#6

[speedpro]

Got a bit of time in the shed. Collected a few MB bits, machined a head for squish and compression, and set the port open/close angles. Opened the exhaust port up but left the duct more or less the same size from 15mm in right to the pipe flange. First run on the dyno saw 20hp and after 5 runs had 23.5hp. The piston is a bit loose so a new one is going in. I also set the squish .1mm tighter than I normally do and there is just the barest evidence of the piston tapping the head so depending on time I'll either remachine the head or just shim the cylinder up .1mm.

23hp in Gary's bike which weighs more or less 70Kg, with Cricket on it, should be fun at Tokoroa.

I'm gonna freshen up my old MB cylinder and my 30hp cylinder so will have plenty of options.

Had the FZR on the track at the last meeting. Apart from being ridiculously overgeared it wasn't too bad. The motor ran faultlessly. Getting off the line at the start was a bit of a mission. With the gearing I didn't really need to change up and used 1st gear everywhere except towards the end of the straight. Running it out to 16,000rpm it was sweet. No real horsepower with the intake manifold/plenum which is made to be fed by the turbo. The cams are also timed for forced induction which I suspect is not helping.

[koba]

Got a bit of time in the shed. Collected a few MB bits, machined a head for squish and compression, and set the port open/close angles. Opened the exhaust port up but left the duct more or less the same size from 15mm in right to the pipe flange. First run on the dyno saw 20hp and after 5 runs had 23.5hp. The piston is a bit loose so a new one is going in. I also set the squish .1mm tighter than I normally do and there is just the barest evidence of the piston tapping the head so depending on time I'll either remachine the head or just shim the cylinder up .1mm.

23hp in Gary's bike which weighs more or less 70Kg, with Cricket on it, should be fun at Tokoroa.

I'm gonna freshen up my old MB cylinder and my 30hp cylinder so will have plenty of options.

Had the FZR on the track at the last meeting. Apart from being ridiculously overgeared it wasn't too bad. The motor ran faultlessly. Getting off the line at the start was a bit of a mission. With the gearing I didn't really need to change up and used 1st gear everywhere except towards the end of the straight. Running it out to 16,000rpm it was sweet. No real horsepower with the intake manifold/plenum which is made to be fed by the turbo. The cams are also timed for forced induction which I suspect is not helping.

First gear all the way, Woah!

I've left the duct standard size on mine, I'll probably continue to do so given that post.
Can I ask what kind of reed setup you have on the 23hp job?
I'm part way through a VERY short inlet with a standard block and the big single reed, it's planned as just an interim step though.

[speedpro]

The reed is of unknown origin but a substantial 6 petal type similar to the one in my 30hp cylinder. It's pretty basic with no splitter and no proper insert to transition from the carb flange to the petals. The only attempt at a transition is short extensions of the rubber carb flange into the reed block. The transfer ports are completely untouched except at the very entry to the ducts where someone has taken them out quite a bit giving the ducts a pronounced taper.
The exhaust port from about 15mm down from the piston face is untouched as far as I can tell. At the pipe flange it is slightly oval with a pronounced lip at the top, probably about 5mm at the centre. The port at the piston face is 70%ish chord width and has a shape that gives the most blowdown, though it is still deficient in that area.
On my old MB sidecar engine I used the standard reed block but cut the centre divider out and fitted a single fibre petal. That motor made a nice 19.9hp and it had major design flaws. The reed block definitely will benefit from careful shaping of the transition from carb flange to reeds. A few I've played with sounded noticeably different on the dyno and the engines were a lot cleaner at part throttle and transitioning on and off throttle.
With the reeds, because we want to rev the engines high the reeds need to be short because we want the resonant frequency to be above the operating frequency. When the reed stop is flattened out it leaves a shorter reed available to open reducing the cross-section of the reed block port. To regain the cross section required the reed block needs to be wide, hence the 6 petal reeds being used. As supplied though they are normally too long and once the free reed length is reduced it is back down towards the ideal reed cross-section.

