I am completely stumped!

[Morris]

Seriously... I am so frustrated I am considering selling the car.

A little history. My head has been rebuilt TWICE in a year's time. The second rebuilder is supposedly the "best in town." The head has all new components except for the valves which were checked and passed by the rebuilder... And still it exhibits symptoms of poorly sealing or sticking valves! I have spent uncounted hours and $$$s on this stupid head and it still SUCKS!!!

But the most perplexing thing of all is that the head passes a compression and leak down test. And I have removed the springs on the intake valves and checked their motion—they all seem to be moving smoothly and easily.

Here are the symptoms:

On cranking, MAP bounces regularly between 75-80 Kpa.

At idle, vacuum is a bit low (35-39 Kpa... should be 30-33 kpa) and engine vacuum fluctuates violently.

On acceleration, vacuum fluctuates extremely violently. There is a miss between 3000 and 4000rpm on medium to hard acceleration. The miss is accompanied by a sudden 10-15kpa increase in engine vacuum.

Previously, vacuum would smooth out a bit at cruise, but now vacuum is bouncing around quite a bit at cruise, too.

The car has plenty of power, but it's getting crappy gas mileage.




Before I remove the head for the 1000th time, I would like to get some opinions from you guys on what the heck is going on.

Any ideas???

 

[jlaird]

I suspect that your engine is just fine.

Get rid of the strange carb and injection etc, a couple of SU's will really make it sing.

No really, if you have a good compression check all is well there. Take a look at the dizzy seems like maybe the vacumn advance is sticking or worn.

Leave the engine alone.

 

[JerryB]

""""""And I have removed the springs on the intake valves and checked their motion—they all seem to be moving smoothly and easily."""""""

how about the exhaust valves.... what is the pressure on each spring at installed height?

BTW.....whadda we working on here...

Jack mentioned "injector"........besides being clairvoyant is this an A motor with a TB or port injection?

What is the size of the intake plenum?

 

[Morris]

It's a 1500. Currently I am running a single injector setup that uses the stock manifold and the stock carb as the TB.

How do I measure "the pressure on each spring at installed height?"

 

[JerryB]

Remove the springs and use a spring pressure tester.

IF you dont have acess to one (your head rebuilder should have one and IF he is competent he would have checked each spring) you can use a bathroom scale and a drill press and two blocks of wood top and bottom of the spring.

Pull down to the installed height of the spring (spring surface on the head to under the retainer) and lock the quill stop on the press. Read the scale. Might be 55#...do every spring. Then redo every spring relocking the quill installed height plus 3/8" and read the scale again....maybe 120#. That is your closed and open spring pressure. What your looking for is a dead spring...(20% less than the others.)

""""""the stock manifold and the stock carb as the TB."""
"""""It's a 1500"""""""

So its a four port in and out.....I thot it might be a A motor which requres a rather large plenum. In your situation that not might be the case because it a log intake that you are using.
Still there might not be enuff plenum area.

If all the valve springs check ok then the next thing I wud do is recheck cam timing and lobe lift.

If the compression is ok, springs ok and youve given the head the liquid test (head upside down spark plug in and fill the chamber with solvent) you can eliminate head problems.

 

[JerryB]

Part 2 of the book.....

When you converted the carb to TB did you make sure you have no vacuum leaks or weird passages and no manifold leaks and are using what the dist wants to see as to vacuum...ported or manifold...?

 

[Morris]

Dizzy is locked out and advance is controlled by the ecu.

I am going to address some possible leaks tonight (if I can get the wife and kids to bed early enough. I have absolutley drenched the carb and manifold looking for leaks and have found nothing conclusive.


Seems unlikely that air leaks would cause these symptoms... right???

 

[eschneider]

is the camshaft stock?
overlap will cause a flicker and lower readings.
if the valve springs don't match the cam, they will perform like weak springs, especially at higher RPM?

also, is the ecu timing curve based on RPM only, or is there a vacuum/MAP sensor that's complicating matters?

Is this a megasquirt system? (just curious, I love the concept)

 

[Morris]

Yes the camshaft is stock.

The springs are new from either VB or Moss if I remember correctly. Of course, that does not mean they are good.

The timing curved is bassed on MAP and RPM.

Yes, it is a Megasquirt system.

 

[Morris]

Yes the camshaft is stock.

The springs are new from either VB or Moss if I remember correctly. Of course, that does not mean they are good.

The timing curved is bassed on MAP and RPM.

Yes, it is a Megasquirt system.

 

[eschneider]

The timing curved is bassed on MAP and RPM.
Yes, it is a Megasquirt system.

so what happens if you set the timing to a constant value and remove that variable from the equasion?

is it possible the cam timing is off?

is it possible that a cam lobe or two are significantly worn?

Hope I'm not insulting your intelligence.

BTW, your project is way cool. Stick with it! I'd love to see pics of the injector setup and how you've configured the distributor.

 

[Morris]

You are not insulting my intelligence.

It is very, very possible that cam timing is off... even though I triple checked it when installing.

