| Author |
Message |
    
George Nichols
Visitor
| | Posted on Saturday, May 10, 2008 - 06:35 pm: | 
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After the last trip out the boat ran great it is a 7.4 bravo lll, carburetor, mercrusier outdrive, My question would be could reving up the motor on dry land with the flushing ears attached cause the rods to get bent?????? If not what does this? |
Bondo
Advanced Member
Username: bondo
Post Number: 999
Registered: 12-2006
| | Posted on Saturday, May 10, 2008 - 06:51 pm: |
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Ayuh,.....
Anything is Possible.......
Over reving a motor without a load on it Could do it.....
In boats,... Hydro-locking is a common way of it happening.... |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1274
Registered: 08-2006
| | Posted on Sunday, May 11, 2008 - 01:24 am: |
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An I/O should not be revved over 1500 RPM when running on muffs.
Your manual will tell you this.
How do you know the rods are bent?
Rod |
Jeff Waters
Member
Username: scarab_excell
Post Number: 51
Registered: 10-2007
| | Posted on Sunday, May 11, 2008 - 07:26 am: |
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how is he not burning up his water pump? |
George Nichols
New member
Username: pyroteh
Post Number: 1
Registered: 05-2008
| | Posted on Sunday, May 11, 2008 - 12:05 pm: |
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we pulled off the valve covers and the rods were obviously bent 6 of them on one side, so far. My partner has this thing about reving up the motor on dry land, I told him a hundred times that this is not a good practice. I'm trying to figure out if this did it or could do it so it doesn't happen again. I am freaking out on this as the fishing season nears. Is it better to rebuild or replace the motor????? Other than the reving up of the engine there is nothing else that was done other than running it at an idle with the muffs on. This is in a 25' Crownline 1995 7.4 bravo, mercruiser outdrive. |
George Nichols
New member
Username: pyroteh
Post Number: 2
Registered: 05-2008
| | Posted on Sunday, May 11, 2008 - 12:08 pm: |
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what is hydro locking, and what makes it happen? |
Bert Goodrich
Member
Username: bertg
Post Number: 85
Registered: 10-2006
| | Posted on Sunday, May 11, 2008 - 12:36 pm: |
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George Nichols
If you are referring to the push rods, then over revving is the main cause. The valves and pistons meet and the result is the push rod takes the pressure. If this is the case it wouldn't hurt to pull the heads and check for valve or piston damage.
Hydrolocking is when water is ingested into the combustion chamber due to backwash or exhaust shutter problems
Bert |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1279
Registered: 08-2006
| | Posted on Sunday, May 11, 2008 - 02:54 pm: |
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Bent pushrods are easy to change.
I would do a compression check and let that dictate as to whether a teardown is in order.
Marine engines are low RPM compared to cars, and over revving with no load just for fun can surely bugger up the pushrods. Lets just hope you don't have any other issues.
Rod |
allan in st pete
Visitor
| | Posted on Sunday, May 11, 2008 - 03:38 pm: |
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Those bent pushrods are from stuck or sticking valves. with all of them being one one side , I would have to say you were getting water intrusion on that side. A bad exhaust riser or manifold will do this.
Note; It is very hard to bend those pushrods, thay are large compared to small block pushrods.
But I have seen them pushed right through the rocker, or bent in an S from rusted(Stuck) valves.
7.4 L is a clearance motor, which means the valves will not hit the pistons unless you have broken valve springs.
hope this helps
allan |
Guy Gaspar
Senior Member
Username: guyjg
Post Number: 2006
Registered: 08-2006
| | Posted on Sunday, May 11, 2008 - 04:31 pm: |
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"I told him a hundred times that this is not a good practice"
I would let him pay for it and open a can of WA on him! |
George Nichols
New member
Username: pyroteh
Post Number: 3
Registered: 05-2008
| | Posted on Tuesday, May 13, 2008 - 12:42 am: |
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we only checked one side so far. 2 rods are actually broken and 6 are bent alot! Alan could the valves stick or rust in just a week out of the water. We just spent 3 days out and all was great, this started about a week after. We did flush the motor when we got home that evening. The reason we pulled the valve covers was no compression. What would make there be no compression other than valves or god forbid piston/ring damage? :-( So I do probabally have serious damage to head/valves and cyl. walls. Oh man, you guys better hang in there with me on this one, I'm sure we will need lots of guidance. Thanks for being there. |
Bert Goodrich
Member
Username: bertg
Post Number: 86
Registered: 10-2006
| | Posted on Tuesday, May 13, 2008 - 12:56 am: |
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George Nichols
For my money take off the heads and find out for sure what is going on. You may have bent valves or piston damage.
