What is the best charging and ignition system for wide case 450

[Eldert]

conrods are 140 mm for the 450 and 145mm for the 860 and 900'

750 has a 150 mm long rod .

Eldert

[Duccout]

So the 450 rod is seriously too short?

[Eldert]

Hi Colin

rod lenght is OK . the rod ratio is 140 : 75 = 1.8666 . a Sebring engine however has a rod ratio of 125 :75 = 1.66 . that is not the optimum .

way back BSA development engineer Roland Pike did a lot of research of rod ratio's and bore / stroke dimensions . the optimum ratio was 1.85 or 1.86 ( dont remember exactly ) and he build 3 diff B31 engines with diff bore / stroke configurations . the best 350 by far was a 69.5 stroke and 80 mm bore .

Eldert

[DBDBrian]

Colin, as Elderts post, the figures quoted would give the 450 a connecting rod ratio of 1.866 virtually the same as a DBD Goldie 1.857. The rod length ratio effects the piston deceleration, dwell at TDC and acceleration, which in turn has an effect on the ignition timing. Maybe this goes some way to answering your question, but I must agree, 28 to 35 degrees is quite a step.

[Duccout]

That information about Roland Pike is interesting: the premature failure of 860/900 Ducati big-ends has been blamed on the shorter con-rods compared to the 750, which Ian Falloon describes as perfect, at 2:1, whereas the 860 engine is 1.95, which is still higher than the Roland Pike optimum. I had always believed that the optimum was 2:1; it makes me wonder why Taglioni did not shorten the 750 engine's rods, to allow a more compact engine, but it all depends on the engine characteristics the designer is trying to achieve I suppose.

[LaceyDucati]

You can theorise as much as you like about Bevel twin premature big end failure, frankly with the quality of many of the crank components used in the past I'd hold back unless those are addressed. Without consistency, quality of components and workmanship the full truth can never be found. What I have seen over the years is poor components and some lousy workmanship on many failed or failing twin cranks.

I've run and raced Sebring's with a rod ratio of 1.667 to Widecase 250's at 2.336 and none have had a propensity to eat bigends or pistons. There is probably pro's and con's and sweet spots for particular performance, but none in my experience are "big end" killers.

When I became involved in racing Ducati Singles 30 years ago there was a crock of sh*t circulating why Single cranks failed prematurely in racing. After years of involvement in the UK racing scene, Ducati singles are now ironically considered to be fairly strong compared with other Marques. When I started out racing singles the paddock gossip was all doom. By the time we were in the new millennium I was bemused to be stood in the Manx GP pits with Fred Warmsley telling me how lucky we were with our reliable Ducati singles. Lucks a funny thing! I took his comments as a compliment and as usual I take all theory and old wives tales whoever spreads them as information to be considered.

Off subject here, just felt compelled to reply.

Regards Nigel

[Jordan]

I'm just a backyard mechanic, but I tend to agree with Nigel.
It's a myth that Ducati only made high quality stuff.
Nevertheless, some parts of it are excellent. For example, castings and top end accessibility.
And it's a good thing that the gear selector box is easy to remove and service, because it needs it more often than most.

[Duccout]

Hi Nigel,

I've read your posts regarding big-ends with interest, and obviously, with all your years of experience, you have found the real reason for failures. Inconsistency of assembly would explain why some people managed many thousands of miles out of an assembly, and others only a few thousand. I remember reading about a US racer who had done over 90000 miles on his 750 SS without changing the big-end. I was surprised when you described the care needed in assembly, and I'm guessing that most assemblers just press in the bearing as received and true up the flywheels.

[samsmc1]

I'm looking for an alternative ignition / charging system for the little 350WC that I'm assembling as a street legal play bike. I zeroed in on this post to see what's best.
All of my Ducati experience was as a dealer in the late 70's - early 80's sponsoring several 900SS race bikes (which I still have), so I already know what's good and whats junk ignition wise on them. The little 350 is a different deal.
I was interested in this post when it switched to cranks. We messed up the first 900SS crank with a gube on my part - one that was corrected - no more crank problems. The absolute best combination of rod length versus bore and stroke is 6" rod center to center - 4" bore and 3" stroke or any combination using that formula.. I first saw this in the late 60's with the Z28 Camaro. Later racing an SV650, I learned that the same formula was applied by Suzuki on many of their later sport bikes. I believe most of the drag racers and other types of race engine builders still adhere to this formula or close to it.
I seriously doubt the reliability of a crankshaft has anything to do with the Italians quality of materials or precision in manufacturing. There are too many other variables. Example - most folks think that any name brand oil is of a reasonable quality or they couldn't sell it - not true. The way I learned this is a tale for a different day.
Back to the electrical issues with the Ducati singles - I always thought the Italians were the dumbest i****s on this earth coming out with the kick starter on the left side. I'm paranoid enough as it is with a left side kicker to chance having the thing kick back. What do I buy that's reasonable price wise for a bike that's not really worth very much? If it had a value on par with the twins, cost wouldn't be a factor.
Thanks
Sam

[Duccout]

Hi Sam,

The two most common ignition systems fitted to Singles AFAIK, are the Sachse system from Germany and the Electrex World kit from here in the UK. I'm assuming that both are good quality systems that give very good results; have a look at the respective web sites.

I was interested to hear of your experiences with bevel twin big-ends. I know that this is a Singles club, but I find it strange that some people have nothing but big-end trouble and others none. Have you read Kevin Bracken's account of racing a 900 bevel and how he cured big-end failure by increasing the rate of drain back to the oil sump from the heads? It is interesting that Ducati themselves introduced a new deep sump on their WSB racers around 2000, because they found that the oil was not draining back quickly enough and allowed air to be sucked in to the pump, although this would have been more serious on the plain bearing engines.