Does the sealing surface of the crank need polished?
We receive many emails and calls from customers buying our TIP-RM300 and TIP-RM325 Viton ® rear main seals asking about the crankshaft serrations on the sealing surface of their crankshafts. Most ask if the serrations will shred their new TIP rear main seal and if the crankshaft needs polished. For those not familiar, the crankshaft serrations are located in the sealing surface area of the crankshaft between the flinger ring and the end hub that your flywheel attaches to. These grooves are sometimes referred to as rear main seal lubrication grooves. These small grooves were put on the stock cranks to help lubricate the original rope type seals from the factory. Without sufficient lubrication, the rope seal can burn and shrink from excessive friction / heat.
All stock cranks will have these serrations. When we look at stock type cranks we typically see this area as being very worn down / polished due to years of the stock crank rubbing against a rope type seal. Most aftermarket cranks have these serrations as well but not all of them.
Stock Cranks? As stated earlier, we normally find that all stock cranks are worn down to be very smooth in the sealing surface area. If you take your fingernail and have a hard time getting it to snag on the grooves, you should be OK to install your seal without any further work. If by chance you do feel that the serrations are too aggressive, you can have the sealing surface of your crank polished when you send your rotating assembly out to be balanced during your build.
Aftermarket Cranks? Some aftermarket cranks don’t even have the serrations. This will be just fine if you are using a TIP Viton ® seal. If your aftermarket crank does have serrations, then you need to use the same fingernail test we use on the stock cranks. Same process / principals apply. The only time we have seen the serrations be too aggressive on aftermarket cranks is when Eagle first came out with their aftermarket cranks which was quite a few years ago.
Keep in mind that if you feel that the serrations are too aggressive for your TIP Viton ® seal, then they are going to be too aggressive for your rope seal too! Aggressive sealing surface serrations will tear up / damage a TIP Viton ® seal just the same as it will a rope seal. Please note that you should ONLY have the sealing surface area polished by your crank grinder / balancing shop as polishing removes very little material. Removing too much material from the sealing surface of the crankshaft will change the amount of crush the seal lip has and will ultimately have a negative affect on your rear main seal sealing.