Vinny P

Let me first say that if you never did this before, I would suggest having someone around who has experience with this. If is not done right, your cam can wear out prematurly.

Since it has studs and nuts, the lifter preload must be adjusted accurately, or this motor will never run right. There are a few ways to do this, I have been doing it this way for a long time. Others may chime in here on their own procedure, but essentially the end result will be the same.

The object is to adjust the rockers while the lifter is on the base circle of the cam. Meaning zero lift, or when the valve is fully closed. To get the valves fully closed is not hard but you have to be careful. You also have to make sure the lifter is fully pumped up with oil before adjusting the rockers. If the lifter squirted out its' oil, you will not get it right.

First remove both valve covers. Remove all the sparkplugs to make it easier to turn the motor over. Remove the distributor and drop in an oil pump primer tool. Start at the #1 cylinder. While watching the rockers, turn the motor over slowly by the crank bolt with a 1/2" ratchet and 5/8"socket. Be sure to only turn it over clockwise so you don't loosen the bolt. Turn it until you see the #1 intake valve open then close and the exhaust valve open most of the way. Now you are on the #1 intake valve cam base circle. Back off the adjuster nut on the rocker. Prime up the motor for a short time, this will make sure the lifter you are adjusting is full of oil. Stop priming. Slowly tighten the adjuster nut on the rocker while turning the push rod with your fingers until you can not turn it freely anymore. Stop, turning. Next give it about 1/2 a turn more. That valve is done. Now go the exhaust valve and crank over the motor in the same manner as before, following the same procedure of watching the valves. Only this time substitute the intake and exhaust valves in the procedure. This will get the #1 exhaust lifter on the cams base circle. Do this for all 6 cylinders. You must prime the motor before adjusting each valve.

GNJ

CM454Mag - Thanks - the motor was primed with oil before starting. Also, I believe member "Ichornet" mentioned the Mercruiser manual stated non adjusting rockers arms and torque specs for 1996. I did try to back off the nuts on the rockers just for kicks to see if it changed the way it ran. Unfortunately, no change. The motor mainly seems to stumble and be powerless. If I really push down the throttle, then it will backfire occasionally. Something else is going on and it seems to me, it might possibly be the only 2 things left that have not been addressed.
1) Module
2) Sensor

Does anyone know or have a test for these?

bowtie

I can fax or email the tests for the sensor and module. The sensor can only work or not work. So you would have no spark if it was bad. The module controls spark advance so it could be malfunctioning. The tests only check for a no spark situation. I still would check the sensor wheel, I've seen this happen, wrong sensor and the mechanic that I worked with spent hours on it. Sputtering and missfiring.

blkhorse

iTrader: (1)

the rockers are torqued to 20 ft lbs,no particular engine postion.it's a roller so little chance of a flat lobe(but I would check,a wheel could have failed) have you ruled out carb problems? what kind are you using?

US1 Fountain

iTrader: (1)

May be a long shot, but none the less.
A couple yrs ago a spent the winter rebuilding my blower motor. Had the distrib and ignition parts in a box for safe keeping. Took the motor to dyno shop when done, and it did same thing as yours, idle fine, and up abit. But then it backfired and missed real bad when the throttle was open up. Turned out that while the distrib was sitting in the box over winter, oil from the gear area was able to run up the shaft and get into the the pickup sensor for the rotor. Wiped the gap out and all was good.

GNJ

Funny, I do recall wiping out some oil that did get into the distributor when it was on the engine stand and the motor was rotated before disassembly.
Tomorrow, I will try cleaning the sensor as US1 Fountain stated and experienced. It might just be it. Behavior sounds very similiar. Will post results.

The carb is a Holley 600cfm vaccum sec.

Vinny P

GNJ,
In your previous post, you stated that the motor has studs and nuts for adjusting the rockers, not shouldered bolts. You can't simply torque down your rockers. You must adjust them in the way I described using the cams base circle. The fact that the engine was primed once means nothing when adjusting valves. Being that the engine is not running , thus no oil pressure, as you are manually cranking over the motor, a small amount of oil squirts out of the lifter when it pushes open the valve. It is that oil that must be refilled before adjusting the rockers.

Griff

If its got stud with nuts and you did not adjust them, then that is most definately the problem. Valves are staying open and that will cause all kinds of popping and backfiring.

You said the plugs are black. You will need new ones before starting it again also.

blue thunder

Do you have a pic of the top of the assembled head? If you are torquing down adjustable rockers you found the problem. I would be suprised it would even run at all.

BT

GNJ

Well the saga continues. I did remove and clean the sensor in the distributor and found some oil and crud in and around it. Reinstalled and it started initially but then immediately quit. Tried over and over. started then stopped. Then would not start at all. Pulled off the #1 plug wire and hooked a grounded test plug to it and did not see any spark at all. Therefore, we must be getting close.

Bowtie or anybody: Can you or someone email or fax me the test procedure for the module and sensor? (Thunderbolt IV ignition.)
[email protected] or 813-855-5397 (fax)

Thanks