Rare Scottish Tree Badger

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.

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Ok, I've taken it apart a bit and taken a few pics (4): * * * * The big end rod bearing has failed and both rings are siezed in their grooves. ... The damaged side of the head is the same color as the top of the piston; it just looks darker in the pic. So what failed first? ... Does that look like detonation, or has the big end bearing failed and the piston's been mashing against the head and the shock's loosened the plug? Or did it 'lean-out' on that side's carb, cause detonation, loosened the plug, and then bearing failure? Or even the advanced timing was enough to fail the bearing. BTW, this was an out of spec crank from an RZ that I took the risk on. I think I bring my own bad luck sometimes! Does everything look fine on the good side? All I do know is that this is going to be damned expensive to fix! Rare.

I don't know? ... The bands were re-cut after the last piston failure. What do you mean by "... a good place to start"? And what am I measuring? ... Sorry, but this 2-stroke stuff has been a fast learning curve for me, and I'm only just touching on port timings and head design. Rare.

Nope! ... I break it enough with only me riding it! Rare.

I think that says it all. My set-up: Std. Mikuni carbs with K&N filter and pre-filter, lid removed. ... 300 mains, 25 pilots, 1.25 out on air screws, needle on #5 (richest). Premix: Silkolene Pro2 @ 33:1. The head is milled to 20cc and the barrels have MX porting (bored 1mm). ... Wiseco Prolites. ... Fresh rebuild showed 148psi @ 660ft. I've only just fitted the DynaFS recently and had jetted up from 270 to compensate for improved ignition and proposed timing advance. ... I ran the bike on the stock curve last w/e on an MX track for about 6 x 15 min sessions with no problems and plugs looked fine. (Rich if anything ... Dark chocolate porcelain and black base ring). Yesterday I wanted to try the advanced curves, so went to the track, (cruised back-roads for 3 miles to get there), and did one 15 min session on the stock curve, and the second on curve number one. ... After a 20 min break I checked the plugs and headed back, low speed to the road for 1/4 mile. Still on curve 1, but this time had it pinned all the way for the mile or so of fast road. I think I've caused this failure from a combination of errors: - I normally run 97 Octane, but for the first time ever I used 95. (All I could get). ... If I'd remembered about this, maybe I wouldn't have been so hard on the bike yesterday! - Curve #1 on the Dyna does continue to increase the timing in the upper RPMs as wayfst pointed out. - Not sure about this one? - My carbs are too small for this set-up to run top gear WOT for extended periods and 'leaned out' under too long running. (Drained the bowls - Is that "leaning out" ). But the bike would have died??? Ultimiately, I think I was jetted too low in the mains, and the plug colors were disguised from the MX type of running and not showing WOT running. I'll take it apart later, but expect to see more signs of detonation. Rare.

Nope. ... MX maybe (IMHO). ... Or bling show-bikes. Rare.

BOLLOCKS!!!!!!!!!!!!! Here we go again. ......... Man, that's not even 7 hours on this rebuild! I can't afford this. ... But there's just nothing to replace that buzz of mid-gear, WOT powerband hit and pull. And then you knock it up a gear and go through it all again! ... I refuse to give up. Long story short: Same right cylinder, long WOT run over about a mile, came off the gas to slow down, and the right side started to rumble. About 3 or 4 seconds before this, there was just a split second stumble, but it came back strong (I think). ... Still turns over (by hand), hear clicking, and the plug's covered in little bits of alloy. (I guess piston ). The plug was also loose. ... Just like the last time. 'cos I'd just checked and tightened the plugs. (From two 15 min. MX track sessions). I'll get tore into it tomorrow, 'cos I went for beer tonight. Rare.

Go over what Shee-Male said above. If it was me, I'd do a compression check to rule out a ring problem, (good for a fresh rebuild reference anyway). I'd pay good attention to the plugs. ... They're probably choked up from the rebuild and long idling from the heat cycle if your low running settings are on the rich side. But you said two weeks later ( ) it cleared after "a lot more gas" so they might be ok. ... Put some fresh plugs in anyway and get it warmed up good and before long do some running in the lower end of the power band to clear out the cases. It takes a decent amount of RPMs to get the oil lifted into suspenssion from the bottom of the case. Should be good to go after that. Why the rebuild? ... Time for it, or a failure? Rare.

... Next we'll have a He-Shee signing in for abuse. Rare.

Might just be excess oil from the rebuild that's been lying in the bottom of the case and is now getting burnt away. Rare.

I bet it was!!!! Catch that dude and pin every stolen Banshee on him! Rare.

I agree with you about mods accentuating borderline situations, but still believe that advanced timing burns more mixture. ... However, there's more to overcoming this than just jetting up. (As this only richens up the same amount of mixture). Very difficult to put down on here, but I guess you know what I mean. I jetted up 3 sizes to cover the advance of the dyna (I was a little lean anyway), but have only put a few hours on the ignition at the stock curve (no advance). So it's not surprising I've been showing a little on the rich side just now. (No problems tho' - perhaps a slight bog just below the powerband, but I've moved to a 15 tooth front sprocket from a 14 so it's a bit of both there). ... Tomorrow I hope to get a few hours on the advanced curves and see how Shee goes and keep a good eye on the plugs. Rare.

Sand is not good in a carb. Something's blocked or partially blocked in there. Is the fuel tank vent clear? I would take both the pilots and the main jets out and use the compressed air again. A sudden lack of fuel will cause the revs to increase before dying. Rare.

Did you clean the carbs out one at a time, so as not to mix up parts? ... Also, the base plates for the needles have to be in the correct way around (holes lined up so as not to cause a vacuum). ... Choke tube back on between the carbs? Rare.

Scott, I hear what you're saying about air/ fuel ratio going into the motor. I assumed that the point of advancing the timing is to allow a longer burn time for the mixture and to therefore increase performance. The instructions that came with my DynaFS suggested that rejetting "may" be required "to supply more fuel to maximize performance gains". ... "The stock curve is least likely to require any sort of jetting adjustment. Using the other curves may result in a lean misfire condition at high RPMs when the jetting is not properly set". Does this back up my 'assumption', or do you have other theories? Rare.

... It's taken nearly 30 pages for this thread to get interesting. (IMO). Rare.

Could be a head gasket leak to the water jacket. Was the head torqued down correctly and re-torqued after heat cycles. ... A compression check will help to confirm or dismiss this. Rare.

I notice you didn't ask NYUK. ... I guess John's with the church of 'bla bla'. I think I've joined him after reading these posts over the last few months. FYI, I was brought up 'Church of England' ... I go once a year at Christmas. (Plus weddings, funerals, etc.) Rare.

But your screen name suggests you might see anything you want too! j/k Still no forum! ... LEEEEEEEEEEEEEEEEEEEEEEEEEEEEE. Rare.

That sounds like a recipe for disaster. ... Assuming a piston has let go. ... If the rod bearings (and crank bearings) haven't allready been contaminated with parts from the piston, they sure will from trying to tow-start it. There would also be a risk of busting something through the case. Head and cylinders need to come off. Rare.

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Have you lost all the oil in the tranny and seized something? ... Footpeg, gear changer, side cover and front sprocket off. Clean aroud the gear lever seal and the seal behind the sprocket. re-fill with tranny oil and see where the leak is. ... You can use some kind of silicone for a temp. fix. But you'll need to tip the bike up and make sure it's really dry where the leak is. Did you do it while landing a backflip? Rare.

... With the silencers removed! Rare.