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Premium Member
11,196 Posts
Discussion Starter · #1 · (Edited)
AMC V-8 Oil Pump/Front Cover Rebuild Thread.

What I'm starting with is an AMC V-8 Oil Pump, Front Timing Cover, Filter Head from a '86-Older AMC V-8 engine.


This is what you might get for front covers,

LEFT is what you might get from E-bay, and is virtually useless.
CENTER is a Fresh Take Off and only has one water pump bolt twisted off on the front.
RIGHT is a scraped one I use for demonstration purposes when I teach this in a class... It's cracked so students dropping it is no big deal.


This one is virtually useless.
Recently, a customer of mine though that $100 for a completey rebuild and ready USED front cover from me was too much.

This is what he got from E-bay for $75 plus shipping!

All kinds of broken bolts in the front cover around water pump,
Oil pump body was corroded and grooved, unuseable.
The oil pump 'Driven' gear pin ("Idler Gear") pin was missing entirely.
The filter head was missing entirely...

This is what happens when you think you know more than the guy who races AMCs for 25 years.... Scrap Aluminum, and since it's not 'Clean' aluminum, you won't even get 'Breakage' price at the scrap yard...


This is a fresh take off from a 1975 orignal engine.
One water pump bolt broke off in the cover and greasy, but remember, nothing protects the aluminum/steel/iron parts better than the engine crud!

DO NOT take an engine, transmssion, axle apart until you are ready to work on it!
Leave that crud on there!
Where oil residue, old oil, ect. is, you won't have rust...

Notice some Dilbert used silicone 'Form-A-Gasket' on the water pump instead of correct water pump gasket...

Explains the leaking drool down the front cover from the water pump!
Too bad it didn't steam clean the cover for me :(

See where the water pump didn't have clearance and was grinding on the timing cover?
The correct gasket would have stopped that...

This is another cover that some Dilbert didn't use the proper gasket, and the water pump was dragging on the aluminum...

If you want leaks, water pump impeller dragging on aluminum, then by all means, go ahead and leave the gasket out and use 'Form-A-Gasket'...

If you want things clearanced correctly, and you DO NOT want leaks,
Then use a Fel-Pro gasket set when you rebuild, and leave the 'Rubber Goop In A Tube' alone!


All of the filter head/oil pump floor plate bolts came out.
Factory Grade 5 bolts and they look pretty good.
If you twist one of these off, do your BEST to get the broken bolt out and restore the facotry threads!
This is a VERY bad place for drilling oversize and using Heli-Coils for repairs!

Notice the DRIVEN oil pump gear on the LEFT,
The DRIVING oil pump 'Gear' on the RIGHT...


This is a pretty good looking floorplate/filter head, this one can be saved easily if it doens't have any other problems I'm not seeing just yet.
The grooves from the 'Gears' haven't dug in to the point I can catch my fingernail on them,
So this one won't need a 'Mid-Plate' to fix it, just sanding/lapping the floor plate should be sufficient.

*IF* you have a badly grooved filter head floor plate, then you will need to order a 'Rescue' part called a 'Mid Plate'.
It's a steel shim that goes between the filter head and pump body and restores a flat floor to the pump cavity. Runs about $25.


Oil pump Impellers, commonly called 'Gears'...
The DRIVEN is on the left,
The DRIVING is on the right, and now you can see the shaft that goes up to the distributor gear bottom to turn the pump...

A pump too tight will kill your distirbutor gear, stretch the timing chain and cause other problems.
Make sure your pump turns FREELY later on during the pump clearanceing trial fit so you don't wind up with problems else where...

If you decide to run one of those 100 PSI pump ideas,
Remember, the filter is only rated to about 80 PSI,
And somewhere around 80 PSI, you will wear out the distributor/cam gears and stretch the crap out of the timing chain.

Those 100 PSI modifications are for RACING VEHICLES ONLY that have steel gear drive cams and hardened steel cam/distributor gear sets.
Not practical or nessary for a street or trail driven Jeep, and HATELFULLY expensive, along with being very hard on everything in the engine...


Now, you come to the part that is ALWAYS fun... :(
Getting the plunger out of the bypass valve bore.

*IF* You have a running engine, you disconnect the ignition,
Take the plug, seal washer and spring out of the bypass bore,
And crank the engine with the starter.

