#6

[TZ350]

Gary was circulating nicely taking it easy and the bike was sounding sweet. Upped the pace a bit and a couple of laps later it nipped up exiting the hairpin. A check of the plug didn't show anything suspicious and the motor turned over smoothly. We decided to give it another go but it nipped up again in the same place. I've dismantled it and found the piston has scuffs up the intake side and the piston is now a gentle push fit in the bore. My initial thought was that the piston was faulty but after talking to Wobbly I'm now thinking that although the ignition was more or less right for top end, as determined on the dyno, there was probably too much advance in the mid range which caused detonation which has damaged the piston. If we'd just gone out and run it hard we likely wouldn't have had a problem as the motor wouldn't have spent enough time in the dangerous rev zone to cause a problem.

Sounds much like the problem we had at Taupo, where optomising the ignition advance everywhere in the rev range for WOT was a mistake, I guess we are learning all the time.

Good to see your progress, these fast strokers are starting to get sorted.

[speedpro]

I love long weekends. 3 days where I was able to visit Darren's workshop and spin up a few bits and roll up Gary's new chamber. I've machined up a proper exhaust nozzle but need to confirm the ID with Wobbly. I've also spun up an exhaust spigot and slip on piece for the pipe. The alloy is thick enough for an o-ring but in good bucket racer style I can see it being assembled with a squeeze of hi-temp red. I still need to match the spigot to Gary's cylinder but we probably won't get it back until this weekend. It'll be a sort of freehand CNC spigot.

Big thanks to Darren, for the pie and McDs as well

[speedpro]

Gary was over for a bit tonight. He fixed crash damage and I finished welding the last piece of the new pipe. I need to visit Darren and make everything as round as possible before trying to assemble the pipe onto the bike. I'll tape it all together first and then weld one piece at a time.
Got the cylinder back from the kart shop. They've made it quite a bit looser and it seems to rev a lot freer than before.
It is a bit chilly tonight but as my garage had been converted to a sleepout it is fully lined and has a low ceiling with insulation. Couple of minutes with the fan heater running and it was all cosy.
Measured the diameter of the centre section. It is a fat one at 120+mm

[speedpro]

Gary's bike survived the last meeting with some OK results but Dave's bike got rattly and then stopped whilst leading a race. Gary's pipe was looking a bit light down inside the muffler at the track. A little bit of a concern considering you can't really hold it flat out. The plug looked good though so we left it alone. Just pulled the head off to have a check and it is looking fine tuning wise with the crown of the piston a lightish tan colour to match the plug. The head needs some work but that's planned and will be done when I sort out the compression.

I've also dummied up the new pipe and it fits sweet with just one joint rotated to make it fit perfect. Hopefully Gary's pipe is reliable now and I just need to extract the horsepower.

Update on Dave's bike to come.

[Moooools]

Gary's bike survived the last meeting with some OK results but Dave's bike got rattly and then stopped whilst leading a race.

Update on Dave's bike to come.

And what a pity it was to watch him fall in front of me.

May I just point out the 4 stroke was still fastest into the first corner and was pulling up on the pesky two stroke down the straight.
Too bad the rider was able to match the bike.

[speedpro]

Both bikes were making less than 20hp so nothing flash. Both bikes had a history of seizing. Dave's bike was reassembled with a well used piston and a bore that had seen better days. I used Drano to remove aluminium from the bore and emery tape to "hone" it. The piston got the emery tape treatment as well. Dave says the plug looks dark after it stopped but earlier in the day his pipe was a light tan colour right to the end as well so it should have been light tan as well. It was making rattly noises so probably a bearing. He seems happy that it lasted 6 months or so. I have greater expectations and am pretty dismayed that it stopped. We'll do a proper rebuild then see how it lasts. The problem was that it ran OK and Dave could get round on it pretty good so he was happy, so after I got it going that was it.

Dave and Gary make any bike look better than it really is. A chat about how they are going is a real eye opener with talk of deliberately hauling on front brakes till the front sledges, deliberately, and it being OK as long as you already have a knee on the ground.

[koba]

. A chat about how they are going is a real eye opener with talk of deliberately hauling on front brakes till the front sledges, deliberately, and it being OK as long as you already have a knee on the ground.

Is that not normal?

[Moooools]

Dave and Gary make any bike look better than it really is. A chat about how they are going is a real eye opener with talk of deliberately hauling on front brakes till the front sledges, deliberately, and it being OK as long as you already have a knee on the ground.

I'm sorry mate but that sounds like a dig at my riding. Which I will take offense to. However I would appreciate it if you clarified on what you actually meant. Do you mean to say that I am block passing them too late into the corner? Or that I am trying to scare the shit out of them?
I don't recall doing anything intentionally dodgy.

Do tell. They had plenty of opportunity to tell me this at the track, and I am not sour about taking first hand advice.

[husaberg]

I'm sorry mate but that sounds like a dig at my riding. Which I will take offense to. However I would appreciate it if you clarified on what you actually meant. Do you mean to say that I am block passing them too late into the corner? Or that I am trying to scare the shit out of them?
I don't recall doing anything intentionally dodgy.

Do tell. They had plenty of opportunity to tell me this at the track, and I am not sour about taking first hand advice.

Are i reading the same text as you cause i don't see any digs there.

[Moooools]

Would you care to explain what he is meaning then?

I may be wrong here. Hasn't been the best off days.

[sidwyz]

Would you care to explain what he is meaning then?

I may be wrong here. Hasn't been the best off days.

Mike is referring to there riding skills (purposfully losing the front but keeping it) being "above average"

don't worry mate nothing to do with your riding.

[Moooools]

Oh shit.

Apologies.
It makes sense now that you explain it. Got a bit ahead of myself there.

No doubt they are extremely talented riders. Dave had absolutely no trouble with passing me back. Could have done it in his sleep.

[Buckets4Me]

Oh shit.

Apologies.
It makes sense now that you explain it. Got a bit ahead of myself there.

No doubt they are extremely talented riders. Dave had absolutely no trouble with passing me back. Could have done it in his sleep.

Dave has had a history of sliding the frount of borrowed bike till he can get the power on and lifting the frount wheel off the ground thereby stoping the front sliding
and garys bike was I belive built to finish of old rs125 pistons (or so the story went)

both are nice guys to race with ( leave me plenty of room when passing)

[speedpro]

Well I've been real busy. Rebuilt Dave's engine with new main bearings. The original 30 year old one on the ignition side was a bit past it's "use by date". Found a good crack in the original 30 year old piston as well so took it out to 1st oversize and fitted a new (old) piston I had lying around. I still haven't done anything to make it faster. The transfers are still completely stock and the exhaust port is probably stock width but someone has squared it up a bit. Given time I'll have a look at it.

Gary's new pipe is finished and has come out OK. I had a quick check inside after one meeting on the new piston. Again it has been trying to pick up on the face below the exhaust port and also in 2 places in the intake side. At .003" clearance it's a bit surprising especially considering that tuning wise it looks close to perfect. I've run a bit of emery tape over the rub marks on the piston and chucked it all back together. Apart from the pipe it's the same as before. Both motors need the squish tightened up about .1-.2mm but the heads have to be located more precisely before that.

Looking forward to this weekend racing.

[koba]

Both motors need the squish tightened up about .1-.2mm but the heads have to be located more precisely before that.

I've worried a bit about the location of my head. (on the bike!) Do you dowel them or something?