Cam Shaft Thrust Bearing Broke

[Matt Satchell]

Chris: No, never heard of this happening before, but I have now! When you lost the previous motor, did the oil pump jam?? If so, the skew gears would try to push the cam axially, and that could account for the crack in the cam retainer plate (a.k.a., thrust bearing). Actually, you are lucky to find it when you did, as opposed to the end of a straight at 6500 RPM.

[Aiken Racing]

Well when I lost the engine last year I just lost oil pressure and nothing jammed. The only thing I can think of is that the thrust bearing had a hair line fracture and when I torqued the bolts down it split it in half. It looks to be cast iron and maybe it was dropped at one point and a small crack developed. It's a $10 part plus two gasekts so it is not that big of a deal. I am just glad it happened now before I put the engine back on and BEFORE I drove it.

Luck must be on my side now!

Thanks,
Chris

[Aiken Racing]

I've been rebuilding my Kent this winter and I was just about to put it back on the chassis. I deceided to spin the engine over a few times to make sure everything was ok. Well I spun it about one half a rotation and it just stopped dead. I got scared so I ripped everything back off to make sure nothing was jamming. I was extremly careful when rebuilding the engine to make sure everything was up to spec.

Well I found out what broke, the cam shaft thrust brearing broke right in half and it jammed the cam gear from turning. It didn't damage anything other then the bearing breaking. So now I just need to replace that thrust bearing and seal things back up... BUT

What in the world would cause that to break? I don't see any forces on that bearing from side to side. Maybe it had a hairline fracture already that I didn't know about.

Has anyone heard of this before?

Thanks,
Chris More

[StuartW]

Chris,

Check the lengths on the bolts holding the chain sprockett to the cam. Make certain that they are not sticking out the back of the cam and interferring with the thrust plate. I had one set of bolts that bound the cam to the thrust plate after installation and torquing. They were just a hair too long.

John Mihalich, Jr.

[Aiken Racing]

wow! you figured it out.

As soon as you mentioned the length of the bolts it hit me. just before putting the timing cover back on I remember I removed the tach drive on the gear since i use an electronic Pi dash now. That plate is about 1/16" thick and it would make the bolts go in a little farther. It probably smashed the gear when I tightened it down. I will either put a washer behind it or better yet get shorter bolts.

Thanks!
Chris

[DENIS]

DANM, now this is what makes this forum tick! Sure some of the engine guys knew this already, but I can't recall ever looking at it to see if there would be a problem. Live and learn.

[Dale Carter]

Something similar I have seen a few times - using standard bolts with "thick" heads which then hit the tach drive fasteners on the inside of the front cover. Two solutions: make sure the fasteners used for the tach drive are shallow on the inside of the cover. I have also seen countersunk heads in this location. Usually, the nuts are on the outside of the cover - or should be. The other technique is to grind or mill down the heads of the cam sprocket bolts.In any case, clearance should be checked during assembly.