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11/13/2021 8:01 PM  #1


Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Some of you are familiar with my 351w rebuild: it was a rering with only a hone job and all new bearings. All went well and it ran strong BUT it sounded like a diesel below 1500rpm. Did lots of testing and parts swaps, it was getting good oiling, but couldn’t find the issue. It was determined through this group that it was probably a wrist pin. Yesterday I tore it down and it looked good, bearings looked great, rings were seating well and getting shiny on the friction surface, and the cylinder walls were two different colors where the rings were seating. It was very interesting to see. What I couldn’t find was an obviously bad wrist pin. If you had the piston in hand how would you identify a bad wrist pin?

 

11/14/2021 6:42 AM  #2


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

I'm assuming the pins are stock type pressed in pins.  There should be slop between the piston and pin.  The pin would be tight in the rod, but have slop in the pin bore in the piston.  Its tricky because the pin can't be so tight that the piston can't turn on it, but any slop is bad, because as that piston heats up its going to get amplified since aluminum has a greater thermal coefficient of expansion than steel or iron. 

 

11/14/2021 7:47 AM  #3


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Wrist pin can also be too tight, in a seized up manner.  That makes the piston really slap around side to side in its bore. And destroys rod bearings.

Two obvious things to check:  piston and rod move freely on wrist pin.  (I'm sure in this case, the pin is a press fit on the rod). Point being, if you can hold the piston perpendicular and the rod doesn't travel to the bottom, there is a problem.

Check and make sure all of the rod chamfers were to the outside.  They are chamferred on one side to clear the radius of the crankshaft.

I've seen some things over the years.   Thrust bearing in the wrong spot, and rods backwards are a couple of them.

Last edited by Greg B (11/14/2021 8:10 AM)


If multiple things can go wrong, the one that will go wrong will be the one that causes the most damage.
 

11/14/2021 8:17 AM  #4


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?


If multiple things can go wrong, the one that will go wrong will be the one that causes the most damage.
 

11/14/2021 9:51 AM  #5


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

If the rod or cap were in backwards you will see damage to the bearing.  I've unfortunately done that before in my youth. 

 

11/14/2021 10:15 AM  #6


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

It is the stock press styile wrist pins.  The pistons move extreamly freely but there is no slop.  They rotate as designed, no drag.  The noise I was having was imediate.  The engine cold was just as loud as the engine hot.

     Thread Starter
 

11/14/2021 2:01 PM  #7


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

A gazillion years ago I rebuilt an Isuzu 4ZE1 4 cyl for my wifes Amigo. All internal parts and gaskets were supplied by the machine shop. I put it together and stuffed it in the car. First startup it sounded like a diesel at all RPM's, warm or cold. The machine shop and I pondered on what to do.
I pulled the head and found the problem. The shop had supplied me with a head gasket for the smaller 4cyl and the gaskets are identical except for bore size. The gasket supplied was the exact same as the bore so when torqued down the gasket squished into the bores ever-so-slightly and the piston was hitting the gasket every time it reached the top of the stroke. The proper gasket fixed the problem.


Gary Zilik - Pine Junction, Colorado - 67 Coupe, 289-4V, T5
 

11/14/2021 2:57 PM  #8


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

I think you may need to really look at everything.  Ii it possible that a valve cover or the oil pan, or the timing cover is having an interference issue?  What is on the engine now that wasn't there on the original engine when you got it?  My guess is that's probably the issue.  If the bearings look good its not the bearings, if the wrist pins don't show any slop probably isn't them, etc.  Start looking for little shiny areas on stuff.  Something's hitting something else.  It doesn't take much to create a noise that's loud and worrisome. 

 

11/15/2021 6:39 AM  #9


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Would a cracked piston skirt cause this?

 

11/15/2021 7:10 AM  #10


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Back in the day I helped a friend tear apart his engine for a very similar issue. We did everything, measured bearing clearances, piston skirt clearances, check every lifter, valve stem clearances........everything BUT look at the fuel pump eccentric and fuel pump!!!!!!!!!!!!!!!!!!!! Sometimes it is the little stuff.

 

11/15/2021 11:34 AM  #11


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

TKOPerformance wrote:

I think you may need to really look at everything.  Ii it possible that a valve cover or the oil pan, or the timing cover is having an interference issue?  What is on the engine now that wasn't there on the original engine when you got it?  My guess is that's probably the issue.  If the bearings look good its not the bearings, if the wrist pins don't show any slop probably isn't them, etc.  Start looking for little shiny areas on stuff.  Something's hitting something else.  It doesn't take much to create a noise that's loud and worrisome. 

TKO mentioning the valve cover made me think of maybe the rocker arms just slightly hitting the valve cover, or the baffles within the valve cover, just a thought.
 


65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
 

11/15/2021 12:36 PM  #12


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

When we first started to try and solve this issue as a group (previous thread), we looked at valve train.  I primed the system and had good oil at all 16 valves, I replaced the lifters, I shimmed the rockers for correct preload, I replaced the oil pump with a high volume unit, confirmed all pushrods were strait, and I even swapped the heads out to a set I knew were good from another running engine.  No change.

I know it is NOT a clearance issue.  This combination was using an electric fuel pump, there are no contact points on any surfaces AND the sound goes away above 1500 RPM.  If it was lifters hitting valve covers or something in the bellhousing RPM would only change the intensity of the sound and the pitch but more RPM would not make it go away.  It also goes away at idle if I choke the motor or lean it way out. (this is why I figured it was a wrist pin issue by changing the combustion I eliminated the sound)   I discovered this when I was burning up the last of the fuel in the carb.  As the bowl ran out of fuel and the mix went way lean the noise went away.  On the flip side if I covered the carb with my hands and just let enough air in to keep it running the noise went away.  It has to be in the rotating assembly, I just wish I could find an obvious cause.  That is why I was asking about the wrist pins and how to inspect them.

