screamin_banshee_2003 Posted January 5, 2009 Report Posted January 5, 2009 (edited) last weekend i drove my shee quite hard. I had the wire that is going out from the coolant box (the one which is down not above) melted. My right cylinder spark plug pop out from the cool head. The shee ran like shit. I thought i had a problem with the cooling. I bought a compression test and found out that my right cylinder had a compression of 207 psi and the left had 154 psi. I had my top end changed before one and half years ago and both piston compression were around 160 psi. I bought three compression tester and they all gave me the same reading. I wonder how did the right cylinder shoot up to 207 psi. I did the compression test withought the carbs but with the intake and reeds. Any body can give me any explanation. My mods are in my signature with 22c doomes 35 pwk boss intake Another thing is before two weeks i cleaned the vforce reeds there were low and high on both side of the reed. I don't remeber how i did install them but maybe the right cylinder has low heading upwards. I didn't know about the high low just two days ago. Can that be the problem Edited January 5, 2009 by screamin_banshee_2003 Quote
Handyman Posted January 5, 2009 Report Posted January 5, 2009 If you did the compression check right afte the build without breaking in the motor that could be why the compression only ready 160. after the break in the compression could have gone up but i can't see how it went up that much... I'd check your reeds and do another compression test with the carbs and throttle wide open..make sure the motor does not start(Imake sure both spark plugs are out) and make sure that you keep kickng until the needle no longer moves. Quote
screamin_banshee_2003 Posted January 5, 2009 Author Report Posted January 5, 2009 i did remove both sparks and kicked it untill the needle stopped. Can reed increase compression I am planning on removing the head Quote
Handyman Posted January 5, 2009 Report Posted January 5, 2009 yes they can affect compression readings if they are not in or are bad allowing air to bypass back thrpugh the reed. Quote
screamin_banshee_2003 Posted January 5, 2009 Author Report Posted January 5, 2009 i have removed the cool head. Both piston were perfect but way rich. They were blacked out and oily. The right cylinder doom had a very small chip at the inside on the tip. Could this increase my compression or rather decrease it. I was running my shee with 91 octane fuel fo r a year. I bit that with a compression 207 my piston would have cracks. Am thinking of buying new doomes but i am afraid that it may not be the problem Quote
RIPPEN Posted January 6, 2009 Report Posted January 6, 2009 Not sure how or why you would have compression jump up like that but with you saying 160 PSI cranking comp and 91 octane fuel = detonation or close to it.. Maybe why the plug pushed out and your looking at piece missing out of the top of the piston.. Personaly if I were you I would plan on a top end rebuild and go from there.. If it was detonating hard your pistons could be beat up harder than they look.. Good luck. RIPPEN Quote
blowit Posted January 6, 2009 Report Posted January 6, 2009 (edited) The first check I would make is dome displacement. We have seen the mis marked before. 154-207 is a huge difference. That would be about a 4-5cc difference in chamber displacement. The reeds can hold back cranking compression numbers (very rare) but they have no way to increase them. You can test the motor with them out. I really doubt I would tear that engine down till I knew what was going on. Make sure both pistons come up to true TDC where the outer top edge (timing edge) of the piston is flush with the top of the cylinder. YOu have something obviously off here. wrong piston, dome, huge amount of carbon, plug in pipe, etc. You are kind of proving my point to others though that a stock stroke banshee CAN hold more cranking compression than most people think. 207 on pump fuel, impressive but not disasterous. brandon Edited January 6, 2009 by blowit Quote
RIPPEN Posted January 6, 2009 Report Posted January 6, 2009 The first check I would make is dome displacement. We have seen the mis marked before. 154-207 is a huge difference. That would be about a 4-5cc difference in chamber displacement. The reeds can hold back cranking compression numbers (very rare) but they have no way to increase them. You can test the motor with them out. I really doubt I would tear that engine down till I knew what was going on. Make sure both pistons come up to true TDC where the outer top edge (timing edge) of the piston is flush with the top of the cylinder. YOu have something obviously off here. wrong piston, dome, huge amount of carbon, plug in pipe, etc. You are kind of proving my point to others though that a stock stroke banshee CAN hold more cranking compression than most people think. 207 on pump fuel, impressive but not disasterous. brandon Yeah i was kinda missleading in saying doing a top end and didn't really mean it as the "fix" even though thats how I wrote it- my bad lol.. Was moreless trying to say after the problem is found a new set of pistons might be a good idea.. Otherwise Brandon, did I read that right that you think 207 PSI is not asking for trouble on pump fuel? RIPPEN Quote
