401 wont crank

AMX69PHATTY

If the Oil Pressure Relief Plunger is too tight in the bore and sticks it will cause high oil pressure. Sounds like the relief isn't relieving for some reason. If the plunger is stuck it can be a bear to get out of the bore on the filter adapter.

Mudrat

AMX ... me? Wasn't a problem getting out. The problem was finding the spring on the other side of the shop. :shock: My problem was a bad "new" sensor - took it back and got my $$ back when I bought the mech guages :t: Note to self ... put a rag over the cap when you unscrew the damned thing next time !! :?

guffey24

AMX69PHATTY wrote
If the Oil Pressure Relief Plunger is too tight in the bore and sticks it will cause high oil pressure. Sounds like the relief isn't relieving for some reason. If the plunger is stuck it can be a bear to get out of the bore on the filter adapter.

The oil pressure relief plunger will not move at all, it is stuck

give me some ideas on how to get this thing out :-|

I thought about taking a tap or a long easy out and trying to get it out, but that would be a stretch

any ideas

guffey24

alright guys got it unstuck and cleaned it up real good the releif valve and the cavity it sits in put everything back together and it did not change anything I am thinking that the red HD spring might be the problem I am also going to change to a mechanical oil pressure gauge which will get rid of another thing that it could be the sending unit

jeepsr4ever

I doubt your actually reading 100psi. If it was 100psi your filter would be bloated. Check to see if it had bloated on you. The plunger goes in nipple end first then the spring goes into the plunger and then the nut. Are you sure you installed the plunger correctly?

guffey24

yeah I installed it correctly both times it is dripping oil out of the oil filter, and around the oil pump housing gasket, I havent looked at the filter to see if it is bloated when I pulled the plug the spring came out and the plunger didnt, it was stuck I got it out cleaned it up, and reinstalled it put oil in it and the gauge went right back to 100 psi where the gauge ends 0-100 psi

jeepsr4ever

Red springs are rated at 70psi not 100psi

AMX69PHATTY

Sounds like the Relief Plunger is stuck again. When I measured a new one from a Sealed Power Kit it was .0001 to .0003 bigger O.D. than the stock one out of a '76 304. Doesn't sound like much, but it don't take much. The new one caused me same problem and ballooned a filter. MC, would you happen to know the Plunger Dia. Spec & Tolerance ?

jeepsr4ever

Plungers should not be larger than .561. The hole it goes into is actually a precision bore that should be held pretty close to .5625 or 9/16". We ream the 626 and the 534 oiling plate holes out to .563 when they are being made here in house. I am suspecting you may be bypassing your filter. Whats the scoup on your oil filter adaptor?...is it new or used and what is the date code on it. Pre 1988 means oil filter bypass...1988-1991 means no oil filter bypass. Some 1987's had it either way. Maybe you forgot to put your bypass back in if was dis-assembled.

guffey24

the 401 came from a 78 Waggy the oil pump housing still has some of the AMC factory paint, so it is used the oil relief housing points downwards towards the oil pan the oil filter angles back towards the frame rail, and the oil sending unit mounts right above the oil filter in the block with an adapter into the block looks identical to the setup that came on the 304 that was stock it has a little circle on the outside of the housing with 3 numbers in it dont know the order, but the numbers are 2,7,4 it is pushing oil out of the oil pump gasket, and also dripping out of the screw that holds the spring and the plunger in place any other ideas? what should be my next step?

82Waggy

I had a brand new one that was stuck due to casting debris and machining flash. Make sure the plunger drops all the way in so that the point on the end touches the far wall, and that it is free to move easily back and forth without the spring. If it won't bottom and fall out freely without the spring you need to ream out the plunger cavity to the proper diameter and get rid of all the garbage.

guffey24

82Waggy wrote
I had a brand new one that was stuck due to casting debris and machining flash.

Make sure the plunger drops all the way in so that the point on the end touches the far wall, and that it is free to move easily back and forth without the spring. If it won't bottom and fall out freely without the spring you need to ream out the plunger cavity to the proper diameter and get rid of all the garbage.

so what you are saying is that the plunger should slide in and out easy, I get that part

If I am under my Jeep and slide the plunger up in the hole it should freely fall back out?

If that is the case, the plunger I have fits real tight and will not come out on it's own, when I push it up in there, with or without the spring it stays and does not come out on it's own

1980_Cj7

I'd work the bore a little, real slow and by hand, with some real fine emory paper on an appropriately sized drill bit. Go slow and do lots of test fitting. Check and make sure the plunger is smooth too.

82Waggy

guffey24 wrote
82Waggy wrote
I had a brand new one that was stuck due to casting debris and machining flash.

Make sure the plunger drops all the way in so that the point on the end touches the far wall, and that it is free to move easily back and forth without the spring. If it won't bottom and fall out freely without the spring you need to ream out the plunger cavity to the proper diameter and get rid of all the garbage.

so what you are saying is that the plunger should slide in and out easy, I get that part

If I am under my Jeep and slide the plunger up in the hole it should freely fall back out?

If that is the case, the plunger I have fits real tight and will not come out on it's own, when I push it up in there, with or without the spring it stays and does not come out on it's own

You need to pull the filter adapter off the timing cover to be able to see what I am talking about and to clean it up properly. I assumed you already had it off. If you have never done this, get a copy of the TSM before you attempt it as the pump gears will come out too and you will need to remove and replace the old gasket properly.

If you try to machine/clean the filter adapter while it is on the vehicle the chances are you will release all kinds of chunk into the engine that may tear things up.

jeepsr4ever

Your probly much better off getting a new updated oil filter adaptor than trying to deal with a bad/grooved one. I am sure we can find a *Flat one. :wink:

guffey24

jeepsr4ever wrote
Your probly much better off getting a new updated oil filter adaptor than trying to deal with a bad/grooved one. I am sure we can find a *Flat one. :wink:

I will take mine off again, and see what it looks like, and I am guessing that this is the one I would need to replace it with

http://www.bulltear.com/catalog/product_info.php?cPath=21_35&products_id=135

jeepsr4ever

Yes that is the replacement

guffey24

alright guys I got everything fixed for now, took the oil filter adapter off and cleaned the whole thing real good, installed a new gasket also installed a mechanical oil pressure gauge I am in Fuzz's good range now 70 psi cold and 25-30 PSI when it warms up thanks for all the help

mika01

jeepsr4ever wrote
Plungers should not be larger than .561. The hole it goes into is actually a precision bore that should be held pretty close to .5625 or 9/16". We ream the 626 and the 534 oiling plate holes out to .563 when they are being made here in house. I am suspecting you may be bypassing your filter. Whats the scoup on your oil filter adaptor?...is it new or used and what is the date code on it. Pre 1988 means oil filter bypass...1988-1991 means no oil filter bypass. Some 1987's had it either way. Maybe you forgot to put your bypass back in if was dis-assembled.

Wow this was quite a revelation for me. I just fired up my 401 which had a 75 timing cover with oil filter adapter and was getting about 12 psi cold. Once I read this I scavenged an oil filter adapter from a 89 and voila 50 psi cold! :!:
Thanks for info MC never would have guessed it! :t:

Holeshot

I also have seen a bunch of stuck plungers.

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