470 bent pushrod, what next?

[nola mike]

Trying to start, and it wouldn't turn over. Pulled the valve cover and found a bent #4 exhaust pushrod. I imagine it's from an exhaust mani/gasket leak. I thought I had pulled the plugs and turned over prior to starting, but maybe I only did that after it wouldn't start. Can't remember. Either way, no geyser from the cylinders. So now what? I know I need to pull the exhaust manifold. Do I need to pull the head? What's the chance of piston damage? What else would need replacing?

 

[HT32BSX115]

Re: 470 bent pushrod, what next?

Hi Mike,


Bent pushrods on cranking are usually due to stuck (shut) valves. The head needs to come off.

On marine engines, if you have a stuck exhaust valve, it MAY be due to a corroded exhaust valve stem rusted into the guide/seat etc.

That can be due to water that ran back into the exhaust from a leaky riser gasket, cracked manifold, cracked riser, etc.

If the valve was partially open, and you last ran in salt water, well........it won't be pretty.

Pull the manifold, pull the plugs, turn the engine, see if you can free up the valve.

If you had water in the cyl....and it has sat all winter (or more than several days) you probably should pull the head.

It should be painfully obvious once you get the manifold off.....


Sorry about that....


Rick

 

[nola mike]

Re: 470 bent pushrod, what next?

Hi Mike,


Bent pushrods on cranking are usually due to stuck (shut) valves. The head needs to come off.

On marine engines, if you have a stuck exhaust valve, it MAY be due to a corroded exhaust valve stem rusted into the guide/seat etc.

That can be due to water that ran back into the exhaust from a leaky riser gasket, cracked manifold, cracked riser, etc.

If the valve was partially open, and you last ran in salt water, well........it won't be pretty.

Pull the manifold, pull the plugs, turn the engine, see if you can free up the valve.

If you had water in the cyl....and it has sat all winter (or more than several days) you probably should pull the head.

It should be painfully obvious once you get the manifold off.....


Sorry about that....


Rick

Well, it's FWC, so corrosion less of a concern. How would turning the engine over at this point free the valve? Maybe I didn't mention, pushrod was BENT. And is now sitting beside me. I'll start with pulling the manifold, and check back in...

 

[HT32BSX115]

Re: 470 bent pushrod, what next?

FWC, so corrosion less of a concern

It's absolutely a concern because when you have a cracked/corroded-leaking manifold or riser, OR a leaking riser gasket, it allows SEA water into the exhaust area. IF an exhaust valve is open (as 1 or more usually IS) that "SEA"-water runs right into the cyl.

 

[nola mike]

Re: 470 bent pushrod, what next?

Good point. Well, the valve appears closed, and the seawater system was drained over the weekend. Valve train rusty with some milk in there. Hole in the interior of the riser, so that may be my problem. At this point, not much more work to remove the head, so that's next. Pics to come when I have access to a PC.

 

[TilliamWe]

Re: 470 bent pushrod, what next?

Common problem with the 470. It's the exhaust manifold/riser as you suspect. Fix that, (Big $) replace the pushrod and hope for the best, if you want to do it on the cheap. My dad got lucky and fixed one for a guy like that once.

 

[nola mike]

Re: 470 bent pushrod, what next?

Ok, removed the head--here's what I think happened. There was a small hole in the riser, allowing coolant to flow back into the exhaust manifold. This was probably not enough to notice during last season (coolant level never dropped, even now). Because the boat was tilted back, the coolant flowed preferentially into the #3/4 cylinders. Oh yeah, when I took it apart, the #3 exhaust pushrod was bent as well. Both valves were closed, and the valve stems got corroded. Actually, I guess that it was more likely sea water that leaked back. Zoinks. Could have been ugly had that made it to the cylinders. Crappy thing is, I just removed/inspected/replaced gaskets on the manifold and riser at the beginning of last year. The cylinders look pristine. I got the valves free more or less, but they are still definitely less enthusiastic about moving than the others. So what do I need to do now? I've never worked on a pushrod engine, so this is a bit new to me. Thinking that I'll need to remove (replace?) the valves and seals, and lap the valve and seat. Parts needed:
1. Gaskets--head, valve cover, riser, exhaust mani, intake mani
2. Head bolts--are these reusable? I damn near rounded 2 of them, first using a 12 pt socket, then a POS harbor freight 6 pt. Glad I stopped, drove 40 min roundtrip to the hardware store to get a good 6 pt socket.
3. Pushrods--I understand I need to measure my old ones to get the correct length.
4. Valve seals, maybe valves, as above. Valve guides? Are these easily replaceable?
5. Riser

Anything I'm missing? Any reasonable "while I'm in there" stuff to do (I don't want to go nuts)? Glad I checked this before replacing my starter...this could have been much worse, I think.