It is also very possible that cam lobes are worn. I replaced the lifters but did not replace the cam. The cam checked out before I replaced the lifters... but I have no previous experience picking lifters and breaking in a cam.

I learned this morning that I put too thick of a gasket on the dizzy pedestal. As a result, the rotor has a little too much wiggle room. I will fix that tonight.

Also, this morning I tried a new vacuum diagnosis trick... bassically, you fire up the car and block the throttle with a piece of cardboard. Ideally what should happen is the engine dies. If the idle bounces before it finally dies, you have a vacuum leak. On my test... the cardboard did not even slow down the idle. Oops.

Currently I am going through and sealing and tightening and gasketing every possible leak.

 

[jlaird]

Ahhh, I was going to say earlier that there was a huge vacumn leak somewhere but did not as you had said you checked.

Yep the cardboard trick works great so does hands blocking the intake.

Is there still a throttle rod in this car. If so I would look there first I think. A bit of carb cleaner squirted on both sides while engine is running will tell you with a speed increase.

 

[Morris]

Only problem with using the hand is backfire. Ouch!

Jack, I have gone through two bottles of carb cleaner on that thing. I think the problem is that it's several tiny leaks, instead of one big one. Hopefully I will have more info tonight.

Thanks for all the ideas guys... keep 'em coming!

 

[jlaird]

Well you can always do what I did, sigh. Remove it all and start over with fresh gaskets etc. You know if you get any movement in the throttle shaft side to side at all, any at all, it is too much.

 

[JerryB]

"""""problem with using the hand is backfire. Ouch!"""""""

if its backfiring thru the tb it could be very lean.

By this time you have checked the valve springs make a simple lever that attaches to the rocker and use a fish or pull scale (or calibrated hand) to get an IDEA of spring pressures nad have fixed your vac leaks.

Recheck cam timing and cam lift as well as correct valve lash.

 

[Morris]

My plan is to put everything back together with (hopefully) fixed vacuum leaks and proper clearance on the dizzy pedestal and see if things improve.

Next I will check valve lift and spring pressure. I will check cam timing last, because that will be a major butt pain.

 

[jlaird]

Timeing can not be off more than a tooth and that can be adjusted out with the Dizzy. Don't think that's it in any case.

 

[eschneider]

Also, this morning I tried a new vacuum diagnosis trick... bassically, you fire up the car and block the throttle with a piece of cardboard. Ideally what should happen is the engine dies. If the idle bounces before it finally dies, you have a vacuum leak. On my test... the cardboard did not even slow down the idle. Oops.

Actually, if you had a significant vacuum leak and the mixture was way lean, restricting the airflow through the throttle body would make the idle go way up, at least for a second or two. same thing would happen if you sprayed some carb cleaner in the intake.

it would immediately choke and sputter if the idle mixture was rich. ditto for spraying carb cleaner in the intake.

if the mixture is good, then the idle will raise slightly, then drop.

you can also verify, with the engine warm, the O2 sensor readings - assuming with the megasquirt system uses a single-wire oxygen sensor, the o2 voltage should oscillate around .7 with the system is warm and in closed loop - a lean condition caused by a vacuum leak would definitely bottom it out to a constant .1

I would think you could check cam timing and cam/lifter wear with a dial indicator measurement on the rockers? Can anyone help here? But I tend to agree - I think you've triple-checked everything, and there's some small culprit that's toying with you.

the loss of power and vacuum drop at mid-range keeps echo-ing in my head..... can you capture ignition timing data? Or at least set the ignition timing to some constant, independant of RPM and vacuum input?

Just some thoughts. Easy to offer advice from the comfort of my chair. 8)

 

[aeronca65t]

First, I'd retry the "spray method" to look for vacuum leaks. But I'd use WD-40 and judge if the engine is slowing down (when it sucks in the WD-40).

Once you're sure of that, double check the cam installation. As you know, the 1500 has no real cam marks and it should properly be done with a dial indicator.

One method I found, which gets thinks pretty close is the following (but I'd still double check with a dial indicator afterwards).

The Spitfire cam sprocket has 4 holes but only 2 bolts. The holes are slightly offset from each other and if you turn the sprocket over that gives you 4 different settings. Set the crank so 1 & 4 are exactly TDC. Set #7 & 8 valve adjustment at .080" and set the cam so that #7 & 8 valve are in their "rocking" position. Rock the cam back and forth until the clearance of both valves are exactly the same no matter what that clearance is. Then slide the crank sprocket in place and the chain on and put the cam sprocket in the chain and check to see that two of the bolt holes line up. DON'T move the crank nor the cam. If the holes don't line up then take the sprocket out of the chain and rotate it 90 deg. and try again. If it doesn't line up remove the sprocket and flip the sprocket over and try again. If it still doesn't fit rotate 90 deg. One of the four possibles will fit.

You can use this to see if the cam is at least close without taking anything apart.....set your engine to TDC and have a look at the #7 and #8 valves (you may have to turn 180 degrees).