curious cam sprocket wear- 340

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Neal Zimmerman

Neal Zimmerman

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while inside my timing case today I noticed something i had never seen before. Basically the front teeth (double chain roller) of the cam sprocket were being eaten away from the front towards the back. It was the chain doing it. the front teeth were noticeably thinner in a front to back direction, although chain tension was excellent. It appeared to me that the cam was too far forward.
I rushed over to my machinist and he agreed.On returning to my shop i decided to yank the timing case on a 1972 steel crank 318 i had laying around, granted it was a silent link type but when i compared the two cam sprockets, the 318 one was perfectly flat on the back side where it kisses the cam, but the one that is wearing (340) has about a 1/16 inch raised shoulder, i assume that shoulder was holding the sprocket forward and causing wear. what gives?? or am i crazy?and yes i already thought about where the worn away sprocket material might be.
neal
 
Are you running a crazy oil pump pressure? Trying to think what causes the cam to be driven forward. Resistance to turning the oil pump would drive cam forward. So does lifter turning.....? But cam walk is prevented by the retainer and the upper cog.? Improper clearance?
 
thrust plate in place, & well tightened. As to oil pressure or pump i dont know. I don't see how cam could move forward with thrust plate in place.
 
Sounds like the cam gear was not installed as far back on the cam as it can go. I've seen that before one other time and that's what caused it.
 
In the case I saw, it was just like oldkimmer said. The cam key kicked up in the back and caused the cam gear to "sandwich" the key between the front of the cam and the gear not letting the gear go all the way back.
 
heres some photos, hope they get thru, note grinding on inside of timing case, its an eccentric pattern, from the fuel pump eccentric, and what i previously thought was a machined shoulder on back of cam sprocket is actually wear which matches perfectly the "ditch" dug into back of thrust plate. note teeth shots, the little teats on very tip of every tooth.
neal

P1010037 (640x479).jpg


P1010038 (640x479).jpg
 
"Somethin" has very obviously been between the cam gear and cam keeping it from seating properly.
 
Hughes engines make a nice retainer that works with a fuel esoteric or not. Not a lot of money. Just a thought when you put it back together.
 
Rays69Cuda said:
Hughes engines make a nice retainer that works with a fuel esoteric or not. Not a lot of money. Just a thought when you put it back together.
Click to expand...

If you are talking about their "nose extention" for adapting a non mechanical fuel pump cam to a mechanical fuel pump, I wouldn't recommend that one. I don't see how one small block of aluminum can replace my keyway. I had to make improvements to mine to make it more durable... POS....

Instead of sending me the right cam, they got to charge me an extra $30 for an "adapter".... Haven't used them since...
 
Are you using the proper components for the fuel pump eccentric??? You need to use the 'washer' with the crown/cup shape so it properly seats. You can't substitute a standard washer for the cup shaped one...
 
Sorry i don't know what a "spring loaded button" is. Yes the "cup" was there holding down the eccentric. it all looked standard to me when i pulled the timing case, just like every setup i have seen before,nothing jumped out at me. I did notice though there was no oil slinger on it or the little dripper that goes on the thrust plate but i dont see how that could affect this. I looked the cam key over and it doesnt appear chewed up. I wonder if the fuel pump eccentric might not be a small block eccentric, is a big block one deeper??> I agree it looks like the cam was riding too far forward, but i put it all back together and it slid over crank and cam ok. I measured face of block to front of chain up high at cam sprocket and down low by crank, appears to be same depth, in other words chain appears to be running parallel to block face. I expected a big difference.
Also I placed the cam sprocket front side down on a table next to the one i pulled from the 318 that I mentioned earlier and there is a1/4 inch difference in height from front to back, but its apples and oranges because the 340 is a double roller chain and the 318 is a silent link style, so i don't know if that's any kind of comparison.
neal
 
disregard spring loaded button comment, Im hallucinating. I agree with rusty, if the cam key was cocked up in the back that could explain the cam gear being "forward" and shoving the eccentric into timing case, but it doesnt explain how the front of the thrust plate and cam sprocket did their bump and grind as seen in photos.
neal
 
Agree the with all the above, plus. Was the camshaft sprocket bolt torqued and loctite used? Camshaft end play was probably not checked when the cam was installed. Pull the distributor drive and check the bushing in the block and shaft for excessive wear. Also check crankshaft end play while everything is apart.
 
Or . . . . . .
cam sprocket is not made right {chinese made like most of our parts are}????
 
Have a look at the screws that hold the water pump on. I'm betting that they are too long and were machining the cam gear. Of course, that pushed the cam gear into the thrust plate, pushed the cam rearward, chewing it up, too. That sprocket is pretty tough, if it all happened the way I think it did.
 
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