Oil Mixture

[jse]

FIO - twin cylinder 2 stroke rotax microlights in UK generally run at 50:1 and are so over cooled that 80% of radiator is covered in winter.

Good info for me. I live a mile from a small airport and guys here (they call them "ultralights" here, propably the same thing as the micros) run a 2 cylinder, boxer air-cooled 2T for the most part. I imagine the Rotax is probably a more sophisticated 2T. Do they run the rotary-valve types?

Jon

[b40rt]

Hi Jon, in line twin, disc valve. 4 stroke 4 cylinder rotax microlite are boxer config'

[jse]

Hi Jon, in line twin, disc valve. 4 stroke 4 cylinder rotax microlite are boxer config'

Ah yes. The 2T inline twin sounds like a takeoff of their old 250 roadrace engine. I found it to be a good, strong unit

that made good horsepower.

Is the microlight a fixed wing? The ultralights here are like motorized parasails.

[dadof2]

I can’t really suggest a one size fits all mixing ratio, there are too many variables.

Firstly the type of oil is a compromise in itself. Ideally the rolling bearings, mains, big and little end need a low volume of heavy oil (SAE 50) whereas the piston needs a much greater supply of lighter viscosity (SAE 30) oil.

Oil lubricity / quality also varies greatly, some synthetics are less than £10 per litre whilst some are about £30 per litre.

Research shows that whilst idling a ratio between 80 and 100 to 1 is adequate whereas at high throttle openings between 20 and 30 to 1 is needed, hence the development of pumped oil systems.

Some riders use good quality oil, keep the air filters clean, the carburation correct and don’t work the engine too hard (avoid high sustained RPM) and never have any problems at ratios over 50:1. Others tend to buy whatever oil is handy, are a bit careless on carburetion and maintenance and work their bikes hard and their piston / bore is worn out or mains fail in a season or two. They would have been far better at 30:1.

Many years ago I used mineral 2T at 25:1 in trials and 20:1 in MX. Never had any wear or seize problems but did get hard carbon build up. Then along came synthetics that supposedly could run at 50:1. On my local dealers recommendation I used them at 40:1. For several years I persevered with 40:1 but noticed significant increase in rate of bore wear on both MX and trials and even had a big end fail at less than 5 months old. The above applies to 3 well known brands. Colleagues using Castrol’s synthesised versions of castor oil at between 30 and 40 to 1 fared much better wear wise but did get some coke sticking of exhaust power valves. I reverted to mix rations of 32:1 for trials and 20 or 25:1 for MX using mainly semi synthetics and the wear problems ceased.

I understand at least one of the reasons Yamaha developed Yamalube R (now 2R) was because of the variable quality of synthetics being sold.

Air filters do not stop all dust, (nor do they stop water which has a severe negative effect on synthetics) the smaller the particle the more likely it is to get through. A thick oil film and good supply of lower specification oil is more effective at stopping wear due to dust than a thin layer of high specification oil.

There is a lot of rubbish talked / written about the supposed disadvantages of using rich mix ratios such as poor pick up, smoking and carbon build up that are putting it bluntly a pile of crap. Good quality oils and petrol contain cleaning additives and don’t produce deposits, poor oils and cheaper petrol don’t contain sufficient additives and produce deposits. Carburation is also important – take a look at Souwesters “Beta tar factory” despite running fully synthetic at 75:1. Some of the cleanest pick up bikes I have ever ridden were during the 25:1 mineral oil / tubed tyre era when clutching was not used and precise throttle response was key to adjusting speed and finding grip.

Detonation and piston temperature. One of the main functions of 2t oil is to transfer heat from the piston and piston rings to the cylinder wall. A thin film of high lubricity oil may prevent metal to metal contact but there just is not enough of it to transfer heat out of the piston and high piston crown temperatures then cause detonation (pinking). This is perhaps the main reason why high revving kart engines need 15 or 20:1 oil ratios and why 4 stroke engines spray the underside of the piston with oil. I have seen trials bikes correctly jetted and running on Putoline MX5 at 40:1 suffer quite severe detonation and overheating problems when pulling hard on sustained climbs (about 60 to 75% throttle). Switch to mineral oil at 25:1 and even with no carburation adjustment the detonation and overheating problems disappeared.

I would always advise to mix at least as rich as the engine or oil maker recommends, whichever is the richer and use the recommended or known better oil, not some uncertified brand.

Jon – I hope I have at least to some extent answered your question and end with the following thought. James Dabill’s Beta seized at the Scott when he dropped it and the throttle stuck open. Perhaps someone will post exactly but I guess he was running at between 50 and 75:1. Would it have seized if oil ratio was between 25 and 32:1 ? I have seen several bikes at these ratios rev their b------s off until the carb ran out of fuel in the same circumstances but not seize.

[dadof2]

0007 in reply to your questions

Dadof2, just avoid quoting the entire post

Thanks for the info, engine testing is very interesting stuff, do you do this kind of work?

