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Results 1 to 8 of 8
  1. #1

    Join Date
    Oct 2007
    Location
    Perth
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    322
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    67

    Cob & Co 250cc Link

    I've decided to make a new thread for this Cob $ Co bike, to keep the info seperate from the long running G4 Hummer thread.

    I bought this bike for my wife & daughter to ride, on account that the seat height is lower than usual at 85cms - which is a lot more managable for the ladies. The bike still maintains the 250cc engine however, which provides a teriffic amount of grunt in a small bike.

    I outlined the good and bad of this bike in the hummer thread - and I've added a few more observations here as follows:

    Good: - High output Zengshon OHC engine, tough frame, nicely finished wheels, quality adjustable suspension, easy component access, good ergonomics for the smaller rider and low overall weight (85Kgs).

    Bad: - Crap quality wiring, some really rough welds, front brake caliper a little misaligned from the disk, front suspension good quality - but a little soft, no rubber anti vibration washers on plastics, crap brake & clutch levers, ****ty throttle, piss poor handlebars & fittings, brakelines and wiring badly routed, external exposed air filter may clog in rain & mud, no bash plate, no assembly instructions, piss-poor manual, a number of unconnected hoses and wires plus flimsy all in one tank shrouds, side panels and seat.

    I actually didn't want to buy this bike, as I much preferred the configurarion of Cob & Co's 250cc ProX - which is the same size, but uses the more modern twin boom frame and is put together with much highr quality components. My wife however didn't like the colour (carbon fibre black & red) - so we ended uo getting the Link.

    Having said all that - I'm determined to make this bike perform well and started work on it today.

    First I took a look at the drive train. The Link runs a 42 tooth rear sprocket and 428 gauge chain. I was hoping I would be able to use a spare Hummer rear sprocket to increase the drive ratio - but unfortunately the mounting bolt holes have less distance between centres and so are not compatible. The good news is that the Link runs a 16 tooth front sprocket, which is exactly the same mounting size and system as the Hummer. I have a spare 15 tooth front sprocket - so if it turns out I need a higher drive ratio, I can fit a smaller front sprocket an achieve the same result. I'll decide if that's neccessary once the bike is ridden.

    I removed the Chinese chain and replaced it with a DID 428NZ black & gold - which set me back $75 from my local Honda outlet. Don't be tempted to run the Chinese chain that comes with the bike - it will definetely break after a few rides and the results can be catastrophic! Replace it ASAP!!

    I had some trouble torquing up the wheel - because the rectangular thrust blocks which the wheel adjusters butt up against, kept rotating when the wheel nut was tightened. This had the effect of pushing the wheel backwards and making the chain too tight. In the end, I got my daughter to jam the the bottom edge of the thrust block with a screw-driver - to stop it rotating. We got it just right in the end, but why the thrust block wasn't made a little bigger to stop it turning eludes me!

    Next I stripped the handlebars, lubed all the cables and greased the clutch and brake lever bearings. This made a huge difference to the weight of clutch pull and general smoothness of operation - but it doesn't alter the fact that the levers and throttle are crap and will have to be replaced. I then replaced the crappy piece of foam padding on the crossbar with a spare piece of renthal foam I had lying about. The crossbar was so loose it was almost falling off the handlebars, so I tightened the screws securley with some lock-tight added for good measure. The handlebars are too short for my liking and will eventually be repaced with Renthals, along with the crappy levers and throttle - but not this week!

    The next job was to take a look at the hydraulic brake lines, as these had been installed so that they chaffed against the wheels - bloody idiots!!

    I first made adjaustment to the hydraulic line clamps to get the tension on the lines pushing in the right direction. I then loosened the rotating hydraulic feed bearing (fits into the back of the calipers) and turned them outwards before re-tightening. This made the hydraulic feed lines bow out and away from the wheel, solving the problem.

    Next I removed the shrouds, side panels and seat - so I could get at the wiring. These are bolted together and so are removed as a single unit, once the screws have been removed. These components are very flimsy when compared to those found on the Hummer - and the jury is out on whether they will take much punishment. I originally thought the panels didn't have any anti-vibration rubber washers - but I found them underneath the scews and crushed to powder! I bought some replacement rubber washers from Bunnings for a couple of bucks.

    I could now get at the wiring - which was a bloody mess!

    There were three prinipal wiring problems as follows:

    1. Poorly routed - The HT lead was lying on top of the hot exhaust pipe and was also getting crushed in the steering limiter when the handlebars were turned - other small wires were lying in contact with the cylinder head, ready to get fried!

    2. Crappy connectors - cheap nasty connectors with a high chance of shorting out in the wet.

    3. Poorly insulated - the cable sheathing was cheap and nasty and in many cases was cut off too short. This leaves long lengths of thin single wires, which are prone to damage. look ****ty and are apt to short out in the wet!

    First I removed the offending connectors, having bought some high quality replacements from an auto shop.

    I then removed the short cable sheathing and replaced it with heat shrink cable sheathing from **** Smith Electronics. This is a great product and you thread the cables through it easily - then heat the sheathing with a low setting on the heat gun. The sheathing then shrinks to form a tight fitting and insulated sheath over your wires. It looks neat and is resistant to the weather and wet. I then fitted my new connectors and re-routed the wires in a more logical and hazzard free route. Plastic self locking cable ties were then added as required, to aviod all potential snags and hot areas.

