opm2000 said:
You are right on with your observations reguarding the variety of physical differences. Since I have an '89 Allante motor and a '90 Crate 4.9, I am expecting the coolant ports at the heads/lower intake manifold to match up. If they don't I have a machinist lined up to weld/fill/machine the excess void to make the match work.
The only reason I haven't begun disassembly of the engines is I'm not sure how to proceed on valve rocker removal. I got an Allante factory service manual. It suggests removal of the entire rocker assy...attached to the bridge....is the preferred method. And I've heard it's easy to break either the bridge or the rocker girdles by careless removal techniques.
David Breeze
You are correct that it is easy to break the rocker arm support bar and/or the rocker arm pivots. The most common problem is stripping the rocker pivot bolts out of the arm if you are not carefull ..... and if you don't break the pivot in the process... or both... LOL
The ONLY way to disassemble the rocker arms is to first take the 4 small bolts out of the projections on the arm that stabilize it. Next break loose the 5 large hex nuts that hold the bar to the stud headed head bolts. Loosen the 5 large nex nuts about 1 turn at a time moving down the bar sequentially until the bar is completely loose. Re-assemble it in the same way. Install the rocker arm support bar onto the head bolts , install the hex nuts and gradually pull them down in sequence until the bar is seated and then final torque them. Believe the service manual.....
The rocker arm pivot bolts should NEVER be removed when the rocker arm is under load. Those bolts are self thread rolling bolts that screw into the aluminum bar. The self threading bolts make a very tight, strong thread and form a self locking thread when they seat. If the arm is under load and the bolt is removed it will strip as the threads will reach the end before the valve spring load is relaxed and the bolt will pull out. There is really need to remove the rocker arm pivots from the bar unless something is broken so I would leave the assembly intact. Removing the self threading bolts repeatedly will weaken the threads.
If you can get a pair of the forged steel bars they are totally bulletproof for about any kind of cam/spring loads. Those were also installed on the European "export" engines if you are looking up part numbers.
BTW...the 4.1/4.5/4.9 engines are all "net build" valvetrain engines that are not adjustable..so..if you are milling the heads, changing cams or such you will need to have some custom pushrods made to the correct length. I have heard of people shimming the rocker arm pivots but longer bolts would be mandatory if you do that and I would not expect that assembly to be strong enough to handle much load if the pivots are not direct mounted to the arm.