[smlblcks10]

ive been reading that its not a good idea to use a full-synthetic oil for break in so how much time do you guys recommend putting on a SBC before running synthetic? i have a rebuilt 283 that has about 6000km's on it and i want to start running mobil 1 or something similar but i want to make sure thats enough time. if not, would it be alright to "ween" it on to a full synthetic by changing it with a semi synthetic now and using mobil 1 or something next oil change?? ive asked everyone from race mechanics to machine shop employees and i get answers ranging from "at least 10,000k" to "just enough time to let the cam break in", so i thought id get some opinions from you guys. thanks alot

[Frisco]

A rule of thumb is after 2000 miles. You should be fine to change it out to synthetic since you say you have 6000 km. on the engine. No need to wean it.

[Centerline]

Originally posted by smlblcks10
ive been reading that its not a good idea to use a full-synthetic oil for break in so how much time do you guys recommend putting on a SBC before running synthetic?

Wives tale!

If that were true the most expensive sports cars in the world wouldn't come from the factory with synthetic. On new cars I change to synthetic at 500 miles. On my street rods, I use it from day one.

Centerline
http://www.hotrodsandhemis.com

[dmorris1200]

Well this must be one of the oldest debates since Ford vs. Chevy. I have not had the time to do any serious search engine digging to find any 'reputable' articles on this issue but I do think at some point I read something that stated certain chemical properties that were in crude oil that were absent from synthetic were recommended for break-in periods. This doesn't mean an absolute must, but recommended. If it were totally false and nothing but a myth why would major parts manufactures (who do plenty of R&D) still to this day recommend crude oil for break-in. I quoted this post in another thread and will paste it here also.
Directly from Crane Cams F.A.Q. sheet...

Crane Cams does not recommend the use of synthetic oils during the initial break-in period for a new camshaft. Use a good quality grade of naturally formulated motor oil during this period. If you choose to use synthetic oil after the engine has been broken in, change the oil filter and follow the oil manufacturer's instructions.

Again you see the word "recommend", not must use. It also recommended crude oil for the break-in of the distributor gear in my Mallory distributors paperwork. It would be interesting to see some paperwork from manufactures that sell products running on synthetic as to break-in procedures. Personally, I have always used crude for break-in just to be safe. But who really knows.

[TurboS10]

I think what alot of people do not understand is the break in period for piston rings today. Most rings are designed to break in about as fast as the cam. The old days of rough cylinder walls and long break in periods are gone. From what I have read and been told, piston rings are fully seated by the time the engine goes through the proper cam breakin period. So, my vote is for switch to synthetic after initial break in. This is what I did on my turbo engine. It had about 20 minutes run time when I switched it, but it is a high output race engine and will see a rebuild before most engines have their second oil change.

Chris

[1BAD80]

On the engines from the GM factory using syn. oil the motors are run first then changed over from the regular oil to syn. type.
Using synthetic oils for break in is False, NEVER brake in a motor or it will be leaking/blow-by oil until its done correctly.
TurboS10 is correct in his posting, after break in is OK to change.
On a new car I change mine after 500 miles using Royal Purple.
LOL
George