#6

[pete376403]

Thinking about this - I've just done a valve grind on a 40 year old bike (GS1100G) and as far as I can tell its the first time the head has been off. Last time the engne was run was in 2009. So thats 14-15 years that the valve springs have been compressed without change, some more than others. All of the springs measured within a millimetre or two of specified length. Same goes for clutch springs. Maybe suspensions springs are lower grade steel?

[speedpro]

Possibly lower grade steel, given the operational requirements. Compressing a spring to the yield point will be well beyond normal operational limits. It might even coil bind before it gives. I'm going to heat it. I know that works although I'm still to actually use the spring I shortened to see if it packs down in use.

[speedpro]

I went out looking for Threebond sealant. The local Repco were helpful but didn't have any "1215", which is the typical sealant I think. I drove up the road to Partmaster and a guy working there used to work for ThreeBond in Australia. After a bit of a chat he told me that "1215" is not rated for use in contact with gasoline. Obviously a problem for 2-strokes and possibly the cause of the air leak which caused the latest siezure as I used it to attach the reed cage and adaptor to the cylinder. The stuff to use instead is ThreeBond "1104 NEO PLUS" which is rated for use in contact with gasoline. The data sheet says it can be used on the flange surfaces of fuel pumps which is pretty definite. The good thing is that it's lots cheaper than "1215".

[speedpro]

I've finished getting the MB/FZR rebuilt after it nipped up at Edgecumbe. I fired it up and it is super crisp with throttle. A little dyno time is scheduled to make sure it's all good.

I've also shortened a stock R6 spring to reduce the preload when it's fitted to the shock. Standard it's compressed about 10mm when fitted. This spring results in only about 1mm preload. It'll be interesting to see how these shocks work and what the difference is with the 7kg/mm cutdown spring on the shock in the MB/FZR. I'll fit the shock to my turbo twin tomorrow. The MB/FZR suspension feels pretty good. There seems to be a nice balance between front and back.

[speedpro]

It hasn't been working out how I hoped. The engine did a soft seize on the dyno, barely any throttle and lowish revs. I ran it again afterwards as I wasn't sure what happened. It seemed OK afterwards but I pulled it down anyway to have a look and found rub marks both sides of the boost port. I fixed the piston with a sheet of 1200 W&D on a piece of glass. The cylinder was fixed by running a reasonably coarse hone down it. With other maintenance I found water in the tank. This was probably from being left outside in the pouring rain for a few days. I suspect water got through the keyhole in the fuel cap. The gearbox oil was also looking suspect so the gearbox has been flushed with kerosene and has full synthetic 4T motorcycle engine oil in it. The chain rubbed on the R6 shock absorber remote reservoir. I moved the engine to the left about 3mm which was not too hard to do with how I have it mounted in the chassis, and to be honest this probably resulted in better sprocket alignment. I have machined 6 washers 2.5mm thick which I will weld to the inside of the rear sprocket to space the sprocket out a bit as well. I've thought about the washers a bit more after making them and will probably make larger diameter ones, weld them on, and then machine where they protrude on the inner diameter. Unusual for me but I'm not feeling confident about the engine. The rear end feels much better with the R6 shock and the modified 7kg/mm spring

[F5 Dave]

Up one on the pilot to be safer starting point.

Diesel is great for water put of gearbox.

[speedpro]

The bike ended up running reasonably well. 1st qualifying was a cautious affair and 2nd qual was getting after it a bit. Cricket qualified in 10th which was reasonable. The bike was actually running pretty good. The suspension was working well enough that we didn't make any adjustments. Cricket was getting his knee down here and there where previously he hasn't, plus, where he had been standing on the pegs to let the bike move around he didn't have to now. Not being an expert but to me the tyres were looking OK as well. He got a good start and ran at a reasonable pace for the whole race. The bike ran great from start to finish. Placed 6th at the end. Due to a previous problem we were very cautious with the amount of fuel. VERY very cautious with 4L or so remaining at the end.

Short video from the start of the race for about 5 minutes, looking back, making reasonable 2-stroke sounds. It highlights just how tractable this engine is with Cricket short-shifting through the double lefts at the back of the track and then pulling clean to the right up the hill - https://youtu.be/0woduTFN90A?si=0WZZK8Sxkr3fCd7t

[speedpro]

Blast from the past with a much younger Jato and his brother Peter. Both those bikes I suspect would be competitive even today. Both certainly fast enough to keep everyone honest.

[speedpro]

Getting the air bubbles out was a problem. A three man job.

[F5 Dave]

Blast from the past with a much younger Jato and his brother Peter. Both those bikes I suspect would be competitive even today. Both certainly fast enough to keep everyone honest.

Gyro (Gary) pictured to the right in those hideousbut long served white and green leathers. .

I borrowed Peter's bike at Tauramanui and found it was very rideable, but a bit lowslung on 17s. Actually the bars were flighty. I did some reversible mods like ace bars and RS muffler when I took it to the BOB in chch. . . and fell off.
But it did promote the sale to a local who rode it there for quite a while. Lost touch with Bren, once a poster here.

[Kickaha]

I took it to the BOB in chch. . . and fell off.
But it did promote the sale to a local who rode it there for quite a while. Lost touch with Bren, once a poster here.

Didn't you fall off everything at every BOB ?

I think Bren still has it, that's the bike called Joe ?

[F5 Dave]

I stayed on my 50 every visit.

. . . Well, except that time it snowed. In 27 years, never raced on a snowy track till then.

Yeah Joe he called it for some reason.

[speedpro]

The Sunday racing at Tokoroa was close to perfect. I rode the MB/FZR which went really well. It was hard work tooling around in B grade. Nothing like a bit of bucket racing to remind you how old you are. I'm still a bit sore. Without really knowing what I was doing I dropped the high speed compression damping 2 clicks after the first ride. The bike was really harsh. I dropped it 2 more and it seemed a bit better. I dropped the low speed 2 clicks as well but figure that could be reduced a bit more as well. Cricket rode it how it was originally in the GP and had no complaints. The suspension wasn't playing up, it simply wasn't all that compliant. I have a reasonably soft spring fitted and very little preload so I figure the harshness is due to the damping, which is no surprise to me as it's an R6 shock. I want to organise a day playing at the track and really play with the damping so I can understand it better.

Anyway, a big thank you to the organizers for an excellent day.

[speedpro]

Had a very interesting and long conversation about turbos and other important things. While discussing compressor maps and how even the tiny turbo I have can't be operating efficiently, a silly comment was made about bleeding off intake air to allow the compressor to run up into it's efficient zone. The compressor might get more efficient but overall system efficiency would probably remain about the same. The idea would be to disable the wastegate in the closed position and control manifold pressure by bleeding it off. I doubt the turbo would overspeed. Possibly, with the turbocharger operating closer to it's efficient range, the charge temp might drop. Something like an external wastegate(blow off valve) on the intake would be worth trying. One benefit might also be that the turbo would spool up faster given that all the exhaust gas would be going through the turbine all the time with no bleed from a creeping wastegate, although I currently have that more or less sorted out with the increased wastegate base pressure and the ECU controlled valve to the actuator.