roberto Posted July 11, 2008 Report Share Posted July 11, 2008 The only other thiung I can think of would be improper tolerances in the piston/cyclinder and like I said before, a bad plug/low octane gas causing premature detonation which should be looked at ASAP. Does the bike have a thermostat?? Could it be stuck closed?? Let us know finally what the story is. This is why I love twin shock!!!!!!!!!!! Quote Link to comment Share on other sites More sharing options...
ham2 Posted July 12, 2008 Author Report Share Posted July 12, 2008 (edited) The only other thiung I can think of would be improper tolerances in the piston/cyclinder and like I said before, a bad plug/low octane gas causing premature detonation which should be looked at ASAP. Does the bike have a thermostat?? Could it be stuck closed?? Let us know finally what the story is. This is why I love twin shock!!!!!!!!!!! The fan cycles in and out very regularly.....I'll keep you posted. P.S. I had a montesa 242 once..never again..! Edited July 12, 2008 by HAM2 Quote Link to comment Share on other sites More sharing options...
peterb Posted July 12, 2008 Report Share Posted July 12, 2008 Hi copemech, I just read your question - "The strobe check would be good. As I recall, they should fire somewhere around 20-25 degrees BTC and show some advance with revs. A noteable change from this, say at only 10 degree BTC would be a good indication of a problem there related to the ignition actually functioning on the slow side of what it is supposed to be doing." I haven't related the timing to degrees before, always in mm BTDC, say 2.8 or 3.0mm BTDC, mark the rotor for TDC and rotate motor backwards for marking the timing mark. The angular rotation is not a linear representation of the stroke so I can not relate the degree advance - well, I could do if I set up the marks and used one of the old "Castrol" degree discs in the shed. Anyway, this doesn't help HAM2 right now. Did you check to see if the needle area was all ok? Everything in it's right place. You may just have a faulty ign module, try a friends one. You mentioned emigrating - not coming over here by chance? Bye, PeterB. Quote Link to comment Share on other sites More sharing options...
ham2 Posted July 12, 2008 Author Report Share Posted July 12, 2008 Hi PeterB, Checked the needle ...all seems to be in order. Good call,the faulty ignition module is looking like a distinct possibility Don't panic the emigration thing was referring to my brother,he's moved to Melbourne (just an advanced raiding party!) and left me way too many loose ends to tie up on his behalf. Spanner time scheduled for this Friday........... Quote Link to comment Share on other sites More sharing options...
jse Posted July 12, 2008 Report Share Posted July 12, 2008 Hi PeterB,Checked the needle ...all seems to be in order. Good call,the faulty ignition module is looking like a distinct possibility Spanner time scheduled for this Friday........... Although it could be an unrelated, coincidential electrical or jetting problem, based on what you've checked so far, I'd probably back up to the last known proceedure that could produce the symptoms, that being the rebuild (assuming no pre-existing problems before) and maybe look at case sealing issues, specifically in the manifold/crankcase-to-transmission areas. I'd start with re-checking all the case capscrews, which can be done without dis-assembling the engine (always try the simple things first) and, if necessary, a leak-down test should be next. A leak-down test is standard operating proceedure upon assembly of any high-level racing two-stroke. Just a thought. Jon Quote Link to comment Share on other sites More sharing options...
ham2 Posted July 12, 2008 Author Report Share Posted July 12, 2008 Cheers Jon, I like your way of thinking and any procedure that avoids an engine removal is a good idea. I would have thought if I had a case-leak I would experience a poor/unstable idle( my idle is good)??Just a thought..a thought that won't really stop me looking for a leak. Thanks again...keep the ideas flowing,looks like I've got quite a few things to check. Wayne Quote Link to comment Share on other sites More sharing options...
copemech Posted July 13, 2008 Report Share Posted July 13, 2008 (edited) Leak-down test? Which leg does it leak down Jon? Do you have the stuff for that? I don't! I would have to build block off plates and adapters, Ha! Edited July 13, 2008 by copemech Quote Link to comment Share on other sites More sharing options...
jse Posted July 13, 2008 Report Share Posted July 13, 2008 Leak-down test? Which leg does it leak down Jon?Do you have the stuff for that? I don't! I would have to build block off plates and adapters, Ha! Actually, a simple kit could be made of expanding plugs (like block expansion plugs for auto blocks) for the exhaust port and a plate for the manifold, a low-pressure gauge (say, 0-15 psi) a couple of fittings and a small tire pump. You can then pressurize the internals to about 5-8 psi and then use soapy water to check for leaks. You could add a small shut-off valve and then see how long it takes for the pressure to drop. Kinda of a lot of trouble, but if you do your own work, it's a cheap tool that can tell you a great deal of information. The left leg seems to take the worst of it......... Jon, sometimes leaky, but usually not cranky. Quote Link to comment Share on other sites More sharing options...
