I know you have THE answer...so come inside please
Thread Starter
Launching!
Joined: Jan 2002
Posts: 244
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From: Wichita Falls, Texas
I know you have THE answer...so come inside please I have an 02 SS but I'm having a problem with my 67 Chevelle and I know you guys could probably help me.
It has a 396/350hp motor that was completely stock. I replaced the intake, cam (ultradyne 276/286 514/514 112), rockers (Comp magnum roller tip), pushrods (proform chromoly), and double roller timing chain. The problem is that we put the motor together and ran it on a stand. There was no knocking at that time and the motor ran great. We put another ~20 minutes on the motor (in car) and a slight tap under the valve covers turned into a knock really quick. Well we took it apart tonight and 2 of the pushrods had the rocker end tips broken off/chewed up. Any ideas what could cause this??? I would like to think that it is metallurgy if it was just one but 2? So I know you have the answer so what do you think? We are rebuilding it on Thursday so any replies would be great.
Thank You
Kobwo
It has a 396/350hp motor that was completely stock. I replaced the intake, cam (ultradyne 276/286 514/514 112), rockers (Comp magnum roller tip), pushrods (proform chromoly), and double roller timing chain. The problem is that we put the motor together and ran it on a stand. There was no knocking at that time and the motor ran great. We put another ~20 minutes on the motor (in car) and a slight tap under the valve covers turned into a knock really quick. Well we took it apart tonight and 2 of the pushrods had the rocker end tips broken off/chewed up. Any ideas what could cause this??? I would like to think that it is metallurgy if it was just one but 2? So I know you have the answer so what do you think? We are rebuilding it on Thursday so any replies would be great.
Thank You
Kobwo
Re: I know you have THE answer...so come inside please Did you check your piston-valve clearances before bolting down the heads? Is this a solid roller or hydraulic camshaft setup?
I'd suspect either your valves are being hit by the pistons, causing the rocker to slam back onto the pushrods.
Or
Maybe your pushrods are too long for the application and once the rocker arm hits full allowable pivot, there is no room left for the pushrod to move, so the cam/lifter hits it pretty hard.
I'd suspect a mechanical geometry issue if you broke two of them at low running time.
Tony
I'd suspect either your valves are being hit by the pistons, causing the rocker to slam back onto the pushrods.
Or
Maybe your pushrods are too long for the application and once the rocker arm hits full allowable pivot, there is no room left for the pushrod to move, so the cam/lifter hits it pretty hard.
I'd suspect a mechanical geometry issue if you broke two of them at low running time.
Tony
TECH Addict
Joined: Nov 2001
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From: TEXAS
Re: I know you have THE answer...so come inside please Were the two on the same cylinder? Possible mis-installation? Hopefully it wasn't a piston-valve clearence problem.....
Keep us informed on what you find out.
Keep us informed on what you find out.
Thread Starter
Launching!
Joined: Jan 2002
Posts: 244
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From: Wichita Falls, Texas
Re: I know you have THE answer...so come inside please Thanks for the replies so far,
The pushrods were specific to the application and were identical in length to the stock ones and were the ones recommended by the cam company. There is plenty of PTV clearance and I'm not sure if that is the issue. If it was PTV would that be an issue with more than just these 2. All the other pushrods looked great. The broken ones were the intake on #8 and intake on #5.
Any other ideas?
The pushrods were specific to the application and were identical in length to the stock ones and were the ones recommended by the cam company. There is plenty of PTV clearance and I'm not sure if that is the issue. If it was PTV would that be an issue with more than just these 2. All the other pushrods looked great. The broken ones were the intake on #8 and intake on #5.
Any other ideas?
Re: I know you have THE answer...so come inside please If you broke two intake pushrods, i'd have to suggest relooking the piston/valve clearance. The intake valves are what typically get hit, since they are larger diameter than exhaust valves.
Did you take the engine up to higher rpm? Are you sure the valvesprings are adequate in terms of seat and open pressure to handle the rpm? Valvefloat could have also caused the pistons to hit the valves.
Tony
Did you take the engine up to higher rpm? Are you sure the valvesprings are adequate in terms of seat and open pressure to handle the rpm? Valvefloat could have also caused the pistons to hit the valves.
Tony
Thread Starter
Launching!
Joined: Jan 2002
Posts: 244
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From: Wichita Falls, Texas
Re: I know you have THE answer...so come inside please The cam was designed to use the stock springs and they only have ~1500 mi on them. We never removed the heads during this install. We ran the motor to 5200 RPM on the maiden voyage. The cam was broken in on the stand. The motor seems to run smooth even with the chewed up push rods. Only the top 1/4 inch of the tip is chewed up (not snapped off). How else can I check PTV clearance. Every piece put into the engine was a direct replacement for stock and the cam is not very high lift at 514.
Re: I know you have THE answer...so come inside please How old are the springs? Springs have a fatigue life. Stock springs are typically junk on most engines, that could be your problem right there.
Tony
Tony
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Joined: Oct 2002
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From: san Antonio
Re: I know you have THE answer...so come inside please Are the pro magnum rockers an increase in ratio over the stock rockers. That may be how the cam company made their recommendation, was by the stock ratio. So changing the rockers may mean that you need to change the pushrods to a little bit shorter.