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The dreaded oil Question!!!

Posted: Mon Feb 20, 2006 12:39 pm
by airmale
As a proud new owner of a 1981 900SS I am concerned about the question of what oil to use. I am an experienced rider and mechanic of some 30 years and have owned 18 different bikes over this time. I have spent 7 of those years as a bike mechanic and 5 in semi-pro motorcycle drag racing. I am also a commercial aircraft pilot and perform all maintainace on my 2 airplanes as well as many others.
I have read volumes on oil technology over the years, and personally experimented with many different oils. After reading everything I can find on the bevel drive engine relating to oil, it seems that the majority of owners use straight weight oil. The reasoning seams to be the protection of the bevel gear valve system and that multi viscosity oil will not do that. Because of my experience with straight weight oil in aviation I am very reluctant to ever use it at all. It is common knowledge that 90% of engine wear occurs during cold start and warm up. A 50-weight oil, even in cool temperatures below 65F amounts to little more then glue until warm. It is mandatory in aviation to preheat engines when using straight oil. This is done with either a heating element on the bottom of the engine pan {wet sump lubrication} or a ducted blower of some type {dry sump lubrication}. I can’t express how much engine damage I have seen because of the use of straight weight oil in cool weather. Due to advances in oil technology straight oil is no longer in wide spread use in aviation.
As to how this relates to the bevel engine, it is little different then hundreds of other engine designs. This engine is much better filtered then many, including aircraft and many earlier motorcycle engines. For example both my aircraft are not filtered at all, they have screens that do little more then keep large boulders and pieces of carbon out of the oil. All the smaller 70’s Honda’s use a centrifugal system to trap particles, no other filtration. The key to this situation is frequent oil changes.
When it comes to the bevel gear system in a Desmo engine, there is very little load on the gearing because there are no valve springs. I think the possibility shear damage to the oil is practically nil. This may be more of a concern in valve spring engines, but would not be an issue with 1000-mile oil changes. Modern viscosity oils contain zinc, this is an anti wear additive specifically designed protect against metal-to-metal contact, such as in a gear system.
For the record I have used multi viscosity petroleum oil in all my vehicles, and for racing. I have never suffered an oil related failure. For example I rode my 750 Honda for 60,000 miles. Installed a RC engineering 836 kit and raced it for 5 years without a bearing change. This was done with Castrol GTX 20-50W.

Please, if anyone has some long-term experience with these engines and the oil they use, I would sure love to hear it.


Thanks to Steve for doing what he does!!!

Oil - (oh, why am I doing this?)

Posted: Mon Feb 20, 2006 3:13 pm
by Craig in France

FWIW, Mick Walker was happily using and recommending Castrol GTX 20-50 in Ducati bevels 30 years ago ...

That said, I still use straight 40 in both my Ducrappis - mainly 'cos Tony Brancato tells me to :)

But perversely I use 20-50 in my Laverda Corsa, even though the engine design is basically the same, i.e. air-cooled, roller bearings, low pressure/high volume lubrication system. And 10-40 semi synthetic in my Laverda Formula - also roller bearings, low pressure/high volume, but water cooled.

So I guess the only thing I'm consistent about is frequent changes :)

Craig in UK
'79 SSD
'72 SCR

The Dreaded oil Question

Posted: Mon Feb 20, 2006 3:44 pm
by airmale
Thanks for the input, I have Mick Walkers book and don't know why he bad mouths GTX, I may email him for more info on that. I forgot to mention the synthetic thing. When Mobile 1 first came out, I was working for Honda. I must have repaired 100 clutches the first year due to slippage. The oil was so good it reduced holding power of the plates. I would never use synthetic in a wet clutch engine. Every bike maker I know of at the time, sent out a service bulletin advising against the use of synthetic oil. Synthetic and dry clutch, you bet!!
I don't know Brancato and would love to hear what he has to say, Book????


