#6

[bucketracer]

Interesting looking setup for the radiator, thinking of a water cooled 100 ourselves, just for shits and giggles mind....

[speedpro]

Did a few laps at Mt Wgtn today, between rain storms.
New piston in freshly bored cylinder with the full-on port job, water-cooled head, short stroke crank and big reed valve plus all the rest. Took it very easy for a start. My nice temp gauge doesn't work when the engine is running. Pretty sure it doesn't like the ignition. Felt OK off-pipe, reasonably driveable, but a bit flat further up. Followed by the oh-my-god hit as it all came to life. This engine is a screamer. The couple of times I gave it the revs into the back straight it just revved on and on. The old motor had to be shifted up just before the left into the infield but not this one and I could use that lower gear right round to the hairpin. At a guess I'd say it pulling something like 14,000rpm with no sign of fading out. I only ran the old 32mm round slide Mikuni as the 34mm carb needs a bit of sorting. This'll probably come back to haunt me but it seems to make a bit of power, maybe it's just the transition from off-on power though. Pulling into the pits and killing the motor brought the temp gauge back to life. It read "HI" meaning it was over it's 70deg C max but immediately dropped to 69.9 so I figure it's running at about 70+ deg, just a tad high. Will check all that out on the dyno some time.

[speedpro]

Being the cautious type, I pulled the motor apart to have a quick check. I found the cylinder had a few very shiny patches and a few areas that almost looked like the piston was maybe just starting to pick up.
I took it to the local very friendly kart shop (Alpha karts) to get someone who is familiar with cylinders running KT100 pistons and which had been finished with a cork hone to have a look. As I said, very friendly kart shop, they fitted a new ring into the cylinder and we had a good look at it with a light behind. I'm pretty pissed off as there was a definite section where light could be seen between the ring and the bore. The cylinder is not round. The shiny patches are how it is supposed to be. With a cork hone finish the cylinder ends up with a very fine honing pattern. Once run it ends up being a mirror finish. Kart shop guy was heading out so he took the cylinder to his engine guru. Still awaiting feedback but it should be fixable. I'm just a bit worried about the tiny bits where it looked to be picking up.

[speedpro]

I'm going to stick with the standard Yamaha KT piston and ring till everything is sorted. Once I'm happy I might swap to these new rings that the guy showed me. They have a tiny titanium face and have less tension on the bore = less friction, but because of the material they are made of they don't flex and still seal. Have to use the right piston as well but they are supposed to be worth useful horsepower.

[speedpro]

Got it all back, straight, round, and not tapered. Alpha kart's engine guy has honed it with a more normal 240ish grit hone and it's now out to 52.2mm(ish) bore with a 52.15 piston. I got a 52.15 ring (stupid) but the gap is too big in the 52.2 bore. A minute with the calculator says the gap will be fine with the 52.2 ring the kart shop guys suggested (smart) or maybe even a 52.25 ring.
These KT pistons and rings are great. So many sizes and the prices are great compared to regular bike stuff, plus you can walk into any kart shop and buy off the shelf any size you want. Piston and ring is $118.
I'm going to run in the engine a bit harder this time as well as there was a thought that it may not have been worked hard enough at the start.
The other change which is a biggy for me is I'm changing oil. Currently on Motul 800 which is a great oil and has given me no problems at 40:1 in various motors. I'm going to give Elf 909 HTX a go. It looks like it may be beneficial in a really high revving engine. The high revving kart engines like it but at 20:1 you have to wonder.
I asked nicely and the wife will be picking up the ring tomorrow. One of the few shops I won't have to worry about her grabbing a few extra things.

[F5 Dave]

Misunderstood the instruction & she heads past the jeweler & scores that eternity ring that she claims she's been waiting an eternity for. (that's a double).

[Buckets4Me]

Misunderstood the instruction & she heads past the jeweler & scores that eternity ring that she claims she's been waiting an eternity for. (that's a double).

snap i was going to ask if Michel Hill had kart rings

well shell get the next best thing for ya
and some matching earings

[speedpro]

got all the bits and dummied it up. The squish clearance was a bit tight so measured the paper gasket and decided what size base gasket was needed to get the clearance right. Darren (Morgan Engineering) gave me a bit of stainess sheet the right size which I roughed out using his gear. Spent a bit of time getting it right and assembled it all again to find I'd just wasted a few hours as the clearance was now .1-.2mm on the high side. Darren had also given me a sheet of .1mm aluminium so I cut 3 more base gaskets from that and added one to the paper gasket and reassembled it again. Now it is spot on. Whilst messing round also made sure that the head was pulling down tight in the barrel. I had a thought that it might not be as the o-ring is a real tight fit. Measurement of the squish, with and without the o-ring, shows no differences so I suppose it's all good. Should have it all together properly tomorrow. The head isn't located as accurately as I'd like on the cylinder. It can move about a bit before tightening with the result that the squish can be a bit tight on one side and a bit loose on the other. Only +-.1mm or so but . . .
Looking forward to getting it out on the track.
Scored another bucket as well, lets call it #3. Just got to sort the new rear sprocket. My boy seems sort of keen so I need to arrange some gear for him, and Darren's daughter may be having a ride as well. Got the bits I needed to sort it from Total Motorcycles including a decent size sheet of fibreglass for reed valves if someone needs some made.

[speedpro]

Fired it up last night and if anything it seems even crisper than before. Only problem is I can only find one spark plug which is the fouled one from the MB5 so it won't pull a load without problems. Looks like I'm going to be forced to buy a new plug after I don't know how many years. My eyes are good after a couple of operations as well so I'm really looking forward to this weekend.

Does anyone have a sprocket for a MB5 I can borrow this weekend, please?

[speedpro]

Took it to the track today. Ran it in fairly hard for me. With the B8 plug and not thrashing it came out near perfect. Put a B9 in and thrashed for a session and that looks fine also. Checked it out and it is all looking good. Couple of streaks above the ports but running a finger over it you can't feel anything. The photos are as it was when I took the top off. Clean as a whistle with a sheen of oil. The o-ring looks "worn" but actually is fine.
I don't think it's actually making much power. It revs good, but not much power.

[Rick 52]

Looks good ..

[TZ350]

Checked it out and it is all looking good............
I don't think it's actually making much power. It revs good, but not much power.

It does look good............"not making much power".........I hear its a rocket ship...

[speedpro]

Damn, that confirms what I was thinking, I'm slow

[speedpro]

As that Gary bloke said in his song years ago -
"It's good to be back"

The motor is a screamer. It definitely needs to be in the right gear and even in the straight if I changed a bit soon I had to wait for it to pick up. Doing it all right though it makes good progress. Just need to get it on the dyno and optimise the tuning plus I want to try the 34mm carb before Taupo. An ignitech ignition will be a useful addition I think to pick the power up off peak.

[F5 Dave]

would you look at the size of that exhaust port!