dirtydownunder Posted June 30, 2009 Report Posted June 30, 2009 clean filter, both plugs out, WOT, 45m ASL and kicked as hard as i can with standard head/port i scored 103 and 102 (on cold engine with a new snap on guage) reason for checking was, im about to install 20 cc domes and wanted to know the compression differance. once its hot it will gain a bit of compression so it may be close to the noss compression chart, so with the 20cc domes i should see around 140-150 psi. so tomoz im gonna stick the new head and domes in check the comp and start roosten !! atleast whiles its apart i can see how much film the avgas has left. im pretty excited i love mods. Quote
shee4speed Posted June 30, 2009 Report Posted June 30, 2009 it seems like those #'s are kinda low. I think you should be around 120,stock. Quote
Isaac_62 Posted June 30, 2009 Report Posted June 30, 2009 If i got those #s on my bike i would think its time for a top end rebuild... Those are low #s... looks like its time for a bore and a fresh top end... I wouldnt let it go any further... U could cause more damage by not doing it... Just my 02 Quote
dirtydownunder Posted June 30, 2009 Author Report Posted June 30, 2009 (edited) i thought i would be around 120 aswell but im not haha 102/103 is pretty close so nothing is wrong thats just what it is and for a stock bike it goes pretty good. if it was hot i would get around 120, do you's check yours hot or cold ? i could try differant gauges till i get 120 tho 45 hours and need a top end fuck that, the bike still goes good. Ill check my cousins 08 that has like 20 hours on it for comparison with the same guage. Edited June 30, 2009 by dirtydownunder Quote
Isaac_62 Posted June 30, 2009 Report Posted June 30, 2009 45 to 50 hrs of riding is pretty typical of a top end rebuild... I think ur #s are low...I wouldnt just go adding different domes to bring it back up... but its ur bike not mine... and i check mine cold... Quote
DallasGDub Posted June 30, 2009 Report Posted June 30, 2009 What's your elavation? That will better determine if it is low or not. Quote
dirtydownunder Posted June 30, 2009 Author Report Posted June 30, 2009 about 150 feet above sea level, perhaps the guage is reading low ill check my cousins 08banshee which he hardly rides (20 hours max) if its the same its the guage if not *FUCK*. yeh isaac i never tested it when it was new so i dont know what i started with, i just hope its the guage, my cuz's bike will tell all. its performing as good as it ever has and i still beat and keep up to everything i used to. Quote
Isaac_62 Posted June 30, 2009 Report Posted June 30, 2009 The bike will still "perform" just fine on a slightly low compression. Although once the cylinders are too big u will get piston slap and could possibly have destruction... NOt safe to let ur engine go like that... Top end rebuilds are easy and dont take long...i would say stock is at about 130.. IF it were me... i would rebuild top end b4 it ends up costing u more money cuz ya waited... Quote
dajogejr Posted June 30, 2009 Report Posted June 30, 2009 Check the gauge with your cousin's rig. Does the threaded part go all the way as far as the spark plug itself? If not, it will be a false reading (low) 45-50 hours is in fact typical. Check out the factory recommended replacement on a new 4 joke....much lower. Quote
dirtydownunder Posted June 30, 2009 Author Report Posted June 30, 2009 ah yeh, good point daj. the fitting on the tester is less than half of the plug thread (thats close to a cc) so a substancial amount of compression differance. ill check the other 08 to make me feel better, either way im close in time anyway. the cool head can wait then till i do the top end. 50 hours haha geez. Quote
blu01shee Posted June 30, 2009 Report Posted June 30, 2009 I thought 100 would be fine to but lasted for about two weeks then the piston skirt caught the exhaust port and the piston shatered but i got lucky when it did it 90% of the mess shot straight out the exhaust. That was with oem stuff. But thats just my bad luck lol Quote
blowit Posted June 30, 2009 Report Posted June 30, 2009 ah yeh, good point daj. the fitting on the tester is less than half of the plug thread (thats close to a cc) so a substancial amount of compression differance. ill check the other 08 to make me feel better, either way im close in time anyway. the cool head can wait then till i do the top end. 50 hours haha geez. I wouldn't get too cranked up about redoing the motor. With the stock cast pistons, you likely are still in tolerance and may just need rings at the worst. Yes, the adapter tip of the comp tester will cause a serious drop in comp. I would almost advise to add your domes and run it! I have seen stock motors go for many years without problems. Remember that Yamaha "wants" you to rebuild at 40-50 hrs, and of course with "their" pistons and such. B Quote
2004LEBanshee Posted June 30, 2009 Report Posted June 30, 2009 Who knows mine was 110 stock for 4 years that I rode it and it never went down and was always on of the fastest stock bikes around. If you need a top end at 40 hrs. Your dont warm your bike up right, its jeted or mixed wrong, or it was build poorly. 40hrs is nothing. my new 4 mill is at 160 for 3 years now and well over 100hrs. Quote
Ieat4strokes Posted June 30, 2009 Report Posted June 30, 2009 Who knows mine was 110 stock for 4 years that I rode it and it never went down and was always on of the fastest stock bikes around. If you need a top end at 40 hrs. Your dont warm your bike up right, its jeted or mixed wrong, or it was build poorly. 40hrs is nothing. my new 4 mill is at 160 for 3 years now and well over 100hrs. Them are the numbers I like to hear, all my frinds are saying Im gonna be less reliable etc etc, cant do this and that, we will see when i get my 4 mill together thursday, *waiting on seals* Quote
blowit Posted June 30, 2009 Report Posted June 30, 2009 Them are the numbers I like to hear, all my frinds are saying Im gonna be less reliable etc etc, cant do this and that, we will see when i get my 4 mill together thursday, *waiting on seals* I have a good friend and customer that has had the same 350 motor by us for 8 yrs and still runs perfect. Probably about 250+ hours on the motor. Build them right and warm them up right, and they can last a long time. B Quote
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