750SS Big Ends

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750SS Big Ends

Post by andybaggies »

In the Oct 2020 Classic Bike magazine there was an interesting article about a guy who builds engines and makes parts for 1930s Scott two-strokes. His repertoire includes pistons, cranks, titanium connecting rods & inner/outer races for bearings which use rollers within 2 microns of each other. So he’s no engineering slouch.

Anyway, during the 70s he campaigned a 750SS production racer which suffered repeated big-end failures – ho hum. After investigation he thought there were issues including the use of an aluminium cage which expanded faster than the steel rollers of which there was too many. Unfortunately the article didn’t detail any of the other design faults he felt were present.

Ducati denied there was a problem when he contacted them but they did offer him half-price spares… Some time later a Ducati race technician told him his remedial suggestions were rejected as too expensive. Again, what these suggestions were the article didn’t expand on.

So how accurate do people think his conclusions were?
SD900 Darmah
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Re: 750SS Big Ends

Post by Lumpy »

Interesting because Kaemna Ducati in Germany offer Carillo big end sets but suggest you use your old steel roller cage from the old unit to put the new rollers in if your going to be putting it under greater stress. By that I would assume racing. During my fascination with the marque I`ve been led to believe the helical cut teeth on the primary drive exert axial loading on the crank, the crappy one step Ducati mechanicca ignition advance putting shock loading on the BE when she hits the advance cliff.......I mean curve, and my personal favourite, the big end being fed unfiltered oil. The by-pass oil is filtered but not the lube oil..............still can't get my head around such an elegantly designed motorcycle engine being fed it`s own swarf in its lube oil. If its not the main issue, it`s gotta be helping!!!
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Re: 750SS Big Ends

Post by ducadini »

Just a few remarks.
Racing puts a lot of stress on parts that weren't always designed to take those amounts of stress.
I admit that to overtake one of my fellow competitors I didn't really mind going over 10K on my Darmah racebike.
But it was fun staying with a 851 on the drive to Les Combes and outbraking him into the chicane. Three times :-D :-D before the (bog standard) crank said enough.
Then there's the (dare I say it :oops: ) oil thing :roll:
The insufficient pump ? Or insufficient flowback (as Kevin Bracken found out) ? Or the mesh-filter (??) insufficient filtering ?
The sudden stepping of the ignition isn't really an issue in racing (my Veglia only started moving at 2K) and anyone who winds the throttle fully open under 4K should be removed from his Ducati Bevel and put on any V-twin with lesser angle between cylinders.
A 750 RC only begins charging his battery above 4K (at best) so there's no use in plotting along. Keep it between 4 and 6 and Your Ducati will thank You by going on longer than You.
And of course there sometimes were better solutions for some details on any Ducati. What could've been the implications when Ducati DID really admit they had a problem with the cages ? Change them on every bike they sold and still had warranty ? Well, talking about going in DEEP in the engine (and into the red on their account).
If I didn't find so many "inaccurate statements" in the articles in modern magazines, I would still be reading/buying them.

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