Vintage Mustang Forums banner

1 - 8 of 8 Posts

·
Registered
Joined
·
646 Posts
Discussion Starter #1
As many of you know, I have just finished and started my freshly rebuilt 351W. Unfortunately, it does not seem to be building the necessary oil pressure. My book says that it should be building between 30-45 psi within the first thirty seconds of firing; however, it only builds around three or four psi at idle. I am able to rev up the engine which builds about 25-30 psi. Any ideas as to why this is happening? I checked all the bearings prior to installation with plastigage and everything seemed to check out. I can't imagine what else might be causing the problem other than possibly a clogged oil journal. The block was dipped and cleaned thoroughly prior to reassembly. Both the crankshaft as well as the bearings are forty over. Would it help if I installed a high volume oil pump, or is this something more serious? Is there any way I could fix the problem without yanking the engine? I'm open to any ideas you can toss at me. Thanks in advance.

Deathman68
 
G

·
Guest
Joined
·
0 Posts
I had a similar problem with a 289. Finally chased the problem to a leaking gasket at the oil sump neck. unfortunately it required the removal of the oil pan.
 

·
Registered
Joined
·
2,217 Posts
That scenero is typical of an engine that has popped one of the lifter gallery plugs in the front of the block. These are the press-in little "freeze plugs" that are directly behind the cam gear.

There are 3 of these and they are staked from the factory. If they are removed durring a rebuild they are more likely to pop out at first fire. I always tap them and use pipe plugs, that way they never pop out.
 

·
Registered
Joined
·
646 Posts
Discussion Starter #6
I'm fairly certain that I had those tapped when the block was honed/bored/cleaned. Even if these pieces weren't tapped, wouldn't the plate covering them behind the cam gear keep them from popping out? I know that one of the three is completely covered, and the other two seem to be about 65% covered (based on pictures I took). Thanks again.

Deathman68
 

·
Registered
Joined
·
2,217 Posts
Nope. One is covered and the other two are recessed into the block face, one more then the other. That's where my money is.

The other possibility wth these is if they were tapped and pluged, the plugs may have been run in too deep. The main passage , the one on the top left looking at the front of the motor, has the supply pasage about 3/8" back from the face of the block and must be clear at that level. Tapping with a 1/4" NPT tap will cut about 1/2 depth threads because the hole is larger then the proper drill size for a 1/4" NPT tap starter hole. Most guys just run the tap in to the depth of the oil passage and stop, and then use Loctite on the threads. That way the plug tightens up just about the time the top of the plug is flush and is in the right place and tight. I've seen other guys run the tap in all the way to the top of the threads on the tap and then you're screwed. By the time the plug tightens up on you it is plunged way down too far in the hole.

I don't do either, I'm funny about things like oil pressure. I drill the block out to the drill size for a 3/8 NPT tap and tap it with full depth threads. Then I use an allen socket thin plug and install it with LockTite. Overkill? well maybe, but I don't have to worry about that nasty little problem anymore.

Another place this can happen is under the intake manifold at the back of the lifter galley. There is another 3/4" "softplug" on the lifter crossover.
 

·
Registered
Joined
·
10,587 Posts
Pull the manifold and check the crossover plug Hal mentioned...I just helped another VMFer with a W and we found his was missing....geyser of oil inside the lifter valley but zipity pressure...sounded exactly like your situation...

If your deal is anything like his, you may have to replace your bearings....definitely check them anyway...

Good luck and post back the results...
 
1 - 8 of 8 Posts
Top