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what would cause a pushrod to break in half

Posted By: Tadams

what would cause a pushrod to break in half - 11/28/11 09:57 PM

I pulled the valve covers to adjust the valves and noticed the no. 7 cylynder pushrod was beside the rocker arm. I thought I would adjust the rocker and slip it back in place. Maybe it just jumped off. When I started it just dropped out of site. I was able to pull both pieces out but what would cause this. It was the intake if that means anything. This is a 273 stock Commando engine. The valve isn't stuck as far as I can tell. I can push the spring down anyway. This should help me with my vacumm situation.
Any ideas. I can't do anything till I get some new rods except wonder what went wrong. This engine ran fairly smooth with this problem. I would think it would run great when this is corrected. Thanks for your help.
Posted By: 340SHORTY

Re: what would cause a pushrod to break in half - 11/28/11 10:06 PM

metal fatigue, over rev,
Posted By: Fury Fan

Re: what would cause a pushrod to break in half - 11/28/11 10:07 PM

To my not-unlimited knowledge, all pushrods are steel, and steel is a flexible material. I've never heard of a pushrod breaking, they typically just bend.

But - is the pushrod an adjustable or 'checking' pushrod with a threaded end? Did it break at a threaded end?

Fear not, people more knowledgable than me will respond. Calling JohnRR...
Posted By: Tadams

Re: what would cause a pushrod to break in half - 11/28/11 10:14 PM

It was broken half way down the shaft. I have no idea about how the car was treated before I bought it and has been 6 months to get it to this stage. I had seen them bent but not broken in 2 pieces. This may solve a lot of problems unless I have a sruck lifter or something. The funny thing is after I removed the 2 pieses I started the car just to move it and it runs fairly smooth. It should run great when I find some new rods.
Thanks for your help
These are not adjustable ends, just solid rods
Posted By: Supercuda

Re: what would cause a pushrod to break in half - 11/28/11 11:05 PM

Where is the lifter and what does your oil pressure look like?

Bet the lifter is not on the lobe and the oil pressure is low.

I can't imagine what might have broken the pushrod in the middle other than a defect in the pushrod.
Posted By: Tadams

Re: what would cause a pushrod to break in half - 11/28/11 11:20 PM

Oil pressure was good and the lifter appears to be where it should by looking at the others. The only real sign I had was checking with a vacumm guage the guage was not steady. It would quickly bounce between 19 and 21 and smooth out when you gave it more gas
Posted By: mopar_man

Re: what would cause a pushrod to break in half - 11/29/11 12:25 AM

I believe that the 273 had adjustable rockers. I have seen several broken push rods on a 340.
Your problem could be that someone had the back bone off and when they installed the rockers again they may have used the exhaust rocker on the intake and vice versa. when this happens it pushes the rod over to the side and the p/rod wears on the side of the head . Usually not noticed by most people unless your an experienced engine builder.
I would check and make sure you have all rockers on correct.
Posted By: Tadams

Re: what would cause a pushrod to break in half - 11/29/11 12:59 AM

Gee, it's amazing the things you can learn on this site. I haven't checked, but how can you tell the differance between the 2.
Thanks
Posted By: mopar_man

Re: what would cause a pushrod to break in half - 11/29/11 02:39 AM

Quote:

Gee, it's amazing the things you can learn on this site. I haven't checked, but how can you tell the differance between the 2.
Thanks



They are angled different . If you can find a pick of a set of rockers for an LA engine you will notice the difference between the angles of the rockers ie; intake and exhaust. I have seen many so called good engine builders make the same mistake or didn't know the difference and install the rockers incorrectly. Is your engine solid lifter or hydraulic ?
Posted By: Tadams

Re: what would cause a pushrod to break in half - 11/29/11 03:28 AM

solid lifters. I need to find what size socket I need to turn the crank. I think it would be better to turn it over by hand to make sure all is good before I fire it up. New push rods should be here wednesday si I would like to check and make sure everything is ok.
Posted By: mopar_man

Re: what would cause a pushrod to break in half - 11/29/11 03:32 AM

Quote:

solid lifters. I need to find what size socket I need to turn the crank. I think it would be better to turn it over by hand to make sure all is good before I fire it up. New push rods should be here wednesday si I would like to check and make sure everything is ok.



Sounds good . make sure you spin the engine two full turns as the cam turns at half speed.
Posted By: Cab_Burge

Re: what would cause a pushrod to break in half - 11/29/11 08:36 AM

Quote:

solid lifters. I need to find what size socket I need to turn the crank. I think it would be better to turn it over by hand to make sure all is good before I fire it up.

if it has the stock bolt it is 1 1/4 inch socket size, if it has been replace it may be a 1 1/8 inch socket size
Posted By: Tadams

Re: what would cause a pushrod to break in half - 11/29/11 01:08 PM

Thanks for the info.
Posted By: RapidRobert

Re: what would cause a pushrod to break in half - 11/29/11 03:59 PM

top to bottom: TA/273 solids/hyd. On the valves IE for the .013" intakes want a .012" feelr gauge to have no drag and a .014" to have a slight drag. blade held square. This'll get you to within .001"

Attached picture 6941800-sbrockerarms.jpg
Posted By: Tadams

Re: what would cause a pushrod to break in half - 11/29/11 04:16 PM

Good morning Robert. Thanks for the info. Mine look like the ones in the middle. My new push rods should be here in the morning. I thought about cold setting all of the valves before starting and rotate by hand to make sure all looks good before starting it up. I know I would need to adjust them again once the engine warms, but this would put me in te ball park.
What type spark plug would you suggest for this car? I may as well do that while I'm doing the rest.
Posted By: MR_P_BODY

