660 rebuild

[Uther]

I am in the process of stripping the engine on my '97 Skorpion Traveller.When I got the bike (very cheap) the engine seemed to rattle from the cylinder/top end.Having stripped the top end so far,the piston seems mildly scored in 4 different areas ,but the barrel looks fine.The top of the piston seems very coked up,as are the valves. Whoever had the bike before was using a DPR7EA9 spark plug.Could this cause the coking up?. From what I can see of the crankshaft it looks fine,with no up-down play.Would a rebore and new piston and rings be in order?Any other thoughts ?

[cat]

if i'm not mistaken, the cylinder is Nikasil plated, so you don't rebore them. hone with ball hone or just clean the glaze off with scouring pads. new piston and rings sound like a good idea. 7 plug is hotter than normal. if there's unusual carbon-ing, maybe it's from the rings, the scored piston, letting oil up.

[keithcross]

Sorry to disagree cat, but the cylinder liner on the 660 engine is a cast iron one. Oversized pistons are available in 0.5mm and 1mm sizes. Aftermarket pitons are available in 102mm (2mm oversize = 686cc) and 105mm (5mm oversize), but the 5mm pistons require machining to the crankcase and can only be fitted (or so I am told) if teh crank is stroked as well. This conversion gives 727cc

Keith

[cat]

oh, i must be getting confused with my KDX and the GS.

[Uther]

Thanks for the replies! There does appear to be light scoring of the barrel, in the same 4 areas that are scored on the piston. So maybe a rebore is in order. Does anyone know if BSA Regal carry these parts?

[keithcross]

Knowing Phil, if he does'nt have them, he will get standard, +.5 and +.1 pretty quick. But as you are having a re-bore anyway, why not consider a 102 686 kit. You can get them from slipstream tuning (http://www.slipstreamtuning.co.uk/home/index.asp), or competitive solutions in Germany, web address here somewhere.

Keith

[cat]

Phil at BSA Regal will get them for you if he doesn't have.

If it's light scoring, maybe honing would do it. That saves you the problem of finding a good machine shop, that'll do a good job (straight, in other words). You should try to find someone who can tell you whether or not honing will remove the scoring. If it needs to be bored, find a place that does bike engines - like a place that does race engines.

[cat]

How did it get scored? How does that happen? It's not a 2-stroke.

[keithcross]

My original 660 engine suffered really bad scoring of the cylinder liner and piston. The cause was a failed big end, bits of the bearing took out the oil pump, which caused oil starvation to the piston

Keith

[cat]

The big-end shouldn't fail, they're supposed to be "bullet-proof" engines ...maybe a dud bearing. ...? or somehow oil didn't get to the bearing. ...?

[keithcross]

Dont know why the big end bearing failed, oil changed every 3000 miles, new filter every time. Maybe a bad one, I dont know, but with 35000kms on the clock of a 2½ year old bike, no chance of a warrenttee claim.
Still I got hold of a secondhand XTZ engine unit for £180, and have another as a spare that cost me £200 plus my old engine. Steve in Suffolk wanted a set of crankcases for a race engien and brought a complete engien, so did a deal

Keith

[Uther]

Hmmm, I think another engine might be a better option.I am looking at a rebore/new piston,plus there is a lot of play in the conrod. Anyone know what sort of prices these engines go for?

[keithcross]

It all depends on your luck. I live in the UK, so would expect to pay the same as you. I have picked up engines for the prices above, bit have seen them go for up to £350 for a low milage standard engine, complete with carbs etc.
There is one for sale on this site for £750, but that has had a big bore kit etc fitted.
If you watch ebay, it may even be worth getting a complete XTZ or SZR 660, using the engien and selling the rest on ebay

Keith

[fasrnu]

[keithcross]

I have copied this from an old advert from Slipstream tuning, this is where I got the idea the crank has to be re-stroked as well

Tuning Parts for Yamaha 660 5 Valve Single Cylinder
Piston Kits: 100mm 130.00
101mm : :
102mm : :
105mm 2 ring (for 88mmStroke) :
Camshafts: 6 stages Reprofiled 189.00
New Billet 230.00
Heavy Duty Slotted Cam Sprocket 40.00
Valve Spring Kits 183.00
Carrillo Rod 165.00
Titanium Rod 500.00
Crankpin 2mm offset for 88mm Stroke 105.00
Solid Balancer Gears (pair) 180.00
6 Spring Conversion 275.00
Close Ratio Gearbox 1500.00
Lower 5th Gear only (pair) 270.00
Roller Cam chain Conversion 100.00
Services:
Gasflow Cylinder Head Road 150.00

Race (for STD Carbs) 180.00
Race (for Keihin CRS) 300.00
Downdraft Race 750.00
Crank Rebuild & True 40.00
Crank Modify for 88mm Inc Thrust Washers 60.00
Carb Kits from £345.00 - £550.00
Exhaust Systems Race 2into2 475.00
Slip-on Muffler from 190.00
Full Strip & Rebuild + Dial Cam 280.00
CNC Billet Generator Cover with Seal 100.00
Fully Programmable Ignition 595.00


Prices are probablly out of date now though.

Keith