Not professionally any more - for about 20 years I worked in the oil industry and then after that in engineering with close links to all types of engines from chain saws to turbo diesels and some fuel research We had a 125 HP dyno and oil test equipment. Most of the interesting stuff was picked up from work colleagues who had worked in very specialized automotive fields.

I like to see how and why things happen in engines, amazing how subtle changes make radically different results

Q: for curiosity reasons, were the engines air cooled? (Chainsaw)

Some of the engines were in chainsaws, other variants in motorcycles, both air and watercooled The no problem 32:1 engines ere all hard used chainsaws.

On a waterbrake dyno (rpm controlled by load or electronically limited)

The production engines are electroInically limited - I think the miss alternate ignition sparks at the RPM limit.

I think the dyano was electric generator type

Was there any detonation (detonation applies shock wave loads to rings, damaging ring land etc etc)

On the test engines as far as I know it was just lubrication film became inadequate at about 12500 RPM followed by galling of the rings and bore. On the warranty claim engines the symptoms were the same. As far as I know the engines have not been modified at all but the oil spec and advice to customers has been. It is not improbable that there was nothing wrong with the engines or the oil but the frequency of failure would have been damaging for the manufacturer if it continued. The comment was made that "UK pump fuels are among the least regulated in Europe" Out of interest I wrote to my MP about fuel and received a very detailed reply with info dating back over 50 years. The variability of what they can put in it is quite surprising if not shocking.

[obsever no 1 uk]

Hi I have run at 70.1 for a long time with good results ,this is the way forward to feel comfortable whilst revving hard etc...

Stay Safe

[dadof2]

Observer No 1 - I guess Buckinghamshire is pretty flat - see my comment RE James Dabills bike and revving.

Gas Gas used to recommend 67:1 (1.5%) but have now changed that to 50:1 (2%)

The way some riders seem to enjoy running lean ratios contrary to manufacturers instructions baffles me, as I commented earlier in this thread if any one thinks less oil is best why not try it with gearbox oil, coolant and brake fluid as well.

Edited January 9, 2014 by dadof2

[0007]

LOL, I'm gonna go drop my fluid levels to lower the weight of my bike

Having worked for a manufacturer for over 15 years I can tell you they have politics, joint agreements with oil manufacturers, warranty and other things to consider

Conservative jetting and oil ratio are only 2 examples that apply to this conversation

I bet the oil ratio the engine designer runs in his own bike would vary from the info the compliance department directs the literature department to print in the owners manual of brand X bike

(Note: this does not apply to the Japanese who would not vary from manufacturers reccomenation)

Dadof2 is 100 % right in his comments, it may not work for me and others but is working just fine for him just like higher ratios are working for others, lots of people are right on this subject

Cheers

[breagh]

Interesting points

Must say I've noticed a lot of bikes at our trials that sound less than healthy.

Not old ones too.

My old sy needed mains and a piston which I always put down to drowning it at a trial.

Now sounds like I was not using enough oil.

[shyted]

Two more things i'd like to jib in with. I raced two stroke racing bikes up to a few years ago . Depending on the weather, i ran between 18 and 28:1 and that was with A747 . 100% reliabillity and bizarly there was a coating residue on all the componants on stripdown but never got that prior to switching over to said brand.

The second thing is the oil provides ring seal as well as other atributes.

.

[showershorts]

according to beta themselves its 70-1 on semi synthetic oil. hope this helps.

[dadof2]

Beta UK website says 1.5% on Synthetic oil which is 67:1

I think Beta favor Bardahl VBA 100 which is at the upper end of fully synthetic oil quality.

I am not aware of any manufacturer of semi synthetic 2t that recommends mixing at ratios higher than 50:1

[copemech]

And I doubt you will due to liability.

Even my new Echo Pro weed wacker(strimmer) came with a 50:1 mix pack. Now these things can run near wide open for their duration.

I did see something posted on display by the Mfg. stating that they were rated at only 200 hours life expectancy. Does not sound like much, but put into perspective is a lot better than I ever got out of a 125 MX bike back in the day at 32:1.

I prolly ran the thing for 5 hrs or so this year as well. How many years is that?

I doubt my water cooled 2T trials is that highly stressed going put-put-put with an occasional rev. Most the oil will lay up in the bottom and give an occasional splash!

[0007]

Copemech that is probably an EPA rating, most stuff is required (even generators) to be some kind of compliant for a reasonable period of time

[copemech]

Copemech that is probably an EPA rating, most stuff is required (even generators) to be some kind of compliant for a reasonable period of time

No, this was a small engine cutaway display by the Mfg. highlighting their bearings and plating features to enhance durability.

I am sure they have gone to the 50:1 mix for EPA concerns, however with good oil a non issue it seems.

The bottle I got did not state if it was full or a blend of synthetic, but I think the additives are likely more important as long as a high quality base stock is used if you know what I mean. As they brand their own oil, not sure who makes it for them?