The Stovebolt Site Forums The Shop Area Engine Shop Possible bad pushrod?

Hello all. Newbie posting !
I just bought 1968 chevy 1/2 ton fleet side the other day that I am going to restore. The truck has a 350 v8 engine that the previous owner seemed to think that there is a bent pushrod. He said that he was driving home one day and it lost compression so he pulled over and had it towed home. Now for the questions. How would I go about checking to see if this is a bent pushrod?

Thanks in advance.

Welcome to the Stovebolt
Just one bent pushrod will not keep an engine from running.
If the previous owner had it towed because the engie had lost compression on one cylinder I guess I can accept that.
Does the engine run at all? Many things could be a problem with the symptoms you have briefly described.(need more info)

It will run but due to my lack of experience here I am leary on starting it. Assuming worst case here what would happen if I did start it? Just donw want to duck a flying rod. and thanks for the assistance. It is greatly appreciated.

Well I pulled out the spark plug from 1-4. 2 had wuite a bit of oil on it, 1 3 and 4 had just a little bit and according to the haynes book that I have it said "oily coating caused by poor oil control" Sun went down before I could get the rest out. Will try tomorrow and report back.

Thanks for the help.

A bent pushrod will not cause oiling of the plugs. A hole in the piston will. A cracked head might too.

Thanks for the info. Looks like its time to open it up and see whats going on. Any other suggestions would be greatly appreciated.

Thanks

If you REALLY suspect a pushrod, it won't take you that long to inspect them, although I wouldn't take the pushrod problem as gospel yet - First, remove all the plugs (so you are not working against compression) and rotate the engine by hand (if you've got good arms) or with a breaker bar on the harmonic balancer. does it turn freely? is there any noises, clunking, places that offer resistance to turning etc? The engine should turn pretty free. Go through lots of revolutions and listen, the only sound should be air escaping from the plug holes. If all is well, then crank it with the starter - Still with the plugs out but disconnect either the coil center lead, or red B+ lead to the distributor (depending on if it's HEI or not) This will be VERY noisy, and although you may not THINK you will be able to hear anything, you are only looking for loud knocks here - if there is one, you'll hear it. If all is well here, the engine will spin pretty fast -faster than you'd be used to on a normal start. Next: Put everything back. Check all your fluids, oil, coolant, and start the engine normally. really, you might as well. It will tell you lots without a tear down - if it does throw a rod against the skirt then it was already done before you got the truck anyway. So now it's running (I hope) Do you hear a click, a knock, anything at no load idle? If you rev the motor with no load does the sound change? If you rev WITH load (in drive/first against the brakes)does the sound change? Connect a timing light - does the sound happen at the same intervals as the strobe or half as fast? Same interval means valvetrain - cam/lifter/pushrod/rocker. half speed is bottom end - rod/bearing/wrist pin/piston/cyl bore wear allowing the skirt to hit the bore - these will usually be louder under load. good luck. I'm not sure about where you are, but a Chev 350 goes for about $200 - $300 bucks here, often still in a running rust bucket (in my opinion the ONLY way to buy a used motor that you want to run as opposed to a "rebuildable core") Will keep watching your post to see how you're doing.

Jim

Thanks for the info. I saw that post to late in the day to go try it out. Ran out of daylight. I will give that a try tomorrow and see what I get. I may only have time to pull the plugs and rotate by hand since I get home around 6-630 and it gets dark around 730. Also last night I was checking the plugs and # 6s plug wires evaporated in my hand and #8 wasnt much better. I spoke to the previous owner and he said that he was driving home when it lost power and he assumed that it was lost compression due to a pushrod but now I am not sure whats going on, his details have changed. I bought some plug wires tonight and I will change them out tomorrow after I do the test that youy recommended. Also #2 and #4 plugs haev a sort of heavy oil amount on them and the rest of them have some oil on them but nowhere near as much. I will report back what I find.
Thanks a bunch

Brad

Jim

Forgot to add that I am in san jose ca.
Will be trying this tonight.

