peteg Posted December 26, 2007 Report Share Posted December 26, 2007 Hi I have just bought a TY175 to restore, fully stripped and now i'm scared, will it ever run again? Time is the great healer... There are a few things i'm not sure about but the biggest query is why does it have 2 plugs, 1 coil and 1 HT lead? It's an older orange one if that helps? Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted December 26, 2007 Report Share Posted December 26, 2007 May have been a scottish works bike that they fitted two plygs to? More likely a filler for a decompression valve peeps used to fit, nothing to worry about on an old shed. Quote Link to comment Share on other sites More sharing options...
andy m Posted December 26, 2007 Report Share Posted December 26, 2007 Some 70s 2 strokes had another plug fitted, I remember Suzuki TS and Kawasaki KE models had them. Idea was if you oiled a plug just change it over. A period thing, nothing to worry about. There was a blank plug like a drain plug fitted if you did not want a spare plug. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted December 27, 2007 Report Share Posted December 27, 2007 Hi I have just bought a TY175 to restore, fully stripped and now i'm scared, will it ever run again? Time is the great healer... There are a few things i'm not sure about but the biggest query is why does it have 2 plugs, 1 coil and 1 HT lead? It's an older orange one if that helps? Ah the fun of buying a bike in pieces! A standard TY175 head has only one plug hole and there is no place to fit a second plug or decompressor. Your TY175 probably has a head from some other model Yamaha. There are lots of interchangable parts between Yamaha bikes of the same era as the TY175. Having a different head may not be a problem. You may have a few other non-TY175 components so if you want to know, I suggest you start off by checking a few things; Have a look at the number cast into the barrel between the bottom two fins on the right hand side. It should be 52500 if it is TY175. Have a look at the engine number stamped into the top of the right side engine casing. It should start with 525 or 1N4 if it is TY175. Have a good look at a brochure photos of TY175s and post a photo on the forum of anything you are not sure about. Quote Link to comment Share on other sites More sharing options...
peteg Posted January 8, 2008 Author Report Share Posted January 8, 2008 Thanks for all the help, a local derbyshire dealer confirmed it is probably a Scottish trial bike and would have been fitted in case there was aproblem with a plug going down, simply switch the HT lead, i'm enjoying the project, I appreciate it may be an old shed but we can all buy modern bikes I have a few myself this makes good enjoyment at limited costa Quote Link to comment Share on other sites More sharing options...
kevin j Posted January 9, 2008 Report Share Posted January 9, 2008 The two plug theory had a couple reasons, both somewhat based on misconceptions, so both likely marketing or hype that was never used: 1. hot pug in one spot, cold plug in the other spot, in attempt to not have detonation at high loads and speeds. Road engines. Wrong, a hot plug causes detonation because it heats up from combustion, not because it is firing. So it still caused detonation. 2. One plug fouls, switch to the other. Somewhat true, it could help, but often if one fouled it is because mixture of fuel or oil is off and the byproducts fouled the plug, or the ignition is weak and can no longer fire the plug. The other plug in the head has the same mixture and carbon, the fouling is byproduct of combustion, not really related to if plug is firing or not. Possibly being in different places in the swirling mixture might mean one plug fouled and the other didn't, but I wouldn't bet on it. Big aircraft piston engines had/have two plugs, two complete ingitions sometimes, partly for redundancy and safety, partly because the combusiton chambers were so big, and supercharging so heavy, that the combustion needed to start from two places to burn faster and prevent detonation under heavy load. The flame path is simply too long with one plug, the heating up of the charge puts it into detonation. Soem aftermarket heads had two plug places so could be used on two models with different exhausts. Whichever port was accessible was used. Or the compression release of course. kcj Quote Link to comment Share on other sites More sharing options...
sutty Posted January 9, 2008 Report Share Posted January 9, 2008 probable what you have is a dt 125 or 175 cyl head .on the early 70,s dt,s they were fitted as std can be hand if your plug fluffs up hope this helps Quote Link to comment Share on other sites More sharing options...
matty Posted January 10, 2008 Report Share Posted January 10, 2008 Is this what you have seen only a couple with twin spark plugs. Good luck with the re-build. Matt.. Quote Link to comment Share on other sites More sharing options...
feetupfun Posted January 14, 2008 Report Share Posted January 14, 2008 The head on the bike in the photo from the France Trial Classic website looks like a DT175 head. Quote Link to comment Share on other sites More sharing options...
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