Sands Posted September 8, 2011 Author Report Share Posted September 8, 2011 Let me ask you this. Do your spark plugs come loose? I still think you have severe deto caused by lack of fuel. I just built a 421 cub for a guy. We ended up with 185 mains ( 39mm PWK's) Yes. There was a time that the spark plug jumps out of the engine! Quote Link to comment Share on other sites More sharing options...
Sands Posted September 8, 2011 Author Report Share Posted September 8, 2011 I wrote that wrong last night . .044" is 1.1 mms. .042 or just over 1 mm is often about as close as many will want to run squish clearance. If you were supposed to use a .018 or .022 thousandths base gasket and you used a .012 it could have given you detonation problems with only .32 squish. Especially with any type of pumpgas. Lack of fuel is very common as well. I thought both sides had the problem. Both sides had the problem. Quote Link to comment Share on other sites More sharing options...
Sands Posted September 8, 2011 Author Report Share Posted September 8, 2011 Let me explain a few things. First off you have detonation. No if ands or buts about it you are seeing detonating. Its not sand, or dirt or anything else what you are seeing is detonation. Second off the base gasket does not soley contribute to total squish. The thinner base gasket with the same step in the dome will have a tighter squish. We can run any base gasket we want if we set the step in the dome where it needs to be for the desired overall squish. Now with that said a 68x58 cub or serval calls for a .012 base gasket to get the port timings were calvin blueprints them at. That does NOT mean that is where we have to leave them but that is our starting point or reference point. Detonation can be caused by a lot of variables. Lean is one, whether this means jetted to lean, or running out of fuel, lean is lean. Dome design can cause detonation, a poor dome design can and will cause detonation no matter whether your jetted correctly or not. To tight of squish causes the squish velocity to be to high and cause detonation. There are a hundred things that can cause detonation, and the head design IMO is one of if not the single most important part of a 2 stroke engine. I have spent countless hours testing different dome designs and even more time calculating everything under the sun trying to get what i consider the best. Now like i said in my earlier post i feel your dome design is less than favorable and a different dome is your answer. The detonation is very hard on the motor including the crank. If i were building the motor i would pull the crank and check it out thoroughly and check to see if the welds held, if its still in true, and if the bearing are ok. Then i wouild replace the pistons and put new domes in it. Make sure its sealed and run it. If you have any more questions or need anything feel free to pm me or call me Thanks Andy I sent you a PM yesterday. Quote Link to comment Share on other sites More sharing options...
Sands Posted September 8, 2011 Author Report Share Posted September 8, 2011 all true here!! i've never seen damage like that from deto if deto alone did that to the dome and the piston holy hell!! thats a new one to me!! BUT my PERSONAL bikes i ahve been able to hear them if they deto adn correct it befoe it got really bad.. most time i have seen what looks like a sand blasted edge OR a blown off ring land area. but most time the head lifted and the coolant came in and caused the deto to become much worse and the reaction and extreme lean condition from the coolant introduced caused the piston to blow and the lands to explode off the pistons.. did it eat a plug? just looking at the crank through the cases is not going to tell you shit.. as stated split it. i have found cracked lower rod bearing cages on no slop perfectly tight lower rod bearings, found cranks that were welded with filler rod added that had twisted and th e filler came out taking out the crank totally BUT it seemed fine in the case. i have seen main bearings blow ball retainers and that end up eating cylinders. and blowing completely out the pipes and out the exhaust.. ye ha carnage at its best HA HA split the case and figure it out. get some better domes preferably known CC and for the proper fuel you want to use, and triple check your squish clearance when you reasemble it being that your in portugal i;d order a few base gasket thickness's and save some on shipping. You are right... but I only run with Banshee for a few miles since the rebuilt... about 60 miles. Not more... And running very slow. This is the first time that I run hard for a 1/8 of mile. I think I will only put new piston and domes and choose a base gasket. If it doesn't solve the problem, maybe next year I'd try to split the cases, once again... I will call for Andy to figure out a new setup ( domes, jets, thickness of gasket ). I believe crank, bearings, etc... are in good condition ( I hope ). Quote Link to comment Share on other sites More sharing options...
Sands Posted September 8, 2011 Author Report Share Posted September 8, 2011 Yes I know. We have also 95 E10, 98 E5, 99+ V-Power ans RE85 here in Finland. But those numbers are RON, not MON or even R+M/2 AKI´s. Ask from your OIL comppany. -Pasi S. A friend of mine just told me that our 98 octane ( European ) is like 93 octane in USA... Quote Link to comment Share on other sites More sharing options...
