castrol gtx 10-40 engine oil

bountyhunter wrote: One of many urban myths about synthetic: causes engine leaks, won't let your engine break in, won't mix with regular oil, can't use it in old engines.

All crap. Amsoil syn is just about the best bike oil there is.

The thing that ruins bike clutches is the "friction reducing additives" junk the oil makers throw in (molybdendum disulphide) to try to con people into thinking it "replaces" the ZDDP they took out.

Synthetic oil just flows so much better than dino bones,it will work its way through bad gaskets easier.
my problem with using it for break in oil is the fact it lubricates its a little tougher to seat the rings to my way of thinking anyway,that and I do so many oil changes in the first 500 miles its really pricey to break a motor in with it! :woohoo:

650ed said it best--Don't do it. Make sure it is oil formulted for motorcycles or you WILL be putting a clutch in it.

I have used only "car" oil in my KZ750 since it was new in 1979, now has about 85k miles. Bottom end still original, top redone at 75k.

The only real caveat is to stay away from anything that says "energy conserving" as it has MOLY or teflon or some other crap in it which screws up clutches.

Motorcycle specific oil is OK as long as you don't mind paying $10/quart ($15/quart for Royal Purple). I prefer buying Rotella or castrol for $2 and changing it at 2k miles. If the service grade is SM or SN, add ZDDP.

IMHO, synthetic is a waste of money unless your engine is way souped up or you ride in severe heat all the time. And most oil sold in the USA that says "full synthetic" is Group III dino oil anyway so it's a pure ripoff. I think Amsoil syn and Mobil 1 syn are still true syn (Group IV PAO) but I have doubts about anything else.