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Rocker arm spindle HMB design
850 T3, T4, LM-1, LM-2, 1000-SP, V 1000-G5, Convert, 850 T5, LM-3, Cali-2, Cali-3, Mille GT, SP-2, SP-3, LM-1000, 1000S, Quota 1000, Quota ES, Cali-1100, Cali-1100 i, Cali-Spezial, Cali-EV, Stone, Jackal, 1100-Sport, 1100 Sport ie, V11, V7, 850 GT, V7-Sport, 750-S, 750-S3, 850-T. Cali Classic, Vintage, Bellagio, Griso, Breva, Norge, 1200 Sport
Only at HMB!
Since the original rocker arm shaft has not been available for some time, we had to resort to Italian accessories. As is often the case, this went well for a while, but the quality got worse and worse from batch to batch. We then measured each shaft individually, which is not a permanent solution.
We had to have our own production! At first, "only" a precisely manufactured shaft was planned, just like the original. But in the course of the design, some weaknesses of the rocker arm bracket/rocker arm shaft construction came to light. So a simple shaft became a good piece of design work. It had to be a solution that did not require any further modifications to the rocker arm bracket or the rocker arms themselves, both for the round engines and the square ones.
Since rocker arm lubrication at Moto Guzzi is in the oil pressure circuit, optimal lubrication, in addition to the precision of the shaft itself, was the primary development goal.
The problem:
1.
Inaccurate manufacturing with regard to diameter and roundness, insufficient surface hardness. This can be seen clearly in the wear marks. A hardness test confirmed this suspicion.
2.
Due to the design, the shaft is only fixed at one end. This may be enough to prevent the shaft from falling out, but it allows vertical movement at the other end. Noise and reduced valve lift are the consequences.
3.
At the fixed (upper) end, the shaft is pulled up in the trestle by the fixing screw. This opens a gap under the shaft from which oil escapes. Due to its design, the gap is where you least need it. Namely directly at the oil inlet!
This oil escapes before it can even reach the rocker arm, is then "missing" for the lubrication of the rocker arm and also causes pressure loss in the entire engine. On our engine test bench we could easily see that an unexpected amount of oil leaks out at the upper ends. Moto Guzzi seems to know about this problem, because on the newer Griso/Breva 1100 engines there were 2 O-rings between the cylinder head and the rocker arm bracket to seal the oil inlet to the bracket. This was well-intentioned and certainly an advantage, but the losses at the rocker arm shaft are far greater. That's where we come in.
The solution:
We have developed a precisely fine-ground shaft with a good surface hardness, which is fixed on both sides and prevents unwanted oil leakage. We achieve this with two clamping cones and an O-ring. The cones spread the ends minimally so that the shaft is fixed and tight to the outside. The O-ring provides the inner seal. In addition, the shaft is fixed with a sealed screw in the original bore of the rocker arm bracket.
The principle of the clamping cone is not new, it has been used successfully by a famous German sports car manufacturer for over 30 years.
Of course, the whole thing was extensively tested on the road and our engine test bench. The result shows that oil leakage is prevented and the engine runs subjectively smoother in comparison.
Finally, a word about the price. The original shaft, which is no longer available, cost over 120 euros at the time, with all the disadvantages of the design. The accessory shafts cost only a fraction of that, but were mostly undersized and poorly hardened. Simply unsuitable for a serious engine repair.
Before and afterVideo:
https://www.youtube.com/watch?v=V4JeQGNjqdg
Mounting instructions:
https://www.youtube.com/watch?v=lq9_4S8evrk
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Of course, the wear of the rocker arm itself also plays a role. Experience shows that the shafts wear faster, but you should still consider an overhaul. Especially for engines without oil filters, or engines with high mileage. Over the years, particles embed themselves in the soft bearing bush of the shaft, which then promote wear. |
