Ove Posted July 10, 2016 Posted July 10, 2016 Hi, I bought my dragster 125 about 8 months ago not runing with the intention of bobbing it as my first bike project. I managed to get the engine runing breafly but not test driven as I had not done my cbt and the bike was not road worthy. But the engine was running well so I started restoring the bike, 8 months of a lot of hard work and looking forward to riding it this summer. I finally finished the bike the day before the mot and managed to get a couple of test runs out of her and all seemd good. The mot went excellent not one bad thing said. Glowing in fact. On the way back from the mot was where it all started to go wrong. there was a bit of rattling from the clutch case and taping but I haven't much experience on motorbikes. Then I loose power and the bike struggles to get up to 30mph. I thought I had run out of petrol so I filed up at a station and then I realise I was on reserve. So thought I must have dirtied the carb. Since then I have had side case off only to find rust behind fly wheel which I have cleaned that must have been the rattling. I have checked valve gaps and cleaned carb. Now the bike turnes over but won't fire up. I'm getting a spark. I'm getting fuel through. I also think there could be low compresion from the front cylinder but can't confirm that till the compresion test kit turnes up this week. I'm really fearing the worst and this bike has had a lot of time money and effort in it and only got to ride it once.
slice Posted July 11, 2016 Posted July 11, 2016 Sorry to hear about your problems Ove, but there's only one way to find out what's happening and that's to take it apart, pain in the arse I know but sometimes it's just best to bite the bullet. Do your compression test first to see if that's what's wrong and if it is then out with the spanners mate. As for the rust behind the flywheel? it has to have come from somewhere so your going to have to have a look inside to see where it's come from. Good luck and hope it turn out to be something small !
Ove Posted July 11, 2016 Author Posted July 11, 2016 I'm not going to touch it now till I can do the compression test. If it is the Pistons it's looking like it's going to get very expensive. Any suggestion how this could be fixed cheaper. I have a baby on the way and this project is getting harder to fund Gutted.
slice Posted July 12, 2016 Posted July 12, 2016 Well first don't borrow trouble, it might not be anything major, you could keep a lookout for a 2nd user motor on evilbay or some such. But if it is what you think it might be then only buy what you need not what you would like, sounds trite I know but sometimes folks think they have to buy new or a complete set of something when really all they need is a single part, if your bike was for racing for instance you might need matched pistons but as it's not, a single piston from any source will do for now till your a bit more flush, say 30 years from now when your kids have left home. my youngest is still here and he's 23 FFS! Build it on the cheap, get parts when you see them hunt round local boot sales if you have to. Where are you in the world? someone might be nearby and willing to help out with some advice or even wield some spanners. Best of luck mate.
Ove Posted July 12, 2016 Author Posted July 12, 2016 Cheers bud. I'm from Brighton. Ok well I will leave the compresion issue and cam chain for the moment as this I defiantly know is a problem. I have done test with tea spoon of oil and finger over plug and defiantly better on front cylinder. But I can check again properly when the compression kit turns up. Prior to me riding her to the mot it was starting on the button and ticking over lovely. Obviously compression issues and cam chain would not have got this bad on a one mile journey. I also lost power on way home so Since getting her back I have checked valve gaps and adjusted. Now the bike will not start turns over and wants to start but doesn't until I run battery out. I'm getting spark although the front is brighter than the back. I have also had the fuel tube off the carb and turned engine over and it's coming out. Any more checks I can do. Thank you for the help. Ian
Ove Posted July 13, 2016 Author Posted July 13, 2016 As parts are very expensive for the xvs 125 and vary limited is this engine used in any other bikes. Maybe I could search for a cam chain. Piston and rings. For another bike. I'm finding lots for the xv 125, 250 and xvs 250. Are these the same
slice Posted July 13, 2016 Posted July 13, 2016 I don't know but others on here might, what you could do is nip down to your local Yam shop and ask around in the workshop if they can help out, what's the worst they can say after all? If not your local one then try further out till someone is willing to talk to you. Have what info you can find from the net with you, that way you can explain what your talking about rather than looking demented waving your arms about trying to describe what your on about, these guys are practical and like to see the info in front of them and it gives them something to point at !!! 1
Ove Posted July 13, 2016 Author Posted July 13, 2016 Yeah I will prob pop in to wemoto and get them to cross reference there part codes as they have done that before when I couldn't find a petcock. They looked to see if the part apeared on another bike. As far as my reasurch is going I believe that the xv 125, 250, sach roadster, xvs 125 and 250 share the same engine just the Pistons are bigger on the 250s.
slice Posted July 14, 2016 Posted July 14, 2016 There you go already off to a running start mate, stick with it.
