AMC 304 Damper Woes

Quick Rundown:
1. '72 CJ5 with AMC 304.
2. I've rebuild EVERYTHING, except engine short block, which was done just prior to P.O. over 20 years ago.
3. Took timing cover off last weekend to replace distributor drive gears, and other preventive maintenance.
4. I looked up part number on damper (3196925) which seems to be from a '70-'71 360. This appears to be a big problem as all AMC V8's are externally balanced and I have a 304, not a 360. I don't know for sure, but I highly doubt the P.O. matched the flywheel to the damper. No way to tell.
5. '72 304 dampers (3-bolt pulley) are quite different than 360 dampers as far as weighting is concerned, and I can't find ANY 304 dampers for sale online or otherwise.
6. I had always wondered why I had to shim accessories so pulleys would be aligned. Now I think I know.
7. I'd also wondered why engine seemed to run a bit unbalanced. Not horrible, but not smooth either.

Questions:
-Do I just not worry about it since I've run this Jeep for 20 years and nothing's happened? (This isn't really compatible with my OCD, but I also don't want to rebuild an engine over a stupid damper either.)
-Did Jeep ever put 360 dampers on 304's? (I assume this was done by a P.O., and not the factory, for some reason.)
-Does anyone know where I can find a '72 3-bolt pulley damper for a 304? Better yet, a damper AND a matching flywheel?

Thanks.

 

Can you just switch to the 4 bolt version and get a new pulley at the same time? Google tells me that you can get the 4 bolt from a lot of places including Summit and even Amazon.

 

Amc v8 use to be balance by the flywheel??? never heard about the damper before.

I'll follow this post is some have information.

 

My parts book only goes back to 1974, so I can't comment on the part number issues. Maybe Jim will see this and help by confirming the PNs.

The 360 is the same crank as the 304, so the balance should be pretty close. Only the reciprocating assembly is different. I'm sure you've looked at the side of your block and seen the "304" cast in there.

The flywheels are available aftermarket. Or, you can have your flywheel balanced to the 304 spec, regardless of whether it is for a 304 or a 360 - I'm assuming you have not looked at it.

A couple of possibilities - there are several companies on-line that will rebuild your damper. You could contact a few of these and explain your problem and ask if they will accept your 360-number damper for the right 304-number, with possibly some up-charge. or, when you do your overhaul/rebuild, ask the machine shop to balance the rotating and reciprocating assembly all at once using your existing damper.

You could also try posting on the AMC forums and see if someone there has the right part for you, or a source for it.

 

yes worry about it, simple enough to fix with correct parts..

DamperDr will have the damper and Crown or Omix will have the flywheel.. done.

DO NOT USE AFTERMARKET DAMPENERS...

when I built my 360 I balanced the rotating assembly, flywheel and balancer...
balance is vital to longevity, power, and break in.. think about it.. 1000's of rps with mini explosions going on.. if everything is equal (balanced) you will get better results..

 

http://damperdoctor.com/index.php?route=product/category&path=33_80

 

the only way you are going to get this is by dropping off at a machine shop that can balance..

even these 2 balanced items on an unbalanced motor will help...

 

I understand the need for a balanced assembly, but if you've made it 20 years (!) I wouldn't get too wrapped around this.

It should have failed long, long, long ago if the issue was serious. Perhaps PO dealt with it properly.

 

Some research I have saved when I built my motor...
on an old stock motor... yes.. quality replacement parts


AMC did "detroit balance" every 290-401 they ever built.

Before the cyl heads and valvetrain were installed, they spun the engine with a large electric motor on a machine that would measure imbalance, and then it would automatically drill the vibration damper and the flywheel to bring the balance into spec. This process has been described in the AMXtra newsletter many years ago (author saw the machine on a plant tour) and the process is also mentioned in the AMC SAE papers on the V8. AMC was rightfully proud of this technology for 1967.

All manufactured parts have a weight tolerance. AMC's specs on rods and piston weights were something like +/-3 grams each.

All of the 290-401s are externally balanced. Why? Because they individually drilled the flywheels and dampers on the assy line once the engines were assembled and that's the definition of externally balancing

The 290-343 were originally internally balanced when they were in the development stages- pre-production. What happened was that they had crankshaft breakage in the number 5 main area. So, in order to strengthen the crank, they had to remove a lightening hole that was added in order for it to be internally balanced and they also had to increase fillet radai to add strength. This added weight made it impossible to internally balance the engine, so they changed to external balancing.