[koba]

The reed is of unknown origin but a substantial 6 petal type similar to the one in my 30hp cylinder. It's pretty basic with no splitter and no proper insert to transition from the carb flange to the petals. The only attempt at a transition is short extensions of the rubber carb flange into the reed block. The transfer ports are completely untouched except at the very entry to the ducts where someone has taken them out quite a bit giving the ducts a pronounced taper.
The exhaust port from about 15mm down from the piston face is untouched as far as I can tell. At the pipe flange it is slightly oval with a pronounced lip at the top, probably about 5mm at the centre. The port at the piston face is 70%ish chord width and has a shape that gives the most blowdown, though it is still deficient in that area.
On my old MB sidecar engine I used the standard reed block but cut the centre divider out and fitted a single fibre petal. That motor made a nice 19.9hp and it had major design flaws. The reed block definitely will benefit from careful shaping of the transition from carb flange to reeds. A few I've played with sounded noticeably different on the dyno and the engines were a lot cleaner at part throttle and transitioning on and off throttle.
With the reeds, because we want to rev the engines high the reeds need to be short because we want the resonant frequency to be above the operating frequency. When the reed stop is flattened out it leaves a shorter reed available to open reducing the cross-section of the reed block port. To regain the cross section required the reed block needs to be wide, hence the 6 petal reeds being used. As supplied though they are normally too long and once the free reed length is reduced it is back down towards the ideal reed cross-section.

Cool, I'll have to stew on that for a bit!
I've actually been mocking all this reed stuff up on your old sidecar engine!

I've also notice the 'feel' from good inlet shaping/stuffing, it's something that is ver difficult to quantify but give a definite advantage.
It's actually a big factor in that cheaterbike argument.

[speedpro]

With a fresh KT100 piston in my short stroke bottom end with my old cylinder and head the motor seems sweet. However at the last meeting as soon as Dave gave it a bit of throttle on the track it seized. I cleaned it up but it still wasn't looking perfect so had a hone run through it just for looks and to check it was straight and true. Then fitted a new piston the same size, 52.15mm. Ran OK in the driveway during a couple of heat cycles. The kart mechanic was definite about the motor having an air leak causing it to seize so I filled the sink and dropped the motor in with 5psi pressurising it. It seemed completely airtight. Today though Dave had a repeat where it seized as soon as he went a bit hard. He'd already done a couple of good sessions where he wasn't going too slow. I haven't had it on the dyno so the tuning is a complete unknown but it runs OK and sounded OK. The plug looks good being a bit dark if anything though the inside of the header has an ever so slight hint of grey to it where typically it is light tan.

Going back to kart mechanic guy's assertion of an air leak, and looking at the pipe and mounting flange, I can see where the air/fuel charge is going to the end of the flange and slightly into the pipe and then hopefully being jammed back into the cylinder. The pipe is a reasonable fit on the flange and I assembled it with a bit of high-temp red silastic, but I wonder if that is where the air leak might be. That plug of fuel and air in the port/flange/pipe might be diluted by an airleak and be returned to the cylinder lean causing the piston to seize.

Gary's new motor is going good. I have the exhaust and transfers heights set to work with a good pipe and it has a nice intake which I've fitted my 34mm carb to. I was hoping for a bit more hp but ended up with more or less the same hp as before the freshen up, 23.5 and nice and fat. Considering the transfer ports are untouched at the cylinder I'm reasonably happy. I've found a guy who knows what he's doing who has the tiny tools needed to alter the transfers so that's next on the list after fixing Dave's bike.

You never know but I might even do a bit more work on my FZR125 over Christmas.

[F5 Dave]

Yeah mine seized twice at Ruapuna on closed throttle. I'd run out of time to leak test it but when I do find problems it is usually the intake. Bigger pilot fixed the issue for that meeting. You might just be lean there.

[speedpro]

I find it hard to believe being a bit lean at closed throttle could cause a siezure. However I am going to try a bigger pilot jet or if I can't locate a suitable size jet I'll drill one out and if I can't find one I don't mind driling I'll try a known good carb.

I'm going to test that out using the last piston which I've resurrected using a piece of 80 grit W&D paper on a piece of glass under a running tap in the sink. It's come out "looking" pretty good but as for size I don't know. The kart mechanic suggested a technique where you wipe the smeared face of the piston over the W&D with a turning/curling motion so the whole face gets sanded with each wipe.

[F5 Dave]

Mate, most seizures seem to happen on a closed throttle, lots of revs, not much gas, then you could open the throttle when it was about to nip & go super lean for a millisecond.

At Ruapuna mine seized twice going into the hairpin totally closed for some time and locked the (light under braking wheel). That's why KTM were adding an injector to richen closed throttle.

