Synthetic oils in older bikes
 

Following on from my earlier post about synthetics...

There is a commonly held belief that synthetic oils are not suitable for use in older bikes. This isn't generally true!

Do synthetic motor oils damage seals?

Any oil seals made after 1975 or thereabouts will be entirely compatible with any type of synthetic engine oil. (The same goes for synthetic gear oils and transmission oil seals.) It must be understood that everything associated with lubrication is thoroughly tested. The major oil manufacturers do not make oils that attack seals; seal manufacturers ensure that their products function correctly with modern lubricants.

Are synthetic oils too thin?

It is true that the best synthetic blends can be low viscosity (0w-20 for example), but they do not have to be! It is also true that the latest engines are designed to run on thin oil, which improves power output and fuel consumption. Even so, thicker synthetic based grades (10w-50, 15w-50, 20w-50etc) are available for air-cooled motors, older engines, or severe high temperature conditions. These grades can also benefit rebuilt classic engines dating back to the 1940s.

Do synthetics mean higher oil usage?

No. Oil consumption in well-maintained modern engines is mainly down to the oil evaporating at high temperatures. Synthetic base oils (specially the PAO and ester types) are very resistant to evaporation loss even in low viscosity blends, so oil consumption is minimised. But engines with worn valve guides, defective seals and worn piston rings will use oil regardless, so there is no point in using expensive synthetics in a worn engine.

Hope this helps to clarify the position!

oilman

Hi Oilman and thanks for the info. Any advice on clutch slippage (or more to the point, avoiding it) when using a synthetic oil

What synthetics are you getting clutch slip with?

Cheers

Guy

I have always been led to believe that clutch slip indused by the use of synthetic oil is not actually the oil being at fault but it showing the signs of a worn set of plates much earlier than a mineral oil does.

Also I was under the impression that older engines, such as the Indian Enfield Bullet, are unable to use the more modern synthetics due to their reliance on the scuffing that is needed in the bore. The synthetics are too slippery for the scraper ring to cope with and you end up with a glazed bore and very smokey exhaust.

I'm currently riding a 2001 CCM 604 which uses a Rotax engine. I've stuck with mineral oil in it and had no problems but over on the CCM forum there are numerous reports of changing to synthetic oils (various different brands) and having problems with clutch slip.

It's not just the CCM though, I've come across clutch slip reports on slightly older bikes (older as in years, not as in knackered) when changing from mineral to synthetic and not wanting to have to replace a perfectly good clutch (with seven bikes it could get expensive) because of a bad oil choice have stuck with mineral.

Synthetic does sound like a good "upgrade" though, particularly on my two overlanding bikes - protection in high temps, extended oil change period etc but I'd rather get some further info on what works before just picking a pretty looking can at my local motor factors.

Oilman: synthetic related questions.
 

Without asking you to condone bad maintenance techniques, would you say that a syntheitic oil of good quality will be more resistant to breakdown than a mineral or semi-synth?

I ask this as both bikes I have use small oil volumes, are air cooled and thus have very frequent oil change schedules (1500 miles Ural, 1000 miles XR400R). These run mineral and semi-syntheitc respectively.

Whilst I intend to change oils regularly, if I were to use either bike on a longer trip where oil changes might not be so easy/frequent, it would be good to know that the oil in the engine has probably not lost its protective characteristics... Can you comment?

My next question relates to a principle I learnt to operate by when I first got into bikes. I suspect this is no longer the case, but I have never confirmed this outright.

Is it now safe for the engine to switch from mineral/semi to fully synthetic and vice versa without needing an engine flush?
(I used to be told in my youth that such a mixing caused the oils to thinken through some chemical reaction, but I never witnessed it my self...)

Thanks.

Over the years I have always done the oil changes on my bikes myself. Recently, due to circumstances I asked my regular mechanic to do the oil when he had the bike in the shop.
The bike is a 1989 R100GS and I have always used 20/50 mineral oil. He used semi-synthetic for the change and over the next few days the engine was leaking like a sieve...When I discovered that he had used semi-synthetic I immediately changed to mineral and the oil leaks stopped without any other actions....

Referring to Backofbeyond's experience, I have a 1999 Aprilia RSV1000, the one with the Rotax engine, owned from new.
The handbook is quite specific about what oil to use and I never had any problem until I did an oilchange using whatever oil they had in my local shop at the time. Same grade, leading brand. But it was, don't remember which now, either fully-synth and the book said semi-synth, or vice versa.
The clutch started slipping.
After two more oilchanges using the oil specified by Aprilia (from an Aprilia dealer) the clutch is OK now.
The same happened on my 1986 Honda XBR (also owned from new, same engine as the RFVC air-cooled XRs). The book says mineral, I tried semi-synth once and the clutch slipped. Now back on mineral, the clutch is OK.
I think theory and practice diverge somewhat in the subject of lubrication, and I'm an engineer myself.

