No exhaust leak. Found air intake leak on the rear cylinder, thought I had it sorted, but after re-seating and sealing, sounded a bit better but still getting same O2 sensor data as before. Swapping sensors makes no difference. Unplugged or cold O2 sensors give a reading of 5100mv. Front cylinder O2 sensor starts at 5000mv and drops quickly toward operating range but sticks around 900mv, rear drops voltage very slowly and sits around 2000mv. No fluctuating signal from either. Before front cyl would give a fluctuating signal as it should and the rear stayed around 2000mv. Something seriously wrong with the rear cylinder I think.

Will definitely check cam, thanks for that suggestion. My builder guy did the crankcase and cams, I assumed he would have checked this.


If that is ok I'm going to try leaning out the map again and see if that helps, (both sensors getting clogged with carbon) but the different behaviour of the rear cylinder makes me wonder if something is seriously wrong there. I'm going to have to take it to a tuner, which will be difficult, the only guy here I would trust with it has his dyno out of action, and my other guy in Auckland has no premises for a month.

Thinking about it if the cams were out the engine would not have run ok the first little bit. Whatever is wrong developed after a 100kms or so. Air intake leak made perfect sense. Must be more than one thing wrong.

If you're running aftermaket pipes, you want to check that the O2 sensors are protuding into the exhaust stream. Aftermarket pipes are pretty bad for incorrect placement, some worse than others.
Dave Barnes @ HD Cycles is probably the guy to see in Hamilton, & John McLoud @ Tipple Zee in Auckland. I maybe able to help with the TTS if you like, I'm "just up the road" in the Franklin area.

Sorry been out of action for a while - life is busy, weather is freezing and engine malfunction is driving me nuts. Thanks for helpful suggestions.

Re above - Yes repaired head was on the dodgy cylinder, will take it apart and put it back together if I can't figure this out, could be something wrong there somewhere I think. Can't do any harm, although I don't have spare gaskets and would have to recycle the existing ones and order some more. I don't have a compression checker, although can get that checked locally no problem.

Whatever is wrong, it ran fine for 100kms or so, and developed over time. Air intake leak made perfect sense. Something clogged up with carbon, rings not sealing - something like that would make sense if it could get worse with running time, not a major mechanical fault like cam out one tooth, hole in the piston, bent connecting rod etc.

Re sensor in exhaust stream, YES the rear O2 sensor socket is too deep, sensor won't be in the exhaust stream, that could explain the different behaviour of the rear cylinder O2 sensor readings. Would take longer to heat up, poor reading, carbon clogging, all makes sense. But would that really make bike run poorly at low rpm???? Front O2 sensor isn't reading right either at the moment although it did before. Getting new sensors anyway as I may have fried them with silicon or running too rich too long.

Not sure how to go about fixing the O2 sensor socket though, could grind it 3 or 4 mm but getting the sensor adequately protruding into the stream might be beyond me.

Will have a closer look.

Thanks for help guys.

Took rear cylinder totally apart, rings fine, valves fine, cylinder seals just fine. Nothing wrong with it.

Left with this O2 sensor bung problem, possibly fried O2 sensors and getting the VE map sorted out.

 

John MacLeod was supposed to do the engine build but couldn't, he has been helping me. His experience with twin cam engines is limited though and he hasnt' built any big inch builds like this. He has a proper brake dyno and 4 gas analyser.

I met Dave the other day, good guy. His dyno is out of action though.

 

Picture of sensor bung on rear pipe... not suprised it gives a bad signal.

 

Finding a machine shop is no problem, although I've had trouble before trying to convince them to work on a head or crankcase. Maybe a pipe won't faze them? 

Also these are some Vtune data graphs, in the first one the air intake leak wasn't fixed. Front sensor works fine, rear doesn't except for a little bit in the middle.  First one is about 20-30minutes worth, riding around at 80kph mostly. Second is about 5 minutes of idling.

(Purple coloured line is the front O2 sensor tracing, black the rear O2 sensor, normal operation is oscillation between 100-900mv)

Second tracing is more recent, no oscillation in either cylinder, and map leaned out about 20%.

Neither sensor oscillates (I've swapped them around several times, no difference) and both read way too high.

 

 

Is that O2 port really a problem ? Looks like the leading edge of that O2 sensor would be well into the exhaust stream.

Dunno, someone with more experience than me will surely chime in with the good oil on that one...

 

 

Ok, got that rear o2 sensor re-welded. Much better signal, warms up only a bit slower than the front sensor now, as you would expect I guess.
Bit of help from ozroder with TTS mastertune and a few good vtune runs and bike is running sweet now.

And then my rear brake caliper just fell off. Bolts must have worked loose. Nobody ever touched it before.

Anybody else ever had this happen?

Got that fixed anyway. Going to re-check all my important bolts before I take my boss for a ride. Can't have her falling off... I'd never hear the end of it...

Thanks for all your help forum guys especially ozroder.

Anybody ever needs help or advice with a build like this, send me a PM.

Good to hear you've got it sorted.