Rebuilt engine, bent push rods?

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73DusterPunk

73DusterPunk

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I have a 73 Duster, had the engine rebuilt because I didn't have the time/knowledge to do it myself. Two days ago it was running great, not a single problem. The timing is dead on, and so on so forth. However, I wen to start it up yesterday and it started and ran for only a few minutes before it died, then refused to start. After checking fuel and electronics, I found that 6/12 push rods were bent. This is one of the main reasons the engine was rebuilt. I'm completely stumped, any one have an idea?
Thanks.
 
Sorry to hear that, it sucks. I know what you mean, that happened to me when I did a rebuild on my 318. It was my fault and it was caused by my inexperience. I learned all about, "coil bind", I had the head shaved and didn't check for coil bind and I bent the push rods, sucked a valve, put a hole through a piston and scared number two. Whoever you paid for this should make it right. It might not have been coil bind but what you described is exactly what happened to me.

I am sure you will get the right answer here there are alot of truly great gear heads here.
 
73DusterPunk said:
You mean the spring at the opposite end of the rocker arm from the push rod?
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yes, its the spring around the valve. fully compressed by the pushrod it should have a little space in between each coil.... like .060 i'm thinking is the measurement.. somebody correct me if i'm wrong.
 
Okay, thanks for helping me understand a little better. Is there a simple solution to "coil bind"?
 
did they put new valve springs on it? are they the correct ones? are there spacers in between the valve spring and the seat? i dont recall there being any on mine when i rebuilt it.
 
if it was runnin fine and then bent pushrods, that means somethin changed. did the idiots put a nylon camshaft gear on it? if the engine kicks back against itself trying to start just ONE time, it is possible to strip all the teeth off a nylon timing gear. that's the only thing I could think might have happened. SOMETHING with the camshaft timing has had to change to get these results.
 
StrokerScamp said:
if it was runnin fine and then bent pushrods, that means somethin changed. did the idiots put a nylon camshaft gear on it? if the engine kicks back against itself trying to start just ONE time, it is possible to strip all the teeth off a nylon timing gear. that's the only thing I could think might have happened. SOMETHING with the camshaft timing has had to change to get these results.
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Sorry, you're gonna have to explain what "kick back" means. I wouldn't be surprised if they did, as a lot of the original parts were of the mixed material type. The timing and all are still dead on, and I know the cam was replaced with an rv cam, but the shop should have adjusted everything to within a very close degree. The engine cranks, just won't fire like there's no spark; I've already verified both fuel and spark though.
 
What exactly did the shop replace as they rebuilt it? You say the camshaft was replaced, but were the springs replaced as well? I'd talk to the shop first thing in the morning... 6/12 pushrods means something messed up BIG time..
 
73DusterPunk said:
Sorry, you're gonna have to explain what "kick back" means. I wouldn't be surprised if they did, as a lot of the original parts were of the mixed material type. The timing and all are still dead on, and I know the cam was replaced with an rv cam, but the shop should have adjusted everything to within a very close degree. The engine cranks, just won't fire like there's no spark; I've already verified both fuel and spark though.
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gasoline engines in general have a tendancy to kick back in the opposite direction of normal run sometimes. especially when hot and after being run a long time.....and those with lower compression ratios. haven't you ever started a lawn mower and had it kind snatch the starter rope outta your hand? if not, you ain't cut enough grass. when an engine kicks back, it's NOT a non-violent event and if it has a nylon lined camshaft gear, it can rip off every single tooth and jump cam timing. In fact, I've even witnessed a small block run backwards in on of these kick back fits. really very strange. what actually happens if they do it badly is, they run on the heat in the combustion chamber. nothin you can do about it but wait for it to stop. it's called dieseling. most people don't realize an engine is actually running backwards when it diesels, but it does. if it only does it for an instant, instead of trying to continue to run, that's when it can rip the cam gear up.
 
maybe tight valve guides? The exhaust valves run hotter than the intakes and if the guide is a little tight, the valve can stick. Just my 2c.
 
1 rod per valve, actually, 3 were actually bent to hell, while 3 were just loose. I'm thinking it may be something to do with exhuast, as it's only the exhaust valve rods that seemed to have problems.
 
Alright, guy who rebuilt the engine is giving me 6 new push rods tomorrow and instructions on how to adjust everything.
 
73DusterPunk said:
I have a 73 Duster, had the engine rebuilt because I didn't have the time/knowledge to do it myself. Two days ago it was running great, not a single problem. The timing is dead on, and so on so forth. However, I wen to start it up yesterday and it started and ran for only a few minutes before it died, then refused to start. After checking fuel and electronics, I found that 6/12 push rods were bent. This is one of the main reasons the engine was rebuilt. I'm completely stumped, any one have an idea?
Thanks.
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WTF that is weird cuz when i rebuilt my motor with the old head it did the same thing on the same rods!!! i was running into coil bind.
 
Man, I'm sorry I didn't respond sooner. I took a short trip. What caused my coil bind was : 1) I Had the heads shaved .010 2) I used the old springs with a new cam and lifters. 3) The springs were weak so the machine shop shimmed them as much as .020 to help increase their pressure. That along with the shaved head shortened the travel of the spring by at least .030. 4) I used the same length push rods as before the mods. All this caused the push rod to travel more than the spring could compress thus going beyond the travel left in the spring. The engine ran strong for about 50 miles and with each stroke of the engine bent each rod and a couple of valves in #2 till the valve gave way and broke in half. Then the engine sucked the valve and the engine quit.

Like some said earlier ask the machine shop if they shimmed your springs and always check for coil bind when you do something to your valve train or heads. Check each spring, intake and exhaust when the valve is at the full open position. You can use a feeler gauge for this. As far as how much room should be between the coils, .060 sounds good.

Good luck
 
cuda67 said:
Man, I'm sorry I didn't respond sooner. I took a short trip. What caused my coil bind was : 1) I Had the heads shaved .010 2) I used the old springs with a new cam and lifters. 3) The springs were weak so the machine shop shimmed them as much as .020 to help increase their pressure. That along with the shaved head shortened the travel of the spring by at least .030. 4) I used the same length push rods as before the mods. All this caused the push rod to travel more than the spring could compress thus going beyond the travel left in the spring. The engine ran strong for about 50 miles and with each stroke of the engine bent each rod and a couple of valves in #2 till the valve gave way and broke in half. Then the engine sucked the valve and the engine quit.

Like some said earlier ask the machine shop if they shimmed your springs and always check for coil bind when you do something to your valve train or heads. Check each spring, intake and exhaust when the valve is at the full open position. You can use a feeler gauge for this. As far as how much room should be between the coils, .060 sounds good.

Good luck
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How big was the cam?

I've shimmed 340 springs .100" with a stock cam. The block and head were not cut in my case.

The machine shop should have checked for coil bind on the bench. That's what I did to make sure I could go .100".
 
im not sure i agree with that... u would hav to run a pretty big cam to put the spring into a bind. and taking .010 off is nothing. u can shave .150 off a slant before u need new length pushrods. i have about .115 total off mine with a 340 lobe cam and stock push rods...
 
From standing on the outside looking in the builder of the motor should have checked coil bind, valve clearance, push rod length, etc... before he gave you the motor whether he installed it or you did. Ask him did he check the above mentioned?
 
possibly new valve guides that are too tight. they got hot on the exhaust side, expanded and made the valves too tight.
 
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