I have a 98 454 MAG MPI gen 6. I did a leak down test and determined the intake valves were leaking, I took the heads off had them rebuilt. when I took the heads off I was following the mercruiser #23 manual, I found TDC for cylinder #1 then began disassembly. im 95% certain that I did that step correct. however today I started reinstalling the push rods and rockers (in there original places) and when I got to cylinder #1 exhaust valve I noticed that as I was tightening the rocker bolt down, it started to depress the valve. I am new to working on V-8s but I have a lot of experience with Dirt bikes, snowmobile, etc.

if I am at TDC shouldn't the intake and exhaust valve be fully closed?

when I had the heads off piston #1 was all the way up. my worry is that I may have pushed the valve into the piston and damaged the valve or piston, when I was tighting the rocker bolt I did not notice any abnormal resistance until the bolt bottomed out.

any help would be appreciated

thanks

Dave

sounds like your 180* out on the exhaust stroke, if Im reading right

Did you remove the cam or replace the timing gears??? Are you using the shorter pushrods for the intakes??

but even at 180* shouldn't the exhaust valve be closed? just my thinking, please correct me if im wrong

all I did was remove the heads, since I never touched the timing chain or the cam, (I did remove the distributor) is it possible for me to have any piston to valve clearance issues?

no I did not do anything with the cam or timing chain, im using the original push rods. I bagged them and marked the bag's with the cylinder number and intake or exhaust. are the intake pushrod's a different length then the exhaust pushrods? are you suggesting that I mixed them up?

Exhaust valve should be closed either way. It will start to open a just after TDC.
With what you have done, there should not be any clearance issues.
The stock shoulder bolts for the rockers should just need to be torqued down and it really shouldn't matter what cylinder is at TDC.
You will really only need TDC on #1 to set the distributor at the correct position.

Exhaust pushrods are the longer ones so that should not be an issue for you either.

Agree with speedy, your 180 out.
You thought you where on TDC, so 180 out puts you at the end of the exhaust stroke

Edit:
Guess, could also not be 180 out if the exhaust lifter is not sitting all the way down on the cam, kind of hung

TDC will come up on the damper at 1 and 6, see which cylinder has both valves closed and that's the cylinder you're on.

rule of thumb to find TDC put your finger in the #1 hole and spin it around if it doesn't push air out the exhaust valve is open one more time around pushes your finger out with air, compression stroke for TDC.

Edit: and make sure the push rods are in the correct hole as mentioned.