Oil Filter

[blethermaskite]

Hi Hans, "Great minds often think alike".. My 350 also has 35mm ceriani GP forks fitted,I was lucky to buy a genuine pair of legs and sliders about 12 years ago which I fitted to the std marzocchi tripple clamps, (they transformed the handling of the bike from wonderful to exceptional) my best buy ever, I have also invested in a desmo head for the bike ......not because it will make it go any better, but just because (for me) a 350 desmo is just the perfect Ducati single, I have a very nice 74 250 desmo disc and I may just swap 250/350 engines around to suit my mood I have not looked inside my 350 engine for several years and I am frankly amazed that it hasn't blown up yet
Cheers,
George

[Jordan]

the oil becoming trapped in the heads and above the sump, allowing the big-ends to run dry and overheat.

The whole gallon?

[Duccout]

Yes! C R Axtell found that the oil flows to the heads at such a rate that as it returns to the sump it is trapped in the cam boxes and above the sump baffle, with no easy route back to the filter, which then sucks in air. The Ducati factory racers had two large holes drilled in the baffle to allow the oil to drain past. Axtell's remark about the sump baffle went something like this: "Our Italian friends are so clever, but they've slipped up here!"

[LaceyDucati]

My personal opinion on bevel twin cranks is the issues lie with design and poor tolerances. Having rebuilt many bevel twin cranks over the years, I do have the advantage of having seen and measured a lot of big ends at various stages of their life. My observations are:

1) Early twin bearings mostly appear to start to fail due to having a double row of rollers. Mostly what you see is the hardening on the pin starting to break down where the rollers meet in the middle (see also later 75 singles....) Cranks rebuilt with one piece rollers don't seem to suffer the same issue. Personally I neither see the alloy cage or the Size of the 5mm rollers to be an issue. It should be noted Japanese singles all use rollers 3.5mm to 5mm.

2) Later twins use that use 3mm rollers and silver plated steel cages (in road use) seem to be no longer lasting than many of the early cranks. What I see is the wasted away cage seems to were the rod eye away so that eventually the working bearing area is reduced to about 8mm. Most Japanese cages are "plain" and have no wasting in the middle much as the single and twin alloy cages which don't seem to wear the rod in the same way. I know there it much talk of 3mm rollers reducing skidding etc etc, but I'm not convinced in road use these later bearings achieved the desired goal. It should be noted as far as I can see no other modern manufacturer uses 3mm rollers in a motorcycle crank.

3) I have noticed that the pin bores in the crank halves on both twins and later singles are sometimes poorly toleranced, I am of the opinion this can't help either. With fit varying from just under 4 to over 6 thou that must effect the journal diameter for parallelism. Out of curiosity I've measured pins on the journal diameter before and after installation, parallelism is compromised. If the pin isn't parallel (much like some original pins) then the rod is likely to side thrust. Side thrusting is on many cranks the start of the end and will eventually lead to bearing failure as well.

4) Clearance in the Ducati big ends is on the tight side and again out of step with many other manufacturers. That said I have seen cranks towards the top end of that specified running well after many years of life. I have seen suggestions that running much larger clearances is advantageous (2 thou plus) but how many of these cranks have done "many" thousands of miles to evaluate the life expectancy. Personally I aim for around 1 to 1 1/2 thou clearance, sometimes a little less or more depending on the size of the bearing. As I've been doing this for many years and over 20 years now in business, I'm guessing I'm not that wrong. With Single race cranks I advise those doing full seasons (7 to 10 two day meetings and even the Manx/classic TT each year) to replace the rod kit at 5 years. I know they will last longer, but after that "you're on your own"! Many things like oil, oil changes and build cleanliness etc will of course effect life expectancy. Quality of components and careful measurement and matching of components is in my opinion vitally important. I've not so far ever rebuilt the same crank twice for a road customer, I'm guessing some of these bikes must have been used over the last 20 years......

Regarding oil and crank life - I've not seen any evidence to suggest whether using either multi grade or straight oil effects crank life one way or another. I raced and have helped racers for many years firstly using straight 40 mineral race oil, then lately a 20w 50 semi synthetic. Probably around equal amount of years on both, with no real issues or difference in crank life. Any advice I took was from Silkolene and the advice seemed to be that the make up of the oil/additives was probably more important than anything else. I have stripped a few engines running on Castor oil and did'nt see any evidence that Castor oil is of any advantage over some modern oils, in some ways a disadvantage. I would however add caution to running a Ducati single on a thin modern race oil, as I've heard many a sorry story.

