maca

Hey all
I have just finished building my Australian hemi 6 cylinder. It has hydraulic lifters and a fairly big cam. 10-5 comp, I am running a 4 barrel manifold and carby.
What its seems to be doing is breaking down under load. It seems to break down almost like someone has pulled a lead off. When it gets to about 5000rpm it runs great briefly as the cam maxes out at around 6000.
I have tried different valve preloads. 2 electronic dizzys, 1 points dizzy, 3 different coils and 3 different carbys, 3 sets of plugs and leads but still no luck. I have tried 95 and 98 octane fuel. I have a constant 13-9v at the coil and 14-4 at the battery. I have tried running a wire from the battery to the coil instead of running it off my ignition but it didn't help.


On the weekend I put it on a local dyno and they could not find out why it is doing it. The AFR was fine but as the motor got hotter after a dozen runs it got better and wasn't missing at all. When I pulled it off to drive it home it was terrible and missing again. Its driving me up the wall.
Any ideas?
cheers Greg

RacerHog

So Ignition has been ruled out as being the problem.....
What do the plug readings look like....

On another note... With the heat or higher temp being a factor.....
Sounds like the motor might be heat sensitive. combustion chamber might be running to cool causing a rich condition?

440roadrunner

Lean, rich, plug readings. Any dyno operator worth their salt should have been able to shed light on this

Is it using coolant?

If this was lower RPM I would have suggested carb icing.

Valve float except you said it "ran good briefly" at high RPM

I sure donooo.............

TVLynn

Have you done a compression test ? Or a leak down test ? Check the valve spring pressure..Maybe a flat cam

maca

comp test was fine. all pretty close.
Plugs look ok as on the dyno the AFR was fine.
The carbys I tried were all off other running motors so I don't think its carb. Maybe manifold if anything.
Once it got pretty hot it ran better on the dyno but they only ran it flat out. not cruising speed.
I have tried so many things I am out of ideas.

RacerHog

Are you sure the engine is not (fat Rich) on the inner cylinders and lean on the outter cylinders....
AFR.... Give us the reading's On. The Low range, Mid Range, High Range,

Drag Pak

Maca

Can you tell us what preload you are/have been using for your valve adjustment?

Have you tried "0" preload?(just enough to get the pushrods rotating)

Have you tried a hot set on the valve tappets?

maca

I will try to get a pic of the dyno graph and post it.
The dyno is not a great example as it ran better on there. AFRs were around 12-5. It got lean down low for a brief second but then the secondaries opened and it went back to 12-5 again.


I have tried .040 and heavier but set at cold.
I don't think its preload as it ran well on the dyno after a while.
These engines are very common here in Australia and preload seems to be fine between .020 and .060 and even more in some cases.


Because I was thinking its electrical when it started playing up in the beginning on the dyno I disconnected the alternator and it instantly ran 100% perfect. So I thought I had found the problem. When I connected it back up it still ran fine. So as soon as it started playing up on the way home I disconnected the alternator again but this time it still ran bad so it must have been a coincidence.

bigblock

Sounds like the lifters are pumping up.As the oil gets hotter/thinner it sort of corrects itself.

RacerHog

Sure its not a bad ground?

maca

I did think that too so i checked the ground and on one of my drives I hooked a jumper cable from the battery- to the engine but didn't help.

RacerHog

How Large is the Exhaust header and exhaust pipe?
I'm thinking that this engine is just on the lean side..

maca

The exhaust system is a single 2-5 which is a very common size for these motors here.
I ran it today with points but no luck again
So I started looking again for other things. I put it up on the hoist and noticed oil running down the side of the block under the intake. I removed the starter motor to get a better look. It looks like it may be coming from the head gasket area but I cant really tell. I think I will have to pull the exhaust & intake off to find out. There is a tiny bit of oil on the very back corner of the rocker cover but the oil on the block is further forward which I wouldn't have thought the oil would travel forward and it only looks damp on top, not that much oil. Here is a video, Maybe I shoul comp test it again or do any other tests before I pull the intake/exhaust off?
http://www.youtube.com/watch?v=HroXl0-V ... e=youtu.be

RacerHog

Just re-torq the head.... Clean it up and recheck it after a few miles....
I might do a Cyl. Leak down check and a compression test just for the record.

Run a Vid of the missing...

maca

My son took some go-pro video of it missing.
You can hear it best at the beginning
http://www.youtube.com/watch?v=o4rLN...ature=youtu.be

RacerHog

I don't hear the miss....... I hear the exhaust reverb / reignites (??) but that's all I hear.

maca

It's hard to hear with my exhaust but have another listen. One of the videos is better than the other.

RacerHog

Pull The plugs and let's have a look .... (Photo)
Have you tried the NGK Spark plugs?

maca

I will get a pic up asap. Number 6 is the richest.
Yes running the Ngk plugs.

TVLynn

Over advanced ign

pro-tech

Start backing the timing off 4* at a time seems to far advanced...Bill

maca

I have played with timing quite a bit. I have a mopar mechanic coming next weekend for a look so hope he can find the issue. Here is a pic of the plugs
cheers

maca

also this seems unusual to me. See the burn marks on the poles in the dizzy cap. This cap has only had a few hours running since new.

TVLynn

the one plug is lean others are rich Are you adding any gas additives ? Try a different distributor, cap and rotor

RacerHog

Ok.... Here is where I am at with this.....
Those spark plugs BP5ES or 7333 (Gap of .051) are not the rite plugs, at least I dont think.
Use a NGK GR4 or 2635 NGK and gap to a .035

Have your Dist Recurved if you can. It is pulling way to much advance.....
If not then, try this.
Start off with about 4* of timing and lets see if that helps.

Also The carb is way to rich... But leave it for now, till we get the other stuff rite, Maybe it will only take a little fine tuning? If not it looks to me like its about 6 jet sizes too big.

Your #4 Cylinder is not firing at all.
Check: Spark Plug... Plug Wire.... Valve adjustment.... Check for a Vacuum leak. Make sure it is sealed.

Just My 2 Cents....

Cap looks ok... Could be from the wide gap on the plugs or weak wires.