Pulled my 06 TC88B cam chest apart for new cams, tensioners, etc.. 14k, stock motor; FP, exhaust and heavy breather. Lifters, cams, oil pump, all looked good.

There was a thin sliver of brass on the end of the pinion shaft, the pinion shaft is scored on one half only, along with the top of the bushing being scored. Crank run-out measured at the pinion shaft is .0035. Running my fingernail across the end of the crank, I can just barely feel the scoring.

What to do? I had planned to use a new '07 cam plate with hydro tensioners. Ream the bushing in the new cam plate? Polish the scoring out of the pinion? Seems to me, the problem is the bushing was not aligned or reamed properly, and crank run-out, while not real bad, is contributing to the issue. If it was just a run-out issue, I think the whole bushing would be scored, not just the top half. Conversely, if it was just a misaligned bushing, the pinion would show scoring all the way around.

Besides having the crank trued, any thoughts?

Thanks

 

Scoring, in the world of machinery is never a good thing, as it will only get worse over time and sooner or later it will lead to another failure of some sort. Will it last for a while? Sure it will. So get it re-machined/re-built correctly and start fresh. It'll keep you on the road and not on the side of it somewhere.

 

Interestingly, I just pulled the cam chest apart on my '09 to check the crank. Looks almost exactly like yours, but the cam plate bushing on mine is worn evenly all the way around.

 

Your crankshaft runout is over .003" and that is why it looks so bad.

No need to worry because the MoCo solved these types of issues by changing the maximum runout to .012".

 

looks like about 90% of the motors we take apart,

 

I think I'd be happy to have only 0.0035" TIR and put it back together with your planned upgrades. Most have 0.006"-0.008" from talking to some builders. Maybe something got between the pinion shaft and bushing at some point and caused the marks.

 

The cam plate marks the shaft where the runout on the crank is most positive. It's not a bushing alignment / cam plate issue.. If it were out of line the crank pinion would have a mark all the way around. The cam plates are typically set up with 0.002 clearance on the bushing. If the plate / bushing were dead center of the pinion, you'd have 0.001 clearance all the way around on a perfect crank. If the crank runout is more than 0.001, the pinion will touch the bearing and you'll see the rub marks.

Don't worry about it.. 0.0035 ain't that bad. Especially if staying with chains.

 

My brain totally agrees with you on this, wallet is putting up fight though.

I mic everything today. Pinion is .8500. Bushing is .8502, except the top where it's scored is .8597, above wear limit.

I saw your pics. How many miles on yours?

With a .012" runout, the bushing would have to be huge to accommodate runout like that. The shovels used to loose oil pressure when bushing got worn, wonder if same thing would happen with a TC.

Going to talk to a local big twin machine shop, see if they have reccomendations on a fix, without dismembering the entire motor.

Thanks for all your input. I'll let you know what happens.

 

Mine has about 24,000 miles.

 

0.8500 is right for the pinion.. I suspect that the bushing was really 0.8520.. Not sure how you measure the top but is sounds like the horizontally you had 0.852 and vertically you had roughly 0.860? 0.008 out of round is a concern and the camplate may be off but I'd expect the wear rings to go all the way around the pinion, You runout was 0.0035?

FWIW the plate simply wears. The TC is something like an 0.030 orifice to feed the grove in the middle of the cam plate bearing. if the plate wears oil pressure won't drop.. Rod might not get as much oil but they really don't need much anyway.. What is more of an issue is that a bit of runout can cause the cam plate to start moving and o damage the oil pump..