     Thread Starter
 

11/15/2021 1:28 PM  #13


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

In a Diesel engine we'd call that a fuel knock.  Something to consider.

 

11/15/2021 2:10 PM  #14


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Since it's all apart, take the time to measure the pistons and bores. If there is a tad too much clearance, the pistons might be rocking in the bore. 


John  -- 67 Mustang Coupe 390 5 speed
 

11/15/2021 4:52 PM  #15


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Bolted to Floor wrote:

Since it's all apart, take the time to measure the pistons and bores. If there is a tad too much clearance, the pistons might be rocking in the bore. 

how much is too much?
 

     Thread Starter
 

11/15/2021 5:02 PM  #16


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Bolted to Floor wrote:

Since it's all apart, take the time to measure the pistons and bores. If there is a tad too much clearance, the pistons might be rocking in the bore. 

Okay I have researched it a bit and if that was the case it should go away or at least decrease as the engine warms up.
 

     Thread Starter
 

11/15/2021 6:16 PM  #17


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Daze wrote:

Bolted to Floor wrote:

Since it's all apart, take the time to measure the pistons and bores. If there is a tad too much clearance, the pistons might be rocking in the bore. 

how much is too much?
 

Ford should have it noted somewhere in their specs for that motor.


John  -- 67 Mustang Coupe 390 5 speed
 

11/15/2021 6:25 PM  #18


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Daze wrote:

Bolted to Floor wrote:

Since it's all apart, take the time to measure the pistons and bores. If there is a tad too much clearance, the pistons might be rocking in the bore. 

Okay I have researched it a bit and if that was the case it should go away or at least decrease as the engine warms up.
 

Go away or decrease sounds reasonable with a warm engine.  Taking the measurements will help to eliminate it for certain.


John  -- 67 Mustang Coupe 390 5 speed
 

11/15/2021 10:37 PM  #19


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Have you checked the diameter of the lifters to their respective bores?

Perhaps….
At higher rpms, more oil can pump up the lifters to lessen the clatter.
To me, it never goes away in first video.

Perhaps more stuff made it’s way inside the lifters.

 

11/15/2021 10:50 PM  #20


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Nos681 wrote:

Have you checked the diameter of the lifters to their respective bores?

Perhaps….
At higher rpms, more oil can pump up the lifters to lessen the clatter.
To me, it never goes away in first video.

Perhaps more stuff made it’s way inside the lifters.

Lifters were a good fit (both sets)

     Thread Starter
 

11/15/2021 10:57 PM  #21


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

I remember pulling plug wires to identify a rod knock in a buddy's 305 chebby. I wonder if you covering up the carb was essentially doing something similar. Instead of pulling spark altogether you were greatly reducing cylinder pressure by restricting air flow.

Anyway if you have the tools you should measure the cylinder bore and then the pistons, what year is the motor again? 1996? I have a full set of Ford 1994 truck service manuals. I will look and see if it has bore size specs for a 351w, might not be exactly the same year but I imagine it's close. 

 

11/16/2021 7:47 AM  #22


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

This is so perplexing, without direct examination.   I reread your post.  Just trying to think of anything we've missed.   

What did the ring ridge look like?  They make a tool to cut that down and AutoZone used to rent it.  Not saying this is the problem, because I think that would have ended in a broken compression ring, but other than the crankshaft just ever so barely touching the oil pan, I'm just about out of ideas.


If multiple things can go wrong, the one that will go wrong will be the one that causes the most damage.
 

11/16/2021 9:39 AM  #23


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

I once developed what I first thought was a rod knock in an engine. I had to have the vehicle towed home close to a hundred miles.
On disassembling to I found a 3/8” piece of a piston ring imbedded into one of the piston tops. Every time the piston went tdc it made a loud rap. There were pit marks from the broken ring bouncing around all over the piston top. To my knowledge the engine had never previously been apart, the car the engine came from was owned by a fellow worker since new.
The heads and cylinders were pulled off the crankcase and every ring on all pistons were intact,  not a broken ring anywhere. Cylinder walls were unmarked.
I put it back together with new seals, gaskets and it ran fine til it was sold many years later.
To this day I have no idea where that piece of piston ring came from.
Oh by the way, it was a Corvair engine in a modified VW bus chassis with a home made fibre glass body.

Last edited by Rudi (11/16/2021 9:43 AM)


Good work ain't cheap, Cheap work ain't good!   Simple Man
 

11/16/2021 10:13 AM  #24


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

Daze - piston to cylinder bore clearances from years ago, may have changed as materials have changed through the years
Stock engines: 0.0015-0.0020"
Performance Engines: 0.0030-0.0035"


65 Fastback, 351W, 5-speed, 4 wheel discs, 9" rear,  R&C Front End.
 

11/16/2021 10:28 AM  #25


Re: Disassembly of a fresh rebuild is fascinating, wrist pain issue help?

BobE wrote:

Daze - piston to cylinder bore clearances from years ago, may have changed as materials have changed through the years
Stock engines: 0.0015-0.0020"
Performance Engines: 0.0030-0.0035"

I'm assuming they are cast pistons, use the first spec.  Be aware the hypereutectics can run as tight as 0.0005".
 

 

Board footera


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