Will I get my 100 ready in time for Taupo?

**mr bucketracer** · 16th October 2013, 15:56

Originally Posted by koba

My wind-up was spotted far too quickly, it was from an RS125 of some description.

think it put rich in hospital

**F5 Dave** · 16th October 2013, 16:16

yeah our top 6 finishers side bet is looking a little more shaky.

Get well Rich.

**F5 Dave** · 21st October 2013, 20:07

Well the autopsy after the BOB,

slight pick up on ring which was the power loss. New piston & light hone and it back to new. And the rooted main bearing & broken crank/pin. Bugger. So did it muller a main creating the vibration first?

**husaberg** · 21st October 2013, 21:57

Originally Posted by F5 Dave

Well the autopsy after the BOB,

slight pick up on ring which was the power loss. New piston & light hone and it back to new. And the rooted main bearing & broken crank/pin. Bugger. So did it muller a main creating the vibration first?

Mag side Dave?

**F5 Dave** · 22nd October 2013, 08:17

yup. can't remember what the bearing was but pretty sure it was phenolic cage. I was running 20:1 castor so there was a heap of oil there. I had been thinking it was a bit rumbley on the dyno at lower rpm, but that was just the rebalancing & didn't notice any tingles at higher rpm, but the acetyl inserts must be doing their job more efficiently than I thought.

**husaberg** · 22nd October 2013, 15:46

Originally Posted by F5 Dave

yup. can't remember what the bearing was but pretty sure it was phenolic cage. I was running 20:1 castor so there was a heap of oil there. I had been thinking it was a bit rumbley on the dyno at lower rpm, but that was just the rebalancing & didn't notice any tingles at higher rpm, but the acetyl inserts must be doing their job more efficiently than I thought.

I guess the Mag side doesn't have the same support as the drive side?

**F5 Dave** · 22nd October 2013, 16:28

and its not in a constant oil bath like the Gbox side. a couple of hundie would get me some microblue ceramics, but I'm a bit shy of that on top of other costs I might find (+ I'd set some money aside for an igni for the 50 by selling stuff, & don't want to let go of that yet). + I'm not sure they do C3 or 4s, not clear on their site.

**speedpro** · 22nd October 2013, 21:32

You have some odd shit happening with that engine. Normal C3 & C4 bearings should be fine. Thinking back to that clutch problem you had at Tokoroa I wonder if there is a connection. I always thought MB cranks were pretty good, way better than Suzuki cranks anyway.

**Grumph** · 23rd October 2013, 05:42

Odd shit indeed - I was frankly surprised at the amount of movement on the motor mounts. IMO if you've got to turn it into a Norton Commando (isolastics) to make it rideable I'd have another look at the balance factor..When it can shake the plug loose and back off the head bolts too, it ain't right.

Another point must be crank truth...Did you check the crank between centers when it came back from, I assume, the local kart shop ?

**F5 Dave** · 23rd October 2013, 08:26

Std RS have a rubber mount system at the front. The mounting system on an MB is a bit of a drag as the front mount is virtually unusable. Everyone I know who has used it except Mike has had the cases break there. But I've repositioned the mounts at the back so they are closer together as it fits in the RS frame like that & no other acceptable way (with a decent size carb).

I'd used RG rubber mounts but the engine did move a bit too much so I remade them from acetyl & there is a mount at the head, but that is able to move sideways slightly (urethane washer either side & R-clipped nut) so it doesn't twist the barrel. It was quite sturdy. But there is definitely more movement now so the Acetyl has worn pretty quickly.

There was sod all vibration as the revs got up from a riders point of view & I hate vibration, I remember riding DaveDs MB & hated the vibes.

Pulled the bottom apart & actually the mains don't look poked. They have quite a bit of clearance & with a broken pin allow a bit of rock. So that kind of blows that theory. It was over-revving for quite some period every lap. I figured the revs themselves would be under the limit, but I guess the deto was taking its toll.

When I tightened the head down I should have lifted it, noticed the torn o-ring & replaced it. Ideally unstuck the stuck ring & thrown in the spare, but time was tight & I just wanted to see if it ran.

I'd had the crank rechecked when last apart & Kart guy was quite happy with how straight MikeC had made it.

oh yeah I found the Quick shifter sensor wires melted (against the pipe I guess) so that explains the erratic performance there & subsequent failure in race 1. Never did it without the fairing.

**F5 Dave** · 23rd October 2013, 15:45

So I hands the sorry parts to Mike & while we're talking I say the scribe line on the webs scared me as I though it was a crack; game over for those, but then with a wipe it was a scribe line, phew.

So he says yeah it was lining up where the stepped pin was . . . oh dear, the line on the pin is about 30* out. Its moved, probably the most when it twisted the pin break off, but clearly it could have moved a little causing the vibration that undid everything & possibly flogged the Acetyl mounts out. Obviously running it at those sort of revs for any time was going to end badly.

Next time a spot of weld.

**husaberg** · 23rd October 2013, 16:19

Well i am confused......... was it rebalanced for the offset pin. Also how long did that offset pin last.

**F5 Dave** · 23rd October 2013, 16:47

It was rebalanced when I destroked it using Speedpro's suggestion, obviously I run considerably higher revs than a roadbike & no balance shaft (that's where the inlet is now for case reed). When we destroked it we used a bigger pin & offset where it enters the web. Of course that weakens the pin but we put on as much radius as pos anticipating this & at its thinnest point (the bit in the web) it is the same thickness as a std MB. The size for the interface into the web was based on the std MB pin measured very carefully.

But I don't think the offset grinding of the pin was at fault, of course I don't know. About a year with this setup.

It was not a full pin, it had a drill centre. Perhaps a solid centre may be a stronger opition, but you won't get much added strength for rotational stress.

**Grumph** · 23rd October 2013, 18:19

Originally Posted by F5 Dave

It was rebalanced when I destroked it using Speedpro's suggestion, obviously I run considerably higher revs than a roadbike & no balance shaft (that's where the inlet is now for case reed). When we destroked it we used a bigger pin & offset where it enters the web. Of course that weakens the pin but we put on as much radius as pos anticipating this & at its thinnest point (the bit in the web) it is the same thickness as a std MB. The size for the interface into the web was based on the std MB pin measured very carefully.

But I don't think the offset grinding of the pin was at fault, of course I don't know. About a year with this setup.

It was not a full pin, it had a drill centre. Perhaps a solid centre may be a stronger opition, but you won't get much added strength for rotational stress.

Depends where it broke...I've noticed that a lot of aftermarket pins don't have a particularly good finish on the inner bore. When i make a pin - and i've made a few....I bore and then hone to a fine finish. I've always assumed that any marks on the ID could be stress raisers.
The offset grinding may or may not be the problem - it's hard to avoid getting the radius grind a tad too hot...

Gizza pic, Dave - forensic engineering is fun - when it's someone else's motor....