markshelley Posted December 16, 2008 Report Share Posted December 16, 2008 I am going to do a precationary top end rebuild on my new TY80 as there is a very sligth top end rattle. Presumably it will be pretty much the same as the one I done to my FS1E about 32 years ago! Are there any things I need to look out for? If it has been rebored will it normally be stamped on the barrel to say what size? I will be doing piston, rings, little end, gudgeon pin and circlips. Anything I have missed? How long does it need to be run in for? Quote Link to comment Share on other sites More sharing options...
stork955 Posted December 16, 2008 Report Share Posted December 16, 2008 Gday, oversize pistons are usually marked so on the crown. Look for scoring/damage to the bore, deep stuff that you can feel with your fingernail will need reboring. Make sure you clean everything properly, including gasket surfaces. Check the reeds are closing properly while you are there. It would pay to get the exhaust cleaned, there are many methods all documented around in here. It would pay to have your piston and bore measured properly if there is an existing rattle, your local engine rebuilding place should be able to help here and possibly with the exhaust cleaning as well. Run it in at no more than 3/4 throttle with varied engine speeds for an hour or so. The initial ride should be easy with a burst or 4 of high gear/almost wide open throttle to load the rings up and help them seat. (Not too much of this!) Look at the aircleaner also, very cheap from Yamaha. It would be a shame to rebuild the engine and use a less then ordinary filter with that. HTH, Cheers, Stork. Quote Link to comment Share on other sites More sharing options...
markshelley Posted December 17, 2008 Author Report Share Posted December 17, 2008 (edited) I whipped off the head today and the marking on the piston crown were (as you sit on the bike) the arrow pointing to the front, a letter g on the left hand side and the letters 25 on the bottom. Looking at available piston sizes I assume this means it is 0.25mm oversize.? The bore is in perfect condition. Am I ok just doing the little end bearing with piston pin and circlips or MUST I do rings also? Edited December 17, 2008 by MarkShelley Quote Link to comment Share on other sites More sharing options...
zippy Posted December 17, 2008 Report Share Posted December 17, 2008 You are already there, it so much easier to do rings now than to tear it apart later and spend money on the gaskets all over again. Quote Link to comment Share on other sites More sharing options...
stork955 Posted December 17, 2008 Report Share Posted December 17, 2008 Gday, get it measured while its apart, as Zippy says, its easier to check that out properly now than have to do it again later on. Even if the bore looks perfect it may not be, and of course the piston can wear as well. Do it once and properly and you can sleep easy then! Cheers, Stork. Quote Link to comment Share on other sites More sharing options...
markshelley Posted December 18, 2008 Author Report Share Posted December 18, 2008 I have a horrible feeling my top end rebuild may become a bit more extensive! I took the barrel and piston out today and there is lots of lateral (left to right, as you sit on the bike) movement of the con rod. It is very wobbly. Surely that is not right? I am guessing you are all going to tell me my big end is shot and probably the crank as well. Quote Link to comment Share on other sites More sharing options...
stork955 Posted December 19, 2008 Report Share Posted December 19, 2008 Stick a 20 thou feeler gauge in beside the rod. If it wont fit in you are OK. If it does keep going until you find one that wont go in. Much more than 25 thou is too much. Feel the bearing - is it rough? (wind the crank over while holding load on the rod in an up and down fashion) If not - good. See how this goes. Cheers, Stork Quote Link to comment Share on other sites More sharing options...
markshelley Posted December 19, 2008 Author Report Share Posted December 19, 2008 Thanks for that advice. I will try it this evening, but my guess is that it will be way over 25 thou as it must be waggling 5-10mm at the little end end. I have a CD manual in the post and I am thinking I may have a go at fixing it myself. Is it a very difficult job to split the engine and change the big end bearing? Are any special tools required? Does anything else need to be done at the same time? I have already decided that if I do the bottom end I am going to have a 0.5mm rebore and new piston kit. May as well go the whole way! Quote Link to comment Share on other sites More sharing options...
grahamjayzee Posted December 19, 2008 Report Share Posted December 19, 2008 Hi Mark, Sorry to hear about the issues on your TY. In itself, the actual act of changing mains and big ends is not difficult. However, deciding what size shells to fit is slightly more tricky. I have done this on an FZ750 road bike and you have to use things such as 'plastistrips' that you crush between the journal and the crankpin to determine the amount of wear on both so the correct sized shells can be fitted. Also, if the big end has been worn for a while, there is a chance the crankpin will be slightly oval. This will require a 'regrind'. I'd be half tempted to talk to a decent motor engineer about getting them to fit the big end shells, or recondition the crank. Good Luck Quote Link to comment Share on other sites More sharing options...
markshelley Posted December 19, 2008 Author Report Share Posted December 19, 2008 I have posted this problem on another forum (for RG/RGV Suzukis, as I have one of them also) and one of the guys says that lateral movement is not necessarily an indication that anything is wrong. He suggested checking up and down movement perpendicular to the crankshaft. I actually done this yesterday and there did not SEEM to be any movement in that direction, but the rocking from side to side was so great I just can`t believe it is OK. It almost feels like the conrod has a universal joint connection to the crankshaft! Quote Link to comment Share on other sites More sharing options...
grahamjayzee Posted December 19, 2008 Report Share Posted December 19, 2008 Side to side movement is no problem, but it can only rock if there is clearance in the big end bearing. If it's just sliding along the crankpin, there's no major problem, but ifyou can move the little end 5-10mm from side to side without the big end moving side to side, there has to be big end wear... Quote Link to comment Share on other sites More sharing options...
markshelley Posted December 19, 2008 Author Report Share Posted December 19, 2008 I am going to pop the bike to the mechanic I use for him to examine it tomorrow hopefully. I will let you know what he reckons. Quote Link to comment Share on other sites More sharing options...
jon v8 Posted December 19, 2008 Report Share Posted December 19, 2008 I ended up doing a total rebuild on my sons TY80 a while ago,my advice is to get one who knows to tell you what needs doing - and do it.The other thing is that I spent over Quote Link to comment Share on other sites More sharing options...
stork955 Posted December 19, 2008 Report Share Posted December 19, 2008 Gday, these little singles use a pressed up crankshaft and fitting a new big end is not the job for a home repairer. They are pressed together and aligned in a jig and then trued using dial gauges. Its tricky but most bike shops will do it for you for not too much money. That is if it needs replacing, check the rod side clearance as mentioned before and check for roughness. Too much side clearance means the thrust washers are wearing and this will lead to a rod failure which you dont want. If all of that is OK no need to worry! HTH, Cheers, Stork. Quote Link to comment Share on other sites More sharing options...
markshelley Posted December 22, 2008 Author Report Share Posted December 22, 2008 My mechanic confirmed my suspicions and I have left it with him to sort out. He told me a bout the crank being pressed together. I should get it back a couple of weeks into the New Year. Quote Link to comment Share on other sites More sharing options...
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