As a general note, regarding rod bearing life. Is 35000 to 70000 miles unusually small when compared to other manufacturers using needle roller big ends? We know some cranks failed prematurely, but that I think was down to poor quality control. If you took a Honda 250 single and rode it continually, servicing it regularly it may well do 200,000 miles plus in a few years. In reality most bikes will fail at much lower mileages mainly due to low use. Let's face it at 45 to 63 years old it's amazing any of these engines are still going if they haven't had a major overhaul. They are all long past their "life expectancy". With the mileages of 30 to 70 K being banded around in these time frames, we are all mostly likely to be out lived by our rebuilt engines if they are built to a good original spec..... Personally after several years of reliable running I'm more than happy to have a little fiddle and repair

A few thoughts in a bit of a ramble

Regards Nigel

[blethermaskite]

All wise hard earned words Nigel, my concern amongst others with rapidly ageing singles (or twins for that matter) is condensation, the single engines are pretty big lumps of metal and the twins even more so, taking into account in reality (now that many of us are getting a bit old ) we are in many cases not using these bikes as much as we used to, (I mean I used to go to work on my 350mk3 ) I certainly agree with your point that a well rebuilt/reconditioned Ducati engine will likely outlast its owner, but in several cases I have come across these older less frequent use owners have a bit of a habit of starting the bike and running it "round the block" for a few laps, or worse just starting the engine for their mates to listen to....then back into the garage to sit for a couple of weeks till the next time...I reckon on a widecase single you need about 30miles under your belt to get the condensation fully evaporated off from a cold start, if less you still have water in your engine and I think we would all agree that condensation and bearings surfaces don't go that well together...(how many of us have suffered from stuck clutch syndrome?) I have certainly striped a couple of widecase single engines with bearing surface damage that can only be attributed to condensation corrosion, my motto for long bearing life... is only start it if you are really going to go for "a proper blast" on it.
Cheers,
George

[LaceyDucati]

George
I would agree entirely with your condensation observations, engines like being used (hard or otherwise). Starting an engine and not warming it thoroughly is worse than not starting it at all.
Regards Nigel

[Jordan]

Thanks Nigel, always fun to read your tech observations, some of which I can follow but I can't visualise your descriptions of cage variations.
Have you any comments on reported short life of 860 bigends compared to 750? Could it be a myth?

[marsheng]

I forgot to mention that CR Axtell, the famous Harley tuner, discovered the reason for Ducati big-end failure in the bevel twins was due to the oil not returning to the sump quickly enough at high revs - the oil becoming trapped in the heads and above the sump, allowing the big-ends to run dry and overheat. This would probably apply to a bevel twin that was used for high speed motorway cruising, and I'm assuming that this is why the Singles have direct drains from the cambox when racing?

My thoughts as well, the whole gallon ?

However a valuable comment. I certainly will look at this when I rebuild my 900.

I was always told to use a 50wt in my 900 SSD. I'm not too keen on multigrade unless it is for a car where driving conditions can change quite a bit. What I have learned from quite a few valve train failures with the 1980 CB150 is that older bikes need the Zinc. I now routinely use the zinc fortified oils.

We had quite a few bigend failures on Suzuki FXR150 race bikes. My understanding is that the bigend cage cant accelerate and decelerate quick enough through the 720 degree engine cycle at high RPM which leads to slipping which then causes the failure. On a race build I install a new rod kit, and tell them to use the high zinc oil and have never had a failure in the past 8 years (Did some 12 bikes) They put out around 20HP at the back wheel after a bit of fettling.

The start of a 1 hour race. A few Hondas in there as well.

Bob.JPG

The Suzuki is an amazing bike. These are converted road bikes and I normally can still the original cylinder hone marks with bikes on 40K km. (HaHa I'm going to be using the same filter on the Duke.)

[Ventodue]

Many thanks to Nigel for his analysis. Most insightful and educative.

FWIW, C.R. Axtell's observation that Colin quotes is from a well-known article written by Kevin Bracken about his race engines. To learn more, go:
http://ducatimeccanica.com/kevin_race_engine.html

Craig

[Duccout]

Thanks Craig, I was going to post that link as well for people that don't know it. It is a fascinating read relating one man's journey from fun racer to full-blown tuner-rider, with technical help from C R Axtel, possibly the greatest Harley tuner in history. I particularly like his opinion of the Italian school of port design!