Posted: Mon Feb 20, 2006 4:43 pm
by Craig in France
Hmmm, so Mick badmouths GTX in what you're reading, does he? Well, he certainly didn't back then ... Which book is this, btw?

Mick's retired now so I don't know how contactable he is. I used to phone him rather than e-mail - and preferably when I had at least 40 minutes to spare :-)

Tony Brancato is a UK based Ducati guru of many years experience, including working with Ign. Taglioni in Bologna on the design of the Pantah plain bearing engine. He makes many parts for our bikes too, either as improvements to the original or 'cos stuff is no longer obtainable - you'll see some examples on Steve's main site. Again, Tony can be hard to get hold off - he's a busy boy.

Yeh, I've heard similar about Mobil 1 and other fully synthetics causing clutch slippage in bikes, especially when they've previously been running on mineral oil.


Craig in UK

Posted: Mon Feb 20, 2006 6:24 pm
by airmale
The book is Ducati Twins Restoration, Page 103 under "engine oil grade". He says good things about multi grade, but doesn't like GTX as too high in detergent content. I agree that detergent in a dirty engine is bad, but in a clean engine it will stay clean. Perhaps he was talking specifically about old dirty engines, but it's not clear. Thanks for the tip on Tony, I looked up his website. I'm sure his recommendations are not in question. I found a good article on oil for those interested.
So glade to talk to such knowledgable folks
Thanks Craig

Posted: Tue Feb 21, 2006 4:41 am
by Colin Linz
When it comes to oil shear I would suggest that the gearbox would have a much higher effect on this than the bevel drive system. This is also why I prefer the mono grade oil, mono’s tend to be more stable in their viscosity in this environment while multi grades can loose half their viscosity in a very short time.

Your rational regarding cold running is very true, most engines can take some time to complete a full cycle of pumped oil and the thinner cold rating of multigrade shortens this time frame. I think the high volume of oil pumped in the bevel engine may counteract this effect to an extent. In any case many of the long time bevel specialist still recommend a mono grade giving shorter life of the crankshaft as their reason. I’m not in any position to judge the validity of their claims, but I’m happy to stick with the recommendations of people like Ian Falloon.

Regarding synthetics. Their use in motorcycles can cause other problems other than drive clutch related ones. A few years ago I bought a new Yamaha TRX850. I wanted to run synthetic oil in it so I rang the national distributors of Yamaha in Australia and spoke to their head service tech. He advised me against it as they can work a little too well and cause the starter clutches to fail. I have also heard that they can cause roller bearings in engines to fail due to the roller sliding on the bearing surface, this is supported by the starter clutch failures many manufacturers experience with customers that use synthetics.

With GTX I would think that if you have a clean engine it would be fine. It is a very good mineral based oil. I have read wear comparison reports that show GTX causing less wear than some synthetics in controlled testing.

Roller bearings 'skidding' on full synthetic oil

Posted: Tue Feb 21, 2006 3:12 pm
by Craig in France
Hi Colin

Yeh, I know some of the Zane Laverda engine failures have been put down to roller bearings 'skidding' instead of rolling - and thereby developing flats - with the finger being pointed at full synthetics as a contributory factor ...

And I can certainly see why a friction device like a starter clutch might fail on full synth.



High detergent oils

Posted: Tue Feb 21, 2006 3:52 pm
by Craig in France
Hi Airmale

Ah, thanks for the reference. If I'd seen that before, I'd have queried Mick about it ... :)

But anyways, I've certainly been led to believe that high detergent oils should generally be avoided in our engines 'cos of the danger of them carrying too much crud in suspension thru the (Ha! Ha!) filters used on Bevels. For example, see ... eaflet.pdf.

Maybe GTX wasn't that high back in the 80s ...