Ove Posted July 14, 2016 Author Posted July 14, 2016 Running start I feel like I have all ready done a couple of marathons lol. Ok I have done a compression test. The front and back should be 12 kg/cm2. The front is 5 and with oil 6 and the rear is 5.5 and with oil 6. Surly with the oil it should be up to the 12
Moderator Cynic Posted July 14, 2016 Moderator Posted July 14, 2016 Ok, comp is down. Do you know the mileage, the oil making little difference suggests its not piston related. Also the fact you have 2 cylinder heads makes cracks or bad gaskets unlikely again because the values are similar on 2 separate elements. And the big plus, no smoke. That to me says look at the top end (valve gear) for the compression loss, could you be out on your valve adjusting propping valves?, or maybe a valve failure somehow?, but again on both cyl. Could the rattle have been cam chain?, bad tensioner maybe?, if that chain jumped a tooth or just whipped due to the slack affecting timing slightly and you bumped some valves that would do it? I may be wrong, but that's my logic and where I would start. 1
Ove Posted July 14, 2016 Author Posted July 14, 2016 I will try to answer all the questions. Millage - 39905 the front cam chain is loose but not loose enough I think to jump tooth yet. I have had the tentioner out and it's working fine I believe, screws in then springs out nicely. The noise I believe coming from the front cylinder was like a sewing machine that's why I checked the clearances and they were to big so adjusted them. And have checked twice more. But will do again as I want to double check tdc. I also had rattling from the clutch case so had that off as well. There was lots of rust in the oil which was from the back of the fly wheel. That's been all cleaned. I think that was he rattle from there. So how do I do a valve test. I wish I could get her started too. At least I could test her then. When I checked the spark plug the front was bright yellow and the rear was a weak blue. As I have to change the manifold, it split in me keep taking the carb off. Which is hear and a rebuild kit for the carb so will check all the conections on the bike at the same time. Do you know where the framed earths are on this bike?
robbo 167 Posted July 15, 2016 Posted July 15, 2016 Hi New on here but have been lurking for a while..just finished my dragstar 125 bobber and its going well..as you are having trouble thought I would offer a shoulder to cry on,all the above advice is good..compression is down but they are pretty even..check cam timing?..rust on flywheel could be a red herring?..my money is on camchain jump but have been wrong before. I'm not far from you..got manual,got tools,if I can help let me know. Cheers
Ove Posted July 16, 2016 Author Posted July 16, 2016 So should compression be 12 for both cylinders or combined and why would cam chain jumping loose compresion? Whe I bought the bike I was told it was running on one cylinder but the guy didn't really have a clue about the bike. So I took the gamble. I did manage to ride my bike up and down the road the day before the mot and it seems to be running fine lots of power. Why would this suddenly go and loose power on the way back from mot if the guy I bought it off was oviously having this trouble before. Which were talking he had it working years ago. I'm a bit confused now. And not sure what to do next. And thank you robo that is much apreciated. I'm still learning and a very sharp learning curve on this bike, also the fact that I really haven't heard or rode this bike when it's running right isn't helping much as its all gues work, reasurch and forums. I do have the service manual but that's a bit vague some times lol. Maybe it would help having some one look at her that knows this bike a lot better than me. And for my moral as all I want to do now is go out and ride her. It's a very expensive paper weight at the moment.
slice Posted July 16, 2016 Posted July 16, 2016 Take the heads off then fill them (turn the head upside down with valves facing up) with petrol and if it leaks through you have your problem sorted, if they leak then you can lap the valves in and remove some of the coke build up to get a better seat. YouTube is full of vids that tell you how to regrind your valves and it should only take a few hours. From what I've heard yours is not an interference engine ie the valves and piston never fill the same space so you should not have a bent valve stem to worry about.
Ove Posted July 16, 2016 Author Posted July 16, 2016 Thank you I will check my valves out when I do my cam chain. do you know if my cylinders should be a combined 12. Or each cylinder should be? It's not clear in the service Manual.
slice Posted July 16, 2016 Posted July 16, 2016 This is just a guess mind but I mostly believe that if it's below 100 psi then it's in need of work 150 to 175 psi is usually about what you should expect from most 4 stroke engines. It will run with less than 100psi but will run poorly.
robbo 167 Posted July 17, 2016 Posted July 17, 2016 Hi Time has proved to be too tight this weekend...happy to come over one weekday evening this week to lay a fresh set of eyes on this....just let me know if thats any help?. Out of interest..was this the bike advertised in Worthing a little while back as a non runner that the owner(and his garage apparently) couldnt get to the bottom of ?..... 1
Ove Posted July 17, 2016 Author Posted July 17, 2016 Yes this is that bike. It don't look anything like it did when I bought it now though.
Ove Posted July 18, 2016 Author Posted July 18, 2016 Here's a bit of an up date but not much. Cleaned all the conections. Coils etc. Checked pipes again and replaced manifold. put back together. And still nothing. It sounds like it wants to start but just doesn't. Is there anything more I can try before I start delving into the cylinders. As that's going to start getting expensive quickly. Urgh and it's really good weather for a ride too. I still can't find an earth from the battery to the frame. But if it needed one why would it start before without one.
Recommended Posts