Old83@pincher

So I noticed these triangular shaped etched on arrows on both the driving and driven gears of my old oil pump (new one is still in transit). They don't seem to align as both point towards the crown of the gear tooth on each. Nor is the any such marks on the pump body which they should align to. The drive gear one was on the back of the pump (facing the rest of the engine) and the mark on the driven on the front side (facing the radiator). When I took the pump off the driving gear stayed on the pump drive but was just an easy slip fit so I have really no way of knowing the original point of mesh. Playing around with the pump it takes about 4 revolutions for the gear to get back to the starting engagement point.


So what and why are the marks?


I'm the original owner and this is the first time its been removed so unless its a Monday truck and someone messed up assembling the engine its been this way for 33 - 34 years and 235000KM's with no oil pump/pressure issues.


And just to add, for anyone else starting work on a truck this age, that during the dis-assembly I had no issues removing the crank bolt, pulley or any of the drives/timing gears that I read about guys having. 1/2" breaker bar and 19mm socket and out the bolt came, every thing else just slid or wiggled off.

MudHippy

They're matchmarks. They're there to tell you which way the driven gear should be reinstalled. If the mark on the driven gear is on the same side as the drive gear, it needs to be reinstalled in that direction. If you can't see the mark on the driven gear, because it's on the other side, it needs to be reinstalled in the opposite direction.

At least that's the only sense I can make of it. It made no sense to me either. Until I pulled one apart, that had never been apart, and it had the driven gear with the mark facing the opposite direction. So it stands to some reason that they must have done so purposely. It makes no sense to have a matchmark on the drive gear though. To me anyway. Maybe it does to them.

Old83@pincher

Thanks MudHippy...It made no sense to me either that there are marks on the drive gear, it will only go in one way no matter how stupid one is! But as I said the mark on the driven gear was to the front of the pump so I didn't see it till I got curious and took it out. That when I gave that big Hmmm to myself and tried figuring it out. And as you said it makes no sense to me...if you have matchmarks they match to some thing which these don't, at least what I could see with both pairs of my glasses! Sounds like I'll treat this with a big dosage of forget about it and put the new pump in.


I may go and harass someone smart at the dealership and see what they say. From what I've just read else where both marks should be on the same side which mine weren't, and its never been apart since new as I drove it off the lot with exactly 12KM's on the dial.

MudHippy

I've tore apart 2. First one the driven gear had the mark on the same side as the drive gear. Which I thought meant "this side up". Then the second one blew that theory(since the driven gear wasn't facing "up"). Neither had been apart before I got in there.