View Full Version : AMC 304 high oil pressure problem.

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02-18-2008, 10:47 PM
Hi, new here, stumbled onto the site by some good fortune. I've read up a bit on the oil problems these motors have, and I'm wondering if I fall into one of the known categories.
I have a 304, I ordered it about a year ago and installed it after the junkyard runner I had in my CJ bit it. After moving all the crap over from the old motor to the new one I noticed that the recommended oil filter (Fram PH25) didn't fit onto the oil filter connector properly. The filter spun on, but was quite loose on the threads and oil pressure would push the filter back from the filter adapter and oil went everywhere. The PH8A filter didn't fit on the connector, it was too small to thread on. I ordered a new filter connector from Chrysler so the PH8A would fit on properly, and it does. Tonight I fitted the new connector on, put the new filter on (Fram again, yeah I know about them now), filled up with oil and again there was too much pressure. Enough to bend the filter and allow oil to get on everything in the shop. When spinning off the filter, there was a noticeable wobble to it. Can this be happening just from a non functioning pressure relief valve?
The motor has been damaged somewhat as this originally happened on the highway, however it's still running (whenever there's oil in it). I do need it to get around for a short time, but I'm pretty sure I'll need to replace this motor probably sooner than later. The place I got the new motor from has closed it's doors, so my other question would be what's a good place to order a new motor from? Are the only things available out there long blocks? Does anyone offer turnkey setups? I'm not made of money but I don't mind eating macaroni and cheese to keep my baby running.
Thanks for such a great website.

02-19-2008, 07:58 AM
Welcome aboard Ibby! I would start with a better filter choice like Wix, napa gold or K&N. The Fram filters are known for collapsing and they have changed over the years from a decent filter to a horrible piece of crap. I would start there..also I would pull the spring and plunger on the relief (large 7/8 nut) and see if the plunger is stuck. It is also possible you have a issue with your oil pressure sending unit. Do you know the psi you were at? The factory relief is set between 65psi and 70psi and wont go any further.

02-19-2008, 08:00 AM
Welcome to Bulltear! :!:

Sounds like a stuck pressure relief valve. It's under the spring and big nut on the back of the filter adapter. The piston should go in point first (I've seen them put in backwards), and it should slide in and out freely.

It sounds like you have a new adapter, so make sure you put it in properly. If it doesn't slide freely, work it with a scotchbrite pad until it does.

Over pressure usually doesn't damage anything but the filter. My preference for filters is Wix or Napa Gold (made by Wix).


02-19-2008, 09:30 AM
Thanks for the replies. I won't get a Fram filter again, I've had enough problems with them. I've never seen Wix in Canada but Napa and K&N shouldn't be hard to find. I did look up that filter comparison website, lots of info there.
Last summer was when this problem started. A fellow at work noticed oil all over the parking lot one day, and that's when I discovered the Fram PH25 had popped loose. I managed to get it to the garage and when I was working on it I noticed the filter didn't fit on the connector properly. I happened to have a spare connector from another motor and the filter didn't fit on it properly either. A buddy was good enough to run down to the local store with the spare connector and found a filter that fit the connector much better, but still not perfect. I was also aware of the pressure release valve problem, so I took the oil filter adapter off. I found the plunger almost impossible to get out. I did manage it, and cleaned it up a bit but not terribly well. I also cut the spring down a bit thinking it would lower the psi that the valve would open at, and take care of the high pressure problem. The engine ran well until this weekend when the high pressure problem came back. I'd already seized one engine (the junkyard runner) and when this one began to sound ugly I pulled over and stopped. I'm sure the damage has already been done though.
The oil pressure sending unit is a new aftermarket one and it was pinned at 100 when this happened. It's been pretty reliable so far.
I'll pull the adapter tonight and Scotchbrite it till it slides proper. Are replacement springs easy to get a hold of? The city I live in is terrible for ordering parts for older cars. I've had to order quite a bit of stuff off the Internet out of the US.

02-19-2008, 09:50 AM
You cant get just the spring you will have to order a complete rebuild kit.

02-19-2008, 10:36 AM
You can order the kit here at the E-store (click products at the top).


If you're comfortable with a used one (they do deteriorate from heat and use), PM me your address, I'll mail you one.


02-19-2008, 11:19 AM
I have an extra HD spring sitting in the box on the work bench... :sa:
If you have Purolator Filters up there then that's also a good choice in my opinion... I think Purolator is similiar to the Ford style (Internally)??? Maybe somebody can correct me if I'm wrong... There's an actual site that has a cut-a-way of most name brand filters and they compare one another... When I get off from work I'll head home and do a search for it...

02-19-2008, 06:57 PM
You dont want to install the HD spring on any AMC unless you run *excessive bearing clearances. You especially dont want it on a newer oil filter adaptor without the oil filter bypass. This will pop the filter right off.

02-19-2008, 07:56 PM
I had thought a HD spring might not be a great idea. The motor's pretty much stock, just has an RV cam in it.
I took the adapter off tonight, and sure enough the piston was stuck closed. This had happened before, and I had chamfered the edges and reinstalled it. Tonight I took it out, polished it up with some 600 grit using the poor man's milling machine. I did the same to the tube in the adapter plate as well, and now the piston moves in and out very smoothly. The motor started up and there's a few new moans and groans, but it kept pressure at around 60 psi. As long as it gets me through til warm weather I'll be happy. It did seem to spit out some water drops with black oily flecks from the exhaust pipes.
As for replacing the motor, is there a good rebuilder that would be preferable to order from? The motor I have now came from www.precisionmasterengines.com but it looks like they've closed their doors. I'll also be reading up on the forum for the oiling mods and such, and looking over the great upgrade parts here to see what I'll put on the new motor when the time comes. Any suggestions on how to set up the new motor? My CJ's primarily used on the trails for rock crawling in the Rocky Mountains up here.
Thanks again for the great info. I wish I had found this place earlier.

02-20-2008, 09:54 AM
as long as you have a good pump with proper clearances and new bearings you shouldnt need any oil mods as long as your not running high rpm's for long periods. at normal speeds the oil system is usually adequate.

02-20-2008, 12:33 PM
Good to know, thanks.

02-20-2008, 01:31 PM
As for replacing the motor, is there a good rebuilder that would be preferable to order from?

Barry Allen, Herman Lewis, or Hemi Adkins if you are looking for an excellent quality performance engine.

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