351C Engine knock :(

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Gibson_Junk

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Nov 25, 2012
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Location
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My Car
1972 Mustang Coupe 351C
1969 Mustang Coupe EMPTY
Turned on my 72 this morning as I was going to take it for the monthly drive to make sure all was good. Turned it on and a knock was there. A tapping I guess. A revved it up a little bit to hear a 2 loud thuds. That that point I let off the gas and shut her down. I removed both valve covers to inspect and on one of the rods it looks as if it was hitting the edge at the opening where the rod is in. I am not entirely sure just yet.

It just came from no where. Oil level good along with all the other fluids.

Think its rod knock? Time for a rebuild?

Suggestions please. And if its rebuild time. Whats the difficult of a intermediate mechanic. I know how to do a bit but never really messed with engine internals.

Suggest a good kit or brand to get the parts. Also if it is rebuild time. .030 over a good choice? After the walls are inspect and checked for thickness

 
Turned on my 72 this morning as I was going to take it for the monthly drive to make sure all was good. Turned it on and a knock was there. A tapping I guess. A revved it up a little bit to hear a 2 loud thuds. That that point I let off the gas and shut her down. I removed both valve covers to inspect and on one of the rods it looks as if it was hitting the edge at the opening where the rod is in. I am not entirely sure just yet.

It just came from no where. Oil level good along with all the other fluids.

Think its rod knock? Time for a rebuild?

Suggestions please. And if its rebuild time. Whats the difficult of a intermediate mechanic. I know how to do a bit but never really messed with engine internals.

Suggest a good kit or brand to get the parts. Also if it is rebuild time. .030 over a good choice? After the walls are inspect and checked for thickness
Push Rods can get bent and go bad......Does she got alot of miles on that motor?

I would recommend not buying anything for it till you get it apart...And have it checked over...Heads...Crank...Rods..Piston then block...you realy dont know what your in for till you get in the middle of it...Counts how many miles..Has she been rebuilt?..and if so did they do it right or wrong? Is it over bored all ready? Hard to know till she all tore apart...But i would take the push rods out..See if there bent..They can sound like a rod knocking sometimes....I had a freind with a ford 460...It started bending rods while we was going down the road...It sounded like the motor was toast!! It was making horrible knocking sounds...Come to find out..Soft valve seats in the head turned out being bad..and it started bending push rods left and right.

 
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Sounds as though your lifter stuck/top broke and the rod popped out of the lifter. Shine a flashlight down a hole near it on either side and see if you can't see what happened. Or just pull the suspected rod out and look down that hole but I would do that second since strat down the hole lifter may look O.K..

Replacing lifters is actually quite easy and a good time to throw in a new cam/timing gear set. They sell them in a kit with everthing you need.

 
Well I pulled off the side I thought it was coming from and yup. Pulled out a push rod. Bent and scared up. I shined a light down there and its looked fine. As I think I caught it time enough to prevent tons of damage. As I am sure there is still more then just push rod damage I will be inspecting more.

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Turned on my 72 this morning as I was going to take it for the monthly drive to make sure all was good. Turned it on and a knock was there. A tapping I guess. A revved it up a little bit to hear a 2 loud thuds. That that point I let off the gas and shut her down. I removed both valve covers to inspect and on one of the rods it looks as if it was hitting the edge at the opening where the rod is in. I am not entirely sure just yet.

It just came from no where. Oil level good along with all the other fluids.

Think its rod knock? Time for a rebuild?

Suggestions please. And if its rebuild time. Whats the difficult of a intermediate mechanic. I know how to do a bit but never really messed with engine internals.

Suggest a good kit or brand to get the parts. Also if it is rebuild time. .030 over a good choice? After the walls are inspect and checked for thickness
Push Rods can get bent and go bad......Does she got alot of miles on that motor?

I would recommend not buying anything for it till you get it apart...And have it checked over...Heads...Crank...Rods..Piston then block...you realy dont know what your in for till you get in the middle of it...Counts how many miles..Has she been rebuilt?..and if so did they do it right or wrong? Is it over bored all ready? Hard to know till she all tore apart...But i would take the push rods out..See if there bent..They can sound like a rod knocking sometimes....I had a freind with a ford 460...It started bending rods while we was going down the road...It sounded like the motor was toast!! It was making horrible knocking sounds...Come to find out..Soft valve seats in the head turned out being bad..and it started bending push rods left and right.
As for miles it has 72xxx original miles on its. The previous owner said its was rebuilt 30xxx miles ago. I doubt it though since when I got it everything was covered in tons of grease. And if it was rebuilt they most likely were not professionals. Its not bored that I know if. But when I get it check all this will be questioned.

 
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Pushrods only bend 1 of 2 ways. They hang on the edge of the lifter as they popped out. OR valve never opened.
You need to take a block of hardwood and place it over the affected valve and give it a few taps with a hammer to make sure it's not stuck in the guide...[should have a springy feel]

 
As James says, it may not be bad at all. But I would question the 72,000 original miles statement based on the "everything covered with grease" and more importantly, the rebuild 30xxx miles ago. Why would someone need to "rebuild" an engine with only 42K miles?

