jalewood Posted December 28, 2005 Report Share Posted December 28, 2005 Hello, I'm riding an '85 TY 250, and it seems to suffer from pinging quite a lot, as well as pre-ignition. The current spark plug is an NGK B8ES, and I'm unsure whether a colder or hotter plug will remedy this, or if there's more involved. Is this fault common to this particular model?The bike is in good condition, originally being registered on the road, with 600 km. on the odometer. Thanks, Jason. Quote Link to comment Share on other sites More sharing options...
james111089 Posted December 28, 2005 Report Share Posted December 28, 2005 i would probably say a hotter plug most mdern bikes use a 5 maybe its got a colder plug in for road use so it doesnt get too hot and burn a hole in the piston James Quote Link to comment Share on other sites More sharing options...
jalewood Posted December 29, 2005 Author Report Share Posted December 29, 2005 I am trying to find out now which plug to go to.Yes, I agree I need a hotter plug.Anybody out there with a similar running problem on their TY ?Thanks mate. Quote Link to comment Share on other sites More sharing options...
kevin j Posted December 29, 2005 Report Share Posted December 29, 2005 hotter plug will increase the chance of starting preignition because the tip runs hotter. Preignition is normal combustion, started by a; hot spot, too early in the cycle. Detonation is the sudden burning of the end gas mixutre before the normal flame front gets there. Preignition off course can lead to detonation, but they are separate phenomenons. Mostly likely its detonation. I've never had a 250, but the 350 detonates badly due to combustion chamber design-toomuch squish band space that knocks badly on hot days especially. Option on the 350 are: mill the head, run without the head gasket to lower the head, richen up the pilot, use higher octane fuel. all help. I think the Chris Johnson's mods files are here somewhere, talks more about these issues. kcj Quote Link to comment Share on other sites More sharing options...
brucej Posted December 30, 2005 Report Share Posted December 30, 2005 (edited) Jalewood, the recommended plug on my 84 250 is a BR6ES NGK, I would imagine your 85 should use the same or similar. Changing the plug won't likely help your problem, though. Detonation is common on the 250s, just like it is on the 350s, for the same reasons - so kevin j's cures will work on your bike, too. Higher octane fuel helped my bike a lot, I would recommend trying that to start, then seeing if you think you need to do something more. Cheers, Bruce Edited December 30, 2005 by brucej Quote Link to comment Share on other sites More sharing options...
brucej Posted December 30, 2005 Report Share Posted December 30, 2005 (edited) I think milling the head, or removing the head gasket, to reduce pinging is a really interesting solution to this problem. It's interesting because it is the opposite of the advice often given for other engines - which is to lower compression to reduce pinging. My understanding is that lowering compression reduces pinging in many engines because it lowers the temperature in the combustion chamber, preventing end gases or hot spots from getting hot enough to self-ignite. I can't say that I completely understand why reducing the squish clearance makes the TY run better (better heat transfer from piston to head, or less fuel trapped at the outer edges of the cylinder, maybe?), but I have heard it from enough people that should know to accept it. Maybe someone with better technical knowledge than me could comment on that? My own bike has had the head milled, reducing the squish clearance from .080" to .065", and it seemed to help slightly but not cure the problem. Taking more off might work better. So what I'm wondering is this: Is reducing squish clearance in these bikes less effective than it could be because it is raising the compression, and thereby increasing the heat produced in the chamber? It shoudn't be terribly hard to mill the head to bring the squish clearance down to where it should be, and then take some material off the inside of the chamber to bring chamber volume back to stock, or maybe even larger. Has anyone tried something along these lines, or have any comments about why it should or shouldn't work? -Bruce PS Jalewood, I hope I'm not hi-jacking this thread, making it more theoretical than perhaps you were looking for. I could move it to a new thread if you want me to, just let me know. :hat: Edited December 30, 2005 by brucej Quote Link to comment Share on other sites More sharing options...
jalewood Posted December 31, 2005 Author Report Share Posted December 31, 2005 No Bruce, I'm all ears! I would like to sort the problem out and will take all advice on board.Anybody else out there with any suggestions or advice wanting to share their knowledge on the TY pinging,pre-ignition,detonation etc., feel free to drop a line. Thanks, Jason. Quote Link to comment Share on other sites More sharing options...
