850 Cam End Float

PaulB

PaulB

Be Bold
So I finally have my garage mostly sorted and can get back to working on my Fiona.
I've been plagued by a valve seize issue. I have most of the (903) engine apart now.
Previously I found a worn oil pump, tonight I discovered too much end float in the cam. The Cam to front bearing movement is about 0.010" but the bearing is moving around its retention pin another .016" so there is about .026" of total float. Subsequently the new timing chain cut a .005" deep path inside the chain cover. Which explains the glitter in my oil. Does anyone have a Cam axial play (end float) spec for the 850 engines?
Thanks in advance,
+Paul
 
Congrats on getting the new house sorted out and the way you want it. An amazing undertaking and a really nice job on the design, build and finish.

Jeff Stich has way more experience in this area and I am sure will pinpoint the problem for you, the following is my take on the issue.

I have been perusing my factory manual and can’t find the data for the axial end play. It mentions measuring it but gives no spec, they reference using a Fiat specified dealer gauge but no data.

I suspect you have an issue with your front bearing as it shouldn’t have so much float. The bearing would appear to have excessive clearance in the groove for the retention screw as well as the groove being machined too far outward towards the block face end. You might also look at the distance from the mounting face for the timing gear on the camshaft to the face on the camshaft that the front bearing runs against, is it too great and allowing the camshaft to run too far out? Depth of bearing minus the distance from mounting face of the drive gear equals your runout. Could the drive gear have wear in its back face causing it to allow too much runout (or in this case run in of the cam towards the back of the engine).

The gear end bearing came in four different diameters to suit the diameter of the opening in the block, it might be rocking in the block if its the wrong size (minorly).

I would start by buying an example of that bearing from a few different sources and see if you can see a difference in the measurements from the faces that drive the camshaft location. Fit each one to see which gives the least runout of the camshaft. It may be that the bearings are fine and the face of the cam has worn creating excessive runout.

Also consider getting a few examples of the retention screw to find one whose end has better interference with the groove in the bearing if all the bearings seem to have a similar size slot machined for retention.

I will look more closely at the different manuals I have from different publishers to see if the dimension you seek is evident in one of those. In any case, the gear shouldn’t be face machining the timing cover, something in the stack up of parts, cam, gear or bearing is giving you way too much run out.

My money is on the bearing being improperly machined in a few of its dimensions.
 
Thanks for looking Karl.
Both: The pin retention hole looks a little molested; almost like it was partially pulled without removing the pin first. The the face is also a little worn. I'm sure either one would be ok, but together they're problematic. I'll be trolling for parts this week.
 
IMAG5396.jpg IMAG5369.jpg IMAG5382.jpg Just a little worn.
 
It should have a factory machined face all the way around the inside cam face and the outside, block face. That one looks like it was touched a good bit to fit the block opening, perhaps it was the wrong size when it was originally ordered.

The retention screen/pin interface definitely looks unhappy.

Good luck with getting a better part.
 
Hiya Paul! Sorry to hear about the troubles with Fiona. I hope you get her going again. I've gotten an actual house now in the same town I was in, and sold the RV. Hopefully we both will have running cars soon my friend.
 
Chaostoy said:
Hiya Paul! Sorry to hear about the troubles with Fiona. I hope you get her going again. I've gotten an actual house now in the same town I was in, and sold the RV. Hopefully we both will have running cars soon my friend.
Click to expand...
Nice, Congratulations.
 
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