volume should be between 19 and 20cc domes When using long rod crankshaft (115mm rod X 54mm stroke) Cylinder is setup to use a Wiseco 573M06800 Blaster Piston Kit Should use thin Base gasket , (.010-.012) Head volume should be between 19 and 20cc domes When we had the 9768 made, we made it with the same dome rise as a blaster piston, that way the 68mm domes were both cut for the blaster dome rise."""" Quote
forumsearcher Posted January 9, 2008 Author Report Posted January 9, 2008 What bore/stroke combo are you using?Normally, you can get just about any piston you need right from Wiseco, whether it's a banshee OEM type, 795 series or blaster piston... However, as many of you know, the domes on those pistons are different, so...the domes for the head need to be cut accordingly.... 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. Quote
dajogejr Posted January 9, 2008 Report Posted January 9, 2008 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. It should, because you should measure the squish band as well, not only how much it squishes it, but for how long as well.. Quote
Dave I. Posted January 9, 2008 Report Posted January 9, 2008 Sounds like you have the right pistons and domes. squish is gonna be tight with that .012 gasket. your compression reading is low for 21cc domes....I dont know what a .012 gasket would do to port timing and your compression but I dont think it would make that much difference. I dont know where you are at in California but if you are up north you could try my 392. You definitely shouldnt be losing power with a 15 tooth up front either. You should need a 15 tooth to keep from spinning the tires so much. There is a missing link somewhere. That thing should run hard even if it is a little rich. I didnt think t5 would hold it back that much but maybe they are. Quote
J-Madd Posted January 9, 2008 Report Posted January 9, 2008 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. I don't think that is the Blaster piston. I didn't look at the website, but my 392 has pistons from fast (i.e. the Trinity pistons) and his domes. You may have blaster domes with Banshee pistons. If you order 68mm domes and specify they're for Blaster piston, those are domes for a 4 mil 68 mm Cub (421). That's your problem. The thin base gasket is the only reason you have the compression that you do. You've got pistons for a long rod with different shaped domes on a stock rod motor....jmo. Quote
Dave I. Posted January 9, 2008 Report Posted January 9, 2008 (edited) What I read by the description calvin gave is......the pistons that he has are the correct ones for the stock rod length, if he has that part number. They have the blaster crown. They should work fine with any 68 bore blaster dome. The difference between the 392 and 421 should just be deck height of the cylinders themselves. domes should be the same if they are cut for the blaster piston. Maybe im not getting it correct but i think thats how its designed... Edited January 9, 2008 by Dave I. Quote
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