Nighty Posted June 27, 2005 Report Share Posted June 27, 2005 imo: 1 side looks ashgray meaning totally lean. -out of spec crank causing additional vibration. -plug comes lose -lose plug causes airleak == totally lean additional heat and forces on the failing side caused the big end to give up completely. i can see a cheetah engine comming for our scotisch mate Quote Link to comment Share on other sites More sharing options...
Koolguyson Posted June 28, 2005 Report Share Posted June 28, 2005 First, a plug comes loose because of detonation. A plug wont come loose unless the motor is knocking. It can happen, but is often rare for it to just back off for no reason. You banged up piston took a lot of abuse. The piston is melted and the top is beat up bad. This is caused by excessive heat. IMO you ran the motor tight, this caused the motor to detonate (that is the main piston damage on the crown) and then the pounding from the detonation caused the rod bearing to let go. Why do i think this? For one, when a bearing lets go the needle bearings smash everything, big chunks...little chunks...it all leaves big indentations. The markings on your piston are small pin pricks which is detonation. PLUS the piston is melted. This is detionation, then the crank failure. Check your squish for me. It will be tough now since that piston is so beat up. But put your head back on the motor. Tighten it up and torque it down with the head gasket on. Now take a peice of solder and stick it in your spark plug hole. have it bent so that the solder touches your cylinder wall. have the solder come to the left (or right) side of the cylinder but never front or back. Turn the motor over so that it presses the solder between the head and piston. Once you've done this take a pair of calipers (of veniers) and measure the thickness of the solder. This tells you how tight the piston to head distance is. Once you do this let me know where its set. If you need further instructions or more help PM me and ill walk you through it. I also see an EGT in your future. Long runs at WOT is tough on a motor and your jetting accuracy needs to be tripled. I do agree that your on/off mx riding will give you inaccurate plug readings. Quote Link to comment Share on other sites More sharing options...
Rare Scottish Tree Badger Posted June 28, 2005 Author Report Share Posted June 28, 2005 Thanks, Your instructions are pretty straightforward. ... Problem is that with the big end bearings now busted up, the piston isn't even getting near the top of the cylinder. What I will do is try it on the other cylinder. How come the other cylinder shows no sign of detonation? Rare. Quote Link to comment Share on other sites More sharing options...
bradrs Posted June 28, 2005 Report Share Posted June 28, 2005 Thanks, Your instructions are pretty straightforward. ... Problem is that with the big end bearings now busted up, the piston isn't even getting near the top of the cylinder. What I will do is try it on the other cylinder. How come the other cylinder shows no sign of detonation? Once detonation starts, it creates more hot spots, and causes more detonation. In addition to the other suggestions here, I would consider a few things when rebuilding: 1) Check your plug heat ranges. A plug that works fine for MX may not get enough heat out when you hammer it for a mile or more. 2) When you adjust timing, do it in smaller increments, and try to keep other things more constant. You dropped your fuel octane, and changed to a timing map with 3 more degrees of advance on the top end compared to what you had been running, and decided to go WOT for a mile all at once. Not a good combo. 3) I'd even consider running a different timing map for holding WOT for so long like that. There are instructions on how to wire in a handlebar mount switch on the dyna website, that would allow you to switch between them easily on the fly. Quote Link to comment Share on other sites More sharing options...
Rare Scottish Tree Badger Posted June 29, 2005 Author Report Share Posted June 29, 2005 Once detonation starts, it creates more hot spots, and causes more detonation. In addition to the other suggestions here, I would consider a few things when rebuilding: 1) Check your plug heat ranges. A plug that works fine for MX may not get enough heat out when you hammer it for a mile or more. 2) When you adjust timing, do it in smaller increments, and try to keep other things more constant. You dropped your fuel octane, and changed to a timing map with 3 more degrees of advance on the top end compared to what you had been running, and decided to go WOT for a mile all at once. Not a good combo. 3) I'd even consider running a different timing map for holding WOT for so long like that. There are instructions on how to wire in a handlebar mount switch on the dyna website, that would allow you to switch between them easily on the fly. 386595[/snapback] Great advice there, thanks Brad. ... Like I said earlier it was a combination of errors which I made that look so obvious when written down the way you have done so. I've spent hours trying to learn plug reading and choping, "My window into the engine's health", but still can't get it right. ... I'm disheartened, but now feel sure I understand where I'm going wrong. Rare. Quote Link to comment Share on other sites More sharing options...
