Resetting timing

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littlebookworm

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I have twin Mercruiser 1997 7.4 TBI inboard engines. I did a valve job on both engines over the summer and was only finally able to leave the slip last week. (Long story; problem caused by 2-year layup.) Before I pulled each distributor, I marked the respective housings as to the locations of the rotors. However, I think the timing is off slightly and would like to check/reset it. From what's I've read online, I can't do that without a Mercruiser or similar diagnostic device. Is that correct? Hy
 
The relation of the rotor to the dist housing also has to align to #1 cylinder at TDC on compression stroke. The rotor should have been pointing to 5-6 o'clock when you pulled the dist and the engine wasn't rotated at all.

Oops,you did the valves. You have to find TDC on the compression stroke allover again.
 
The allignment of each rotor was marked on each distributor housing before the distributors were pulled. The crankshafts and camshafts were not turned so each distributor dropped back in exactly as removed. However, I still want to check the timing on each engine. That is something I've done on every engine job on auto or boat I've ever done. Unfortunately, I can't set the timing at 'base mode' without a diagnostic computor, according to what I've read. That is one device, among others, that I do not have because my experience has been with carburated engines, not computor-controlled fuel-injected engines. I was hoping someone knew a way to set 'base timing' mode, such as be connecting two of the leads on the distributor harness, as can be done with MPI/EFI engines. Hy
 
It all depends on if you have a Thunderbolt IV, or T-Bolt V? As you can see the procedure is different. You can find TDC of #1 on compression stroke, by disconnecting the coil temporarily, and taking out #1 plug, crank the engine, and feel for compression as the crank comes up to TDC #1. Then take out your Dizzy, & set the rotor to #1, and drop it back in. Or, you could also pull out all your spark plugs for faster cranking.
 
I think they're Thunderbolt V, but I'm not certain because they dod not have two wires with barrel connectors coming off the bases. All the wires connect via two locking connectors. I have two manuals on my computer which should cover the engines, #16 and #23. Each gives different instructions to set base timing. Doing it wrong could screw up the computors, something I don't want to do at an cost. I may just have to pay the marina's mechanic to check the timing, knowing any screw-up would be on his dollar.

The irony is that, even though the boat looks and runs great, I'm probably going to be selling the boat soon anyway because we're planning on moving off Long Island and can't afford the yacht club near where we're moving. I wasn't able to use the boat last season because of spinal surgery and didn't use it this season because both engines needed valve jobs because of stuck valves as a result of being laid-up for two years. The previous owner kept the boat in excellent condition with full maintenance even before things were needed to be done. I had hoped not to have to spend much money on maintenance or repairs for a few years, but it didn't happen that way. It's been a rough couple of years. Hy
 
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