Thanks
Brad

Hi Brad,
Ah wow, California - I'd die for the iron that you guys send to scrap! We salt the roads heavily here and even a late 70's car is very rare now. Body cancer sets in very quick, and because of the rarity, you pay huge $$ for anything that can be put on the road. Who in CA would believe a '71 Toyota would go for $12,000??
Is starting to sound like there's not much at all wrong with your truck. I think the guy you bought it from just didn't know. I wouldn't overly concern myself with a bit of oil on the plugs. The magazine publications that we all grew up with that "tought" us how to wrench, are in the biz of selling parts advertising and will convince you that everything must be a-1 to have a car/truck that won't self destruct at the stab of the pedal. The truth is, that if you tear down a chevy with 50000+ miles and look at it, you'll be convinced that it's dead by the measurements you take. In the real world there IS some scoring of the cylinder wall, the bearings ARE worn, there IS an ungodly ridge at the tops of the cylinders, and the piston skirts ARE scuffed. That engine also would have run for years if you hadn't torn it down! I just took apart an '80 400 V-8 that spent 20 years as a plow truck - still ran great, not a knock, and just the swish-swish sound of the bearings when you listened to it run with a stethoscope. Oh, but what a mess when I tore it down. Haven't miked it yet, but all the pistons had noticable wobble by hand in the bore, and a big honking ridge. It also would've run for ever. I often see S.B. chevy's with leaky valve seals - besides guide wear, the seals dry up fairly quickly. I'll bet at the most, your truck will give one puff of blue when you fire it, and clear up in seconds. It's probably fine. One bit of advice; If you've got a points ignition and aren't worried about keeping it original? Swap to an H.E.I. Unless I'm mistaken (anybody correct me if so please) it's a one 9/16 bolt, one wire swap that'll take under an hour, cost $20, and give you power, better emissions, idle, (especially if you are blowing oil) and reliability. You'll be happy you did it. P.S. as for oil on plugs - is the crankcase vent working properly?
Good Luck, Jim.

Now I hope sombody can help at my posting...

Yep calif has some nice old stuff driving around. Guy up the street has a 69 chevelle and one guy 2 blocks over has a 56 chevy if I am not mistaken. TO be honest I dont think that the guy knew. I am not trying to put him down at all please dont get me wrong there he is a helluva nice guy who after talking admitted that he didnt know very much at all about working on trucks. Thats ok though I dont either Im learning though. 12000 for a 71 toyota? Thats one months rent out here Back to your question about the crankcase vent. To be honest I have no idea. I am very new to this as well. Where is it? What does it look like? How do I test it? What do I need to test it with? And as far as the point system goes dont you have to change the dist as well?

Thanks a bunch

Judging by the condition of the plug wires I would say that the wires are WAY past overdue for replacement. Replace the wires doing one at a time so you do not get the order messed up. Plugs are around a buck a piece and since you are going to take them out I suggest replacing them as well.
You may find that the engine runs well with good wires and plugs

Mechainiac. You are probably right. I have the plug wires. What I am going to do is replace them one at a time and use a clothspin to mark them. Saw that on a post here somewhere. Once all of the plugs are out I am going to try what Jim said. Would be a good time to do it. Hopefully I will be able to do that tomorrow or Fri. If not then Friday then on Sat. I have 3-4 hrs set aside for for working on it.
Thanks guys..

Brad

I'm just worried that it's been so long since I did this stuff daily that I've forgotten something and will p*** somebody off with garbage info. It's easier when you're actually under the hood! Yes, the entire distributor will be replaced, and the coil is part of the new cap. The whole shebang comes out with a 9/16 bolt that retains the distributor via a bracket on the manifold. I THINK (see above disclaimer) that they all interchange on s.b. chevy's, gear and all - I've swapped dozens so far, but as the oil pump is driven from the distributor base, maybe one of the other guys here can confirm that? Everything that the ignition needs will be on the new distributor including the coil. There is one wire to make it all go marked B+, and an available tach lead. They're virtually maintenence free. As for crankcase venting: I don't THINK the modern PCV valve came in until about '72, so I'm not actually sure how it was done before then, but somehow the crankcase must be vented to atmospheric pressure or vacuum. If it's not, the blowby (gasses and pressure from combustion escaping past the rings) will pressurize the crankcase and can force oil past seals. You may simply have a hose running from a breather cap to the air cleaner if pre P.C.V. Interestingly, the PCV valve, because it uses engine vacuum to evacuate the crankcase does a better job of clearing out corrosive gases (I think it's sulfur dioxide that mixes with the oil to form sulfuric acid and eats the bearings) so it's better for your engine in the long run.

Jim
Where can I get one of the HEI systems. Sounds a lot better than points. And I think I saw a post on that a couple days ago. I will take a look and see what I can find.

