oil seals on a DT400

[robdyk]

Hi Guys,

Just one question.

I'm installing a new crankshaft oil seal (L and R) on my yamaha DT 400 1978, but I'm not quite sure which way of the seal faces inwards.

You have a open side which shows the metal ring and the other side is the closed side. The rubber with the markings stamped on them with the castellations.

Should the open or closed side facing inwards ?

In other words, installing like this:

Or like this:

The last couple of days I've heard several opinions. So who knows the correct way of installing these suckers ?

[Sacha]

The "closed" side goes opposite the oil. So the open side goes toward the crank (inward) and the closed side toward the gear lever. If I understand right. Someone will know.

Edit- install it the way the old one came out?

[robdyk]

Hi sacha,

The way the old seal came out was with the "closed" side facing outwards. I've ordered new oil seals with a company in the UK. That guy saya just the opposite.
This is what he says:

Many people, including Yamaha dealers make that mistake.

The closed side has some castellations on it

_|||____|||____|||____|||__

Which are designed to disrupt the flow of the fuel mixture forcing it back through the bearing for lubrication.

Most crank seals are fitted with the closed side facing outwards but not these ones.

We have had many bikes through the workshop with the seals fitted the wrong way round, because that is the normal way and this makes them fail quicker. The factory manuals show the seals with the closed side inwards and I have had a couple of zero mileage bikes to restore with the seals fitted the way they left the factory, closed side inwards.

One or both of these seals were used on every Yamaha single cylinder 2 stokes of 250cc plus throughout the late 70’s and 80’s DT IT MX TY YZ WR and every manual & every parts list shows them fitted with the closed side inwards.

This guy seems to be very sure of himself. So it might be the right way ?

[Airhead]

open side faces the crankshaft flywheel, dunno what the castellations are for unless they are to aid removal by pulling on them?

[robdyk]

Well, these satellations have nothing to do with aiding of the removal.They're just pieces of soft rubber. In fact, it's probably even harder to remove them using one or two screws. The castellations should help establishing a better oil flow towards the bearing, if I may believe the distributor of those oil seal.

I've looked real close on the picture from the Yamaha motor company, and it shows that part no 19, the oil seal, is indeed mounted with the "closed"side inwards.