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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
So I haven't been inside of a SBC in ages or any motor really. I bought a TPI 88 Iroc recently and the seller told me the motor was making a "bearing noise" and wouldn't start. I started tearing down today while in the car and found a bunch of broken vacuum hoses and an alarm de-install that was done very badly so I have wiring to fix now.
What would cause this bent pushrod? It's a 305 TPI with 70K miles on it. Inside the motor looks stupid clean (Used my inspection camera) and these pics are of the cylinder with the bent pushrod. Would I need to pull the whole motor and rebuild it?
The lifter on that bent pushrod looked great, no damage. I'm confused.
The thing about push rods bending, especially stock 3-pc POSs like that one, is that once it starts, it's a positive feedback process. Applying force to one with even a very slight bend just continues to bend it, until it gets like that. With those, the metal is soft, so it doesn't just snap like a better one might; it just continues to deform.
That one was probably bent at the factory somehow, and of course never healed itself. I'm guessing it was an intake. I bet the PO of that car drove himself nuts trying to figure out why it seemed to have a dead hole no matter what he did.
Just replace em all and run it. I wouldn't tear down a motor for that. https://www.texas-speed.com/p-8292-t...set-of-16.aspx You probably need 7.300". Get an adjustable push rod and use it to compare to a non-bent one, to be sure.
One would expect that particular cam lobe to have less wear. After all, the push rod hasn't been transmitting the lobe profile to the valve spring. For however many miles (probably about 70,000 more or less) there's been no load on that lobe.
Okay then, I should have specified......
If everything is correct on the lifter side of the rocker arm, then the cause for not rotating after a straight pushrod is installed must be on the valve side of the rocker arm.
Post pictures of the cylinder head and rocker arms for the cylinder in question.
Will your inspection camera be able to get a shot of the valves from inside the combustion chamber (through the spark plug hole)?
Last edited by NoEmissions84TA; 07-27-2023 at 08:59 PM.
I'd suspect the valve associated with that bent pushrod is stuck in the guide. I've seen this happen even in an engine with heads as clean as those in your pics. By chance would the suspect valve be the one with the different valve spring retainer?
Those all look completely stock and all the same to me, except for the one exh valve at the end of the head that's missing the oil splash shield. Which is OK in and of itself; I always throw those away anyway, along with those stupid "rotators" on the exh valves. But it does point toward maybe somebody has been working on it: I don't think I've ever seen one missing from the factory although I suppose almost anything is possible like that.
SO I can only get the first 2 plugs out on each bank. Not sure how anyone is supposed to get to the others lol. Here is a pic dump I just took with a scop camera. It's hard to get a good pics in there. The cyl walls and pistons look great to me and the valves appear to be super clean with one being clean and dry and the other wet with carbon. The pic of the puked oil running down the cyl wall I THINK is the offending cyl with the bent pushrod. When it cools down a bit I'll try to get more pics of that cyl. I think both valves are wet with oil though.
I'm not about to suggest anything for the root cause but I will ask that you put a break between pictures and a description of what it's a picture of. It makes it much easier to digest.
Can you spin the engine over with all of the rocker arms loosened off?
Yeah my apologies, I realized it would be jumbled. I tried to turn it over with 2 plugs on drivers side removed and only the 2 front rockers. No turn on the crank with a breaker bar. I'm going to remove everything on the pass side and try it again.
I'm working on a very sloped driveway and the car is really lowered so I don't have the luxury of a flywheel tool. I'm looking for a flat place to work on it now.
I went ahead and pulled the rest of the pushrods, rockers and lifters out. There was a loose rocker arm on the passenger side. Cyl #4 but the rest were tight/snug. I pulled the timing chain off and tried to spin the motor over via crank bolt. Nope. I'm beginning to wonder if the trans is coming out of gear. I need to get the car flat and get under it. If I can get the headers off, I will pull the heads.
Since I don't know, I will ask. If I pull the cam out, can I snake an inspection camera in the lifter bore and see down toward the main bearings to see if anything got hot or if there is metal shavings?
You are on a slope. The engine is what is holding the car in place. If you disconnect the engine from the drivetrain (neutral), the car will roll - hopefully you will not be under it at the time. Like you said - get the car flat before you get under it.
You will not have to pull the cam if your inspection camera will fit through the oil drainback holes in the lifter valley.
Front drivers side and it was the second pushrod from front of car.
That's the #1 intake.
Inspect that valve, spring, etc. carefully; make sure the valve moves, the spring is intact, the stud isn't pulled out, no debris anywhere, etc. etc. If it's OK then there's almost certainly nothing wrong with anything else. I would NOT in that case start tearing unrelated stuff down.
You should not try to turn the engine over from the crank bolt. You will have a very good chance of breaking the bolt off in the end of the crank.
Since you already have all the rockers off, use a cylinder compression tool and fill each cylinder with shop air. There should be some leaking going past the rings but no leakage coming out the exhaust or intake. If there is, then you have a valve not seating for any number of reasons.
Got the engine pulled today and removed oil pan and heads. Everything up top looks amazing, no damage anywhere. Still wouldn't turn with light pressure on bolt so I quit messing with it. My pops broke out a flywheel tool and bam! A little movement. Let some Marvel soak in it for a few hours and went to try it again. She spins now! The oil in the pan was SLUDGE. It HAS been sitting for a total of like 18 years though. I already picked up a low mileage 350 for it though so I will just use it since I know its good.
07-26-2023, 07:19 PM
They act like a "mechanical fuse". 