charliechitlins Posted December 31, 2005 Report Share Posted December 31, 2005 Milling the head or removing the gasket (I use 'fake chrome' spraypaint when doing away with gaskets) will raise compression.It's my understanding that the knocking on a TY is caused by the shape of the squish area, which causes a weird flame propagation. Raising the compression seems to help it burn a little better. I suppose a good welder/tuner could reconfigure the head to work better. Quote Link to comment Share on other sites More sharing options...
marky g Posted December 31, 2005 Report Share Posted December 31, 2005 I,ve had quite a few TY's over the years and I've never had one do it yet..even my current Pinky is sweet as. Sounds a bit OTT to have the head machined, I'd check out igntion, carb spec etc before I work the head... Quote Link to comment Share on other sites More sharing options...
brucej Posted December 31, 2005 Report Share Posted December 31, 2005 (edited) Thanks for the reply, Charlie. No doubt a good tuner would be able to sort it out without much trouble. That would be the easy way to fix it. It wouldn't satisfy my curiousity much, though. Having a good tuner explain to me what they do and why they would do it would be much better. I'll try and restate my question to make it clearer what I'm looking for: Milling the head, or removing the gasket, does two things to the combustion chamber - it reduces the squish clearance and it raises compression. These are separate factors, even though they are changed by one operation. General knowledge (by that I mean for engines in general and not for the TY in particular) states that reducing squish clearance will lessen detonation. General knowledge also states that increasing compression will worsen detonation. So, when the TY is modified by milling the head or removing the head gasket, is some of the benefit of the reduced squish clearance being cancelled out by the raised compression? If it is, that presents an opportunity. It is possible, and shoudn't even be very hard, to reduce squish clearance in the TY head without raising compression. All it would take is an additional machining operation to remove some material in the deep part of the combustion chamber, away from the squish band. This operation would restore chamber volume (and therefore compression) back to what it was before the squish clearance was reduced, and so allow the full benefits of the reduced squish clearance to be gained. This idea sounds reasonable to me, but I'm very much aware that my experience with this stuff is limited, so what I'm hoping for is some feedback on it. I could just go ahead and try it, but it would be nice to know if anyone else has tried something along these lines before carving up my head. Bruce Marky G, I didn't mean to snub you, I just took too long putting this together - you hadn't posted yet when I started. I'm curious to know if you have done anything to your bikes to help the problem or just never had a problem to start with? I do think that with good enough gasoline it would never be a concern. :hat: Edited December 31, 2005 by brucej Quote Link to comment Share on other sites More sharing options...
marky g Posted January 1, 2006 Report Share Posted January 1, 2006 Hi Brucej Sorry mate, can't be of much help, none of mine have ever done it....pretty sure all of the ones I've have (1985 to 1991 models) have been std bikes....I've used petrol / oil ratios of anything from 50/1 to 80/1 mix and std plugs. I have had detonation problems on the more highly tuned engines of modern bikes but the old Yams just keeps on running,I would try a fuel additive and check out the ignition settings first. Happy new year Quote Link to comment Share on other sites More sharing options...
charliechitlins Posted January 2, 2006 Report Share Posted January 2, 2006 I'll try and restate my question to make it clearer what I'm looking for: Milling the head, or removing the gasket, does two things to the combustion chamber - it reduces the squish clearance and it raises compression. :hat: <{POST_SNAPBACK}> Actually...it does a 3rd thing. It changes the shape of the combustion chamber, too. It is my understanding that the shape of the combustion chamber on this bike (the 350, anyway...I don't know about the 250) caused a strange flame propagation, and something like a double ignition...and one of the '2' ignitions causes a knock. So...I guess the compression change has something to do with improving the burn, but the primary problem is the actual shape of the squish area. When folks started to put high-domed "pop-up" pistons in Harleys, they found that this divided the combustion chamber in 2, and caused a similar knocking. The problem was solved by adding another sparkplug on the other side. Quote Link to comment Share on other sites More sharing options...
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