Can I use a synthetic oil when breaking in my flat tappet cam? I’ve been to every auto parts store around me and can’t seem to find anything but synthetic. Bought a few qts of royal purple and some Lucas break in additive will I be alright or do I have to use conventional? Was planning to swap it this weekend if I didn’t have to order conventional.
No, synthetic oil should not be used to break in flat tappet cams. You need oil which has zinc in it so you don't wipe your cam lobes. After the cam break-in, then the initial oil change, then you can use synthetic oil in your engine.
If you'd like something other than opinion, here is what Comp Cams has to say about it for their flat tappet cams (most every other cam manufacturer is going to say the same):
Important: On hydraulic flat tappet cams that require dual valve springs, the inner spring must be removed during break-in. Also, we do not recommend the use of synthetic motor oils during the break-in process. COMP Cams® recommends using Part #1590 (10W30) or #1591 (15W50) Engine Break-In Oil. Other non-synthetic, heavy-duty motor oil along with COMP Cams® Part #159 Break-In Oil Additive may be used. This allows the lifters to establish rotation and develop a good wear pattern. As soon as the engine fires, bring the RPM up to 2000 to 2500 during the first 30 minutes of operation. Slower engine speeds will not supply the camshaft with an adequate amount of oil for the break-in period. The engine RPM may be varied periodically from 2000 to 2500 to direct oil splash to different areas of the camshaft. After the 30 minute break-in period, change the oil and filter to be sure all contaminants from the initial break-in period are removed from the engine. Refill crank case with COMP Cams Part #1594 (10W30) or #1595 (15W50) Muscle Car & Street Rod Oil or other quality name brand oil with the addition of COMP Cams® Part #159 Break-In Oil Additive. COMP Cams® Oil, as well as the Break-In Oil Additive will assist with ring seal during the early break-in period of your engine. The inner valve springs can now be replaced.
Engine Builder magazine also states this in their Flat Tappet Camshaft Break-in Procedure.
You just installed a chunk of change in your engine (whether rebuilt engine or just replacing the camshaft/lifters). The last thing you want to do is kill that investment by not following directions.
Again, use a break-in oil which contains zinc (or use an additive), then run your engine up to 2000-2500 RPM for approximately 20 minutes in one shot. You want to make sure your engine is ready to run when you start it up. Running it up for 5 minutes at a time doesn't cut the mustard. You need to run it out for the entire time. If you follow the right procedures (along with proper maintenance), your new cam/lifters will last for a long time.
Yes you can use syntetic oil as long as you use the recomended viscosity for your engine,Syntetic oil do often have a better film strenght than petroleum oil but this is only positive for your engine.
as long as you use the additive it should be safe
The only negative thing is syntetic oil cost more than petroleum oil but it is your money and the difference is small.