men8ifr Posted July 22, 2008 Report Share Posted July 22, 2008 (edited) Maybe your compression is way out after the rebuild due to different piston rings and base gaskets? A compression test is quick and easy to do and the gauges cheap - also use it in the future to determine when your rings are wearing which will affect performance, often the user does not notice as it is gradual. If the compression is too high it can cause pinking/knock/engine damage. The only time pinking will generate significant heat in the engine is when it is close to destruction! i.e. the engine is auto-igniting (igniting the mixture far too early before the spark fires) which can lead to erosion of the piston, rings and cylinder damage. This will also lead to loss of performance/power though when this occurrs it's usually too late as damage has occurred.. Remove the pipe and plug, shine a light down the plughole and inspect the piston - any signs of erosion in the centre or at the edges? any shiny silver patches where detonation has worn away the carbon coating? Any silver specks on the spark plug (signs of aluminuim piston erosion). A small inspection mirror will help you see all of the piston. Check for severe scrape marks on the part of the side of the piston you can see as well an engine running that hot with a close tolerance piston/cylinder may have partially seized. Oil getting into the air/fuel can cause an engine to detonate. A faulty ECU or connection to it may not be altering spark timing as revs rise this could cause all the symptioms you describe as could ignition timing being out or a coolant problem. I hope it's none of these and/or your engine is still fine mechanically... Edited July 22, 2008 by men8ifr Quote Link to comment Share on other sites More sharing options...
ham2 Posted July 22, 2008 Author Report Share Posted July 22, 2008 Thanks for your input men8ifr, I have drained the gearbox ready for further inspection and I've had to throw a blanket over the bike and concentrate on something else....my motor...the dreaded nissan cam-chain stretch ....to be continued Quote Link to comment Share on other sites More sharing options...
ham2 Posted March 1, 2009 Author Report Share Posted March 1, 2009 Update time....Foot's nearly healed so I've been looking at the bike in anticipation: After replacing the main seals with viton and changing the water pump seals just for the hell of it (too much down-time on my hands!), I think I'm on to something now. If I had a small hairline-crack (whahey )in the weld at the top of my radiator, would that cause the bike to overheat because it couldn't hold pressure? There is a very ,very small bead of water appearing in one spot every time I try my bike out on the drive . So small, that when I shut the bike off, it evaporates in minutes . I can only spot it when I run the bike without the fuel tank on??? Does anyone know how to do a ''home pressure-test'' or where can I buy some of that aerosol spray you use to highlight welding/brazing cracks? Any answers appreciated. Wayne Quote Link to comment Share on other sites More sharing options...
totalshell Posted March 1, 2009 Report Share Posted March 1, 2009 dont mess about with a pressure test get some rad weld and job done.. if your tight chuck an egg in that'll do ( i did all bar two stages on the circuit of ireland way back when with two large eggs in the rad and coca cola in the clutch...) Quote Link to comment Share on other sites More sharing options...
copemech Posted March 2, 2009 Report Share Posted March 2, 2009 Did you ever check the quantity of atf that came out? As it was suspect due to the seals. I don't think the thing with the rad would set things off unless you lost a lot of coolant nad does not explain smoke from exhaust. I do not quite know how one would run a pressure ck on it , as I have no adapter for the cap. Guess one could remove it and just use the hose ends to pressure it up. There may be some type of pressure rating on that cap, measured in bar or something, not quite sure how that works out relative to PSI or such. You would likely have to do the conversion. Quote Link to comment Share on other sites More sharing options...
sherpa325 Posted March 2, 2009 Report Share Posted March 2, 2009 Hi, before I went too much further pulling apart the engine I would check to see if the crankshaft is bent. I know this sounds silly but if you have split the cases it is not too difficult to bend the crank either getting it apart or putting it back together. Take the plug out and the magneto cover off and rotate the motor - checking to see if the flywheel is running true, not wobbling up and down { should really use a dial indicator}. If the crank is bent the motor will run fine for a period of time - after awhile the main bearings start getting hot! and the crank seals will stop sealing as they lose their elasticity creating problems similar to those you have mentioned. This is an easy check to perform, and by the way I hope this is not the problem as you will have to split the cases to fix the crank. Cheers and good luck Greg Quote Link to comment Share on other sites More sharing options...
ham2 Posted March 2, 2009 Author Report Share Posted March 2, 2009 (edited) dont mess about with a pressure test get some rad weld and job done.. if your tight chuck an egg in that'll do ( i did all bar two stages on the circuit of ireland way back when with two large eggs in the rad and coca cola in the clutch...) Man! Even Ray Mears couldn't have come up with such an excellent survival tip for those long distance trials..problem is, if it were me I wouldn't have been able to resist the smell of those poached eggs so I would have consumed the lot..cola and all. I once saw a prison chain-gang documentary where two fellas put rice in a car radiator to stop leaks...or was that a Laurel and Hardy film??? Eeeh,my memory?What am I like? Back to the real world...the bike's had many ,many hours of practice (post re-build) before it got hot at a trial,there was nothing wrong with the nitrile seals I took out recently..just thought I'd put some viton in to be totally sure that wasn't the problem. The fix??....anyone used this before..seems too good to be true...LINKY... watch the demo Edited March 2, 2009 by HAM2 Quote Link to comment Share on other sites More sharing options...
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