Assessing An Engine Core For Rebuild... -
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post #1 of 2 Old 11-04-2013, 08:54 AM Thread Starter
Running On Empty...
1973 CJ5 
Join Date: Aug 2007
Location: South West Indiana
Posts: 11,180
Assessing An Engine Core For Rebuild...

Time to put your 'CSI' cap on...

Failure Analysis is the best way to determine if your prospective engine needs some tuning up, or it's junk.

Everything leaves behind signs, traces, and sometimes outright screams there is an issue.

There isn't supposed to be any Coolant in the oil for any reason. If you drain the old oil and find coolant, it's an almost certainty the engine is cracked or at least has a blown head gasket...

Looking for fuel/coolant in the old oil is worth your time to drain a sample into a glass jar and have a sniff (Fuel) and allow it to separate.
ANY BROWN COLOR means coolant, and it means that engine was ran at high temperature with the coolant in the oil.

Coolant that just leaks into the oil won't mix and cause 'Brown' or 'Green' in the oil.

The only 'Acceptable' oil is jet black, anything other than black means you don't give the guy what he's asking, or you pay once the engine is torn down & inspected...


Top End,

When you take the rocker covers off, have a look inside the rocker covers and between the rocker arms. Most people don't take note of the TYPE of crud you find there...
A tar like sticky coating that is BLACK all the way through means the engine had it's oil changed once in a while, and it was kept under cover to keep moisture from condensing or running directly into the engine.

A black coating with a tan/brown gel on the surface means there was condensation allowed to happen. This usually means water (Separated) in the oil, which you should have already found.

A tan/green gel means there was a coolant leak to oil at some point, never a good sign.

Hard carbon that cracks off in chunks means the engine was ran very hot at one time, or for a long time, and crystallized the carbon sludge into hard carbon.
Overheating or excessive piston ring blow by are both bad signs, overheating in particular...


Rocker Arms are probably the first things you are going to encounter.
If you are doing a complete rebuild, then it makes sense to buy new rockers, push rods, ect.,

But if you are just 'Refreshing' the engine, getting a head job done, stuff like that,
Then you need to VERY CLOSELY take a look at the rockers...

If the engine is still somewhat functional, turn the engine over by hand, have a look at the valve train in action. You are looking for broken springs, coil bind, stuck valves, rockers with too much slop in them, ect. valves that aren't opening fully, stuff like that.
This often tracks down why the engine was pulled in the first place, and the home rebuilder almost never does this type of assessment.


Pull the adjustment nuts off the rockers, or in some cases bolts out of the pivots.
Nuts will be 'Prevailing Torque' nuts that are designed to be 'Lock Nuts', so replace those with new 'Prevailing Torque' nuts.

Check bolts for signs of bending or unusual wear that would indicate something is misaligned.
Bent bolts are a dead give away the valve train was binding, stuck valve, valve spring coil bind, lack of lubrication, Something kept that rocker from doing it's job and the stress was transmitted to the bolt.

Once the bolts or nuts are pulled, pull ONE ROCKER AT A TIME, KEEP THEM IN ORDER IF YOU INTEND TO REUSE THEM!

Have a look at the 'Fulcrum', that will be the 'Ball' or the 'Shoe' in AMC engines, it sits inside the top pocket of the rocker arm...
There should be OILING GROOVES in that 'Ball' or 'Shoe'. If the oiling grooves are warn thin, or missing, both the rocker and fulcrum need to be replaced.

This image shows the bridge between rockers to stabilize them, and the fulcrums for both intake and exhaust, and since they are flipped over, you can see the oiling grooves on the underside.

Then next thing you look at is the rocker itself...
Check the push rod end with the small half sphere stamped into it.
If the shiny wear ring reaches the small hole for oil to escape and oil the rocker, valve stem end, ect. Then it's junk. That wear ring through the oil hole indicates it's worn enough that the oil flow is being blocked when the rocker works.

Also look for a 'Worble' in that wear ring, it should be smooth and shiny. If there is a 'Ridge', even a polished ridge, this is an indicator the hardening is worn through on the pushrod end and you are getting a double wear pattern. Replace both rocker and push rod.

Have a look at the valve stem end, if there is a groove in it that you can catch your fingernail on, it's junk, replace it.
This means there is enough wear to seriously effect your camshaft lift and it's time for replacement.
Now remember, this rocker is worn in for this particular valve, and the placement of the rocker mounting hole, so you SHOULD NOT put another 'Used' rocker on here with a pre-established wear pattern or you will wear the valve stem end unevenly, and that will lead to uneven valve guide wear.