Also the reason why the #5 main bearing clearance is larger than 1-4 is because there is deflection at that end of the crank because of the loading. So, they got rid of the breakage but still have some extra deflection they could not eliminate so they increased the clearance so there would not be bearing scuffing by the deflecting crankshaft.

These are the facts.

 

Personally I would consider this an opportunity to make it right. AMC forums or IFSJA might be a good place to look also.

 

72 V8 304 in a CJ used P/N 3196924
73 V8 304 in a CJ used P/N 3216083

In full size Jeeps, Wagoneer, Pickup, etc:
304 V8 used P/N 3196924 (1971 ?)
360 V8 for 1971/1972 used P/N 3196925
360 V8 for 1973 used P/N 3216084
parts manuals don't specify 3 or 4 bolt etc
fwiw

 

Very likely your having to shim is due to the wrong waterpump not the damper. 72 WP was a one year only deal, longer shaft. Most solve it with shims or a WP pulley from a 73 up. Part number for the 304 damper is 3196924 just for reference. 360 number changed in 74.

 

Unless those gears are flat worn out or you're having some type of problem with them, I'd leave them be.

 

Thanks for the advice; it's appreciated. As of last week, DamperDr's website indicated they were out of stock on '72 304 vibration dampers. If they had one, I'd buy it today. I'll have to do a little research about retrofitting a 4-bolt pulley damper and buying a new pulley. If the pulleys are the same depth, this may be a possible option. I've not heard much good about the aftermarket AMC dampers (Professional Products Brand) sold through Jegs and Summit however. Correct me if I'm wrong, but I believe the only way to truly fix this "right" is to tear the entire motor down. Then take the rotating assembly (crank, damper, and flywheel) to an engine shop that is able to rebalance the mismatched parts. Even if I should find a 304 damper, it won't be balanced to the rest of the assembly unless I have this done. The more I research AMC peculiarities, the more I understand why people convert to small block Chevys. That being said, I'm committed to sticking with AMC. As far as the distributor gears go, my HEI dist. gear wasn't matched to the dist. drive gear on the cam and this concerned me. I don't want to break down on Rubicon Trail this summer. I got a set of matched MSD gears. I've heard nothing but good about them, but...?

 

Just ordered a P.P 4-bolt damper for '76 and later 304. Also ordered a new 4-bolt pulley through CVF racing. I think it'll work, but still not 100% positive. While I'm waiting for parts to arrive, I'll go ahead and rebuild oil pump and replace dist. gears. I'll post a few pics of my success or defeat when all is done in a couple weeks.

 

I finally wrapped up this project. As can be seen from the date of my original post, this has taken way too long. A project which should have only taken a weekend took a couple of months. If you derive joy from others' misery, read on for a good time.

This project began as a simple timing cover gasket replacement on my '72 AMC 304. The following photo shows how a small amount of antifreeze was leaking between the cover and the block.


Replacing the timing cover gasket is no big deal. Simply remove the distributor, alternator, water pump, and vibration damper. Then the timing cover can easily be unbolted and removed. Whenever I take something apart, I thoroughly clean all the parts and inspect them for wear or damage. This is highly timing consuming, but generally worthwhile. The problem is that this quickly leads down the road of "might-as-wells." (As long as it's this far apart, I might-as-well...)

("Might-as-well" #1) The old water pump had some internal corrosion, so I figured I "might as well" replace it. I ordered the Crown replacement through Quadratec which was listed to fit a '72 (part number 51212 01). I waited for a week for it to arrive only to find that it is NOT the same as the stock. The shaft is much too long to work with all the pulleys. I mailed it back to Quadratec and ordered the Edelbrock high volume water pump through Summit (part # 8831). The Edelbrock pump shaft is the exact same length as my stock unit, but $225 was more than I had wanted to spend.

("Might-as-well" #2) On to the vibration damper-the original topic of this post. While cleaning it, I decided to research the part number, and I discovered that a p.o. put a 360 damper on a 304. As all AMC guys know, this is very bad as all AMC's are externally balanced and the 304 damper is weighted much differently than the 360 damper. After hours of research, I discovered that '72 dampers are about as rare as hens' teeth, and that my best option was to retrofit a later damper and pulley set-up onto the motor. I opted for the Performance Products damper. I like that it has removable weights in order to match the engine displacement. I ordered a 4-bolt aluminum crank pulley through CVF racing. I didn't realize that this pulley is smaller in diameter than the stock unit. Of coarse, this means that the engine accessories will now be spinning a bit faster. I've decided that this might actually be a very good thing while crawling in the rocks. Another good thing is that the new damper/pulley assembly is 5 lbs lighter than the old assembly. The only negative is that the old belts needed replaced with belts that were about two inches shorter. I'm quite happy with how this set-up works. The engine is running MUCH smoother than it was before.

