BigRed350x Posted January 9, 2008 Report Posted January 9, 2008 38pwk sound huge for that setup. 33 or 35's would be plenty for a stock stroke. might sound stupid, but you are holding the throttle wide open when you do your compression check right? Quote
J-Madd Posted January 9, 2008 Report Posted January 9, 2008 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... Good to know. Sounds like you did the research. So..........Blaster crowned pistons but Banshee lengh (for stock rod) I never really checked into it. I've got 160 psi with 20 cc domes on my 392...and ran 35 mm pwks on gas (now 38s on alky). That biatch should run a heck of a lot better than some ported stock cylinders (in most cases). I just can't understand that compression #. Did you hold the throttle open like BigRed mentioned??? Quote
Dave I. Posted January 9, 2008 Report Posted January 9, 2008 Yea there isnt a lot of info out on those pistons....this guy either needs to call jeff or trinity and see what the deal is.......something is mismatched somewhere in this motor. He said he kicked 30-40 times wot and got 110psi....30-40 times and my leg would fall off. I was talking to shayne about it, I wonder if the pistons are in backwards. If that would cause compression issues? Would definitely make it run like crap. Quote
forumsearcher Posted January 9, 2008 Author Report Posted January 9, 2008 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... Quote
dajogejr Posted January 9, 2008 Report Posted January 9, 2008 38pwk sound huge for that setup. 33 or 35's would be plenty for a stock stroke. might sound stupid, but you are holding the throttle wide open when you do your compression check right? J... they might not flow right at your altitude...but at or near sea level they work fine... Hell...brady080 has a stock stroke cub that puts out 119 on methanol with 39PWKs....carbs aren't the problem, with a .012 base gasket and the correct pistons, his compression would be sky high... He needs to check the squish and squish band before he goes any further. Quote
No Limit Powersports Posted January 9, 2008 Report Posted January 9, 2008 To start with we need to know if you have a short rod (110mm) or a long rod (115). I would definately check the squish. There is some science in making domes and just about every motor needs something different this is why on custom setups i never would run a off the shelf dome i always custom cut them for my customers that way i know everything is right. The 9768 piston is a piston that Calvin designed to run the 110 rod so it has a lower pin height so it compensates for the shorter rod if it was a 115mm rod which is the same as a blaster Calvin just used the readily availble blaster piston (573m06800) Quote
forumsearcher Posted January 10, 2008 Author Report Posted January 10, 2008 To start with we need to know if you have a short rod (110mm) or a long rod (115). I would definately check the squish. There is some science in making domes and just about every motor needs something different this is why on custom setups i never would run a off the shelf dome i always custom cut them for my customers that way i know everything is right. The 9768 piston is a piston that Calvin designed to run the 110 rod so it has a lower pin height so it compensates for the shorter rod if it was a 115mm rod which is the same as a blaster Calvin just used the readily availble blaster piston (573m06800) 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. Quote
forumsearcher Posted January 11, 2008 Author Report Posted January 11, 2008 (edited) 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? Edited January 11, 2008 by forumsearcher Quote
Dave I. Posted January 11, 2008 Report Posted January 11, 2008 Yea you are way off......are you POSITIVE you have the correct pistons? 9768M06800 If the pistons are correct then you have the wrong domes. I am pretty positive you need the blaster domes from what ive read. I would call jeff or whoever you got your parts from. They should be helping you. I bought my cylinders, pistons, and domes from jeff and it was perfect. If the people you bought your parts from arent helping then you need to be calling someone else anyway. Quote
forumsearcher Posted January 11, 2008 Author Report Posted January 11, 2008 Yea you are way off......are you POSITIVE you have the correct pistons? 9768M06800 If the pistons are correct then you have the wrong domes. I am pretty positive you need the blaster domes from what ive read. I would call jeff or whoever you got your parts from. They should be helping you. I bought my cylinders, pistons, and domes from jeff and it was perfect. If the people you bought your parts from arent helping then you need to be calling someone else anyway. 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. Quote
dajogejr Posted January 11, 2008 Report Posted January 11, 2008 Yeah...that doesn't even look right... I have my clutch cover off to put a new lockup on, or I'd kick mine over to show you what mine looks like... Do yourself a favor, hit Harbor Freight and get a digital caliper if you don't have one already...you don't need a professional machinist quality Mic, you don't need .0000001 accuracy... I think you found the problem...work through Andy to get the right domes! Or you can call Dave Noss direct, I'm sure he'd more than steer you right. Quote
J-Madd Posted January 11, 2008 Report Posted January 11, 2008 You have to measure the thickness, not how much is flattened..but your solder looks way to thick, i.e. not flattened enough. EDIT: nevermind. I looked back at the pic. You just put the ruler there to give as a scale to go by. It looked like you were showing the length of the flattened part, but on your rule, its more than 0.1''. Your measuring correctly (but calipers are necessary for greater accuracy) and you have found your problem. Quote
forumsearcher Posted January 11, 2008 Author Report Posted January 11, 2008 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. Quote
forumsearcher Posted January 12, 2008 Author Report Posted January 12, 2008 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? Quote
shanYE west Posted January 12, 2008 Report Posted January 12, 2008 Possible 4mil cylinders? That would give you another 2mm at TDC and BDC. Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.