The oil pressure will build up, push the plunger out of the bore,
When the oil flows... STOP!

With this filter head, like most 'Take Offs', the plunger is stuck in the bore. (RATS!)

About the only way to get this plunger out of the bore with the 186,000 miles of oil sludge built up in the bore is to blow it out with air pressure.

That means blocking several different inlet & output ports at the same time, you will probably need a buddy's fingers for this one!

Don't worry about the plunger, if it gets away it's OK, a new one comes in quality oil pump kits.

This image shows the new oil pump kit, along with some of the old components in the upper right hand corner...
They are setting on the plate glass I acquired this morning for $1 at the local glass shop.

Once the filter head is disassembled and cleaned out (and I mean CLEAN!), then you are ready to do something with it...


The first thing I usually do is start with making the pump floor surface flat & true again.
This involves a process called 'Lapping'.

What I use is a piece of plate glass laid on something flat.
Plate Glass is floated on liquid tin, so it's 'Gravity Leveled' or as close to flat as the layman can come without buying a lapping block.
(Lapping Block = A piece of hard stone, usually Granite, ground PERFECTLY flat)

These pieces of stone aren't cheap at all!
Well out of the range of 'Common Tools' the home builder would own.

So for a guy doing two or three of these in a lifetime, going to the local glass shop and getting a 'Break Out' piece of plate glass is the best idea.
(Break Out = A plate glass window that has been broken, but glass shop can cut some reasonable size pieces from the Broken Out window.)

If you can't find real plate glass, then start looking for HEAVY mirrors in the thrift store.
You can usually find a cheap mirror large enough to do this project for cheap.

Vehicle window glass is TEMPERED Glass, and you are looking for PLATE glass,
Tempered glass is usually pretty thin and will flex,
Plate glass is usually thick, and it doesn't flex like tempered glass will...
If you use a flat vehicle window, then be VERY careful when using it, it will shatter into small pieces if you bump it very hard!

If you are going to do this fairly often,
Another option is a monument company that sells stone monuments like tombstones and marker stones.
They often get smaller pieces that can be purchased reasonably, look for one that isn't too thick, and is polished flat.
The surface of a flat stone monument is usually flat/true enough to get the desired results for this part of the rebuild.


You will also need some lapping compound.
This can be anything from a fine EMERY CLOTH, SECURELY to the flat surface,
But make sure it's a CLOTH BACKED Emery Cloth, the paper backed kind usually gets holes in and causes gouges.

Most sand paper is sharp pieces of aluminum oxide, and that cutting compound will in-bed in the work piece and ruin your new pump gears!

Lapping compound, or good quality emery cloth, the grit (Cutting Particles) are ROUNDED edges, and won't in-bed in the work piece and can be cleaned off when you are done so they don't grind away at the oil pump!

I use a true lapping compound, which is a specific size cutting 'Grit' held in suspension by some sort of grease.
This is the same stuff you buy for lapping valve seats, polishing paint or metal, so there are several sources for it.

I have the best luck with 'Garnet' based grit compounds, Aluminum Oxide doesn't seem to do as good a job or last as long.


Nothing like grit hiding in the pump on on the 'Gears' to ruin you new pump right away!


Once you have the flat plate ready, and the proper lapping compound, then you are ready for the 'Boring' part.
I have more time than money, so I sit in front of the boob tube and lap my oil pump parts!

This Image shows the different GRIT SIZE of lapping compound I use for this stuff,
The plate glass I acquired for $1 at the local glass shop this morning,
And the filter head.

What you are looking for is a flat, true surface,
Straight lines, swirls, round and round, side to side it's all good...
Just remember to keep the work piece FLAT on the lapping table at all times!
You don't want bevels, angles, ect.

STOP when you have a smooth, flat surface! Don't remove any more material than you have to...

You can start out with a larger grit compound and finish with a smaller grit compound if you have fairly deep gouges in your surfaces,
But with this filter head, I'm starting with 280 Grit and seeing how it works for me...
If you have heavy scratches, start with a 180 and work toward smaller grit from there.

Lapping the oil pump floor plate in progress.

This part isn't so bad, but lapping the cover surfaces is REALLY AWKWARD!


