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Tech Tip "Installing crank seals to correct depth"
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Posted by: Pete Payne---------------------
This is something I have seen several times over the last couple of months. Guys have done their own rebuilds on the bottom end only to have the crank bearings fail prematurely, within about a month.
They have brought the engines to me and upon inspection I found they have installed the seals too deep into the cases . The seals were drove in all the way down to the bearing cage or race of the crank bearing. This has blocked off the oil feed hole that helps provide much needed lubrication for the bearing. There are two feed holes , one for the left bearing and one for the right bearing.
They are drilled vertically down into the cases to the area of the bearing.
A simple check to do after installing the bearings is to look down into these holes and make sure you can see inbetween the seal and bearing . Or you can put some of your favorite 2-stroke oil into the holes and it should run down quickly. If the hole stays full of oil , then the seal is in too far and is blocking this hole off.
On many engines there is a fine line for the seal to be properly installed . It should seal on the end on the crankshaft(left /ignition side) or spacer(right/ clutch side) , be into the cases far enough not to be blown out by crankcase pressure , and not block off the oil feed hole.
The bearings also get some lube from the small space inbetween the crank and cases . Normally this side clearance is .010" - .020" so you can see it is a good idea to make sure the seals are not installed too far . These bearings need all the fresh oil they can get!!
Happy moto-ing !!!
Pete
Posted by: gasgasman---------------------
Thanks for the tip.
I'm about to do one on a friend's bike.
Posted by: Jim Cunningham---------------------
Thanks for the tip. Tech tip is a great idea!!! There's just to many things you need to know. Thanks again:D
Posted by: Papakeith---------------------
Excellent tip! And, awesome timing. I'm getting ready to replace crank seals and bearings on my winter rebuild project. I'll wager you've just saved many shadetree mechanics a couple of dollars. Thanks.
Posted by: jmics19067---------------------
It appeared to me that the crank seals are flush with the outer edge of the cases. I always used a seal driver that was bigger than the actual seal so I couldn't drive them in no further than just in . Would this be the proper depth?. I have never noticed anything wrong before and I am curious am I missing something. I definately know I am not driving them in to far but is there more to not having them in enough ?
Posted by: Pete Payne---------------------
That is a better method than just driving them in until they stop. Normaly I go past the chanfer on the outer edge of the seal bore . This way 100% of the outer edge of the seal makes contact and is less likely to be blown out due to crankcase pressure (this does not apply to bikes that the seal goes into from the inside--aka-Kawasaki KX250 and others of similar designs). Be sure to always check to make sure the oil feed holes are unblocked. --Pete.
Posted by: jmics19067---------------------
Great insight. Thanks!!!
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