Re: what would cause a pushrod to break in half - 11/29/11 04:29 PM

It broke because it jumped out of the rocker and
got bound up on something SOLID and the lifter came
up... the center is the weakest point... as to WHY
it jumped out thats the thing you need to find out...
MAYBE the adjuster backed out OR the cam lobe went
away but they dont just jump out... I've used those
rockers up to 7800 rpm(not advised)
EDIT
I've had a few P/Rs break but normally its at the
tips where they have been sized and heat treated
and were brittle(over heat treated)
Posted By: RapidRobert

Re: what would cause a pushrod to break in half - 11/29/11 04:36 PM

NGk is pretty good but in a stock app I'd find the cheapest ones on sale maybe. Glad ya got it up & running. I was just about ready to pack my bags & come out & buy it from you, just to reduce your stress level
Posted By: Tadams

Re: what would cause a pushrod to break in half - 11/29/11 05:12 PM

After being hurt on the job and out of work for almost 4 years after driving an 18 wheeler most of my life what do you mean stress.
Just because I have 3 kids at home the youngest is 19 then 21 and the oldest is 24. Stress, what do you mean stress?
If I know how to scream on-line I would. HaHa

I am trying to find about an 1 1/2 in pc of the rod that is missing. I don't see it on the top end so hopefully its in the oil pan. I guess it broke in 3 pcs. If you lay the 2 pcs. beside a normal rod the broken one is 1 1/2 in short.
Posted By: OneOfMany

Re: what would cause a pushrod to break in half - 11/30/11 07:08 PM

Banged my 440 A-body console shifter from 2nd to neutral while winding it out. When the engine came back down, it was running rough. Found two bent pushrods, and one broken in half. The bottom half was in the lifter still, but the broken top edge had wedged itself against the bottom of the head where it sticks over the valley. Other piece was just laying there. You never know

Grant
Posted By: Tadams

Re: what would cause a pushrod to break in half - 11/30/11 08:49 PM

Hi Grant, Thats a scarry feeling. I bought this car about 6 months ago and did have it running but never more than a fast idle. It actually idled fairly smooth and showed good oil pressure. I was checking things and the vacumm while around 20 lbs would rapidly jump from 19 to 21 so I knew somwthing was up. I thought a good valve adjustment would take care of it. When I pulled the covers and started to adjust I noticed the 7 intake wasn't moving and the rod was beside the rocker arm. I shut it off and thought I would just adjust it to where I could slip it over rhe rod. When I touched it it dropped out of site. The bottom piece was stuck in the lifter as it should be and I was able to lift the pcs out. Now I am putting it back together and pray there is no damage other than that.
When you buy an old car that has been setting you have kno idea what you have.
Have a good day and keep the rev's down a little.
Tommy
Posted By: MR_P_BODY

Re: what would cause a pushrod to break in half - 11/30/11 09:14 PM

Quote:

Hi Grant, Thats a scarry feeling. I bought this car about 6 months ago and did have it running but never more than a fast idle. It actually idled fairly smooth and showed good oil pressure. I was checking things and the vacumm while around 20 lbs would rapidly jump from 19 to 21 so I knew somwthing was up. I thought a good valve adjustment would take care of it. When I pulled the covers and started to adjust I noticed the 7 intake wasn't moving and the rod was beside the rocker arm. I shut it off and thought I would just adjust it to where I could slip it over rhe rod. When I touched it it dropped out of site. The bottom piece was stuck in the lifter as it should be and I was able to lift the pcs out. Now I am putting it back together and pray there is no damage other than that.
When you buy an old car that has been setting you have kno idea what you have.
Have a good day and keep the rev's down a little.
Tommy



If you were to switch plug wires on 5 and 7 it really
doesnt change alot so if you lost #7 it MAY still
idle fair but you would notice it at higher revs
Posted By: Tadams

Re: what would cause a pushrod to break in half - 12/01/11 02:40 AM

Well, I replaced the push rods, adhusted the valves, Changed the oil and filter, and installed new plugs. I was really surprized how good this thing runs now. The vacumm is 19 and steady. The car starts easy and seems to have plenty of power. Now I get to go back to replacing the leaf springs with new ones. Thanks everyone for your help, especially rapidrobert for going out of his way to answer all of my questions.
Posted By: drago

Re: what would cause a pushrod to break in half - 12/01/11 02:48 AM

Hi,
there's no offset on the 273 solid lifter rocker arms. The hydraulic type were all offset including the TA arms.
Posted By: Tadams

Re: what would cause a pushrod to break in half - 12/01/11 01:12 PM

I didn't see any differance in the rockers, but sure wanted to make sure before this happened again. I didn't find any thing that would show me what caused it. All I can say is it sure runs good now.
Posted By: bboogieart

Re: what would cause a pushrod to break in half - 12/01/11 03:30 PM

probably just spun the heck out of it, over revved.
I never saw one break myself, usually it's the rocker arm that lets go right in the push rod cup.
Posted By: Tadams

Re: what would cause a pushrod to break in half - 12/01/11 03:33 PM

As I said, I bought it from someone so have no idea how it was treated before. She sure sounds great now. I can't wait to get her on the road.
Posted By: bboogieart

Re: what would cause a pushrod to break in half - 12/01/11 03:36 PM

Yeah I was just tossing out my guess. Glad it was not too bad, and it's running good. Have fun with it.
Posted By: OneOfMany

Re: what would cause a pushrod to break in half - 12/01/11 07:45 PM

Good to hear it was nothing expensive

Grant
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