rransome Posted January 12, 2007 Report Share Posted January 12, 2007 Hello I have a 1991 Fantic 309 which had the throttle stuck open during a crash, when i finaly got it to stop it wouldnt start again. After many hours of trying i deceided to take it to bits and find out what was wrong, I found that it had snapped a piston ring, scrapped the cylinder and wrecked the piston. I had the barrel re-bored and plated and purchased a replacement piston. After re-building the engine and fitting it back into the bike it was finaly time to see if it would run, To my supprise it did second kick and away we went, But !!!!! it runs like a three legged dog. It wont idle correctly picking up revs on its own untill you have to switch it off. won't settle after opening the throttle. Does this sound like an air leak iv purchased a new gasket kit and crank seal set but just wonderd if anybody had any advice on what to change first before i started to strip down the engine for a second time. Thanks for any advice givern. Russ. Quote Link to comment Share on other sites More sharing options...
lee harris Posted January 12, 2007 Report Share Posted January 12, 2007 The crank is wrecked Quote Link to comment Share on other sites More sharing options...
rransome Posted January 12, 2007 Author Report Share Posted January 12, 2007 That seems a bit drastic how do you mean wrecked as in new seals and bearings or as in throw it away and forget it. Quote Link to comment Share on other sites More sharing options...
blocky Posted January 12, 2007 Report Share Posted January 12, 2007 I think what Lee is getting at is that there may have been some damage to the crankcases and/or crankshaft. A small amount of metal such as a broken piston ring can do when it drops down into the lower part of the engine. Remember that piston is moving so fast at top revs that it becomes invisible. Did you completely strip the engine or just the top end? If not you'll need to do even if its just to check for damage. Look out for signs of impact in the crankcases and pieces of piston ring embadded into the alloy. I remember going to look at a second hand Beta and the engine jaming flat out when the owner demonstrated the bike to me. I can tell you I backed off pretty damn quickly when things began to clang. Needless to say I didn't buy it. Quote Link to comment Share on other sites More sharing options...
rransome Posted January 12, 2007 Author Report Share Posted January 12, 2007 (edited) OHHH i see No i only stripped the top end down and Bill Pye had a very quick look at the whole engine he said there was no movement when it was at TDC so i left it but i think that as you say it may be time to strip it down tO the bare bones and just find out what realy is in there. Cheers Edited January 12, 2007 by rransome Quote Link to comment Share on other sites More sharing options...
lee harris Posted January 12, 2007 Report Share Posted January 12, 2007 Soory I woz short with my answer, I was catching a plane. If you can imagine 6000-7000 rpm and then a sudden piston seizer, you can expect the big end to have a flat spot. The main seals are unlikely to be visualbly damaged but such an engine will never perform the way fantic built it after such a seize. I think it is advisable to strip. 0.02mm on the crank pin is enough to make it run rough and only experienced people can "feel" that. If the crank is still oily, which it will be if not stripped. even these peole wont feel it either. It will run like a dog thjough lee Quote Link to comment Share on other sites More sharing options...
rransome Posted January 12, 2007 Author Report Share Posted January 12, 2007 Looks like iv got my self a busy weekend, how big a job am i looking at, im prety handy with the spanners but never done a complete strip down before is there anything to be carefull of i mean like hugh spring that might pop out and slit my wrists. Quote Link to comment Share on other sites More sharing options...
lee harris Posted January 12, 2007 Report Share Posted January 12, 2007 Soory I woz short with my answer, I was catching a plane. If you can imagine 6000-7000 rpm and then a sudden piston seizer, you can expect the big end to have a flat spot. The main seals are unlikely to be visualbly damaged but such an engine will never perform the way fantic built it after such a seize. I think it is advisable to strip. 0.02mm on the crank pin is enough to make it run rough and only experienced people can "feel" that. If the crank is still oily, which it will be if not stripped. even these peole wont feel it either. It will run like a dog thjough To put it anougther way, if you want to keep the bike, be prepared to change the mains and big end? If you want to sell it, you might just split the cases to remove the bits! lee Quote Link to comment Share on other sites More sharing options...
