Will I get my 100 ready in time for Taupo?

[F5 Dave]

Well a fairly ignominious start. Bit cold blooded, didn't want to idle. Gentle practise laps, didn't like off closed throttle. Pilot must be too small now. Decide to keep away from that range if I can & will change. Lap 2 it feels like it nips when I have the clutch in changing gear, so i don't let it out.

back in the pits, engine rotates fine, plug & top of piston look fine. Wonder if it did seize? Pilot jet is possibly blocked, but change 30 to a 50 to be safe. Needle from leanest clip to mid & go from a 300 to a 310mj.

Starts up easy as. Warms up well & idles. Lap 2 Siezes. Apart & the ring is not smeared but there is ally on the bore.

Clean up best I can but after an hour of sanding (in between racing the 50) I can still only get the piston to go up & down in its normal position. If I rotate the piston 15* it is sticky. The bore should be round so orientation shouldn't matter. Clearly it is not round. So I got the bore done last week, but I had also ground a little of the spigots. perhaps that relieved the stresses & it took a new set.

So I can't say if the seizure caused the issue & it was just a little lean (ign had been retarded from where I used to run it & the piston top looked new + the ring didn't smear over so its not real excessive heat). -Or that it was not round & was a bit doomed as soon as it got some real running heat in it. But that seems most likely.

Still better than this happening in the SI BOB. Apart from that it ran ok it not imediatelty super powerful (I wasn't thrashing it of course) & it was on initial retarded settings. Didn't vibrate unduely so the crank appears to be fine.

Given the barrel to the local Kart tuning chap who has all the measuring gear to check for roundness & is well versed in torque plates on anything that gets hot, so I should have an answer soon + he can rehone it straight.

[F5 Dave]

Well I'm wrong again. Bore is straight & true. Piston is picked up in a funny manner. I have another one arriving but in decent light we could see & actually feel how there were ridges. I've mill-filled & sanded them out so it drops in cylinder in any position, perhaps they were just dropping into the ports instead of sliding past them.

I've re leak tested & I did find my reedblock that was salvaged from the 350 had been re-drilled to suit & the elongated holes created a path up the bolt holes, + there was some more damage from the conrod creating a passageway through a crack that had not been fully devconed so I've redone that.

[jasonu]

Hey Dave maybe if you spent more time actually doing stuff to your bike instead of jacking off on KB you might just finish it.
Also any chance of me and the missus dossing on your couch sometime next Feb? I'll supply the beer.

[F5 Dave]

I seem to be getting out of the garage the following day I went in too many times.

Feb? Yeah should be no drama.

[F5 Dave]

Bah. Sometimes they just are hard to shake the numbers out of. I was reasoning a 1mm bore increase & a slight destroke & port timing to the same numbers should not have that much effect. Same pipe, same ign & same carb.

Fit to cases that don't leak & have a reedblock that is the same width as the cases (the last one was ~5mm wider but had to taper in & was an issue of reeds hitting sides) + aim is now straight shot, not smack into the crank. + the manifold is a straight shot instead of 20 degrees.

It just has to be better. Maybe a couple of HP better I'd have thought.

So why am I 6hp down on previous? Things that have changed: Destroke, bore. Piston is pretty similar to the YZ one I was running. I also cranked the comm up from a very conservative 14:1 to 15:1. The timing & mainjet is right on what they were previously so I'm not making up for too high comm. I spent a lot of time & ended up back where I started with these settings.

Where is my 6, or more hp hiding? if it were reeds totally unable to keep up you'd hear them & the power curve doesn't flatline like fluttering reeds, infact it pulls nicely to 13 & the curve has the same shape & humps as the previous engine at the same revs, which is hardly surprising. Rules out the slipping clutch too.

I'm thinking internal friction on the crank.

[Bert]

Bah. .....

Where is my 6, or more hp hiding? if it were reeds totally unable to keep up you'd hear them & the power curve doesn't flatline like fluttering reeds, infact it pulls nicely to 13 & the curve has the same shape & humps as the previous engine at the same revs, which is hardly surprising. Rules out the slipping clutch too.

I'm thinking internal friction on the crank.

Bugger; maybe there is something in the fact you had to press the main bearings in???

[F5 Dave]

or the crank is slightly wider when set up loose & we took a touch skim from the faces. Thought that would have been accounted for with my thicker centre gasket. Might need to remachine bearing deeper or a thicker gasket still. Where's that cork sheet?

[husaberg]

so what did the crankcase reed MK2 end up looking like Dave.
Did you end up deleting the balance shaft.

Like these.



Its amazing how much these Swedish MB50 ones end up looking like the Honda RS ones

[F5 Dave]

Yep & yep pretty much. 100 crank is bigger so the biggest compromise of the deal is the inlet does neck down a little more thank I'd like, but it does mean it fits into an RS chassis.