    A redundant wire harness exiting the crank case was also secured with a self locking tie - out of the way and in a safe position.

    That was it for the day. The next job will be to change the oil, secure the fuel line properly, change the spark plug and have a look at firming up the front suspension. After that I'm going to give all the nuts and bolts a going over with the torque wrench - and she should be ready for a first ride.
    Last edited by rodbox5; 31-03-2008 at 12:10 AM.

  2. #2

    Join Date
    Mar 2008
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    Good stuff, keep up the great work!

    I read it's quite a letdown now though?

  3. #3

    Join Date
    Oct 2007
    Location
    Perth
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    The next schedule of work was carried out on the Link today as follows:

    Changed the oil to Castrol ACTIV 4T
    Fitted an NKG DEA8 spark plug
    Tightened all nuts and bolts – using the torque wrench on critical items
    Put the battery on charge

    After that, I took a look at the suspension – since as supplied it is very soft.

    The first disappointment was that the front forks are not adjustable – so I’ll be forced to firm them up with a more viscous oil – and perhaps add a few mils more than was originally in there.

    I then adjusted the rear shock and increased the pre-load on the spring. Having done all possible tinkering with the existing equipment – I have to say the suspension is still way too soft and will no doubt bottom out frequently in the rough.

    If we decide to keep the bike, heavier springs for the forks and rear shock will be a must!

    With the basics complete, I decided to add petrol and fire the bike up. In keeping with the rest of the experience, there was no joy from the electric start and it stubbornly remained as dead as a Dodo. A check with the Multimeter showed that the start switch was working fine – as was the starter relay. There was plenty of juice in the battery – but not a peep out of the starter motor.

    A further check showed that the wiring was at fault and was not activating the relay. Unfortunately the wiring is not a straight forward hook-up from the starter button, since it also routes to incorporate the ignition and clutch switches in the circuit. This makes fault finding a lot more extensive and tedious.

    Having cleared the integrity of all accessible wiring, the most likely culprit would be a loose connection on one of the internal switches – which I wasn’t game to frig around with today. I therefore decided to try a kick start - and whoop-de-do, the bike started first time!

    The engine raced away a little, but a tweak on the Mikuni’s idle adjustment screw soon got things under control. The 250cc Zongshen OHC is a real purler of an engine and is one of the few redeeming features of the bike.

    Having warmed up the donk, I ran the bike round our property a few times to see how it would go. This was a good experience – as the bike was light, nifty, manoeuvrable and powerful. Unfortunately the third time I kicked the bike over, the kick start slipped on its pivot and ended up dangling on the ground. Attempts to tighten up the lever were useless – since the bolt thread was stripped. Another piece of crappy Junk! Remember to add decent kick start and gear shift levers to the aftermarket list!

    This has been a really frustrating project! The concept of putting a 250cc OHC into a light frame for the smaller rider is great! The frame itself is innovative, giving you easy access to all the working parts and containing a fast, light and powerful package. On the down side, some of the welding on the frame leaves a lot to be desired and the suspension (whilst nicely manufactured), lacks suitable adjustment and is totally inadequate for the weight of the bike and rider. It is definitely not suited to anything larger than a 140cc pitty!

    All the bolt on stuff like handlebars, levers and fittings are absolute crap – even by Chinese standards! The difference in quality between these fittings and those on my Hummer are profound – and aptly illustrate the difference between the older Chinese offerings and the far superior new China’s on the market. The wiring is inferior and poorly fitted – as are the brake lines and other critical items.

    I now really have to look at how much it will cost to fix all this stuff up. The question is whether I should buy an Orion or Pro X and maybe get something close to what I want – or spend some time & money fixing up this bike – and just maybe end up with something special?

    I might just take the punt!

  4. #4

    Join Date
    Aug 2007
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    adelaide hills, south australia
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    i reckon keep that one as parts get the pro-x and then you will have basically all the spares you need

  5. #5

    Join Date
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    Fix it up - Having the light frame would really make for a funner ride, as you said. But then again you are probably gonna have the fix/replace EVERYTHING...

    lol @ kick start

  6. #6

    Join Date
    Jan 2008
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    Launceston
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    Great thread. I was seriously looking at buying a Link as they are shorter than the some other 250's out there, and that a small bike with a big engine would have plenty of punch (no point having lots of power if the bike lacks the quality to cope with it). This has been a real eye opener and shall be weary, may even look at other options in the way of 250's.

    Hope all goes well with it.

  7. #7

    Join Date
    Oct 2007
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    Perth
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    Having got a fair bit of the bike fixed up without spending too much money, I took it out for a ride today. The combination of the 250cc OHC and the light frame make this bike very fast and manoevarable machine.

    I've managed to get a heavier spring for the rear shock - but the front forks are still way too soft.

    I've decided to spend the money and fix everything up - this will be expensive - but the end result should be worth it.

  8. #8

    Join Date
    Oct 2018
    Location
    Adelaide, Australia
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    Szymon

    Hi,
    How good is the Link 250cc dirt bike just cruising around on smoothish gravel roads with some long hills but no jumps or extreme terrain? Do you recommend it for a 15 year old teenager with motorbike experience on a farm just to ride around and not do too intense stuff and is it big enough? We have been looking at buying one for a while but don't know if it's worth it.
    Thanks, Szymon.

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