View Full Version : Difference between lefthand and righthand rear main seal?

03-12-2010, 02:17 PM
I changed my rear main seal last season on my 351, I put in a automotive seal, still have a very small leak. I noticed that skidim har both lefthand and righthand rear seals, I'm then guessing that the seal i put in is for right hand rotation since most car engines is righthand rotation. Would you think that a rear hand seal would leak on a lefthand engine?? What's the difference on the seals?

03-12-2010, 02:36 PM
Great question. I can't wait to learn what the answer is. :popcorn:

03-15-2010, 05:05 PM
just an assumption here but we use the same type of seals in jet engines. They are called Labriynth (sp) seals. The have helical groves in them or "threads" if you will. So depending on crank rotation depends on the direction of the cut or groove. If you put the wrong seal in it will actually "walk" the oil out of the seal and create a leak. Again, not exactly sure if this is correct but I'm pretty sure this is the case...either that or you have a grove in the crank. Hope this helps

03-15-2010, 05:24 PM
That is the correct answer! Not sure how I could forget something as simple as that. Then again, that was a few years ago that I learned that.

03-15-2010, 05:46 PM
Learjet's answer is correct. The difference between the RH and LH seals is the direction of the wick lines.

That being said, I dont think you would be seeing a "very small leak" with the incorrect seal... it would be much worse than that! If you have the LH seal in there, youre most likely good. In the marine world, the direction of rotation is viewed from the REAR of the motor. In other words, a standard automotive (LH) rotation will spin the pulleys and belts in a clockwise direction, as viewed from the front. RH (reverse) rotation is the opposite.

I havent heard of many reverse rotation MC's... and those that were, were built in the mid 70's. Correct Crafts on the other hand used RH engines pretty much exclusively (until '89, anyways). Long story short, youre *probably* ok with the seal youve got. Whether it was installed properly is another question. The easiest way to tell which way your motor spins is to look at the prop. LH prop = LH (standard rotation) engine.

03-16-2010, 06:00 PM
Ok, my engine is LH, so the automotive 351's are LH as well then. I have a small grove in the shaft as well, do you know it anybody has tried to put av small spacer of some kind behind the seal to move the seal lip out of the groove?

03-16-2010, 08:38 PM
My dads old 46 Chris Chraft had the same problem. We ended up polishing the shaft with emery cloth working our way down to some very fine grit. It worked well. Dont know about a spacer as I think it would probably cut through the back of the seal. Other option is to replace the part!!