Well after striping the engine I find a litany of problems. Bore looks horrible & so does piston, can't see a good ring seal going on there. Hmm big end has been grazing the reedstop plate just as it comes up there is enough angle to touch it. There's only a 1mm of material chamfered off but I think its been enough to do the damage to the bore finish & rark the piston, ring, little end & pin.

Crank is still giving more resistance than expected. Back off the case bolts a turn & give a tap with the mallet to open them. Spins freely & hey! the gearbox is freer too.

So yesterday took the day off & had a great day at the zoo with the kids. In the arvo went to see the local kart guy & on the spot he honed the cylinder & had another ring & pin in stock (I had a spare brg & piston). I'd also pulled the left bearing off the crank & taped up the rod & spun the crank in the lathe with some sandpaper strips for 20 min until the bearing just about slide on.

I was worried about the crank after all this & Stu checked it & it was like spot on. Schweet!

The bearing shop had a bearing & all I needed was some thicker gasket paper. last was .75 so I really needed 1.2mm. Figured I'd get some 0.5 & have to sandwich them. Walked in & on the carpet in the corner was a big roll of 1.2mm.

After dinner I cut a couple of gaskets (1st one always has mistakes) & fitted it all up & with some heat slid all the bits together & pushed the cases together by hand the last few mm of the dowels. Crank is free as but gave it a tap each was to ensure as free as can be.

Finally a stretch of luck. My mood was hiccuped as tightening the last reed bolt it sheared. Took block off again. In a really inaccessible point but there was 5mm showing. Pliers started it turning easily & it just wound out!! Whoohoo.

All back together now on the bench. A quick leaktest this morning showed promise, but the inlet manifold is leaking again. I must make it a gasket, clearly the original isn't cutting it with some goop. But overall I should be able to dyno it in the weekend.

I'm glad I did get to the track as there were a few things I just don't think I would have found without a shake-down test of the new engine. But having the time to re-go through things was well useful. Mike was totally right, the crank I wasn't happy with, it needed a re examine. The cases were licked & obviously more than a tickle came off so along with slightly wider (looser built crank) the cases were just too close together & needed a thicker gasket.

[husaberg]

The bearing shop had a bearing & all I needed was some thicker gasket paper. last was .75 so I really needed 1.2mm. Figured I'd get some 0.5 & have to sandwich them. Walked in & on the carpet in the corner was a big roll of 1.2mm.

After dinner I cut a couple of gaskets (1st one always has mistakes) & fitted it all up & with some heat slid all the bits together & pushed the cases together by hand the last few mm of the dowels. Crank is free as but gave it a tap each was to ensure as free as can be.

I am sure Dave is well versed in Gasket making but if anyone else isn't but i use a combo of Grease to stain the gasket paper i apply a little pressure to ensure a accurate outline with a rounded piece of wood and a ring spanner to mark the holes by turning the ring end inside the holes in the crankcase timing cover otr whatever.
I always punch the holes with a bit of sharpened Ariel as it makes nice holes and is available various sizes and normally lying around.

All this was shown to me by an old school mechanic.

[F5 Dave]

I try use darkened sump oil. Last night's was too fresh. Gasket paper in this case too thick to impression. Isn't an Ariel an old english nail? I meant the bike not the tack. I just use hole punches, tap & turn. Only about $20 a set.

[husaberg]

I try use darkened sump oil. Last night's was too fresh. Gasket paper in this case too thick to impression. Isn't an Ariel an old english nail? I meant the bike not the tack. I just use hole punches, tap & turn. Only about $20 a set.

Brocket Telescopic Aerial free and about 10 different sizes in each (Available most car parks)
as i'm to tight for punches and for new oil also too.

So you did end up ditching the balance shaft tunnel on MK2?

[F5 Dave]

Ahh Koatanga! Had no idea what you were on about. Car Aerial.

Never run a balancer in any of them, even my H '(cause when I got it it was disabled).

[husaberg]

Ahh Koatanga! Had no idea what you were on about. Car Aerial.

Never run a balancer in any of them, even my H '(cause when I got it it was disabled).

old Radio ones work well too
But wasn't the tunnel left in place for the balance shaft on the original (modded case induction) crankcases?
I was just wondering if you used the counter-balancer area on this version as it would make for a straighter inlet track as above on the Swedish MB/Derbi?

[F5 Dave]

Mk1 I could have run the balancer if I needed to, but tract was horrible, mk 2 looks like pics pretty much which was the obvious progression. But mine doesn't look like it was done with a chisel. Theory is all very well, but I'm nowhere close to the power I was getting with Mk1 so we'll see if that changes.