Author Topic: Cam movement and interference  (Read 9060 times)

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Offline 1989marathon

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Cam movement and interference
« on: January 06, 2013, 06:13:52 pm »
Hey guys. I'm new here. You have a great site.
I've got a Briggs 303447 16hp horizontal Vanny with a weird problem.
I found these pics on the internet and this is not my motor, but mine has the same issue.
I pulled my motor apart for rebuild and I found that the cam has been running into the cylinder casting.
The pilot hole in the main casting doesn't show ANY signs of wear that would allow the cam to move further back. The original dimensions just don't stack up to prevent the cam from moving back. What I'm wondering is how does this happen, and has anyone else seen this. I think it has happened from the force of the governor on the camshaft. I have removed the governor. I will likely just add a washer on the back end of the cam to control the thrust.
Any ideas?
Don

Offline Jim Knutson

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Re: Cam movement and interference
« Reply #1 on: January 06, 2013, 06:55:41 pm »
seems like alot of play there. i would be weary of using a "washer" to shim with....maybe it would work with an actual hardened shim.
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Offline 1989marathon

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Re: Cam movement and interference
« Reply #2 on: January 06, 2013, 07:02:41 pm »
I will use a hardened washer to only allow minimal movement.
Don

Offline Huffy044

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Re: Cam movement and interference
« Reply #3 on: January 06, 2013, 07:46:15 pm »
Movement in that diresction can be caused by a lot of things, most not goood. Something is out of alignment, could be the relationship of the cam being "square" to  the crank, could be the crank not perfectly aligned straight (you would be amazed on the tolerance level from the factory. The lifters could be out of alignment with the cam. Most of this is fixable, you just have to find it.

99% chance it was like this from the factory, core shift in the casting process or bad machining. You just have to start looking or band aid it like shims or they make thin flat roller bearing you might put behind the cam. There should be very little float on it, look for wear wear behind the cam gear.

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Offline 1989marathon

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Re: Cam movement and interference
« Reply #4 on: January 06, 2013, 08:07:18 pm »
Even if everything is aligned perfectly, the force of the governor would apply pressure on the cam in that direction. There is nothing to stop the cam gear from hitting the casting.
Don

Offline birdman_express

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Re: Cam movement and interference
« Reply #5 on: January 06, 2013, 08:33:23 pm »
Is the ball in the end of the cam?
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Offline 1989marathon

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Re: Cam movement and interference
« Reply #6 on: January 06, 2013, 08:36:01 pm »
Yes, but the cam is moving the other direction. The ball is in the end in the front cover.
I'm wondering if the case was just a bad casting. While the pilot hole for the cam is machined, the top of the hole is not. Maybe there wasn't any material there to machine and now the cam is able to move back into the case.
Don

Offline birdman_express

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Re: Cam movement and interference
« Reply #7 on: January 06, 2013, 09:37:04 pm »
Grind it out so it clears.
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Offline 1989marathon

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Re: Cam movement and interference
« Reply #8 on: January 06, 2013, 09:41:35 pm »
What should I grind out?
Don

Offline birdman_express

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Re: Cam movement and interference
« Reply #9 on: January 06, 2013, 10:17:18 pm »
What should I grind out?

Where it is touching, to clear the cam gear.
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Offline 1989marathon

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Re: Cam movement and interference
« Reply #10 on: January 06, 2013, 10:23:39 pm »
The problem is if I do that, I would probably break through the cylinder, and the gears would be seriously misaligned. That's why I think the casting is flawed. I think a shim or hardened washer is probably the best answer.
Don

Offline birdman_express

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Re: Cam movement and interference
« Reply #11 on: January 06, 2013, 10:37:21 pm »
Also make sure the cam itself has not worn to make a point on the side.
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Offline 1989marathon

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Re: Cam movement and interference
« Reply #12 on: January 06, 2013, 10:42:52 pm »
The cam looks brand new. You can tell the gear teeth have been meshing, but there are no other signs of wear.
Don

Offline fordman21

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Re: Cam movement and interference
« Reply #13 on: January 10, 2013, 09:46:16 pm »
I've seen this happen quite often. Don't shim the cam, just clearance the cylinder a bit with a die grinder or porting tool. You don't have to go very far don't worry about going into the cylinders you are a mile away from that. Its pretty well self machined about as far as it will go so just clean it up and you are off to the races.
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Offline 1989marathon

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Re: Cam movement and interference
« Reply #14 on: January 12, 2013, 05:38:59 pm »
Started assembling the motor today. Turns out the interference and wear wasn't from the cam gear teeth. It was from the roll pin for the compression release return spring. I tapped the pin in further and no more interference.
Don

 

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