blowit Posted January 6, 2009 Report Posted January 6, 2009 (edited) Yeah i was kinda missleading in saying doing a top end and didn't really mean it as the "fix" even though thats how I wrote it- my bad lol.. Was moreless trying to say after the problem is found a new set of pistons might be a good idea.. Otherwise Brandon, did I read that right that you think 207 PSI is not asking for trouble on pump fuel? RIPPEN 207 is more than we would recommend but I do not think I would replace pistons just because the motor has run with that compression. We have several out there at 190psi at 1000ft, +4*, and they are just fine. I will agree though, you get some shit fuel, you could get some detonation. We have a couple small secrets to running higher compression without problems but most is just in proper tuning. Brandon Edited January 6, 2009 by blowit Quote
RIPPEN Posted January 6, 2009 Report Posted January 6, 2009 207 is more than we would recommend but I do not think I would replace pistons just because the motor has run with that compression. We have several out there at 190psi at 1000ft, +4*, and they are just fine. I will agree though, you get some shit fuel, you could get some detonation. We have a couple small secrets to running higher compression without problems but most is just in proper tuning. Brandon Huh, your far more brave than I.. I run 50/50 on mine at 175 PSI with + 4 advance as per my builder suggestion.. Though Iam sure some people have been fine with what you describe I think its a bit risky considering there are allot of variables that can make or break what your saying.. However to each their own I guess. Other wise the reason I said I would personaly get new pistions is for several reasons. First is I rather pay the 150/175 or whatever now and have peace of mind rather than just running it and thats based on him saying he has small hole or piece missing out of a piston.. If there is visable damage like that I just wonder whats there that may not be easly seen.. IF detonation is what he is seeing I know it can be very viloent and hard on stuff and thats why I said I would personaly be looking to do a new top end. Otherwise if this is incorrect information I apologize and appreciate your correction, guess allot of what I was saying is driven off being a worrie wart-lol.. Looking forward to knowing the outcome as I have never heard of anything quite like this.. RIPPEN Quote
blowit Posted January 6, 2009 Report Posted January 6, 2009 seems too high if you ask me Tru dat. I am interested what is going on. Rippen, I might lean towards piston replacement if he indicated visible damage with the pistons but indicates they look perfect as I read. I would agree though, sometimes piece of mind is a good thing. Don't know how many motors we have done where guys felt it is better safe than sorry and we catch a crack in a skirt that would have lasted another hour before failure. We actually had one pop while the customer was demonstrating it's sickness. I heard it and told him to shut it off and it locked just then. I think we were able to save the crank on that one though. :biggrin: Quote
firebanshee Posted January 6, 2009 Report Posted January 6, 2009 I would get a syringe and cc the domes and see were you are at. :cool: Quote
RIPPEN Posted January 6, 2009 Report Posted January 6, 2009 i have removed the cool head.Both piston were perfect but way rich. They were blacked out and oily. The right cylinder doom had a very small chip at the inside on the tip. Could this increase my compression or rather decrease it. I was running my shee with 91 octane fuel fo r a year. I bit that with a compression 207 my piston would have cracks. Am thinking of buying new doomes but i am afraid that it may not be the problem Tru dat. I am interested what is going on. Rippen, I might lean towards piston replacement if he indicated visible damage with the pistons but indicates they look perfect as I read. I would agree though, sometimes piece of mind is a good thing. Don't know how many motors we have done where guys felt it is better safe than sorry and we catch a crack in a skirt that would have lasted another hour before failure. We actually had one pop while the customer was demonstrating it's sickness. I heard it and told him to shut it off and it locked just then. I think we were able to save the crank on that one though. :biggrin: The above quote was the post I was refering to.. Be willin to bet thats the side with the high comp and the one that tossed the plug..? All thats where I was commin up with my theory..:thumbsup: RIPPEN Quote
blowit Posted January 6, 2009 Report Posted January 6, 2009 Guess I read that differently. Would like to see a pic of this anyway. Just does not explain the high comp and that is what I am wondering about. B Quote
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