268 Engine Cam Thrust Plate

[Hurst]

I got the parts all back from the machine shop for my 7610, and started to get the new cam in place, but I checked the gap between the gear
and thrust plate and found I have 0.027 of clearance. Upon disassembly, the thrust plate has significant wear (appears to be about 0.012-
0.014 of wear from best I could measure with a set of calipers) and the gear has some light grooving to the face to contacts the thrust
plate. Couple questions:

1) Can the thrust plate be reversed for more life? The OD of the cam is larger than the gear, so it rides outside of the worn area.

2) Would a new thrust plate be enough? If my measurements are close, I would be 0.009-0.007 of endplay with a flat thrust plate, which is
the high end/just out of tolerance. Or do I need to shop for a new gear? Looking at pictures of used gears, it looks like the side of the
gear in the picture is supposed to be very smooth.

3) Is this a sign of something else? This is the engine's 2nd complete overhaul, and the cam was starting to show pitting on the leading
edges of the lobes. Also had 2 spun wrist pins. I believe they got the motor hot and that was what did it in this time around.

-Hurst

 

[Bern]

I'd say it's a sign of something else. I've lost count of the number of those BSD engines I've worked on, and I've never seen a cam thrust plate that looks like that. Look carefully at the lube passage that feeds it.

 

[Hurst]

Thanks Bern. I think I've located used gear and plates. I'll plan to get those coming in. The block was hot-tanked and I have gone through and washed/brushed with a tube brush all the oil passages from the main bearing saddle to the cam. I will check over for any others. It was a little odd, the tractor spun 2 wrist pins (3 and 4, which make sense from an overheating standpoint), wiped the cam, and now this thrust washer, but all the bearings showed minimal wear. I don't recall any signs I was getting fuel or hydraulic oil into the crank case ever. I am going to replace the oil pump with the OH just as a precaution that maybe it was getting weak (enough to keep the light off, but not much more). If you have any other suggestions or things to look for in the parts as I assemble it, please let me know. Only other assembly I can think of that hasn't been gone through that could be affected would be the balancer, but I don't think there's a lot to them, and they pretty much sit in the sump it looks like.

Hurst

 

[Hurst]

Forgot to say in my first post, this tractor also has the cam-driven hydraulic pump, and it did have a sticky detent on one of the remotes, so I recall getting on the tractor and finding the lever was still deadheading from the last person using it, so I imagine that would put some thrust load on the cam from the load? Or do the gears cancel each other's thrust out by how they are cut?

Hurst

 

[Bern]

I can't imagine that a dead-headed pump would be the culprit here, as that happens a lot with those sticky remotes. As I said earlier, I've not seen those thrust plates worn like that, ever.

As for the offsetting thrust forces of the helical gears, I've never stopped to ponder the theory, but you might be correct on that.