Pull the push rods, mark them for which end was up if the pushrod guides didn't wear them on the top end, and roll them across a sheet of glass.
This will tell you VERY QUICKLY if you have a bent push rod.

Check the ball ends, see if you have an even, polished wear pattern.
If you see that 'Worble' I mentioned before in the wear pattern, it's time for a new push rod.

Check the valve stem ends. Look for 'Mushroom' wear on them that would indicate the rocker isn't giving even pressure.
If it's mushroomed all the way around, and NOT pronounced, that's normal since the valve should rotate in operation.
If you have EXCESSIVE metal pushed off on just one part of the valve stem, then you have a valve that isn't rotating or the rocker arm wasn't pushing evenly on the valve stem.

Before you take the valve locks out, have a look at the valve retainers (washer looking thing on top of the spring) and the valve locks in the center of that retainer...
If you see signs the valve locks are being pulled through the retainer (Deeper) That's a sign of coil bind in the spring or seizing valve guide on the valve stem (Stuck Valve).
It could also indicate a lifter locking up internally and over compressing the valve, but that's rare.

Once you have verified there isn't any really unusual wear, more wear or damage that isn't from just plain hard use of the engine, then move on...



Take head bolts out WITH A MANUAL WRENCH!
I see guys air gun the bolts out all the time, but this gives you no feeling for how they were torqued.
If you find a head gasket issue under the head, you will have no idea if the bolts were super tight or loose around that part of the gasket...

Inspect the bolts as the come out, especially the bottom end. Look for signs they were in coolant...
Some of these bolts are directly into water jackets, but others are 'Dry', and finding coolant corrosion/buildup on a 'Dry' bolt might be a sign of a cracked block...

Some cracks don't cause a lot of noticeable issues in operation, but shouldn't be rebuilt, Others are OK until you try to torque a head back on and you hear that sickening 'Crack' open up with the stress of a bolt torquing down...
And this might be the reason the previous owner decided to sell the engine in the first place...

Remove head, try to get as much of the head gasket INTACT as you can, this will tell you if the cylinders stayed sealed, or if there was a coolant leak between block and heads...

Inspect the top of the cylinder for the 'Ring Ridge', the point the rings reached highest up in the cylinder and caused wear on the cylinder wall.
The more ridge, the larger the engine will have to be overbored to make the cylinders 'Cylinders' again.

Look for pits in the cylinder walls.
AMC was pretty good about adding things like Nickle to the castings, so 'Bubbles' in the cylinder walls are rare, but things like coolant, spark plug electrodes, ect. will cause scratches and pits when they eat into the metal.

Once cleaned and inspected, the cylinders can be accurately gauged to find out exactly how much they need to be over size bored...
You can do a quick check on the cylinders if you have a bore gauge and the cylinders are clean, but don't expect it to be accurate until everything is very clean.

Once everything is clean, you can check for cracks at the tops of the cylinders, bottom of the cylinders where they connect to the rest of the block.
Remember, early AMC engines had an issue with 'Core Shifting' during the manufacturing process.
That means the NEGATIVE (Sand) Casting shifted when the liquid metal was poured into the mold, and the cylinders might have got a little skewed, making the metal thin in these connection points at top and bottom, so they crack easier...

The top dollar way to tell is with sonic testing, and ultrasound machine to tell thickness of cylinder walls and connection points, but not many small shops have those.
If it didn't crack in it's previous 200,000 miles of use, and you do a REASONABLE over bore, it shouldn't crack in the next 200,000 miles of use...
Were aren't running high stress, exotic fuel engines here, and you have to stop the money hemorrhage at some point...
If it's available, it's usually not too expensive, If you have to transport the block, get it tested, ect., it's usually not worth the money.
Magnetic testing, Chemical testing should be enough. Use both, they are cheap and easy.


AMC V-8 Engines have a real Oiling Issue to the back of the block.

Pressure is a function of VOLUME, so we talk about HOW MUCH oil gets places, not necessarily the 'Pressure'

All of the oil Volume is created in the front timing cover!
This is a bad design to start with, and it's VERY EXPENSIVE to change that. You would need an EXTERNAL, Belt driven oil pump, and all the brackets, pumps, accessories that go with that. So we simply don't do it.

There are some ways to INCREASE THE VOLUME of oil to the places that really need it... And you need to determine where those places are during the tear down/inspection process!