FWIW, this is what I use


Craig in UK

Posted: Tue Feb 21, 2006 7:15 pm
by airmale
Hi Again guys,
Colin makes a great point that the trans is the place where oil damage will occur. That being said, most modern bikes have integral transmissions and motorcycle oils have been engineered with this in mind. The addition of anti- wear additives in all modern oils is practically standard in the multi viscosity comparisons I have read.
In fairness to the synthetics I visited Moble 1’s site and the question of clutch slippage has been dealt with by removing some of the friction modifiers that existed in the early oils. I don’t know if this has effectively reduced the lubrication quality of the oil though. It appears that attention has also been paid to the question of oil shear, and the oils ability to withstand its abuse. It was interesting to note that the oil makers have addressed these questions. Regarding Colin’s point that straight weight is more molecularly stable, I agree, but it may be possible that a synthetic is even more so. The bearing info is noted, but I have not heard of those problems.
Craig makes a good point about oil holding dirt in suspension. As I understand it, “all” oil is designed to hold dirt in suspension until it is removed by an oil change. This is one of the reasons for a manufactures recommended oil change interval. It is also agreed that high detergent in a dirty engine is a bad thing. My experience is mostly with Jap bikes, so the info you guys provide on the Italian ones is very valuable. I will consider straight weight, and look for comparisons for them. I also found that auto oil in general, might be on the way out, this is due to the reduction of antiwar additives to comply with the ever-increasing emission control standards.
I was interested to find that the 1976 750 and 900SS owners manual recommended 50W “Racing” oil. However the 1979 900SD manual recommends 10W-50W oil. Any thoughts on this? As I understand it, the original 750 was designed for racing and the general production of it may have been an afterthought by Ducati due to poor sales. Also Multi weight oils were just becoming popular in the mid 70’s. All the manuals were provided by Steve’s site, I wish we had the complete collection.
For the heck of it, I shot an email to “VEE TWO” requesting oil recommendations for the bevels that use their engine parts. I’m sure you guys know of them. I will submit the kind reply without any further comment other then “Hold on to your Hats”

Congratulations on your new purchase. As far as oils go we recommend that a good quality mineral oil be used for bevel drive engines. Most importantly we recommend changing the oil & filter every 8000 miles"

Mark Scott
Vee Two Australia
Phone: (08) 9248 7500

Thanks all

oil question

Posted: Tue Feb 21, 2006 8:30 pm
by Tom Willis
I have also been using Castrol 20w50 for the last 30 years. I still use it on everything except my 74 750 GT. I've been using Aeroshell 100 (50w) for the last 12,000 miles. It may crater tomorrow but so far so good. I do not do much cold weather riding (less than 60 degrees) as we don't have much winter here in East Texas.

Posted: Wed Feb 22, 2006 8:02 pm
by Colin Linz
With regard to high detergent oils. One aspect other than the particulate suspending properties that may hinder their effect is their ability to foam. Engine oils do have an anti foaming agent, but with the bevels high volume of flow and GTX's higher level of detergent additives there could still be concern with this. I have no evidence of this; it is just speculation as to why they had not been recommended.

Regarding anti wear. Earlier oils of around SG ratings used ZDP (zinc di-phosphate) as a last barrier lubrication to prevent metal to metal contact. This was a very effective emergency lubricant used prior to 1993. With the advent of catalytic converters and oxygen sensors this additive could no longer be used and has been replaced by additives like molybdenum disulfide.

Some links that may be of interest.


Posted: Sun Feb 26, 2006 1:28 pm
by airmale
Hi again everyone,
Thanks to Colin and others for the great links and lots of interesting reading. After doing lots of this, my only question is,” Why the heck are you guys using straight weight oil”? The best reason I’ve read to date, is that someone else recommended it. In all this reading, the only recommendations I have seen are “not to use it”. I have found nothing in the design of the bevel engine that sets it apart from most other motorcycle engines, straight weight oil is no longer recommended for use in “any” engine other than lawnmowers, and heavy straight oil is no longer in use in racing. The research I have done suggests the following.

