454 V8 - weird mechanical issue

We are working on my FIL's boat. Two big Volvo Penta 7.4 V8's. I believe they are based on a 454 Chevy block.

We had, so called marine mechanic professionals look at the motors to no help. Everything is fine according to them. But...

Port motor runs great, once started, but the problem is that on a second or third try starting it up - it rips off the starter motor. Bolts just snap. We tried multiple bolts and multiple starters.

Any thoughts on what can cause that?

 

Can it be possible be firing in a reverse order, and running backward? There are two sequences 1-8-4-3-6-5-7-2, and reversed 1-2-7-5-6-3-4-8.

 

Very odd sounding issue for sure.

Is this a cold start issue, or is this a restart when still hot issue?

Fuel injected I assume? Pictures would be interesting too.

Fill us in when it gets figured out.

Reverse firing sounds like a possibility, did it sound like a backfire when starting?

Was this engine worked on right before the issue began? If so review the work done.

At this point I'd be happy that it's only breaking bolts.

 

It goes something like this... my FIL would put in a new starter. Motor would crank and start running. Now he thinks that he has two running engines to move the boat. He would then drive two + hours to pick me up, so we could move it to our dock. We would get back to his boat, try to fire up the port engine, and.... clink another snapped starter bolt.

Motors are fuel-injected.

 

So it starts and runs fine for two hours, then is stopped for "how long?" before trying to start again and immediately snaps bolts?

Could this engine be hydro locked in some way in the amount of time it sits between starts? Doesn't sound likely but maybe.

 

On a twin I/O boat the engines rotate in opposite directions.

Props usually rotate outward.

 

What exactly do you mean by this: "Now he thinks that he has two running engines to move the boat." Is he sure, or not?

I have to guess that he would notice the difference on a two hour boat ride.

 

He would get it running, then shut it down. About 2 - 4 hours later we would try to start it again. Snap, clink..... So a second cold start.

I don't recall which motor was running when he got the boat originally. One was, and one was in parts. It's a project boat with lots of unknowns.

 

Boat is in Carrabelle, FL. I told him that he needed both running engines for us to sail across Apalachicola bay to our dock. We are not going out with just one running motor.

 

Thats what I thought, but we were told that this boat has both screws rotating the same. Which doesn't seem logical.

 

Verify rotation of motors vs what they are supposed to be. One may be marine rotation…backwards from normal car order and the other is normal.

are the starters top mount?

also if this engine was recently assembled maybe the flywheel start engagement is off? Check that

 

A project boat - so someone else's work that you now have to verify every step of the way.

VERIFY EVERYTHING - I'm guessing that you will find a really dumb but easily made mistake in there somewhere.
I can't count the number of times I've been baffled by other folks work on motorcycles.

 

If that's true then either one of the starters isn't correct or one of the engines is not configured for reverse rotation

 

Gotta be hydrolocked

 

Easy determination, look at the props.

 

What the boat people say is "normal" for twins...

In twin-engine fixed pitch installations the standard is outward-turning propellors, ie the starboard engine is right-handed and the port one left-handed. With this setup going slow ahead on the starboard engine and half astern on the port engine will move the boat's stern bodily to starboard. Reverse the engines and the stern moves to port. Outward turning propellors make slow speed maneouvring "simple".
In twin-engine controllable pitch installs inward turning propellors are preferred.
In either case counter-rotating props eliminate the "transverse thrust" effect of a propeller.

If this is weird thrown together clapped out SV of boats...I would physically check and verify rotation of each engine at the fly wheel. Hit the starter and watch the flywheel. Then pull dist cap and verify rotor rotation. Look at plug wires to make sure that all matches up.

Then you can start looking at starter rotation vs mount position, what direction the props turn, etc to make sure it isnt completely fubar.

 

The thing that is confusing here for me is the timeline.

Motor starts and apparently runs fine for two hours or so and is then shut off for two hours or so.

Engine then snaps starter motor mounting bolts when attempting to restart.

"Unknown amount of time later" new bolts and maybe a new starter motor have been installed and engine starts and apparently
runs fine again only to repeat the cycle after sitting for a couple hours.

Is this a correct description? If so what is that unknown amount of time? I am still thinking some sort of hydro lock.

 

I assume if the prop pitch is the same, then engine turning direction is the same. To be honest, I don't know if the props were put back the same way as when they were removed.

Not sure what you mean by top mount. They are held in place by two bolts near the gear of the starter.

What is flywheel engagement? Not clue what that is, or how to check.

Regardless, motor starts easily and runs great, but not long afterwards a starter snapps off.

 

Yes, that is correct. He would crank the motor, let it run, warm it up, test the transmission, etc. Then next morning drive down to pick me up. We get to the boat and he cant get it to fire up, and soon afterward a broken starter bolt.

 

This is old really old school, but is the starter solenoid working properly? (if there even is one) Seems like hydrolock would result in the starter gear shearing, not bolts breaking.