You will want to check progress every 10 minutes or so,
Wipe off a small portion of the lapping compound where the impellers ('Gears') gouged into the floor plate and have a look...

After 15 minutes of lapping in a 'Swirl' pattern, I still have 'Issues',
So the lapping continues while I catch up on 'Pawn Stars' & 'Headline News'...

Saving hands full of fast food napkins works GREAT for disposable small shop towels, so always keep those extra napkins for checking oil, little jobs like wiping away the grit from this project and a thousand other little jobs!

I usually want to work on a SOLID surface, if your work table rocks or moves around, you are wasting MUCH more energy than you should for this.

The GREASE in the compound will squeeze out and collect in the holes of the work piece, on the sides of the work piece, ect. making it VERY hard to move the workpiece at times,
Feel free to use a 'Q-Tip' to recapture that grease and put it back under the work piece,
Or to add a little bit more compound/grease when the piece starts 'Sticking',
Wants to tip sideways instead of stay flat on the glass....

A little lubricant returned to the lapping surface makes things SO much easier on you!

More comming as I get this thing cleaned up and start working on it...

Premium Member
11,196 Posts
Discussion Starter · #2 · (Edited)
When you first start lapping, if you were to clean off the workpiece every few strokes,
You would find out there are 'Warbles' in the pump floor plate surface.

These are from production grinders at the factory, Heat cycle stress lines in the aluminum, ect.

The high spots will polish up first and they will polish out VERY quickly because they are taking the entire load of the lapping down pressure.

As you continue to lap the floor plate, things will go MUCH SLOWER since you are constantly removing more and more material as the surface flattens out...

The last of the deep scratches will drive you crazy they come out so slow!
You are now removing EVERYTHING around the scratches to get them out, and that is VERY SLOW WORK.

Keep with it, this is worth it!

All the smaller gouges are gone, and the plate is truly flat for the first time in it's life.
There are still three small gouges in the floor plate that need to be taken out, so I'm going to continue with that.
Total time invested to this point is about 1 hour, 15 Minutes set up, roughly 45 Minutes of lapping.

If you are NOT totally OCD like I am,
This is probably way better shape than it was from the factory, and the few lightened scratches left would be fine to run since they are under the Impeller,

But it's not good enough for me yet, I want my oil pump to be PERFECT, not just 'Close Enough'...
This IS the heart of the engine after all, so I usually give it the care and time it needs to be absolutely CORRECT before I move on to something else...


Another 30 minutes or so of Lapping with 180 Grit gets me this which is very usable as it is right now...

By removing the oil filter adapter from the filter head (The threaded in steel parts), you can lap the gasket surface for the oil filter at this time,
This IS the time to do it, before you change to a finer grit for other parts of the project.

These gasket surfaces often have VERY rough machining, grind marks, tool chatter marks, gouges, ect., So if yours doesn't look at least this good,
Remove the steel filter adapter and lap this surface while you are at it.


You are asking yourself "Why All This Work?"

Well, you just saved $25 plus Shipping for a steel 'Mid Plate' that may or may not need lapping to make it flat when it comes in,

You have saved yourself an extra gasket & potential leak point!

Remember, there is a PRESSURIZED CHAMBER between the mid plate and the filter head that is the thickness of the gasket.
That chamber gasket fails amazingly regularly and you get a drooling leak.

This lapping removes the need for that 'Mid-Plate' and it's extra gasket, and removes the potential for a leak at that second gasket.


Time to start on the housing...

Just do the best you can for keeping the gasket surfaces flat while lapping, and the same rules apply,
You are looking for a FLAT gasket surface!

This would live the way it is...
BUT, it's got machining marks I don't much care for, some scratches and pits,
And since the oil pump 'Gears' are pushed UP during operation, you can bet the clearance between gears and floor plate have INCREASED in 186,000 miles.

Taking some off this surface will close that gap up where the top of the housing has raised.

Lapping this surface is pretty straight forward, same as before, but you will need more 'Q-Tips' to recover your lapping compound that will collect on the inside of the oil pump cavity.

The oil pump 'Idler' impeller (The 'Driven' impeller) pin is still in place,
I will take that out later and seal up the hole it fits in.


This Image Shows the pump housing and filter head mating surfaces both lapped to an acceptable result.