Sands Posted September 8, 2011 Author Report Share Posted September 8, 2011 Yes they can. The 98 is RON and it is like 93-94 USA gas. The 95 here in FInland, and I think most of the Europe is 91 USA gas. That is the same thing like having 4x45W in your car stereo HAHAAA!! One other thing is that we have to richen up a little here in Finland, because we have more oxygen in our gas comparing to USA. (can´t say that this is true in all Europe countrys). This is out of those Dragracers who have used the same motor in Finland and USA. Do I smell a leaking boost-bottle necks here? J/K I´m sure that Andy will help you out of this issue! -Pasi S. I don't have boost bottle, but my manifold were design for 34-36mm carb, because I bought them before start thinking of getting a Cheetah Cub. To fit PWK39, I cut the boots a little. There is something I hadn't tell you. My Banshee idle high RPM comparing to other Banshee's. Could it be a leak on the boots due to the cut I done? Quote Link to comment Share on other sites More sharing options...
rubberneck Posted September 8, 2011 Report Share Posted September 8, 2011 I don't have boost bottle, but my manifold were design for 34-36mm carb, because I bought them before start thinking of getting a Cheetah Cub. To fit PWK39, I cut the boots a little. There is something I hadn't tell you. My Banshee idle high RPM comparing to other Banshee's. Could it be a leak on the boots due to the cut I done? so you have a huge airleak creating a lean condition. I would think yeah that could do it. Not to be a dick but you realize you just destroyed the top end for the cost of some intake boots. Quote Link to comment Share on other sites More sharing options...
Sands Posted September 8, 2011 Author Report Share Posted September 8, 2011 so you have a huge airleak creating a lean condition. I would think yeah that could do it. I will check that situation as soon as I can. Now I just need what domes will I use, main and pilot jet, thickness base gasket and some good luck for this engine. Quote Link to comment Share on other sites More sharing options...
Jereme6655 Posted September 8, 2011 Report Share Posted September 8, 2011 alot of people know it......BUT alot of people don't know what backing out spark plugs mean. When a spark plug (that has been tightened down correctly) backs itself out is because of the hammering effect that it is going through do to detonation. The constant hammering on the plug will cause it to actually loosen itself....... so word to the wise.....if your plugs start backing themselves out.....you better start looking around for a way to fix it.... Quote Link to comment Share on other sites More sharing options...
Sands Posted September 8, 2011 Author Report Share Posted September 8, 2011 alot of people know it......BUT alot of people don't know what backing out spark plugs mean. When a spark plug (that has been tightened down correctly) backs itself out is because of the hammering effect that it is going through do to detonation. The constant hammering on the plug will cause it to actually loosen itself....... so word to the wise.....if your plugs start backing themselves out.....you better start looking around for a way to fix it.... I didn't know that. Thanks for the help. Quote Link to comment Share on other sites More sharing options...
pabansheematt Posted September 8, 2011 Report Share Posted September 8, 2011 Yes. There was a time that the spark plug jumps out of the engine! You have the exact problem I had this summer. Mine had a blocked gas cap vent. Slowing down fuel flow. Good luck. Shee, will run fine once you figure out your fuel problem. Quote Link to comment Share on other sites More sharing options...
RadarRacing Posted September 8, 2011 Report Share Posted September 8, 2011 (edited) You have the exact problem I had this summer. Mine had a blocked gas cap vent. Slowing down fuel flow. Good luck. Shee, will run fine once you figure out your fuel problem. Take off tha gas cap and try to blow on the vent tube, if you cant blow air into it that could be a big problem, take out all the metlal and drill out the plastic part bigger. Then you wont have any problems flowing fuel or having a vacuum. word to the wise.....if your plugs start backing themselves out.....you better start looking around for a way to fix it.... Those last 2 posts hit it perfectly. Lets ask if your plugs backed out while you were cruising slowly . That tells us it was lean on the needle for some reason but could be from air leaking into the motor. Intake boots can definately cause an air leak, if you ground the inside of the boots to fit larger carbs than more than likely they are not sealing. Cam I can show you a few domes from buds builds that are hammered from detonation. Heres a good example. All from detonation. http://forums.atvdragracers.com/topic/11407-trx-370-cylinder/ Edited September 8, 2011 by RadarRacing Quote Link to comment Share on other sites More sharing options...
252wheelieking Posted September 8, 2011 Report Share Posted September 8, 2011 A friend of mine just told me that our 98 octane ( European ) is like 93 octane in USA... From reading previous post on here 24cc domes would work perfect with 93 USA pump gas. Ask Andy at M&M alot of people know it......BUT alot of people don't know what backing out spark plugs mean. When a spark plug (that has been tightened down correctly) backs itself out is because of the hammering effect that it is going through do to detonation. The constant hammering on the plug will cause it to actually loosen itself....... so word to the wise.....if your plugs start backing themselves out.....you better start looking around for a way to fix it.... I had to learn this the hard way...... http://bansheehq.com/forums/index.php?showtopic=145800&st=0&p=1257153&hl=252wheelieking&fromsearch=1entry1257153 Quote Link to comment Share on other sites More sharing options...
coryv4 Posted September 8, 2011 Report Share Posted September 8, 2011 421 Cheetah Cub, 22cc domes ( live at sea level ), PWK39 178 jetted, VForce 3, +5º timming, Shearer SBIF. well if it is not ported you have way to high comp for pump gas i am guessing you have right around 170-180 psi with my serval at sea level with 22cc domes i have 194psi in both cylinders Quote Link to comment Share on other sites More sharing options...
pabansheematt Posted September 8, 2011 Report Share Posted September 8, 2011 well if it is not ported you have way to high comp for pump gas i am guessing you have right around 170-180 psi with my serval at sea level with 22cc domes i have 194psi in both cylinders My god. Why do you want so much compression? Quote Link to comment Share on other sites More sharing options...
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