What I see the most of is LACK OF OIL VOLUME to the rear of the camshaft, and especially the 7-8 main bearing and rods.

The oil pump produces oil flow at the very front of the block,
That oil flow has to make several 90 bends inside the block,
That oil flow stream is 'Tapped' and looses volume/pressure from front to rear,
And by the time it reaches the back of the block there is virtually none left...

That causes the rear main bearings, rod bearings and back camshaft bearings/lifters to starve for lubrication.

Now, you CAN do something about much of this...
That's where FAILURE ANALYSIS comes in.

Oil volume/pressure is produced at the oil pump, and right away it's RESTRICTED.
The outlet in the pump body/filter head is restricted.
There are numerous sites out there that show which passages to open up to increase VOLUME to the engine itself, look them up and break out the files/dremel tool...


Not the least of issues with the timing cover oil pump is...
It's aluminum.

Aluminum expands three times as fast as the steel gears inside the pump,
And it expands twice as fast as the steel gears inside the pump.

Since there is nothing we can do about that other than to close up the tolerances in the pump and minimize the expansion losses, you need to take particular care when inspecting the timing cover/pump cavity to see if it's or not...

These oil pumps/front timing covers can often be rehabilitated, but it takes a lot of time and some very particular hand work to get the most out of them...
I've written extensively on rehabbing a front cover, and the information is out there from several sources.
This is DIFFERENT than 'Modifying' the oil system, this is just bringing the front cover back to reasonable tolerances...


Oil Volume/Pressure starts at the oil pump, gets transferred to the block through a 90 turn/gasket that likes to protrude into the oil passage, then makes another 90 turn in the block up to the front of the camshaft bore gallery manifold.

Once it reaches that manifold right behind the #1 Camshaft bearing, This is the first big 'Leak'.
The front camshaft bearing leaks like a sieve!

First, The camshaft has a bunch of junk hanging on it, which pulls down on the camshaft.

Second, that stuff is vibrating, Timing Chain Set, Distributor/Oil Pump Drive Gears, Fuel Pump Eccentric, ect. so you get the 'Hammer Drill' effect on that front camshaft bearing.

Third, People INSIST on putting 'Split' camshaft bearings in instead of solid bearings (without a separation split). The opening in that bearing leaks oil like crazy.

When you 'LEAK VOLUME', you automatically reduce PRESSURE. Remember, Pressure is a function of volume. Without VOLUME, you can't build pressure...

Lots of rebuilds start out with a lot of volume/pressure, but QUICKLY DROP PRESSURE in just a few thousand miles, and a bunch of that loss can be directly traced to lousy camshaft bearings dumping oil volume.

The oil makes ANOTHER 90 turn into the oil galleries from the front manifold cast into the block at the camshaft, then starts leaking at lifters, camshaft bearings and crank shaft main caps...

Those camshaft bearings are a HUGE LEAK if they aren't the 'Solid' type that takes honing/reaming to get them to fit the camshaft.
If it's the 'One Size Fits Nothing' with the 'Split' in them, they are going to be too large, the split is going to leak, and you WILL dump your oil volume... Resulting in LOW PRESSURE to the back of the engine...

Check your lifter bores!
Wallowed out lifter bores dump a lot of oil, but this isn't a huge issue since that oil makes it to the faces of the camshaft lobes as it drips off the lifters...
I wouldn't reject a block with slightly over sized lifter bores, and there is a way to 'Sleeve' those lifter bores, but it's time consuming and expensive if they are really out of specification or 'Galled' where they have to be honed quite a bit over sized...


Since connecting rods get their oiling from the main cap journals, You MUST have good oil flow to the main caps.
I do everything I can to make sure those oil passages don't have obstructions,
But also make sure they are drilled into the block so they PRECISELY MEET the oil galleries supplying them through the block longways.

Often, especially in pre '87 (Chrysler years, '87-90), the AMC blocks had main cap oil supply lines that didn't directly hit the lengthwise galleries that were supposed to supply them.
The misalignment drastically cut back on the volume of oil that could reach the mains, and by extension, the rods.

One way to check the galleries meeting squarely is to use a drill rod (Solid round bar stock) up in the gallery, the same size as the gallery passage hole,
Then try to stick varying sizes of wire longways through the feeding galleries in the block.
If you can only pass a very small wire past the bar stock, then the junction is pretty well centered in the gallery...
If you can pass a very large wire gauge past the bar stock, the main cap gallery isn't lining up with the main gallery very well and probably needs to be addressed.