. Posted June 30, 2005 Report Share Posted June 30, 2005 Just a note, your other piston was lean to and detonating. If you look at the picture it was starting to melt Quote Link to comment Share on other sites More sharing options...
Polish Posted June 30, 2005 Report Share Posted June 30, 2005 It sounds like a AIR LEAK...your head has it been milled?.........If so It was prob done wrong!! Quote Link to comment Share on other sites More sharing options...
Bansh88 Posted June 30, 2005 Report Share Posted June 30, 2005 JB weld. Fix it right up Quote Link to comment Share on other sites More sharing options...
Polish Posted June 30, 2005 Report Share Posted June 30, 2005 JB weld. Fix it right up 387390[/snapback] Hell yezza.....or maybe even epoxy Quote Link to comment Share on other sites More sharing options...
Banshee~ Posted June 30, 2005 Report Share Posted June 30, 2005 WOT for a mile ...I never hold mine WOT for over 6 seconds. Quote Link to comment Share on other sites More sharing options...
German Shepherd Posted July 1, 2005 Report Share Posted July 1, 2005 What type of gas and oil and what ration are you running? Quote Link to comment Share on other sites More sharing options...
Rare Scottish Tree Badger Posted July 1, 2005 Author Report Share Posted July 1, 2005 It sounds like a AIR LEAK...your head has it been milled?.........If so It was prob done wrong!! 387388[/snapback] Polish, If you had read the posts you would have seen that this was caused by a combination of things that did not include an air leak. ... Has my head been milled? see post #9. And no, I don't think that one of the top two 2-stroke builders in the UK "prob done wrong". Anyway, in post #11, I mentioned that the (squish) bands had been re-cut. So, if anything, there would have been more clearance there. ... You wouldn't have known this, but this head had been milled for the bike 18 months before I acquired it at the end of last year. JB weld. Fix it right up That's just bollocks! ... And you've jumped in again, Polish, with your epoxy comment. If I wasn't accross the pond in Scotland I'd show you guys where to stick your JB weld and epoxy. What type of gas and oil and what ration are you running? Post #9: "Premix: Silkolene Pro2 @ 33:1." ... "- I normally run 97 Octane, but for the first time ever I used 95. (All I could get)." ... Read the threads. ************************** Please, guys. ... If you're going to answer in one of my posts, then read the threads first. And if you think you can add a sensible comment then go ahead. But I hate to waste my time replying to comments that are just plain stupid. ... There's been some very knowledgeable heads involved in this posting of which some have turned to pm'ing instead of posting. And because of this, a vast majority of BHQ lose out on valuable, or at least useful/ interesting information. If you can't say anything constructive, then don't bother. Said my piece, Rare. Quote Link to comment Share on other sites More sharing options...
sredish Posted July 1, 2005 Report Share Posted July 1, 2005 sorry to hear of your troubles. you should be more than able to run a mile on wot as long as your jetting is setup for that. everyones pretty much covered what I'd be able to say so I'll leave it with that. Good luck on getting her fixed back up. Scott Quote Link to comment Share on other sites More sharing options...
wayfst Posted July 2, 2005 Report Share Posted July 2, 2005 Polish, If you had read the posts you would have seen that this was caused by a combination of things that did not include an air leak. ... Has my head been milled? see post #9. And no, I don't think that one of the top two 2-stroke builders in the UK "prob done wrong". Anyway, in post #11, I mentioned that the (squish) bands had been re-cut. So, if anything, there would have been more clearance there. ... You wouldn't have known this, but this head had been milled for the bike 18 months before I acquired it at the end of last year. Post #9: "Premix: Silkolene Pro2 @ 33:1." ... "- I normally run 97 Octane, but for the first time ever I used 95. (All I could get)." ... Read the threads. ************************** Please, guys. ... If you're going to answer in one of my posts, then read the threads first. And if you think you can add a sensible comment then go ahead. But I hate to waste my time replying to comments that are just plain stupid. ... There's been some very knowledgeable heads involved in this posting of which some have turned to pm'ing instead of posting. And because of this, a vast majority of BHQ lose out on valuable, or at least useful/ interesting information. If you can't say anything constructive, then don't bother. Said my piece, Rare. 387696[/snapback] gosh and i thought that scottish people where supposed to be jolly! just ribbin'ya laddie! Quote Link to comment Share on other sites More sharing options...
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