Refresh my memory about the engine you have. If you need/want to go the rebuild route, I am living testament that it can be done by an inexperienced guy willing to take his time, buy, borrow or rent some specialized tools, and be anal about taking pictures and placing parts in labeled baggies and plastic containers. More to come about that if that's the direction you choose to take.

Keep us posted about what you find, and good luck! :)

 
Suggestions please. And if its rebuild time. Whats the difficult of a intermediate mechanic. I know how to do a bit but never really messed with engine internals.

Suggest a good kit or brand to get the parts. Also if it is rebuild time. .030 over a good choice? After the walls are inspect and checked for thickness
As an intermediate mechanic, it can be done. I have one under my belt. In the middle of number 2. But I do have friends with engine building expertise that come over and help with the hard stuff.

You do need a good machine shop. To save you time, the shop can do all the bottom end work(short block- Install crank/pistons/cam/timing chain)

You can do the top end- Add heads, intake/carb, water pump. But, you need to measure your pushrods, which is a bit of a pain.

Cost will depend on what needs to be done to your motor. Whether you need new pistons, crank needs to be reground, and a zillion other things. Guys here claim to rebuild motors for $800. On my 351C, I am at probably $2700(machine shop and parts).

To check on the current state of your motor, do a compression check of the cylinders. If you get like 120# in each cylinder +/- 10 pounds, that is probably a good sign. You can also degree your cam to measure your lift to give you an idea of what is under those lifters.

Not fun. Good Luck.

 
Pushrods only bend 1 of 2 ways. They hang on the edge of the lifter as they popped out. OR valve never opened.
I'm sure there are more ways than that:)

For example they definetly bend when the rocker stud/bolts break. Ask me how I know:)

Greg
Definelty agree. Me I would charge the cylinder with air and remove the valve spring so I could inspect the valve. Check it with dial capiler gauge while rolling it and if it checks out. I'de just do a cam/lifter build if cost is a factor. If not yank that sucker and let's build a motor!!! :)

 
Pushrods only bend 1 of 2 ways. They hang on the edge of the lifter as they popped out. OR valve never opened.
I'm sure there are more ways than that:)

For example they definetly bend when the rocker stud/bolts break. Ask me how I know:)

Greg
Definelty agree. Me I would charge the cylinder with air and remove the valve spring so I could inspect the valve. Check it with dial capiler gauge while rolling it and if it checks out. I'de just do a cam/lifter build if cost is a factor. If not yank that sucker and let's build a motor!!! :)
I will figure a way of going about this. Along with what the others said. Cost as of now is a factor. Now that its broke..Just means I can take my time to fix it since its not my daily driver. Which means I will probably go for a entire rebuild so I can add a little hp while I am at it. This is a long project.

 
I am almost decided on what to do. Think I might just remove the intake, then the heads, after draining all fluids. Pull it out clean everything, Ziplock baggy and label everything. Clean and inspect it all. Take block to have it inspected and maybe bored if possible and take my sweet ass time rebuilding it.

 
Unless your building for race on 351's it's really not a good idea to just head to the machine shop and tell them "bore it .030". Ask them to merely "Clean up the bore". Many times you may only need .010" or .020". These are also standard replacement piston sets just not commonly heard of. And since our blocks are relatively thin walled, you don't want to remove more than needed (you may need that down the road in the event of another mishap). I just scrapped a .030 over block that would have taken more than .010 to clean the bore just because the rings had stuck from sitting. When I ask the PO why they had gone .030 he said he was unaware they could have done less and the machinist gave him exactly what HE had ask for. Let the machinest tell you what it would take. That's what they do for a living.

 
We'll be here for ya. Just keep posting up.
Thanks for the reply to my pm

Unless your building for race on 351's it's really not a good idea to just head to the machine shop and tell them "bore it .030". Ask them to merely "Clean up the bore". Many times you may only need .010" or .020". These are also standard replacement piston sets just not commonly heard of. And since our blocks are relatively thin walled, you don't want to remove more than needed (you may need that down the road in the event of another mishap). I just scrapped a .030 over block that would have taken more than .010 to clean the bore just because the rings had stuck from sitting. When I ask the PO why they had gone .030 he said he was unaware they could have done less and the machinist gave him exactly what HE had ask for. Let the machinest tell you what it would take. That's what they do for a living.
Thanks as well. I am glad I got this forum for what DOC said and everyone else. I will hold off on the bore. I knew we had thin walls but was unsure how thin. I will be upgrading the internals though with some higher quality stuff whenever I do go around to getting i all fixed. And I think this will make the engine swap of this going into my 69 a little better because I will be able to clean the engine up all nice and pretty

 
There isn't much point spending time/money/effort rebuilding the bottom if there isn't anything wrong with it.

Figure out what happened with the valve/push rod. Pull the head isn't a bad idea at all. A good quality valve job may be all you need. Get the one piece valves if you currently have the original ford.

Maybe swap out the cam while you are at it. You can do that with the block in the bay. You have to remove the raditor and grill. It might just be easier to unbolt it from the tranny and pull the motor.

 
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