Is it ok to use synthetic oil?

[Rooter]

I was talking to a buddy and he mentioned that he never uses synthetic oil in his older bikes as sometimes it seeps where it shouldn't. When I changed it this spring, I added 1 liter of mobil 1 synthetic 4 stroke motorcycle oil along with 2 liters of non-synthetic 4 stroke motorcycle oil. There are no signs of any leaks and it seems to be running well...

[sachiwilson]

Synthetic is known to find holes where none were before.  That makes it a good oil for lubrication but also a bad oil if you have dodgy seals!  On some old bikes, the seal engineering is such that they can hold in the dino oil but aren't able to seal in the synthetic oil.  Also, even if the engineering is up to snuff, an old seal can be so worn out that it can leak when exposed to synthetic oil.  So, those are the reasons that people warn against using synthetic oil in old bikes.

Now, to yours.  Your bike isn't an old Brit twin with dodgy seals but a modern Japanese four.  Assuming you've been keeping it in shape, its seals are likely in decent nick, too.  (I'm American, but I seem to be using British slang here - dunno why.)  So using synthetic is not likely to cause any leaks, at least not anything serious.

[clarkdw]

I won't go into a longwinded discussion of the benefits of synthetic oils versus conventional but suffice to say that I am a very strong advocate of their use from personal race engine building experience on automotive engines of the ancient British variety as well as much more modern Karting powerplants.

As soon as I got my CB-1 I switched it from whatever was in it to Motul synthetic. I have since put on about 10,000 km and I will never switch back. No leaks and no other negatives. As sachiwilson said, if your seals are worn there may be leaks but in that case you need to repair the engine anyway, right?

What I would strongly advise against is mixing the oil types as you have. Mobil 1 and other SAE rated automotive oils are designed to be compatible to the degree that they will not destroy your engine if mixed but it is definitely NOT a good idea to mix oil brands or types because you never know what strange chemical reaction the different additives may have. This is particularly true where the oils are not SAE rated as in some racing oils such as Klotz two stroke or four stroke bike oils. I don't know if the bike oil you used is SAE but even if it is I would suggest getting rid of the mix and change the oil to a single type. If cost is a big issue use one of the semi-syn's any of which would be excellent.

[Rooter]

Thanks guys.

[psubrock]

I heard that synthetic in older bikes sometimes causes the clutch to slip since it rides in the oil. Maybe that was what was mentioned with "seals" but I dunno.
I've never used anything but good ol' fashion pennzoil 10w40, I just make sure that I'm at operating temp before I start bouncing the tach off the redline and change it frequently depending on how it's ridden (2000-2500 miles). Unless you have a race motor or race all the time I don't think there would be a reason to use synthetic. But I agree with DW you shouldn't mix synthetic and conventional because synthetic coats the metal so you can't go back to conventional without the risk of the synthetic coating coming off and gunking everything up.

[Rusty]

On a new motor with under 3,000 miles, use dino oil. This helps to seat the rings. After 3,000 miles, it's ok to switch to synthetic oil. Synthetic oil in a new motor, the rings take forever to seat. Tried that with a 572ci HEMI. With a wet clutch, you have to watch the amount of moly the oil has in it. That is why some oils causes the clutch to slip. Most auto oils have a high moly level. Bike oils have a lower moly level. You want to screw up a clutch, add a oil additive to the crank case!
If the seal is leaking after the oil change, the seal was going bad to begin with. Just speed the process up a bit.

[Rooter]

So far, I have about 1000kms on the bike using a 10-40W 4 stroke motorcycle oil (2 litres) mixed with Mobil 1 10-40W Synthetic 4 stroke motorcycle oil (1 litre). No signs of any leaks - it seems to start better, run better and I'm not feeling any clutch slippage so far. The people who make motor oil for cars make synthetic blends and from what I understand, it's about 10% synthetic so 33% has to be better, right?

[mechdziner714]

Make sure the oil is not " energy conserving" and your OK. The energy consv. oils have high moly content that causes the clutch to not work as well. Otherwise any good quality oil is fine. I use Shell Rotella T Syn, its 15$ a gallon, and the clutch and gears shifts are excellent. Change every 3K and your motor will last a long time. I also use the K&N303 filter, it has a nut on the end for easy removal and wire tying. The K&N gold filters are one of the best out there and cost less than Hondas.

[clarkdw]

Very helpfull article on types of oils and intervals for changes here. Definitely worth a read.

http://motorcycleinfo.calsci.com/Oils1.html

[hurricane]

hi

when i changed my oil i use to use castrol. a friend then said a should try motul so i did and then my clutch started slipping. i used motul 10w40 ester as recommended by the mechanics. and i have new clutch plates. any ideas?