Brad

Heres one..

http://www.ucalgary.ca/~csimpson/Tech/HEI.html

Just about any '75 to '85 chev with a small block V-8. Our emission laws differ here, and they (HEI's) stayed about the same through that time and were replaced with electronic advance HEI's about '86. YOU DONT WANT ONE OF THESE! The one your looking for will only have one or two wires going to it, and one vacuum hose. Boneyards will be full. There will be vacuum and mechanical advance curve differences, (both cheaply tunable) but the engine should run well no matter what you find. Just retro'd an '87 Monte Carlo last month with one from my neighbor's junk shelf from who knows what engine. Fired first crank. I really would go with junk first 'till you get your feet wet. You can buy 'em for a few hundred, but why?

Ok update time. I pulled all of the plugs and turned it over sounded good no clunking or clanging that I could hear. Put the plugs in with new wires. Started it up and clunk clunk. Let it run for about 5 seconds and shut it down. Didnt notice any smoke coming out of the pipe. I got my wife outside for a fresh pair of ears and she heard the same thing. Not sure what the next step is. Any suggestions?

Thanks

Pull the valve covers,,, I am betting you find a broken rocker stud

SUre thing will do that tonight. Man those plug wires were a pin in the bt to get off of the distributor. And by the way is the distributor supposed to move a little from left ot right when pushed. Not much like 1-2 inches? Just curious about that.

wow this site has the best motor detective stories on the internet!

The distributor moving is probably just the vacuum advance.

Move left to right??? are you referring to turning?(clockwise/counter clockwise)
The distributor has a hold-down bolt and keeper at the base where it goes into the engine. If the bolt is loose, the distributor will be able to be rotated left or right but it should be secured when the timing is set.(if you have points still, be sure to set the point gap or dwell (same thing) before you set the timing and secure the distributor.

A messed up pushrod or other valvetrain parts will result in a dead miss on one cylinder and some 'clatter' A bad rod or main bearing will cause a noticable "knock knock" sound when running, but less likely to have a dead miss. A compression test on all 8 cylinders will tell you if you have a bad pushrod or other bad valvetrain parts. One cylinder will have very poor compression PSI, the other 7 will be much higher.

good luck

chip

I dont have any gear to do a compression test but I can remedy that. Also is it safe to let it run with that nasty knock going on?
Thanks

I would not run it until you find the problem. it could take out more parts/pieces.
I have only seen one broken rocker stud on a small-block chevy. I rebuilt a 350 for my brother about 4 years ago. he was playing with a BMW on the freeway with his 3/4 ton 4x4 GMC
He called me and said there was a loud knocking noise but he could not tell where. HWen I went to rescue the truck I started it and heard a steady firm knock but it wasn`t a metal sound. When i pulled the passenger side valve cover I found the rocker and top end of the stud laying on top of the head. That valve (exhaust) was not opening and causing the knock noise. Pulled the head. had the stud replaced and he has been running great for the last two years

Then I will pop off each valve cover and see whats what. Need to head to the parts store and get 2 gaskets tomorrow. Other than pieces being not where they should be is there anything else I should be looking at? Rookie question I know

If you have only a bent pushrod or two, there will be metal flecks or shavings at the point where the pushrod goes through the hole in the head as it is a very narrow hole.
One more thing you may want to look at for sake of curiosity. Pull the dipstick and see what the oil looks like. look at it in good light and see if there is any metal-flake/glitter in the oil (Hopefully not)

Ok I changed out the valve cover gaskets. Didnt see any metal shavings or such or in the oil. The gaskets looked really old. Had to scrape most of them off. Took some pics.

http://bradandcharlottes.com/68/Driver%20side.JPG
http://bradandcharlottes.com/68/Driver%20side%20%232.JPG
http://bradandcharlottes.com/68/passenger%20side.JPG
http://bradandcharlottes.com/68/passenger%20side%20%232.JPG
http://bradandcharlottes.com/68/Engine.JPG

