Hi!

I have a forged 340 crank which upon close inspection shows that the knurling on the oil seal area on the rearmost journal is worn off.

It's not necked down, but the diagonal pattern knurling is gone.

The machine shop has a knurling tool for a crosshatch pattern which I guess I could just remove one of the wheels so it just knurls in a diagnal pattern.

Thing is that the pitch of the knurls is not the same as on the factory crank, if I do it it would end up being straighter (like straighter gears on a transmuission).

Will it make a difference???

Also I have heard about some bearings that help with the oil sealing probelm?

Thanks and please let me know!

Domingo

Actually you dont need that knurl.. that was for the
old rope seal... most new cranks are smooth for the
rubber seal

Really??

I had a crank once that had the knurling worn off, and it would leak oil.

Then I knurled it (I dont remember if the pitch was the same though), put it back togther and its totally dry to this day.

I wonder if it was the worn knurling or if it was somthing else that caused that oil seal to leak like a sieve.

or maybe the knurling expanded the circunference of the journal so it fight tighter after? I guess the knurling cant hurt to force the oil back in the crank case as the crank turns....however the knurling must be hard on the oil seal is it mught wear it faster than a smooth surface???

Sorta hard to see but this is a new crank and it doesnt
have any knurl

I have a new eagle crank here...Ill go and take a peek!

thanks!

As Raff mentions, you do not need the knurling with a modern rubber type seal.

If you look at your Eagle, you will most likely see a failry heavy knurl on that crank, but it as well isnt really needed. I make adjustments to the Eagle cranks, but they will work without it.The cause of the leak was most likely NOT the knurl, but something else, and was fixed when you did the repair.

Domingo

Whatever you please DO NOT knurl that surface area again. The factory knurl is fine but going over it I'm afraid you will create one heck of a problem. Even for a rope seal to survive on.

There are many, many factors that come into play with rear crankshaft seals and I can only go by what the info you provided as I don't have the parts in my possession. So here's a few suggestions for you to consider.

Suggestion #1
Measure how deep the groove is in the crankshaft. Mock the seal up in the block WITHOUT the crank and measure the I.D. of the seal lip. Be careful not to flex the lip when measuring. Subtract the seal I.D. from the crank groove dimension.
If it's less than .015" put a rope seal in there.
If it's more than .015" you can take the chance with the rubber seal. However, I would suggest the minimum amount of crankshaft end play so the seal doesn't ride up on or out of the groove. This will effect the dynamics of the seal and quite possibly cause sealing problems.

Suggestion #2
Have the surface welded and bring the diameter and surface finish back to spec. no need for the knurl.

Suggestion #3
Put a rope seal in there and be done with it.

Another thought Main and rod bearing clearances play a role in sealing this area as well. The more clearance the higher risk of sealing issues as excessive oil can overload the seals ability to stay in contact with the crankshaft surface.

I hope this helps,
Merry Christmas everyone!

Thats bs Greg and you know it!...

Its funny, I've been building engines for over 27 years and have never had to use a " anti leak" rear main...must have got lucky ???...

It must, i went as far to take the motor back out and it went back to the machine shop and after they checked the crank and the seal for fit up he said it should not leak. Put it back in and it still leaked then i proceeded to call indy where i got the rotating assembly from and they told me they all leak a little but since i run a 4spd it is a little hard on the clutch. So at that point i talked to my buddy that was a dodge tech and he starting asking around and found out about the anti leak rear main bearing dodge had to make to fix all the oil leaks in the late 80s early 90s when they quit making the 360s with knurls on the crank.So i installed the anti leak bearing and guess what no leaks. I am no machinest but i had no leaks with 3 other 340s with the knurls on the crank and the motors where all built by a very good machine shop and same shop. The knurls on the crank are cut in the crank in a way that it channals oil away from the seal.I have always used the felpro rubber seal.What seal are you using?

Of the cranks I have, none have the knurl... I
dont recall the company name of the seal but it
has a double lip and I assume the outer lip is a
dust seal and the inner lip is the real oil seal