In my experience, always best to do exactly what the manufacturer says.

Its engineers will have spent a lot of time designing the bike, with some pride, and they really know best how to treat it I think.

Older bikes (air cooled) have much lower tolerances in build quality & therefore can burn off more of the modern hi-spec oils.

Synthetic oils will not necessarily make the clutch slip as long as they are "wet clutch" specific - not car oil :thumbdown: But they do tend to be more "slippery" than non-synths.

As regards to mixing oils, the main problem is when changing between castor based oils (good old Castrol R 40) and mineral :( This can cause the stuff to gel up & any deposts burn & stick to pistons, rings, valves.. etc.

My 1978 Kawasaki Z1000 runs Amsoil synthetic mineral oil no problems.

Another point, if you do run a synthetic oil in an older style "roller" bearing engine (ie: cranks on rollers, rather than shells) it is reported that the synthetic oil makes the ball bearings slip, rather tahn roll.... which ironically can cause wear to the bearing:nono:

Probably best to stick to manufacturers recommended stuff as McCrankpin says... but get a decent one & change often as possible:D

I have watched this perennial thread in different forums over the years.
The Pro synthetic people want it both ways.. Ie They clain it is a better lubricant because it is more slippery and gets in everywhere. Well if this is true it also supports the many owners (partictularly airhead BMW's) who's owners claim to have oil seeping past seals (particularly the rear crankshaft seal). The same applies to the clutch. IF it is a better lubricant it MUST be more inclined to promote clutch slip.
Generally speaking I think you should use what your manufacturer says. Remember also , most modern oils contain little zinc which older flat tappet engines need. You might get away with an SG rated nn/50 weight oil as those are excempted from having little zinc. I doubt however you will find a synthetic SG rated oil as this specification has much more zinc than ANY other.
Personally
I wont run synthetic in my engine due to the lack of zinc.
I wont run synthetic in the primary side due to the wet clutch.
I wont run synthetic in the gearbox because It may leak, my weakest case for not running synthetic is the gearbox.

Just for information for EU located riders (no, I am not working for HG) just wanted to share useful info: Hein Gericke have 10W50 Synthetic motorcycle oil API SG JASO MA. It's really cheap too. I run it in my DR800 and quite happy with it.

When digged for actual source HG get's that oil from - it's Motul.
Since SG MA specs synth was mentioned as difficult to find I thought I'd post that info. Do not think HG have it anywhere outside EU thou.
If this considered marketing - sorry, I will delete it if you tell me.

A good proper synthetic oil PAO/Ester basestocks rather than the cheaper hydroprocessed mineral oils will always be more thermally stable over the long term. In essence, they do last longer without losing viscosity.

These days most oils mix but mixing a quality synthetic with a mineral oil is sort of defeating the object of putting the better one in.

Cheers
Guy

This does not make sense unless the Garage put a different grade oil (thinner one) in as a mineral 20w-50, semi-synthetic 20w-50 and a fully synthetic 20w-50 have the same properties.

They will all have 20w Cold Crank and meet sae50 at 100degC

Cheers
Guy

Many thanks for that information. It may come in usefull even for me, as my Enfield specifies 15/40 sg oil.

It may not make sense, but it happens far too often to be ignored. BMW rear engine seals are particularly prone to this senseless event.

It could be PAO Synthetic as this tends to shrink seals. Some of the higher end companies like Silkolene and Motul add Esters to the PAO as they swell seals which negates the effect.

Cheers

Thanks for the answer.

Re above. I was not thinking of mixing the two intentionally, but rather, if I did change from mineral to synthetic, and possibly back again at a later date (if supply/finances demand it), some of the oil that was in the engine prior to it being drained, will inevitably mix with the new oil being added.

This is the scenario I was referring to.

It is no problem, what you will have in your engine whichever way you do it will be semi synthetic :)
what you dont want to mix is castrol R or any other veggie oil with mineral or synthetic. Note semi (as in semi synthetic) does not mean half and half.

The way oils are graded can be very misleading. Unlike nearly everything else the grades refer to a maximum that the oil does NOT meet. For instance SG rated oil can have a maximum of 0.12% of zinc. SL 0.10%.
So if you had a 45 gallon barrel of 0.000001% zinc (or none) mineral oil, you could put a drip or two of synthetic in the barrel and legally sell it as semi synthetic SG rated oil.
It meets the specification, because it has LESS than 0.12% zinc (zddp).