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Marks 851 / 888


Mark had found some aluminium turnings on his oil pick-up gauze that concerned him, so after a few phone conversations it was decided to investigate the cause of the 'swarf' and what additional work could be done to 'pep up' his 851 without causing too much stress to the finished project.


The engine was stripped and my suspicions were confirmed. This picture is actually from a 916 with the same issues! This was found a lot on early bikes, my opinion is the heat expansion rates of the steel crank and alloy plug causes the locktite to breakdown and the plug loosen off, subsequently winding out. Later bikes have a steel plug that rarely seems to suffer from this issue.

In the past Mark had painted the frame, tided up the electrics and had a 'bigbore' header system made for the Ducati. The bodywork was new so on the whole it was really only the engine cosmetics that let the 851 down a little! It was decided during the rebuild to bead-blast the cases as they did not look their best.

To 'pep up' the Ducati 851 it was decided to increase the capacity to 888, to obtain the capacity increase 'Pistal' hi-comp pistons were used in conjunction with rebored and plated 748 barrels. The crank was subsequently balanced and shimmed into new main bearings. During the bottom-end build a close ratio 'SP' box was also fitted eliminating the 'over-gearing' and long ratio's of the road box.


The standard flywheel (left) was machined and drilled to lighten it giving a faster throttle response and better engine braking.


The build would also include matching the manifolds to the ports, valve's re-faced and SPS cams shimmed into the heads. The piston to head clearance was set and the valve to piston clearance checked. Finally the cams were dialled in for optimum valve timing. The observant amongst you may notice the lack of tacho drive from the horizontal inlet cam, due to this a electronic tacho was fitted. The modifications to this engine were based around a set budget and a brief to keep this older style engine reliable. We could have used bigger valves, race cams and larger cylinders, the final result would have been more power but past race experience has shown the engine cases would be prone to fatigue failure!


Final assembly would included replaceing the coolant hoses with new 'Samco' items and the fittment of a power commander. The Ducati was then ran in and the fueling set on a dyno.






Thanks to Matt (at the time working at 'Dave Cooper Racing') and his careful fuelling of the Power Commander unit. Our engine mods gave us just shy of 110 bhp @ 8250 rpm to 10,000 rpm (approx 120 - 125 bhp - crank) and 66 ftlb of torque at 7000rpm. That's strong usable power from 6500rpm to the rev limit! Not bad for an old 851 and roughly up 10bhp on a 888SP4 from what I've seen!!




If you have any queries or questions, require a quote or just need a little advise then please feel free to mail me at service@gtecperformance.com or give me a call on 01858 535 411 or 0784 1099 998.

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