Hi Brad,
Been busy at work - Man, would have bet $ that your ride would be on the road by now, sorry its still giving you hell. I wish I could hear the clunk, would help a lot. A couple of places to go - maybe, before it's tear down time: A possability that's easy to check (and therefore discount) Are you SURE it's an engine noise? Under the truck there is an inspection plate on the lower front of the transmission - i think held on with four 7/16 bolts. under that is the torque converter which is fastened to the ring gear (that the starter drives) with more bolts (mine are five 15mm bolts - your's will be different, but they'll be there) check that they are all there and tight. It is possible with extreme caution to run the engine with all of those bolts out and the converter pushed "in" towards the tranny to clear the spinning flexplate, (in order to run the engine while it's disconnected from the trans) but there is very little clearence between the two, and it's probably not in the trans front pump anyway (they usually whine, not clunk) - but checking the bolts is free. Another thought - though never tried it - also free - can you get a small wooden dowel through the plug holes and try to "rock" the piston? Not even sure you'd be able to feel anything, but again, it's free. Worn piston thrust skirts (which stabilize the piston "square" in the bore) will make one hell of a racket if the clearance is too high.
You can also back the nuts off of the rocker studs one at a time to reveal collapsed, etc lifters. There is no harm in doing this with the engine running, but it will get messy. Use a 5/8 sparkplug socket. Back the nut off until the rocker starts to click or clatter. Then slowly tighten until the clatter goes away - this is called "zero lash" now turn the nut 90 degrees tight (1/4 turn) the engine may stumble and run rough -don't worry, it should. in a few seconds it will smooth out again - tighten another 1/4 turn, the same will happen. In the end you will be 1 full turn tight past zero lash. do the rockers one at a time. you MAY catch something as you back each one off - the noise may change or go away.
Gotta go back to work now. Good luck. Jim.

No problem Jim understood. Gotta make that money so it can be spent on good things like fixin up trucks Ok update time. While I was changing the dist cap and rotor I looked down and saw this.
http://bradandcharlottes.com/68/crack.jpg
http://bradandcharlottes.com/68/crack%232.jpg

That to me does not look good. Later a neighbor was walking by and was aking about the truck and in coversation I mentioned the noise and showed him the crack he said fire it up and when I did he put his hand over it and mentioned that eshaust is coming from it. He thought thats what it was when he heard me start it after I changed the cap and rotor. My brother n law is coming by on Monday and is bringing a compression testor so I will know for sure if thats is part of the problem on monday. Also what is this thing in the circle?
http://bradandcharlottes.com/68/crack%233.jpg

Also I just want to say thanks to everyone who has been helping me out. I cant tell you how much I appreciate it.
Thank-You

Brad

The big heat-crack on the right manifold can make a sound like a clack or knock.
From the pics I saw I was proven wrong about the rocker stud :rolleyes: :o
The unit on the right manifold is a heat sensor for the auto choke on your carb
Have you replaced the plug wires?
The heads on your truck
462624.....75-86...350/400......76cc chamber, 1.72/1.5, 1.94/1.5 or 2.02/1.6 valves

Yep I have replaced the plug wires. Also replaced cap and rotor today and when I started it up I noticed that it ran somewhat smoother minus that loud clank from the exhaust manifold. Can that crack cause the truck to lose power? Reason I ask is because that was the previous owner said. It lost power.

Thanks again.

Yes it can cause it to lose power. Not a lot but noticeable

Hi Brad, If that's the source of your noise then you're in good shape! i'll bet you can get a manifold pretty cheap there. You can get an ugly white putty at the local parts place to chink that up, although it wont last long, it'll quiet it down to see if that's all it is. Even r.t.v. sealant will hold for an hour or two. You can "vee" out the crack and weld it - I've done a few, but you'll have to pull the manifold anyway, so might as well start checking the boneyard.
Jim.

Ok heres the word. Knocking in the lower end. Cylnder #6. Looking for a new engine. Well looks like its time skokie learned to pull out a engine. Luckily my brother n law is helping

Thanks for all of the help.

What is it that made the determination that it was #6 ?

My brother n law unplugged the spark plug wire and the knock all but stopped. The way he explained it was that since its not firing its not getting slammed in there. He mentioned a bearing. Other than that he said that we can pull it and attempt to rebuild however since we are going to be pulling it out and if we find out along the way that its a no go on this engine it would probably be better to have another engine there ready to go.

Ok update time. The new engine is in the truck and running great, now for the bad news. The original engine #6 piston rod got hungry and ate itself. Then in the process spit up some shrapnel and took out #4 as well. We just had to know so we dropped the oil pan and there was metal everywhere. Top side of the engine is in great shape. Pushrods, valves, rocker arms were all fine. I was amazed at how clean the engine was on the inside. So the mystery is now solved. Thanks to everyone who helped me. It was very much appreciated. Now its time for me to start working on the rest of this truck.