The best oil to use in a bevel is a multi grade synthetic {10W-50W or 20W-50W depending on your climate and designed for motorcycles.

Mineral multi weight oils designed for motorcycles are perfectly acceptable, if the oil change interval does not exceed manufacturers recommendations.

Manufacturers recommendations regarding oil specs should be followed.

“Any” multi grade oil of the correct weight may be used, provided it is changed within 1500 miles.

There is no significant difference between auto and motorcycle oil other than the replacement or additions of some of the antiwear additives. These have not be removed, but changed to comply with new emission control regulations.

“Do not” used a “high mileage” auto oil in a motorcycle, these have additional friction modifiers that may cause a wet clutch to slip, and also may have lower viscosities to reduce fluid friction.

I will suggest the following but I know I run the risk of being crucified in doing so.

The use of straight oil in a bevel is an old school “myth”, brought about from the earlier days of racing and the Ducati engineers failure to keep up with modern oil technology. In fairness to Ducati, multi weight oil was still in development, and they did change their recommendations in later years.

I am really treading on thin ice with the next one.
I am not accusing anyone of anything, I only mention this as a possible reason for an engine builder to recommend such oil, and it is mentioned only for food for thought.

How much business would someone lose by making a recommendation that eliminated their own business? I refer you to the earlier post that has the response from Vee-Two on oil recommendations.

The proof is with you bevel owners, the oil you use, and the reliability you get. I would love to hear more of your experiences.

Tom, I was glade to hear of your similar experience with GTX, FYI Aeroshell 15W-50W semi synthetic is one of the most popular oils in aviation. I know of many owners and businesses that use it. I use Philips 20W-50W mineral oil in both of my aircraft because of the cost factor and the change interval is 20 hours.

Colin I agree with that oil foaming is a major consideration, but nothing will foam oil more then a crankshaft spinning in a wet sump. I would hope that all oil makers dealt with this problem long ago. Thanks for the links, I read it all.

Re: oil

Posted: Tue Feb 28, 2006 11:06 pm
by Colin Linz
airmale wrote:Hi again everyone,
Thanks to Colin and others for the great links and lots of interesting reading. After doing lots of this, my only question is,” Why the heck are you guys using straight weight oil”? The best reason I’ve read to date, is that someone else recommended it. In all this reading, the only recommendations I have seen are “not to use it”. I have found nothing in the design of the bevel engine that sets it apart from most other motorcycle engines, straight weight oil is no longer recommended for use in “any” engine other than lawnmowers, and heavy straight oil is no longer in use in racing. The research I have done suggests the following.
I started using the mono grade oil because it was and still is according to a number of oil company’s recommendations the oil to use. Caltex was recommending it until just recently when they stopped production of their GP50 and replaced it with a racing specific SG 25w 50 oil. I haven’t seen this oil in the shops but I have seen its earlier version and it was quite a bit more expensive than GP50.

I guess that I stick with the mono grade 50 just because I don’t believe the price difference between it and a synthetic is really worth it, I have seen very little data dealing with our types of engine designs and can see that reports of damaged rollers are conceivable, and that the climate I live in is fairly warm all year round.

So far I have had good service from it. I have just finished replacing all the seals and fitting new piston rings to my engine and the internals looked pretty good. This was a pretty good outcome considering the use it gets, it even survived a full track day at Queensland raceway earlier last year where it was thrashed for 15 minutes every 30 minutes all day long and was faster than many guys on much newer machinery (lap times not top speed).

Posted: Tue Feb 28, 2006 11:09 pm
by Colin Linz
If your not sick of reading about oil the link below has some good data in it. ... 1;t=009433

Posted: Tue Feb 28, 2006 11:19 pm
by Colin Linz
The old duke giving to some newer tackle. I entered this corner behind the Repsol Honda replica, as it was a track day and not a race I had to go around the outside of him.

Old Duke, old 50 wieght oil, its all good.