Starting work on the SC500

I’d bought the SC500 back in July whilst starting the trip round for the National Road Rally. The guy at Governor’s Bridge / Huggy’s Speed Shop had mentioned there was no spark from the bike and after a quick faff with the CDI units from the 250 bikes (which are different) I’d not managed to get the bike to fire either.

Rather trying to solve this on its own, time for the complete strip down and to also have a look at the engine. The frame / chassis / cycle parts on the bike are similar (well the same) to that on the MX250, so some interchange will be possible. Frame is essentially the same, which is slightly worrying in terms of performance.

Engine, the external view

The bike looks like its been untouched for a while, with the 1976 California off-road certificate in place of the rear mudguard. The autolube system was still in place, and was first to be removed in the strip down. The fuel tank internals and the state of the carb seem good, so all promising (so far).

Out with the engine and plonked onto the bench (which was clear of the MX250 engine rebuild) and then stripped the rest of the bike. Wheels and spokes good, and fork chrome isn’t pitted and is serviceable. The frame has some rust spots, but not too bad so a strip and rub down will do the trick.

The plastics are also okay and I’ll not look to replace them. They’ve a nice patina so will make a nice look for a 37 year old dirt bike. Once the strip was complete I cleaned and then sanded the frame, before spraying with black Hammerite Satin. This has worked really well on the MX250 . However, tried spraying with the compressor and there’s a bit of overspray to cure and finish a little more neatly.

Now for a quick look at the engine. Removing the cylinder head is a surprise if you’ve been working on 250cc bikes; at 94mm diameter its big. A quick check without getting out the vernier is positive, with the bore and rings looking in good shape. The only problem is that there is lump out of the piston skirt, but not sure if this is recent.

The 'wow' factor

The crankseals are gone (hence the draft when cranking the engine over) and though they can be done without splitting the cases, I’ll probably go the whole hog and go for the full strip.

On the work list:

|Frame|respray and tidy up|
|Wheels|spokes and rims in not too bad a shape, go a rebuild may not be necessary|
|Forks| as well as the yokes seem pretty good. Will replace the steering head bearings, around £20.00 off ebay|
|Shocks|like the 250’s they are not good. Went for NJB shocks before and may do the same here, but longer body, probably 340mm. Had thought about Rock Shocks but need to check prices and performance.|
|Seat|Fine, covering is good|
|Ignition| couldn’t get this sorted before the strip and needs to potentially get a replacement stator, as have spare CDI and ignition coil|
|Exhaust| the main pipe is fine, though the California required spark arrestor may impact power. Got some pictures and prices from Circle F exhausts and will have a think about getting one. Not sure about what the performance increase might be|
|Airbox| in good shape, though the carb rubber doesn’t seem right (too short) so may need to find or make a replacement. |

On the engine
|Autolube| Will remove it and go to premix; could leave it on the bike with an empty tank|
|Crank| seems fine, as do the main bearings|
|Piston| has this missing bit. Its the original piston, so may go for a (relatively) cheaper same size piston and ring. |
|Barrel| is in very good condition and seems not too loose |

The strip will reveal any other problems and will debate the removal of the balancer in terms of power and vibration.

More to come and some shed time in the next couple of months. Also will have an ebay trawl. SC500 spares are slightly more pricey than say MX250 and MX360, but availability is there and still relatively reasonable.

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