By the way, I have a 360 damper with a 3-groove, 3-bolt pulley for sale if anybody wants it.

("Might-as-well" #3) I ordered a set of MSD distributor and cam gears to replace my old ones. This is a fairly straightforward job except that the woodruff key on my cam was so boogered up that the old gear was a bear to pull off. Also, I'm an idiot and accidentally damaged the distributor gear while drilling out one of the holes. The MSD gears only come with one hole drilled out. You need to slide the gear on the distributor and drill out the second hole. This is a little awkward as one hand is holding the distributor while the other is holding the drill. Be careful that the drill doesn't grab and suck itself down allowing the chuck to ruin the distributor gear, or else you'll need to purchase a new gear. This may, or may not have happened to me.

("Might-as-well" #4) The best way to install the timing cover is with the oil pan removed, and I decided that as long as the oil pan was off, now would be a great time to replace the rear main seal which had been leaking a little bit. When I removed the rear bearing cap, this is what I found.

This main bearing is worn...very worn. This is where the project turned into a nightmare. I decided that the main bearings absolutely needed replaced, so I removed the engine and put it on a stand. Most of the main bearings looked like this, but luckily, the crank still seemed to be in good condition. The old bearings were a brand that I've never heard of (DAB). I replaced them with a new set of Clevite. I'm absolutely convinced that having the wrong damper on the engine was a major contributing factor for this kind of wear. Interestingly, the rod bearings looked just fine. No copper was showing at all. At this time, I also discovered that my oil pick-up had been cross-threaded and was barely threaded into the block. I was able to replace it with one that my father had in his shop. Pressing the new damper on the crank was a bit challenging. Most garage mechanics pull the damper onto the crank with the damper bolt. This is a very bad idea because it's very easy to strip out the threads in the crank. The problem is that neither Napa nor O'Reilly's had a puller with the correct threads for an AMC crank. I fabbed a puller out of a long fine-thread bolt, a couple of nuts, and the old steel plate used in my cross-member drop that I no longer needed.


("Might-as-well #5) Despite having perfectly good oil pressure before, I figure now would be a good time to replace the oil pump impellers. So I spent hours lapping the grooves out of the old oil filter adapter, cleaning, measuring tolerances of the new impellers, etc. When I assembled the new plunger into the high oil pressure bypass bore, it seemed too tight to me, but I figured that's how it must be because the old one was also rather tight. Dumb, dumb, dumb. It's crucial that the high pressure plunger slide absolutely freely. Here's how I found out. I go to prime the engine with a drill and the pressure is so high that it nearly rips the drill out of my hands. My dad says he saw the oil pressure gauge go over 100 psi. The pressure was so extreme that the drill ended up slightly spreading out the slotted oil pump shaft just enough that the distributor wouldn't slide on. Additionally, the now spread out oil pump shaft wouldn't freely slide out of the bore in the timing cover. The oil pressure was so high that it actually ballooned out the new oil filter like a can of beer that's been left in the freezer too long. As my plunger was actually stuck in the old oil filter adapter, I purchased a new adapter and another set of Melling oil pump impellers through Bulltear. Since doing this rebuild, I now have about 10-15 lbs more oil pressure than I had before; almost too much. When I start the Jeep it goes to 70-75 psi cold and then drops to about 35 at idle as the oil warms up. I've observed that oil is flowing throughout the engine, so I'm confident there's no blockages. I'm also confident that I measured the oil pump impeller clearances correctly. Maybe it's just the difference of having new main bearings and new impellers versus the old worn out ones. It's just weird that the world seems to be full of stories of AMC's that have too little oil pressure, yet mine has more than enough. Almost too much.




Final thoughts:
I now have a couple hundred miles on the Jeep since this rebuild. At this point, I believe that the job was successfully done, though I won't be fully confident until I get about 1,000 miles or so. It's frustrating that this journey all started as a tiny leak from a timing cover gasket, but that being said, I'm glad that all the hidden issues were resolved now rather than rearing their ugly head out on the trail. I'm very happy with the damper and pulley and would recommend this set up to anyone in the same situation. Now on to the next project...time to make a new set of rocker guards / sliders.