[speedpro]

Got a range of pilot jets, fitted the biggest and worked down until it was good. It seemed best with a 45, from the standard 40, but when I stripped the motor again there was ever so slight scuffs. We've settled on a 50 jet and it seems good. We ended up using that engine in Dave's bike in the races on Sunday and Cricket set a new personal best of 31.5 once he got clear and Gaz was going round and round OK as well, apart from one lap, but we won't mention that lap. Clearly the seizures were caused by going lean on the pilot jet. After sanding the piston and reassembling the motor I dynoed it at 22.7hp. Being the lazy type that I am I didn't even bother adjusting the ignition to try for a bit more. That was Dave's bike with essentially my old air cooled engine.

Gary's bike was going good on Saturday and early on Sun. We'd dynoed it at 23.5hp using Lance Morgan's old MB engine I rebuilt and made some changes to. The transfer ports at the cylinder are completely untouched so reasonably happy with that. On Sunday when Cricket was riding it there was a little problem - see photos. Most likely pre-ignition with some detonation thrown in for good measure. The plug ceramic has gone as has the earth electrode. Easily fixed, though the head won't ever be as nice without being fully machined which at the moment isn't going to happen. I've just very carefully dressed it up with the Dremel.

[koba]

Got a range of pilot jets, fitted the biggest and worked down until it was good. It seemed best with a 45, from the standard 40, but when I stripped the motor again there was ever so slight scuffs. We've settled on a 50 jet and it seems good. We ended up using that engine in Dave's bike in the races on Sunday and Cricket set a new personal best of 31.5 once he got clear and Gaz was going round and round OK as well, apart from one lap, but we won't mention that lap. Clearly the seizures were caused by going lean on the pilot jet. After sanding the piston and reassembling the motor I dynoed it at 22.7hp. Being the lazy type that I am I didn't even bother adjusting the ignition to try for a bit more. That was Dave's bike with essentially my old air cooled engine.

Gary's bike was going good on Saturday and early on Sun. We'd dynoed it at 23.5hp using Lance Morgan's old MB engine I rebuilt and made some changes to. The transfer ports at the cylinder are completely untouched so reasonably happy with that. On Sunday when Cricket was riding it there was a little problem - see photos. Most likely pre-ignition with some detonation thrown in for good measure. The plug ceramic has gone as has the earth electrode. Easily fixed, though the head won't ever be as nice without being fully machined which at the moment isn't going to happen. I've just very carefully dressed it up with the Dremel.

What piston is that?

[speedpro]

What piston is that?

KSI KT100. I've got some genuine Yamaha pistons and a single Burris. You have to be careful with squish angles and stuff when swapping brands.

[speedpro]

Funny flow lines in the combustion chamber. I don't recall seeing that sort of thing before. Any ideas? I wonder if it's something to do with the preignition.

[speedpro]

Finally got the cylinder back late this arvo. Had to sandpaper the piston to fit as the mechanic had left it tight due to the piston being 2nd hand plus it had nipped up previously. I don't know how it works but it measured bigger than it's original size. I've done it before and it worked fine using #120 on a glass plate under a running tap. It ended up with more taper than a standard new piston and just a whisker tight at the bottom of the skirt. The squish is on the limit and I'm expecting the piston to just touch the head, but only just. Will fit it tomorrow night, throw it in the van, and go to Edgecombe Sat morning.
Got nylon all over Dave's bike, not that he'll need it. Just have to keep Gary off it.

[koba]

Finally got the cylinder back late this arvo. Had to sandpaper the piston to fit as the mechanic had left it tight due to the piston being 2nd hand plus it had nipped up previously. I don't know how it works but it measured bigger than it's original size. I've done it before and it worked fine using #120 on a glass plate under a running tap. It ended up with more taper than a standard new piston and just a whisker tight at the bottom of the skirt. The squish is on the limit and I'm expecting the piston to just touch the head, but only just. Will fit it tomorrow night, throw it in the van, and go to Edgecombe Sat morning.
Got nylon all over Dave's bike, not that he'll need it. Just have to keep Gary off it.

Goody!

Can't wait!

[speedpro]

Got home today and Gaz had it assembled, tested and loaded in the van. Evidently it rattles a bit, strange that.

Dave, Gaz, and Blair are heading down tonight. Me and Cricket will go down tomorrow morning.