496 Pita!
Thread Starter
Le Mans Master
Joined: Dec 2006
Posts: 5,557
Likes: 9
From: Oquirrh Mountains
St. Jude Donor '09
496 Pita!
Rant
I've been building a 496 for my buddies '66 and what a pain! All these aftermarket parts aren't playing nice together. I've had the bottom end apart three times now. First was during tear down to clearance the crank case, which was expected. Next came getting the trust right - too tight w/the new crank and then getting the deck machined to the right height. Next, I had to install 0.001 undersize bearings because the crank is high limit tolerance on the rods.
I checked out the valvetrain geometry today; which actually was spot on. I was rather surprized given this thing has been upgraded to a roller cam/roller rockers and Edelbrock heads. It took a bit to even get to this point because the timing chain manufacturer apparently didn't bother to check if their product would actually clear a water pump. So after several hours of precision machining with the 4-1/2" grinder; the water pump and timing chain cover finally get along.
As I was saying the valvetrain checks out EXCEPT every other revolution has a tight spot in it; which definately wan't there before the valvetrain was installed. If you've ever set up a rear end too tight it's a bit like that. In a certain spot you can feel the gears meshing tightly together. My guess is the cam gear on the gear drive has been machined slightly off-center and is binding. I knew I should have stuck with a chain. Anyway, I get to take something back apart yet again.
This thing isn't even mine. I guess no good deed goes unpunished.
/Rant
I've been building a 496 for my buddies '66 and what a pain! All these aftermarket parts aren't playing nice together. I've had the bottom end apart three times now. First was during tear down to clearance the crank case, which was expected. Next came getting the trust right - too tight w/the new crank and then getting the deck machined to the right height. Next, I had to install 0.001 undersize bearings because the crank is high limit tolerance on the rods.
I checked out the valvetrain geometry today; which actually was spot on. I was rather surprized given this thing has been upgraded to a roller cam/roller rockers and Edelbrock heads. It took a bit to even get to this point because the timing chain manufacturer apparently didn't bother to check if their product would actually clear a water pump. So after several hours of precision machining with the 4-1/2" grinder; the water pump and timing chain cover finally get along.
As I was saying the valvetrain checks out EXCEPT every other revolution has a tight spot in it; which definately wan't there before the valvetrain was installed. If you've ever set up a rear end too tight it's a bit like that. In a certain spot you can feel the gears meshing tightly together. My guess is the cam gear on the gear drive has been machined slightly off-center and is binding. I knew I should have stuck with a chain. Anyway, I get to take something back apart yet again.
This thing isn't even mine. I guess no good deed goes unpunished.
/Rant
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
If he's like most folks I know, he'll be fed up with the whine of a gear drive soon enough. They also transmit crankshaft harmonics to the valvetrain which ain't a good thing. I generally plan several trial fits to get all this stuff worked out before I fully torque the main and rod caps. It's a pain, but it beats twice the work.
You might check to see if you have a lifter sticking in a bore or a valve spring set up the wrong height that's trying to bind before you pull it all apart again.
Good luck with it!
You might check to see if you have a lifter sticking in a bore or a valve spring set up the wrong height that's trying to bind before you pull it all apart again.
Good luck with it!
Racer
Joined: Oct 2006
Posts: 388
Likes: 3
From: Guyton, (Savannah) Georgia
Clearance issue
I don't know if it is the same thing or not but I have heard that stroker small blocks have a problem with the crank counterweight rubbing the cam. Since yours is having the problem on every other rotation, you may want to look in to it. Good luck.
