Sorry to beat a dead horse. If I understand correctly, most are saying don't use synthetic oil in the EVO motor, (because it could promote leaks); however, it's okay to use synthetic in the primary and transmission? I apologize in advance for the equine abuse.

 

I do not use synthetic in my EVO or Shovelhead and don't plan to. I know some do, but considering the how different the oil pump is on an EVO compared to a TC or M8, I stay with regular oil.

For decades I used Castrol 20-50 in all holes on my EVO. But more recently I have changed to Lucas non synthetic 20-50. Some use gear oil in the trans, but if you do be sure it is not a GL5 rated gear oil. Straight 50 in the Shovel during colder months and 60e during the hotter months.

Paul

 

Yeah I've been laughed at when I said after 30 years of Dino in my EVO and it's perfect I wouldn't switch to synthetic oil. For the same reason. I also heard the synthetic would cause leaks. My philosophy is, if it works don't change!

To answer your question, the Primary and Transmission are different animals. I run HD Primary+ in the Primary, and Redline Heavy Duty Shock Proof in the Transmission. If you posted a Poll you'd get 1000 different answers on that one.

 

As far as not using synthetic ? been running 15-50 Mobil 1 in mine for the last 45k miles.When I did a ring job after 35k only because of a base gasket leak. Still had the hash marks in the cylinder walls. After seeing that I was sold on Mobil 1.

 

Since you asked:
Castrol 25/50 in the motor. Bosch 3330 oil filter.
I've run just about everything out there in my primary over the years. For the last few years it's been: Drag Specialties "Primary Oil" in the primary chaincase.
Lucas 85/140 gear oil in the transmission. It might be worth noting here that my transmission ( '85 FXRS that I bought, new in 1985) has 317,000 mi. on it. Opened once to replace bearings, bushings and seals. Original gearset.

 

I went Mobil 1 15-50 around 20k, I have 106k miles on my ‘97. She started using a little oil between changes around 90k… uses about 1/3 quart in 3000 miles. She developed a rocker box leak over 100k, but no other leaks.
It’s getting difficult to find and the price has gone up considerably too.

 

I switched to HD SYn3 on my Wide Glide 15 years ago, never an issue. But I shy away from using it in the '91 Sportster, probably in my head. But I would not use synthetic in anything older, good luck.

 

This has been answered countless times in the oil section of this forum.

 

I run synthetic in all 3 holes and no issues. I've always run that in all my bikes and vehicles. The leaking thing was an issue when syns first came out, but that was dealt with about 35-40 yrs ago. Your bike run whatever you like, the bike really doesn't care, just change it when necessary.