This is where the 'Fun' part comes in, cutting the clearance in the housing by lapping the housing bottom so you close up the tolerances on the top/bottom of the 'Gears'...

There is only ONE way to do this, and that is slow, tedious and is ABSOLUTELY REQUIRED to bring low speed pressures up sufficiently...


You will need 'PLASTI-GAUGE' for this next part, and a Torque Wrench, along with the New Oil Pump Parts, so make sure you have those handy when doing this...

'PLASTI-GAUGE' Comes in these two basic sizes,
GREEN, 0.001" to 0.003"
RED, 0.002" to 0.006"
You will need a 'Stick' of both sizes to do this correctly most times.
These two sticks were under $5 at NAPA.


The ONLY way to do this is to...

1. Clean out the housing,


2. Install the 'Gears',


3. Put 'Plasti-Gauge' on the bottoms of the gears between gears and filter head/floor plate,


4. Install the gasket,


5. Install floor plate, Torque to specification, 5 to 9 Ft.Lbs (60 to 108 INCH Pounds),
Some 'Never Seize' or grease on the bolt threads will keep them from galling the aluminum housing.
Use about 85 INCH Pounds on most pumps without any problems...


6. Remove floor plate, check 'Plasti-Gauge' for clearance.
Make sure you PULL STRAIGHT UP on the filter head when you take it off!
Twisting or sliding sideways will ruin the reading.

This 'RED' Plasti-Gague is showing about 0.004" clearance.

Here is the Plasti-Gauge showing showing slightly under 0.004".

So is the 'Green' Plasti-Gauge, even though I don't show a picture of the gauge paper in pictures.

I would like to take another 0.0015" to 0.002" out of that tolerance reading, closing it up to 0.002" clearance.
Factory specifications say 0.002" to 0.006" clearance, but I prefer the 'Tight' side...


7. If you clearance is too large, you need to lap the housing some more.
Removing material from the bottom of the housing (Lapping) will close up the end to end play in the 'Gears', getting you tighter end play clearances...

SO! That's what I'm off to do right now, lap the housing some more to close up the end play tolerances as much as I can get away with, somewhere between 0.002" and 0.0025" is 'Acceptable' for my builds...


8. When you 'Plasti-Gauge' indicates you have the correct clearance,


Then you can lube everything, fill the pump full of Petroleum Jelly or Assembly Lube Paste (something that will stay in place, some of the assembly lubes are now liquid, you are looking for a 'Gel' type),
Button it up, proper torque, and you are ready for the next step...


You don't want to take the chance you will get metal shavings, rust, crud, ect. in the pump while you are working on anything else!


More pictures and work when I get time to post it!

Premium Member
11,196 Posts
Discussion Starter · #5 ·
Yup, I'm pretty complete on this one so far,
Should have taken my own advice and cleaned & inspected, removed broken bolts ect.
But the guys wanted it RIGHT NOW, so it's up...
Still working on it, but had to put a 360 together today for a wheeling buddy that popped his I-6...
He was going to pull that 258, have it rebuilt, put a bunch of money in new intake, headers, carb ect.
So I gave him one of my spare running 360s...

If you are going to take a known bad 258 out and always want more power,
Then 360s grow on trees and you can get one running for under $500...

Some guys want to keep the I-6 because Jeep plugged it in there,
But I'm a V-8 fan, and as long as you don't have to spend a fortune on new clutches, transmissions, ect.
There isn't any reason NOT to throw a V-8 at it while the engine bay is sitting there empty...

Cost effective, and he LOVES mud bogging! So a V-8 is the way to go for him...

The problem is, I GAVE away an engine, now I'm being tapped to 'Freshen' it up and put it back together!
How is it that I get stuck giving a WARRANTY on a Free Engine? :(

There is something wrong with this deal, I just haven't figured out just what yet.... ;)

2020 Rubicon Unlimited
183 Posts
Hey JeepHammer,
Any chance on getting this third part posted?

I've had my timing cover and oil pump filter head surfaces resurfaced by the machine shop when my block & heads were done. All my surfaces are lapped, and now I just need the tips and tricks on assembly from the expert.

Thanks - Jonesie

172 Posts
Hope you don't mind, But I'm printing this up for my personal shop manual.
I'm certain this will come in handy in the near future.