Another way is to use air pressure, see if the junction of the passages are flowing a lot of air pressure, or smaller amounts than they should be.

Re-Drilling a block passage/gallery is better lift to the professionals at the machine shop... But at least you found this issue before it starved your mains/rods for oil.



This collects oil volume/pressure at the front of the block, and 'Loops' the oiling system, delivering pressure to both ends of the oil gallery.
This works VERY WELL and is highly recommended, especially on OLDER ENGINES that might not have oil galleries that are cleanly drilled or meet directly at junctions...

'Looping' isn't new, it's been around since the early days of hydraulics.
When you have 'Losses' along a line, useage that lowers volume/pressure, you get less volume pressure at the 'End Of The Line'.
With AMC V-8 engines, this IS A VERY REAL ISSUE!

By 'Looping' you simply supply oil volume to BOTH ENDS of the oil gallery passages, so the pressure in the line stays more even.

I found this by plugging in a pressure gauge at the back of the block during testing because of several rear rod bearing failures, and the pressure was about zero.
Tracking the issue back to bleeding of the line at camshaft bearings, lifter bores, forward main bearings I found out there was virtually no oil left for the rear mains/rods.
By 'Looping' the oil system the rear oil volume/pressure was restored and the rear rod bearings lived...

I've had issues with hard lines wanting to break fittings off, crack the lines at the fittings, ect,

These are NOT my pictures, but what I do looks something like this,

Soft lines usually take vibration better, but I recommend you DO NOT allow that steel braided line to touch ANYTHING since it will saw on/file off anything it comes into contact with...


Once you have done an evaluation of the 'Hard Parts', then it's time for opening up the engine, removing plugs, cleaning things, and doing either chemical, pressure or magnetic inspections.

During that take down, keep an eye out for leaking ANYTHING.
Any leakage between 'Freeze' Plugs (Actually called 'Core' plugs), between holes, just under the core plug holes, ect. for signs of coolant leaks.

Just above the oil pan rail on the side of the block is where you will see any cracks from things dropped into the water jackets.
Sometimes people push the old core plugs inside the water jacket instead of pulling them out, once wedged in there, expansion and contract during heat cycles will cause a crack just above the oil pan rail on the side of the block.
One large engine remanufacturer used to punch core plugs inside the engine but they don't do that anymore because of this very issue.

Cleaning is the key here. The cleaner you get that engine, the more likely you will find any issues.

I usually use both magnetic ('MagnaFlux') and chemical prep to look for cracks. If your shop has pressure test equipment, that's always worth a few extra bucks to have it done, but most shops don't.

Once you KNOW you aren't wasting time on something that is cracked, then it's time to have the engine checked for tolerances, Figure out what needs to be machined, honed, ect.
Cleaning is fairly cheap, while machinist time and machining is fairly expensive. Cleaning is cost effective simply because it saves machinist time messing with something broken.

Pay particular attention to the area between valve seats, and at the top/bottom where the cylinder meets the block.

If you install studs to hold the crankshaft in, MAKE SURE THE STUDS ARE INSTALLED CORRECTLY!
Virtually every block that had 'Home Installed' studs were cracked!
Someone installed the stud to head bolt torque specifications, and since the stud bottoms out in the block/threads, it cracks the block through the main webs virtually every time!

The threads need to be CLEAN, then use a good PERMANENT thread locker, and install no more than about 20 Ft. Lbs.
If you know how a bolt works, you know they won't loosen, and with only about 20 Ft.Lbs. you haven't cracked the block...

Main cap and head bolts are threaded directly into soft cast iron, so they MUST be completely clean, the threads MUST be lubricated with a LIGHT COATING common oil, and you MUST use AN ACCURATE TORQUE WRENCH.
The torque specifications are just under what will strip those threads out of the cast iron, so you MUST get an accurate torque reading. Lubricating oil will stop the bolt from getting hung up in the block and giving a false reading, Too much oil can cause issues, so I stress LIGHT COATING...

While a LIGHT COATING of plain engine lubrication oil will help you with correct torque readings,
Something like super slippery lube like camshaft lube will reduce your torque readings to the point you will strip out threads.

Also remember, cast iron is SOFT, it moves around...
When you do your head bolts, the gasket will compress, the block will shift with the torque/load of the head, so leave your engine about 24 hours or longer, re-torque before you try and fire it up. You will often find some of the head bolts have loosened up as the block settles and the gasket compresses.


