383 Stroker Need New Cam

[Josh454]

I know you said you replaced most of the ignition components but you verified you have spark?  Swapped plugs and wires?  Before you pull the heads you can remove the springs and stroke the valves in the guides to see how they feel.  You could also see if they were bent.  Have you done a basic compression test?  Did you inspect the rockers very closely to see that they were going down at the same rate?  Is your truck cursed?  LOL

[VileZambonie]

I do not like the idea of adjusting the valves with it running. I would re-adjust the valves with the engine off. If it still runs poor double check your plugs and firing order. If they look ok, do a compression test on all cylinders.

[msc5195]

I know you said you replaced most of the ignition components but you verified you have spark?  Swapped plugs and wires?  Before you pull the heads you can remove the springs and stroke the valves in the guides to see how they feel.  You could also see if they were bent.  Have you done a basic compression test?  Did you inspect the rockers very closely to see that they were going down at the same rate?  Is your truck cursed?  LOL

Yes We did a compression check on this cylinder and while you are turning the motor over the gauge peakes out at about 155 to 160 psi. Stopped turning motor and gauge stopped at 130psi. Gauge held at 130psi for over 5 mins with no leakdown.
I did not replace the wires but we did swap them around to verify that the wire was not bad. Also my mechanic friend  did check the Ohms on the wires.
We did not check the rockers with a dial indicator but too the naked eye they appear to be moving all the same amount.

[msc5195]

I do not like the idea of adjusting the valves with it running. I would re-adjust the valves with the engine off. If it still runs poor double check your plugs and firing order. If they look ok, do a compression test on all cylinders.

Valves were originally set with engine off. They were checked and readjusted with it running to verify there adjustment. I was running a set of Bosch platinum II plugs but my mechanic friend told me to replace them with a set of autolite 25's. 
Yes the firing order has been checked, rechecked and verified to be correct. I will be doing a compression check on ALL cylinders tomorrow when I get off work

[msc5195]

Ok.....More info available. My mechanic friend hooked a vacuum gauge up to the front port of the carb port where the distributer vac advance connects. When the gauge is connected at idle it continuously flucuates from 10" down to 2" of vac. With the donor carb from a second truck the vacumm is still flucuates 10-2" In Hg thus indicating an engine problem and not a carb problem. With my current carb placed on a second test truck the vacumm holds a steady 15-16".

[Josh454]

Ok that is not an actual leakdown test.  The Schrader valve in the compression gauge will hold the pressure.  Perform an actual leakdown test.  A good engine will be less than about 12%.

If you don't have or want to buy the tool you can make your own out of an old spark plug and an air compressor hose fitting.  It's not very accurate but if you don have a valve that's not sealing you can air the air escape out the intake or exhaust.

[msc5195]

Ok that is not an actual leakdown test.  The Schrader valve in the compression gauge will hold the pressure.  Perform an actual leakdown test.  A good engine will be less than about 12%.

If you don't have or want to buy the tool you can make your own out of an old spark plug and an air compressor hose fitting.  It's not very accurate but if you don have a valve that's not sealing you can air the air escape out the intake or exhaust.

We pumped the #1 cylinder full of air with the air compressor and listened for air escaping but did not hear any. None at intake or at exhaust pipes.

[Josh454]

The next step I would perform is a running compression test.  Using your compression gauge, take the Schrader valve out of the gauge.  With the engine running, you should probably see around 75 psi or so.  I would compare it to a known good cylinder.  The needle will bounce around but you should be able to see an average value.

If it's low, you are not building compresion.  If it's high, air is not getting out of the cylinder.  Gives you a good idea how effectively the cylinder is breathing.

[VileZambonie]

Josh is correct the compression gauge will not show you leak down except for what's in the gauge. What does the vacuum gauge read when you 're driving it?

[msc5195]

Josh is correct the compression gauge will not show you leak down except for what's in the gauge. What does the vacuum gauge read when you 're driving it?

I am on night shift so we didnt work on it today. I did call the engine shop that built the bottom end and they are saying that it ia a geometry problem within the valve train. I am getting mixed info as to pushrod length and other concerns. I am running Erson Roller Rockers. They are true rollers. I have the std press in rocker studs. My cam is a Howards .465/488 lift cam and on their web site they reccommend two seperate pushrods. 7609 and 7940. the 7609 rods are  7.3000" and the 7940 rods are 7.2000" but I am running standard 7.8000" rods. This may be a type error on their site. Also, I have been told that it isnt good run press in studs with true roller rockers.

Anybody want to buy a good looking 1984 GMC with fresh engine? Needs slight tune up! LOL!! Seriously I am at the point of selling this demon possesed truck!

[Josh454]

Don't give up yet!  Hang in there you'll stumble across it sooner or later. 

I'm a little skeptical on the valvetrain geometry theory.  I would think that it would affect all cylinders and tyically too long or short of pushrods will increase valvetip wear and side load the valve guides. 

The only problem with press in studs is that they can pull out with higher lifts and spring pressures.  Have you checked to see if that's the case? 

On the other hand that's a pretty sharp truck...would you deliver to Michigan?

[msc5195]

Don't give up yet!  Hang in there you'll stumble across it sooner or later. 

I'm a little skeptical on the valvetrain geometry theory.  I would think that it would affect all cylinders and tyically too long or short of pushrods will increase valvetip wear and side load the valve guides. 

The only problem with press in studs is that they can pull out with higher lifts and spring pressures.  Have you checked to see if that's the case? 

On the other hand that's a pretty sharp truck...would you deliver to Michigan?

Yes we did check to verify that studs are all the same. I too agree that if it was a valvetrain issue then why is it only the #1 cylinder that is cold? Then again what caused the stud on the #4 cylinder's exhaust valve to break. And as far as delivery to Michigan.... I could always use a little road trip. LOL!

[VileZambonie]

I personally run screw in studs and guide plates on any engine I put rollers on. I never adjust them with the engine running either. Start over at zero lash on the base circle of the cam and see what it does.

[msc5195]

We pulled the head today and there was water in the #7 cylinder and all of teh valves especially #1 and #7 cylinders looked like CRAP! We poured mineral spirits in the head and they were all leaking around the valve seats. These heads ONLY have 1200 miles on them since they were reworked. Makes me wonder if they even done anything to the valves like they said they did. Oh well back to the machine shop they go! Gonna request that they make it right AND refund me my 265.00 to cover my labor and down time!

[Josh454]

Hope you finally get it straightend out!