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
OT - Bent Pushrod
Aug 02, 2005
10 Replies
Did you break it in at 3000 RPM for 20 minutes?
I think in addition to possible bad cam and/or lifters, was the offending pushrod too long? Is the cam timing correct?
I think you need to fix it again.
how much valve spring free movement do you have at full lift? and how much valve to piston clearance ?
mrcheerful
Damn, Ray you are a wizard...I was thinking Cam timing, too...Hope he posts an answer...
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"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
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
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 ;-)
During the rebuild were the pushrods re-installed to their original locations?
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