I've seen this time and time again...
Someone gets 'Plug' crazy, puts in ALL the plugs at once.
The camshaft is held in place by two things,
1. The back side of the camshaft sprocket on the timing set,
2. The rear camshaft bore plug.

If you bump that camshaft bore plug in too far, and it happens, your timing set WILL NOT seat against the front of the block/camshaft bore like it's supposed to.
This means a MISALIGNED timing chain, excessive wear, oil pressure loss, and the edges of the camshaft lobes coming into direct contact with the lifter flat faces.

When building the bottom end (Short Block) I usually leave the camshaft bore plug out so I can VISUALLY confirm the lifters are riding on the camshaft lobes like they are supposed to,
The timing set is riding where it needs to be,
And THEN I install the rear bore plug taking care not to move the camshaft someplace it's not supposed to be.

It's perfectly fine to have the plug flush against the back end of the camshaft, that isn't an oil passage, and it will help handle some of the 'Thrust' the camshaft creates, but you DO NOT want that plug to move the camshaft forward of where it's supposed to be.

I could go on and on about connecting rods, timing sets, ect. but this is long enough for now.

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post #2 of 2 Old 11-04-2013, 03:15 PM Thread Starter
Running On Empty...
1973 CJ5 
Join Date: Aug 2007
Location: South West Indiana
Posts: 11,180

Most AMC Connecting rods are CAST IRON, easy to spot, you will see a very thin cast parting line seam up the sides of the rods.
These are a little brittle for my taste, I often replace them in even moderate street rod engines,
But for most 'Jeeps' they will work OK as long as you have them Magnifluxed, chemically crack checked, and replace the rod bolts.

If you are doing a 'Refresh' on a running engine, then at least replace the rod bolt NUTS with new ones since those bolts and nuts are single use and not intended to be reused at all.

DO NOT let some machine shop slug talk you into using larger rod bolts!
The bolts are already stronger than the cast iron rods, so removing more cast iron for larger bolts is nuts!

New, top quality bolts/nuts is never a bad investment!
Also remember, the 'Torque' value given for rod bolts is a SUGGESTION!
Rod bolts should be tightened in a stretch gauge that tells how much stress/stretch you are applying to the bolt, not just a 'Torque' value on the nuts.

If you remove rods for a full rebuild, the shop MUST resize the rod big ends in pairs!
One rod on the reamer can easily, and probably will, get cocked a little making the hole off center.
When you resize in pairs, the two rods together keep each other straight on the reamer/hone/sizer and BOTH come out exactly the same size for the crank journal, and both come out straight through and not canted.

Polishing the rod beams on cast iron rods is like putting lipstick on a pig...
Getting rid of the casting line is difficult, time consuming, and if you use a power tool, you can do more damage than good, and when you are done, you still have a factory cast iron rod.

If you intend to build for horsepower, then simply get a set of steel rods. Many times stronger, come in BALANCED SETS, ready to install with no BS you have to do... Just clean and install. Small investment if you intend to build some power...


Some of the larger AMC engines came with STEEL CRANKS & STEEL RODS!
I think all 401 engines came with steel cranks and rods, and I'm thinking there was a couple of years of 390 that came with steel rods and/or cranks... Although some people say it was an over the counter purchase you had to install yourself, I've run into a couple down through the years.

Steel rods are easy to spot, the sides of the beams will have a forging 'Pinch' line about 1/4" wide where the rod was sheered off the billet it was made from. (where cast iron rods will have a very thin casting separation line).

Because of the journal size, the cast iron cranks will make about 500 HP without failures as long as you don't shock the crap out of them, while the forged cranks don't have much of a limit I've seen.

The factory forged rods are all over the place in terms of balance. They were mass produced, so not much care was taken to get them the same weight, or keep the big end weights about the same. They will take balancing if you decide to turn much in the way of RPM with them.


Not all rod bolts are created equal... I can count at least 7 types of rod bolt changes in the different years of AMC engines I've seen, and I'm not impressed with any of them.

Nothing beats a good set of SPS, ARP, Milodon rod bolts, in that order. VERY HARD to beat good rod bolts since everything the engine does depends on those bolts...

Like I said before, the 'CORRECT' way to tighten a set of rod bolts is with a 'Stretch' gauge. Knowing how close you are to the failure point of that bolt is critical, and 'Torque' is a suggestion, so if you are building a racing engine, invest in a stretch gauge...
And DO NOT final tighten the nuts until final assembly! These are single use bolts/nuts, and there isn't any reason I can think of to stress those fasteners unnecessarily.

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