804 Posts
Great info and written in a way anyone can understand as usual.

I do have a question that I didn't see covered.

I recently picked up a used 360, tore down the front cover and have some similar scratches on the adapter plate but the top of the pump housing where the upper sides of the gears run is really chewed up (worse than the scratches you showed for the bottom).

How do your 3 covers look for comparison? Should I write off a cover that is gouged up in the housing? I can still use my cover off my 304 which holds a steady 50 psi while running and 30 while idling but it does have a couple of water pump bolts that are broken.

Premium Member
11,196 Posts
Discussion Starter · #11 ·
It's all in the amount of work you want to do...
If you have a lot of time and not a lot of money, then you can fix a bunch on these things...

I've been short on money and TIG welded material to cover broken tabs, re-drilled and threaded the holes,
I've 'Touched Up' the tops of the housings where they were just gouged to death, (Which takes some CONSIDERABLE machining skills and tools... You need a fixture that holds the cover bores vertical so the milling machine can work in the bores without eating into the walls, and you need a square shoulder cutting tool the diameter of the bore, so it's time consuming, expensive and not very practical...

It's all up to you how much time you want to spend on making yours 'Good Enough' to reuse.
There is no such thing as a 'Perfect' one, so you get it 'Corrected' enough to do the job and reuse it...

116 Posts
Hi Great thread!
I am in the process of replacing my timing chain and water pump. All has been going smoothly until I decided to bolt the water pump to the timing cover prior to installing it. The vanes hit the timing cover. I had a second new gasket so I put it on and no scraping until I tightened it down, now I can hear and feel it. It is a rebuilt pump from napa. I don't like the idea of two gaskets let alone three or four. Should I just take it back and try another or?

8,890 Posts
scso81 said:
Hi Great thread!
I am in the process of replacing my timing chain and water pump. All has been going smoothly until I decided to bolt the water pump to the timing cover prior to installing it. The vanes hit the timing cover. I had a second new gasket so I put it on and no scraping until I tightened it down, now I can hear and feel it. It is a rebuilt pump from napa. I don't like the idea of two gaskets let alone three or four. Should I just take it back and try another or?
Did you remember to check the cam timing gear oil passage for casting flash before installation, just asking.


116 Posts
I took the water pump back to Napa and checked another pump out. It appears that Quality control missed a bad pump. The impeller was not pressed on all the way as it should have been. My new pump clears even with no gasket.
Now I can get her back together. My question now is I want to pre-prime the oil pump. Which direction does the shaft need to spin????

Premium Member
11,196 Posts
Discussion Starter · #16 ·
First, fill the oil pump housing with assembly lube before you do final assembly so the pump doesn't have to start 'Dry',
Then you spin the pump the same direction as the distributor, CLOCKWISE.

And no, I didn't finish the article, got side tracked and lost interest in taking all those damn pictures, Trying to edit them for size/content, ect. and get them posted...

Doing the work isn't the hard part, dealing with all this 'Computer Crap' is the hard work for me.

1,369 Posts
two things.
(1) I had issues w/ bottom of pump hitting the top of the harmonic balancer ( aftermarket billet balancer) on a cast iron NAPA pump. Had to take the whole mess back off and grind off excess iron on the pump.
Later I put a H/D GNB on it ( aluminum ) and it was cast to clear but I ground it some more anyway and it cleared. That's just a FWIW but it's a real p***er to redo it. :brickwall
(2) ya'll are probably tired of me bragging on the "timing cover oiling mod" for V-8's but if you have the cover off it only takes 15 minutes to drill and tap to do it, even if you don't do it now, screw a plug in the hole. Then if you ever change your mind it's as simple as plumbing an oil pressure guage.

1,369 Posts
lemme see if I can put something together for here. If nothing else, pm me your email addy, I've sent it out to others before, but I'll see if I can do one for here.

51 Posts
Mopar I would definitely be interested in the oiling mod as well. I have tried Googling it in the past and it seems everyone has a different opinion on what the oiling mod really is. I'd be interested to see what yours looks like. I am currently building up a replacement 360 since my last one seized on me and I want to try to make sure I have all available insurances in place. Nothing worse than having a sad, broken Jeep in the garage. :(
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