Synthetic Oil or not?

I am the original owner of a 1979 KZ650-D2 motorcycle with 10,000 miles which remains in pristine condition. It has a 'mechanically sound engine'. I have been researching motor oil brands for the best to use in my bike. AMSOIL has my attention. I have always used Castrol GTX 20W-50 (non-synthetic detergent) with an API Service SE (presently SL). This is what the Kawi dealership recommended to me when I purchased the bike in 1979. In the past many of the forum members have recommended using Castrol oils. Many have recommended not switching to synthetics on an older bike since some have experienced oil seepage after switching and some have concerns about wet clutch slippage.

My questions are:
1 - What are your thoughts on switching from my ever-trusted Castrol non-synthetic to AMSOIL Motorcycle Oil full-synthetic?
2 - Is their any credence to the oil seepage issue?
3 - Is there any credence to the clutch slippage concern?
3 - What SAE should I be using (10W-40 or 20W-50)? I live in the Boston, Mass area.

I don't know about the clutch slippage issue. I do know that in automotive engines, especially older engines with 70+ thousand miles on them, switching to synthetic oil has caused oil seepage from gaskets, seals, etc. Also when I purchased a remanufactured engine for my truck it came with synthetic oil already in it and the paperwork for the engine stated that if I at any time switched from synthetic to non-synthetic oil my warranty would be null and void.

I have several friends who have taken engines apart just to replace all the gaskets and seals so they could switch to synthetic oil. They didn't have any problems with seepage.

Don't know if any of this helps or is even applicable to motorcycle engines (altho I don't see why it wouldn't apply after all a gasket or seal is still a gasket or seal) but I hope it helps!:blink:

I made the mistake of switching to synthetic for my Jeep a few years ago at about 70,000km. There was some oil seepage after a while, then the rear main seal let go. Everybody blamed the synthetic (Mobil 1).
This summer I changed to Castrol 5w50 Syntec Synthetic for the bike. No oil leaks, (other than the persistent one that's been there since the engine went back together), and no clutch slippage. I did notice right away smoother shifting.

Fossil was it the '83 GPz1100 Streetfighter you made the switch to synthetic in? And did you make the switch recently? The reason I'm asking is because I have a '83 KZ650 and now I'm wondering if it might be a good idea for me to switch to synthetic in it.

Bud1, yes the synthetic is in the GPz1100. It was just this summer I switched over, previously it was running on semi-synthetic. With the weather getting colder the synthetic does not thicken the way mineral oil does making starting a little easier.

Thanks. I think I'll try it.

I don't have the link to the specific article, but it recommended synthentic for air cooled engines, since they can run hotter then water cooled, especiallly in stop & go traffic. It also stated that synthetic is no "slipperier" than any other oil. The main benefits of synth is that all the molecueles are the same, and they are oil, as opposed to junk loft over from refining.

Hey there BeeGee, I use Honda's GN4 20W50 when the weather is warn to hot, and GN4 10W40 when it is not so warm to down right cold. But I have friends that own and ride air cooled bikes that use Honda's synthetic (without moly) year round with no problem. My view is that it's the owners call. Get as much info as you can though. Why btw are you thinking about switching oil? If the brand you are using is working then why not stick to it.

Post edited by: zedheadmc, at: 2005/10/23 12:59

zedheadmc wrote:

If the brand you are using is working then why not stick to it.<br><br>Post edited by: zedheadmc, at: 2005/10/23 12:59

I agree. Unlike the 1000+ kZ motors, the 650 has a plain bearing crankshaft. Why risk it. If you really want to go synthetic, you should seriously consider Red Line.

Jay

Nice to have you aboard Jay

My opinion is if Kawasaki say to use mineral oil, use mineral oil. They haven't, to my knowledge, issued a tech bulletin saying it's ok to switch to synthetic.

My personal experience with synthetic in my 750 has not been good either.

I have 42,000 miles reading on my ticker, and I am using synthetic oil. I don't know was in there, but I do see some seepage around the head and cylinders. I'll be doing a top-end soon, and looking to install the 615cc kit(will be sending the pistons and cylinders to APE for this one). I would use whats been in there until you have to do a full rebuild. Stick with the Motorcycle Specific Oils, as they are used for wet clutch systems. Thinner if you ride in the real cold, and thicker if it's real hot, but the 10/40's(30 wt.) and 20/50's(35 wt.) out there should be fine for all-weather riding. Just do 2 things. Let your bike warm up before taking off, and change the oil and filter at the same time, and often. It's cheap insurance. I am also looking into installing an oil temp gauge to my bike because "I gots ta know".


Post edited by: CoreyClough, at: 2005/10/24 08:42

I found the article I referred to that recommended synthetic for air cooled engines. Here it is. I haven't switched yet, but I am seriously considering it.