 

[HT32BSX115]

Re: 470 bent pushrod, what next?

There was a small hole in the riser, allowing coolant to flow back into the exhaust manifold. This was probably not enough to notice during last season (coolant level never dropped, even now).

Mike,

Understand that you DO NOT have coolant IN the riser.


The riser will ALWAYS have "RAW" water in it because it will be exhausted overboard at the "business end" of the riser.....

In (FULL) closed cooling systems, the exhaust manifold(s) and block are filled with anti-freeze and riser is isolated from the exhaust manifold.

In a "HALF" system, the manifold AND riser will have "RAW" water pumped through them. In either case, the raw water usually comes from the heat exchanger discharge.

In your case, it could have been raw water or 50/50 coolant depending on how the 470 manifold is cooled, AND how they separate them with a gasket.......

If it WAS 50/50 coolant that leaked, it might be better because A/F would cause less corrosion presumably.....


......... I am not familiar enough with the 470......Is it a "Full" or "half" system?

 

[stonyloam]

Re: 470 bent pushrod, what next?

the exhaust manifold on a 470 is filled with coolant.

 

[nola mike]

Re: 470 bent pushrod, what next?

Yeah, like Terry said. It's a full system--raw water is in the riser only. The coolant reservoir is also in the riser. So it could be either one. However, it seems more likely that if you rot through the riser, it will be the sea water and not the AF that's the cause. Which it was in this case (I probed the hole with a wire). A bad gasket will leak AF into the exhaust. Still, quite a bit of corrosion considering it was flushed with fresh water (after every weekend) and drained at the end of the season.

 

[nola mike]

Re: 470 bent pushrod, what next?

Here are the pics as promised. Got a bit off track, but still looking for answers to what my next steps should be to get this on the water...

1. Gaskets--head, valve cover, riser, exhaust mani, intake mani
2. Head bolts--are these reusable? I damn near rounded 2 of them, first using a 12 pt socket, then a POS harbor freight 6 pt. Glad I stopped, drove 40 min roundtrip to the hardware store to get a good 6 pt socket.
3. Pushrods--I understand I need to measure my old ones to get the correct length.
4. Valve seals, maybe valves, as above. Valve guides? Are these easily replaceable?
5. Riser

Anything I'm missing? Any reasonable "while I'm in there" stuff to do (I don't want to go nuts)? Glad I checked this before replacing my starter...this could have been much worse, I think.

 

[picklenjim]

Re: 470 bent pushrod, what next?

That thing looks like it was full of water for quite some time.

 

[stonyloam]

Re: 470 bent pushrod, what next?

That looks EXACTLY like my head, right down to the pitting in the chamber LOL. Had a valve job done, new seals, can't remember about guides, needed 1 new valve. Had hardened exhaust seats put in. Was a bad head gasket on #4. The machinist did measure valve height before and after so the pushrod length did not change. Good luck.

 

[nola mike]

Re: 470 bent pushrod, what next?

Well, good(ish) news. Took the head to a machine shop. Walk in the door, guy takes one look at it, and says, "big block Ford? You got a Mercruiser?". Cool. So I ask him what needs done, and after inspecting it, says nothing. Guides feel OK, otherwise head is in good shape. He says that if I clean it up, lap the seats, and replace the valves/pushrods, I should be good to go. Got new headbolts, gaskets, valves, pushrods, and riser. Hopefully I can bolt it up and get 'er on the water this weekend...

 

[HT32BSX115]

Re: 470 bent pushrod, what next?

Well, good(ish) news. Took the head to a machine shop. Walk in the door, guy takes one look at it, and says, "big block Ford? You got a Mercruiser?". Cool. So I ask him what needs done, and after inspecting it, says nothing. Guides feel OK, otherwise head is in good shape. He says that if I clean it up, lap the seats, and replace the valves/pushrods, I should be good to go. Got new headbolts, gaskets, valves, pushrods, and riser. Hopefully I can bolt it up and get 'er on the water this weekend...

You dodged that bullet huh?

Redo the head, new riser and you're back in business!

How old is the riser that rusted thru?

 

[nola mike]

Re: 470 bent pushrod, what next?

You dodged that bullet huh?

Redo the head, new riser and you're back in business!

How old is the riser that rusted thru?

Hope so. Riser might damn well have been original (ducking), but I did take it off last year and perform the "screwdriver test" on it. I think running it in the brackish water makes a BIG difference in lifespan of these things. Always freshwater prior, this will be my third season with the boat.