Ford 460 blowing dip stick out

So my dad's 1978 f150 is blowing the dipstick out when the engine goes under load. I put a Holley street demon 625 carb on it and that started this. The first thought is that the pcv system isn't working but everything up s hooked up and it was working ok with the old carb.

His mechanic couldn't figure this out and he was told by some guys at the parts store that the rings are shot since there appears to be gas in the oil. 

He is planning on selling this truck and I have waffled on buying it and would like to figure this out before talking to him about buying it. 

Yep.  First thought is to make sure the PCV system is complete and functioning. It would seem that for whatever reason the set-up with the new carb isn't drawing enough vacuum.

Did you change the air cleaner/breather setup when you put the carb on it?

I'm going with bad rings. It's pressurizing the oil pan and overwhelming the PCV system. Do a compression test.

Poor man's solution was to crimp the top of the dipstick tube with a pair of channel locks.

One valve cover should have the PCV in it. The other valve cover should be vented (originally to the air filter).

Stock air cleaner. I have a compression tester and that is the next step. I am not sure I am up for a ring replacement.

Carb is to big for the motor or more likley the vacuum confections on the carb are not working correctly.  Putting the old carb back on and see what happens.  If the problem goes away then it is an issue with the new carb.

In reply to dean1484 :

I doubt a 625 carb is too big for a 460. 

Pull out the pcv with the engine running. Feel if it is sucking vacuum. If it does, remove the oil filler cap and see if the blowby blows the hat off your head. If no vacuum at the valve, take the pcv out of the hose and see if it has vacuum. It should have full manifold vacuum. 

Sticks out for Harambe

nderwater said:

Sticks out for Harambe

BAAHAHAHA! 

The issue is if the vacuum port at the base of the carb is providing vacuum or not. Could be as simple as the wrong gasket on the base of the carb or between the carb and the intake. Where are you picking up primary vacuum from and where is the pc2 plumbed in to.  Is it from the carb or off the manafold?  

Did the problem show up immediately after the carb swap or slowly happen over time after the swap?  

It doesn't get driven much and my dad isn't a great mechanic so he could have not noticed it for several months. It seems to have happened over time though. 

Vacuum comes from the adapter plate that is necessary for the carb swap. The pcv is coming from the same plate on a different port.

Vacuum is pretty generic.  Since there is effectively zero vacuum at WOT, the problem isn't the PCV system, nor does it have anything to do with the carb at least not directly.

Barring any obvious blockages to the PCV, what you have basically done is increased the available flow to the engine.  If (and that's a big if) you have increased flow AND the engine can use that flow, you have increased peak cylinder pressures (more volume and mass in the cylinders).  This has increased the amount that is squishing past the rings.

What he has done is discovered that his rings were failing before the carb swap but not bad enough to blow out the dipstick.  Now that he has higher cylinder pressures it is simply increasing the amount of blowby.  Either way, the bottom line is the crankcase is seeing higher pressure than the vent/PCV can flow.  The only way that can happen is blowby; i.e. bad rings.  Do a compression test.  My guess is you'll have two or three cylinders that are much more than 10% off the others, and all of them will be lower than factory spec by a fair amount.  If you want, follow up the first test with a second test after a squirt of oil in each plug hole.  If the compression increases significantly on the 2 or 3 low cylinders and doesn't change much on the higher ones, you have just further confirmed bad rings.

TL;DR: since PCV does not operate at all during WOT given the fact that there is no vacuum, the only thing that can cause this problem (aside from a blocked vent) is bad ring seal.  For 50 years, engines didn't have PCV and they didn't blow out dipsticks.  Not a PCV problem, not a carb problem.  Bad rings.

But that shouldn't be a reason to pass on it in my opinion.  The 460 is a fantastic engine.  Huge bore, short stroke.  I'm not a fan of cam-priority oiling, but it hasn't been an issue in the 60 gazillion examples that Ford put on the road.  Buy it, drop in a freshened up junkyard 460 and drive it.  If you plan on more than 500 hp or 6000 rpm, then fix the oiling.

Edit:  When I say "bad rings" I should be saying "blowby" which could be caused by bad rings or scored cylinder walls.  The correct diagnosis is that the rings aren't properly controlling pressure.

I chased this a while recently on a 302 and it turned out the PCV install port on the lifter valley was partly blocked.  Took me a while to track it down because I was getting decent vac measured at the intake.  Compression tested nice on all cylinders, and everything was fine unless I was doing laps at the track.

But in your case I'm betting your compression test probably won't be all that nice.

93gsxturbo said:

Poor man's solution was to crimp the top of the dipstick tube with a pair of channel locks.

Ugh. That's like putting tape over the Check Engine light...

This is a non-issue; the hood should stop the dipstick from completely coming out, so what's the problem?

Yeah a compression check should be done regardless what carb's on it.

maybe the rings are just stuck from sitting too much? Maybe try an italian tune up.

In reply to Robbie :

Hit it with a hammer?

In reply to singleslammer :

Nah. Take it out and run the ever-loving piss out of it. Might re-seat sticky rings... or it might do nothing. I’d still buy it. The 460 is one of the best motors FoMoCo ever built...

I worked on my BIL's Volvo diesel.  The thing was going through a quart of oil every tank and he wanted to rebuild it.  Got it warm, pulled the glow plugs, and started feeding BG44K into the cylinders with an old pump-type oil  can.  Gave it a couple of shots in each cylinder and worked the crankshaft pulley back and forth.  Let it sit for 5-6 hours and did it again... did this for a couple of days. 

Before it went back together, threw an old towel over the glow plug holes and spun it over with the starter to blow out any remaining liquid.  Put the glow plugs back in and started it up.  Be prepared.  It WILL smoke... like it's on fire... and whatever was knocked loose from the pistons ended up in the crankcase.  You will need to change the oil.  Anyway, the car went from using a quart between fill-ups to using less than a quart between oil changes. 

Will it work on the 460?  Who knows, but BG44K is cheap and you will only be out some time and an oil change.

Ok, I am going to take a look at it on Wednesday. 

Compression checks came back good. Range was 112 - 126. Thoughts?

Apparently I did the compression test wrong. I only pulled one plug at a time and didn't block open the throttle.

In reply to singleslammer :

Was that with all plugs out and the throttle held wide open? Did you try it again with oil put in the cylinders to see if the rings are leaking?

What is the spec for compression on that engine?

That seems low for a 4 stroke engine. I just checked a 2 stroke (piston port with no reed valves) snowmobile engine that had over 120 psi on each cylinder. 

The next two steps I’d consider:

First, I’d put a vacuum/pressure gage on line for the pcv valve and see what the gage shows as you go from idle to higher rpm, with and without the pcv valve in the valve cover.

Second, move the gage to the dipstick tube, plug the crankcase breather and see what the gage shows as you go from idle to higher rpm, with and without the pcv valve in the valve cover. 

Third, if there is good vacuum at the pcv port and no difference with or without the pcv valve in place, then pull the valve cover to check for sludge build up. The returns may be sludged up and restricting vacuum from reaching the bottom end leading to the pressure that is blowing out the dipstick. 

While low probability, it’s a lot easier than rings, and would be the first engine to have clogged returns in the head.