atocp Posted July 2, 2009 Share Posted July 2, 2009 Hi there, I finally got my yb100 running for the first time since i got it 2 years ago. It ran for about 4 seconds, and was the proudest moment of my week. Now the problems: I took the original head cylinder off and replaced it because someone had drilled out the spark plug threads and inserted a brass fixing to take the spark plug. No doubt a replacement for stripped threads. But it isn't tight, and air leaks out past the spark plug and brass fitting, even after a good helping of instant gasket. Is instant gasket usable in this way or is there a better method? The used replacement cylinder head wasn't an exact fit, and the metal gasket doesn't make a proper seal. So when it was started today, the exhaust came out between the cylinder and head. Should I add something onto the metal on each side to create a better seal? Or replace the seal? It was new just a few months ago and hasn't seen any running till today. The other problem is I broke the kick start leg. Snapped through the metal with a great big kick. On the upside, I have a replacement kicker and thats been fixed. 1 out of 3 aint bad for me!! If i need to replace the cylinder head, its gonna cost me about £66 at a yamaha dealer. And although im gonna go to a scrappies tomorrow, if i need to pay 66 quid, its gonna be night night for this motorcycle project for now! If anyone can help with any fixes to either of the first two problems, it would be an amazing help. Getting it started today was like a milestone, even though it was only for 4 seconds. And to get this far and have to give up seems such a disappointment. Thank you in advance for any help or suggestions, cheers, atocp Link to comment Share on other sites More sharing options...
atocp Posted July 6, 2009 Author Share Posted July 6, 2009 Hi there, Anybody got any ideas how i could seal the old cylinder head where the spark plug goes in? Or can i use instant gasket where the cylinder head and block join (including the metal gasket)? Thanks again for any ideas or advice atocp Link to comment Share on other sites More sharing options...
JimR Posted July 6, 2009 Share Posted July 6, 2009 Hi there, Anybody got any ideas how i could seal the old cylinder head where the spark plug goes in? Or can i use instant gasket where the cylinder head and block join (including the metal gasket)? Thanks again for any ideas or advice atocp Hi atocp, are you sure that the cylinder studs are not striped or worn ? the would make you think you have the head tight enough but as your post suggests it is not ! If you have a brass insert fitted to the head make sure it's screwed up tight (they were poor tbh) then dot punch it to the head from the combustion chamber side (assuming it was fitted correctly) in order to stop it undoing. So check the studs & nuts ... fit a new head gaskit/studs/nuts and torque the head down to the specs. with regard to instant gaskit I would suggest it will not suffer the extreme heat of a cylinder. The replacement Head ... why didn't it fit correctly ? Regards Jim Link to comment Share on other sites More sharing options...
atocp Posted July 8, 2009 Author Share Posted July 8, 2009 Hi atocp, are you sure that the cylinder studs are not striped or worn ? the would make you think you have the head tight enough but as your post suggests it is not ! If you have a brass insert fitted to the head make sure it's screwed up tight (they were poor tbh) then dot punch it to the head from the combustion chamber side (assuming it was fitted correctly) in order to stop it undoing. So check the studs & nuts ... fit a new head gaskit/studs/nuts and torque the head down to the specs. with regard to instant gaskit I would suggest it will not suffer the extreme heat of a cylinder. The replacement Head ... why didn't it fit correctly ? Regards Jim Hi Jim, Thanks for the response on the cylinder. The studs aren't that great to be honest, and the nuts are pretty rubbish as well. But I was sure it was screwed in tight enough. The replacement head had its stud holes slightly closer to the block. So when i put on the nuts, I had to add in an extra 2 nuts to every stud so the top ones hit the threads. Imagine the studs being too long by an inch, so the threads don't catch. The brass insert appears to be homemade, because it's off centre, and the threads aren't properly made. So not only did the air come out between brass and head, but also spark plug and brass insert. As per your advice, I'm going to try and get new studs, as I'd imagine they are relatively cheap. Although to use with the new head means some good old bodging. Thank you once again for the advice and help, cheers atocp Link to comment Share on other sites More sharing options...
JimR Posted July 8, 2009 Share Posted July 8, 2009 Hi Jim, Thanks for the response on the cylinder. The studs aren't that great to be honest, and the nuts are pretty rubbish as well. But I was sure it was screwed in tight enough. The replacement head had its stud holes slightly closer to the block. So when i put on the nuts, I had to add in an extra 2 nuts to every stud so the top ones hit the threads. Imagine the studs being too long by an inch, so the threads don't catch. The brass insert appears to be homemade, because it's off centre, and the threads aren't properly made. So not only did the air come out between brass and head, but also spark plug and brass insert. As per your advice, I'm going to try and get new studs, as I'd imagine they are relatively cheap. Although to use with the new head means some good old bodging. Thank you once again for the advice and help, cheers atocp Hi Atocp, the brass inserts were used in the early 70's until helicoil kits became common place .. some people continued to use the insert as to a degree lest precision was needed to fit one (no drill required just a tap) but its thread may be knacked . with the head you have bought it could be one of a few things ... I guess you had to bend (open up) the studs for the head to fit which may indicate the head is from a different year model YB or a YG or even more bizzare an FS (the latter 2 being smaller size motors but of the same family). The studs you have are worn out and need new ones perhaps Yamaha part number 90116-06026 is what you need to order dependant on year the 26 may need to 30 or so but from memory the part no stated should fit. Regards Jim Link to comment Share on other sites More sharing options...
Moderator mervin Posted July 12, 2009 Moderator Share Posted July 12, 2009 is the head warped at all, take a sheet of glasss and some emery paper/wetndry and rub the head on it in a fugure of eight motion and look to see if the head mating surface is flat. if it is not too seriously out you should be able to flatten it like that Merv Link to comment Share on other sites More sharing options...
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