Blown Head Gasket??

Thing is driving me crazy. Valve train noise but all the sorings look fine. All the hardware is torwued correct. Still have the miss. Retimed and no vacuum leaks. Compression check this weekend and after that I'm out of bright ideas.

 

I had a similar low rpm miss, and was starting to think it was distributor/timing/cam related, but groberts helped me tune my carb, and much of that has gone away now.

I am now running my distributor on manifold vacuum and disabled the vacuum advance. Initial timing is 18 degrees and all-in timing is 38. Runs much better now, I don't need to give it throttle while cold to keep it alive (no choke), and it just runs better. It took quite a bit of carb tuning to get the best vacuum I could now that I changed everything up.

Not saying it is your problem, but maybe something to check out?

 

Ive got a good running carb on it. Tuned it very recently. I got the car to idle and all that but its just not what it was a few days ago. Its either the head gasket or a valve train related issue.

 

Wha? :16suspect

 

I HAD a good running and tuned carb.

I swapped out some fuel lines, and it went to crap.

It doesn't take much...

 

Counterintuitive, but...

http://mmb.maverick.to/showthread.php?t=98392&page=2

And at least two people agree that running a holley double pumper on ported vacuum is difficult to tune.

I now have initial advance at 18 degrees, and all-in vacuum advance at 38, and the vacuum advance disabled. In other words, vacuum advance is turned off, only running off manifold vacuum and the weighted vacuum advance in the distributor.

It runs much better.

 

I think the way you worded that may have confused him. You are still running the vacuum advance but it is hooked to manifold vacuum instead of ported. And the "weighted vacuum advance " is called mechanical advance. I don't know why but everyone says ported is better, but every older vehicle I've worked on had it hooked to ported then I switch it to man vac it seems like its got a lot more nuts.

 

Ford ran ported vac because most of the points dist had too much advance, connected to the carb advance comes in slower so pinging isn't usually a issue...

Manifold vacuum only makes it feel better at part throttle, at WOT there isn't any vacuum(or at least isn't supposed to be), so there isn't any difference... For all out performance, ditch the vacuum and tune the mechanical advance for max at around 2500 to 3K RPM... Of course your mileage will suffer at lower speeds because of reduced timing...

 

I had a holley double pumper on the lincoln but ditched it for a vac secondary edelbrock ( what i had laying around ). I put the double pumper on my maverick since its much lighter , manual trans, and 4.10's.

Both carbs worked great on the cars. The only change made to the car before I started getting the miss was adding a fuel filter inline from the regulator to the carb. Since its literally the only thing I changed I will run a solid line without the filter and see what happens although I seriously doubt thats the issue. Sure would be nice though.

 

Yes, worded a little oddly. What I meant was that the vacuum line is still hooked up, to manifold port, and I have the screw in the distributor vacuum canister cranked all the way closed. With it open at the stock setting, I was getting way over 40 degrees advance, with it closed a bit I was getting 20-40 degrees advanced and I wanted it 18-38, so I closed the screw all the way down to get 18-38 range.

 

Sounds like you have a couple of issues to look at here.

Did you check oil pressure at idle?.. and does the "ticking" go away when rpm's climb? As in.. ticking goes away by any amount as the oil pressure rises?

Did you freshen that carb up first?.. or just swap-n-go?

 

They also did it for emissions purposes too. Higher cylinder pressures at idle(which is what heavy ignition lead will do) with less dense fuel mixtures leads to higher NOX readings. Gets even worse on a performance engine with higher compression.

And not to be argumentative.. but since we generally live at part throttle while driving around on public roads.. manifold vacuum rules the roost from an efficiency and drivability standpoint. Obviously ported sourcing still works just fine if everything else is tailored to it(and I still see tons of guys using it on hot street cars).. just over a smaller range of operation, is all. Ther're too stubborn to listen to me and/or too cheap to pay me to show them though. lol

I would go so far as to say that manifold vacuum I one of.. if not THE greatest efficiency improvements one could make to their car over an afternoon's time. The only other thing I can think of is tuning up a car that has really worn out parts.

According to a couple of really smart guys I know who tune high-performance engines for a living. Most guys don't know an engines fuel and timing requirement from a hole in their backside. And I have to admit.. it took me several(many wasted) years of.. "set initial to 8-12 degrees BTDC and make the weights pull in quick" before someone way smarter than I explained the physical properties of the combustion space events at varying densities and loads.

When boiled right down to its simplest form.. when an engine is under increasing loading, cylinder pressure more quickly rises(more fuel and air makes for denser mixtures within the same combustion space so it has to) and also stays higher over a longer period of combustion event time (because the piston can't move away as quickly to allow faster flame-front/pressure expansion) which as most know is what increases the tendency for detonation. And then from there we get into the flame front characteristics and its always changing ignition lead requirement for the various mixture densities, A/F ratios, and the actual speed at which it moves within the combustion space.

This is EXACTLY what manifold vacuum sources offers as it better allows the vac advance plate to constantly monitor for an optimum combustion event. What better way to tailor a "maximum ignition lead that the engine will tolerate with this fuel" type of ignition curve.. than basing it off of one of the most fundamental measures of an engines efficiency? Engine vacuum.

This is part of the reason that EFI is so good at improving part throttle drivability(idle/off-idle torque production) is not just related to improving atomization and equalization among cylinders. The MAP, IAT, TPS, CPS, plus whatever the engine coolant temp thingy is called, and KS all communicate the engine load and mixture density to allow the computer to turn up the ignition lead. I've mapped them out many times and many "learned maps" will allow near 50 degrees advance. Much better off in the long run to think of a manifold operated vacuum pot being an poor man's old school ECM.

 

Ok so the results are in....
Cylinders:
1: 95
2: 0 dry 5 wet
3: 115
4: 100
5: 110
6: 100
7: 100
8: 105

So not what I was expecting.... burnt valve on 2?????
Not sure if the compression numbers are high enough to even make me want to fix it...... are these decent compression readings or is the block done?

 

What is going on with the valves on #2?

What do you see/feel on those two valves when you take off the valve cover?

 

Just got back inside. Broken exhaust valve spring..., debating now whether I replace it or pull the heads and have them cut for the dual springs I got for it.

Don't know enough about gt40s to make an informed decision. Don't know if I will need different retainers / keepers.
Any gt40 experts here?