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OT - Bent Pushrod

In this case "ot" means off-Toyota and is directed to the technical experts here. Anyhow, I just put a rebuilt 390 in my old Ford pickup. It has a big cam (lots of duration, lots of lift), stock heads with hardened seals, new pistons with reconditioned rods, Edelbrock RPM Performer intake and a big carb. I did the 15 minute break-in properly and it sounded great. After only a 20 miles or so I noted a clacking sound that was intermittent. I pulled the plugs from the offending bank and noted all four cylinders had good compression. I pulled the valve cover and noted that #3 intack and exhause were not moving as much as the others. I put it back on, restarted and it sounded and ran great. Later that day, another five miles or so, the clacking resumed with a vengence. I stopped, took off the valve cover and discovered a badly bent pushrod in #4. Some of the cam lobes appear to be trashed and at least one of the lifters is beat up so badly that there is a HOLE IN THE BOTTOM OF IT! My machinist claims that the cam and/or the lifters were defective but I suspect the cam was degreed wrong. What do you think? Thanks. jor

Reply to
jor
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Did you break it in at 3000 RPM for 20 minutes?

Reply to
badgolferman

I think in addition to possible bad cam and/or lifters, was the offending pushrod too long? Is the cam timing correct?

Reply to
Ray O

I think you need to fix it again.

Reply to
J Strickland

how much valve spring free movement do you have at full lift? and how much valve to piston clearance ?

mrcheerful

Reply to
mrcheerful

Damn, Ray you are a wizard...I was thinking Cam timing, too...Hope he posts an answer...

Reply to
hachiroku

Did you break it in at 3000 RPM for 20 minutes?

Break-in: As soon as the engine fired, I adjusted the distributor so it would run, jumped in the driver's seat and moved the revs between 2,000 and

2,500 for 15 minutes. jor
Reply to
jor

"but I suspect the cam was

Well, those are good questions and I should have the answer tomorrow. I'll let you know. I'm just looking for any other ideas that might have caused this. Thanks. jor

Reply to
jor

The springs were supposed to be a match. I don't have the figures now but when I post the outcome, I'll include them. The lift for this cam is .538 and .552 (I/E, 1.76 ratio on the rocker). I know this amount of lift is getting close to the limit of a non-adjustable stock head setup but I was told that it would work. Your second question is the one that I'm afraid of. I'm just hoping I don't have trashed piston(s) as a result of a valve/piston collision. Thanks. jor

Reply to
jor

I'm curious too.

When working on a car, even modern electronic gizmo wonders, remember that they are just a collection of the six simple machines, and the electrical parts are E = I x R.

From grade school science class, simple machines are the lever, inclined plane, wheel and axle, wedge, pulley, and screw. Everything mechanical is a variation or combination of one or more of the simple machines, and IMO, the screw isn't even a simple machine because it is a combination of the wheel/axle and inclined plane.

Whatever I can't remember, I try to figure out based on simple machines and basic electricity. Since the last thing you try always seems to be the solution for a head scratcher, I let everyone else take their SWAGS and then try to give the last solution ;-)

Reply to
Ray O

During the rebuild were the pushrods re-installed to their original locations?

Reply to
Registered User

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