Read before going 851 crazy
With regular servicing the engine is reliable, although it doesn’t take much to make it a potential minefield. Listen for a squeak when starting which might indicate the sprag clutch is slipping.also check the alternator nut has been tightened and that valve clearances have been inspected every 6000 miles.
The weakest point on the engine. Check the tension and condition regularly. Replace every 5-7000 miles or at the first sign of wear.
All eight-valve head gaskets supplied now are a metal type and approximately 0.5mm thick, while the early 851s used a composite type that was 1.1mm thick.therefore, if you’re replacing an old-type gasket you must also replace the base shim with a thicker one to compensate.
By definition any 851 is now over 25 years old and, being Italian of that era, corrosion and/or wear can be an issue. Engine paint is prone to flaking off, thetricolore’s original iron discs rust, plastics crack and paint wears. Inspect very carefully.
A weak spot as with many bikes, and has a bit of a habit of burning out. Needs to be swapped for a modern unit if it’s not been done already.
Weak handlebar clamps
Doesn’t affect all bikes but worth checking – more than a few have one ineffective clamp bolt due to a failed weld. Check that both bolts are tight.
Often inaccurate due to poor design of the spindle plates which can bend or twist when tightening the axle, thereby giving possibly inaccurate wheel alignment. If in doubt, use a tape measure to check the swingarm-spindleto-wheel-spindle distance on both sides.
A spacer on the chain side is often fitted incorrectly, if at all.tapered in section, the tapered bit goes towards the wheel with the flat face against the swingarm. Fitted wrong, the spacer interferes with the circlip in the sprocket hub which makes the wheel very hard to turn. Leave it out and the sprocket carrier face interferes with the swingarm, damaging both. Definitely worth checking.
An uprated battery is recommended to protect the sprag clutch and is a common mod, but requires a different mounting plate.
The 851’s wiring harness is pretty tough but the connectors are susceptible to water and, thus, corrosion. Check for loose or frayed wiring and corroded connectors. Corroded connectors between the generator and reg/rec can cause blown regulators.
The three-spoke aluminium Brembo wheels fitted from 1989 are slightly soft and prone to distortion if ridden over potholes. Check that they run straight and true with both wheels on a stand.
The dry clutch of the 851 was designed primarily for racing and is a little delicate for prolonged use around town, for example. A noisy rattle from a dry clutch is normal, especially when stationary, but if it’s excessive and continues when on the move then the plates will need to be replaced.