rransome Posted January 12, 2007 Author Report Share Posted January 12, 2007 (edited) Thanks very much for the advice i now know where to start which makes it easier, Ill strip it down and have a poke about i think i will replace the parts as its in mint condition ill let you all know how i get on and ill post some pictures of anything i find of interest Edited January 12, 2007 by rransome Quote Link to comment Share on other sites More sharing options...
ask greeves Posted January 12, 2007 Report Share Posted January 12, 2007 (edited) I personally would try changing the oilseals, especially the left one, behind the primary gears, it's a double lip seal, just remove gearchange lever, take off cover, undo nut take off gear, take off flywheel, undo 3 bolts holding the seal carrier change seal and o rings. Edited January 12, 2007 by ask greeves Quote Link to comment Share on other sites More sharing options...
martinm Posted January 12, 2007 Report Share Posted January 12, 2007 After re-building the engine and fitting it back into the bike it was finaly time to see if it would run, To my supprise it did second kick and away we went, But !!!!! it runs like a three legged dog. It wont idle correctly picking up revs on its own untill you have to switch it off. won't settle after opening the throttle. Cant think how a flat spot in the crank pin would cause the motor to rev up on its own ! Would go with Ask greeves suggestion of damaged flywheel side crank seal, only other suggestion, have you checked the reed valves for damage ?? Good luck Martin Quote Link to comment Share on other sites More sharing options...
rransome Posted January 13, 2007 Author Report Share Posted January 13, 2007 Iv had the reed valve out and looked and it seems to be be all ok, The other think i was wondering about was on the carb there was a little plastic tube with a hole in it that went from one side to the other but its missing now, Im guessing it was to direct excess fuel but could that be contributing to my problem. The carb is a dellortto phbl 26 i think. Quote Link to comment Share on other sites More sharing options...
ask greeves Posted January 13, 2007 Report Share Posted January 13, 2007 (edited) Do you read the replies rransome, seems your only alternative then is to have a complete bottom end rebuild. Seems to me you've got very little idea what your doing. your engine is 'Hunting' this is an engineers technical term for your symptons. I'll mention it again..change your main bearing oil seals. Would be interesting to know how exactly you managed to stop the engine. Did you put a stick down the carb, or turn the petrol off and just wait for it to stop, or get your best mate to take off the plug cap, throw mud into the carb, immerse it in the nearest river or did you get a sections ends stake and kill it like you would a vampire. As for plastic tube, it will work with it off, if put on make sure there's a hole in it. Edited January 13, 2007 by ask greeves Quote Link to comment Share on other sites More sharing options...
lee harris Posted January 13, 2007 Report Share Posted January 13, 2007 Come on pete, be a bit nicer, he does ride fantic! The placcy tube does nothing- Sometimes there aRE TWO AND THEY LET AIR INTO THE CARB: iF THERE IS ONE; I E: THEY CARB TUBES ARE CONNECTED TOGETHER; THE HOLE LETS THE AIR IN THERE CAPS LOCK Quote Link to comment Share on other sites More sharing options...
rransome Posted January 13, 2007 Author Report Share Posted January 13, 2007 Certainly do read the replies Mr Greeves. Its been 8 years since this little accident and i have on several occasions tried everything that people have suggested with no luck. So forgive me for being a bit un-sure, as you say i dont realy know what im doing and i have got to the stage where i dont know if i have made it worse. I have never actualy enterd a trial yet and as for stopping the bike as far as i can remenber i held the kill switch for dear life, and stalled it against a tree. Ill say again I am very gratefull for any advice, i have purchased a complete new gasket set and oil seal set, I have taken the engine out of the bike and started to strip it down i am going to change avery seal and gasket that i can get my hands on and then i may with a lot of luck finaly get to ride the bike again. please keep posting as i intend to make it work if its the last thing i do. Quote Link to comment Share on other sites More sharing options...
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.