Checking lets you know what the condition is, trying to repair and run from the top IMHO is not recommended at this time.
Bert |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1292
Registered: 08-2006
| | Posted on Tuesday, May 13, 2008 - 11:14 am: |
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George;
You should heed Bert's advice.
Then you will know for sure where you stand.
Just my opinion.
Rod |
dave_n
Member
Username: dave_n
Post Number: 73
Registered: 11-2005
| | Posted on Tuesday, May 13, 2008 - 01:54 pm: |
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I'm with Allan, stuck valves due to water intrusion. It can happen when the engine sits with water in the exhaust passage of the manifolds which allows the valve stems and seats to rust.
It does seem like a week would not be long enough for the valves to rust up bad enough to stick, but it's possible.
I would pull the heads, I wouldn't try to just stick new pushrods in it. You may have issues with your exhaust system as well (being the cause of the water intrusion). |
MistaHays
Advanced Member
Username: mistahays
Post Number: 686
Registered: 02-2006
| | Posted on Tuesday, May 13, 2008 - 03:26 pm: |
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Yeesh. I feel for ya, George! I would emphasize that what sounds like a stuck valve issue is a symptom... Your boat is of the age when you might have manifold/riser leak issues.
Did it run very bad before your bud revved the p!$$ out of it?
Do yourself a favor and send your heads out to a machine shop for rework. I've seen to many re-assembled only to discover a cocked valve or damage overlooked. We're with ya!! |
George Nichols
Member
Username: pyroteh
Post Number: 4
Registered: 05-2008
| | Posted on Tuesday, May 13, 2008 - 08:18 pm: |
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Thank you all for your support, when we go to do the job we will do it right and complete. Might as well do the pistons and bearings too while we are in there anyway, we will get the heads mag'd for cracks and machined. we figure we are in there, might as well go ahead and do the whole thing. How much trouble are we going to have getting it out and back in? |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1308
Registered: 08-2006
| | Posted on Tuesday, May 13, 2008 - 10:38 pm: |
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George;
That usually the easy part, if you have the right hoist and a little bit of space to work.
Rod |
George Nichols
Member
Username: pyroteh
Post Number: 5
Registered: 05-2008
| | Posted on Friday, May 16, 2008 - 03:17 pm: |
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ok we're going to crack it open. I'll post the results asap. Thanks again everyone. |
George Nichols
Member
Username: pyroteh
Post Number: 6
Registered: 05-2008
| | Posted on Thursday, May 22, 2008 - 05:44 pm: |
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Ok we got one head off and saw one cylinder with water in it, one valve stuck open, (this one may be bent) no piston or cylinder wall damage, not too much rust, not enough to be causing stuck valves but why would one cyl have water in it? Could it have gone in when we removed the head? Are the manifold/risers bad? Please help, don't want this to happen again! |
Rod Stewart
Senior Member
Username: rod_stewart
Post Number: 1359
Registered: 08-2006
| | Posted on Thursday, May 22, 2008 - 06:29 pm: |
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Likely your manifolds and/or risers are rusted out and leaking, especially if you are in salt water and they are more than 3-4 years old.
You can pressure test them, or just buy new ones.
Rod |
Bt Doctur
Advanced Member
Username: bt_doctur
Post Number: 319
Registered: 06-2006
| | Posted on Thursday, May 22, 2008 - 08:41 pm: |
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contrary to popular theory, water ingestion into a engine, (riser,manifold,swamping,sinking,etc)
will stick a valve in it`s guide in as little as 24 hours.thats why it so important to get a motor running as soon as possable to dry things out. |
dave_n
Member
Username: dave_n
Post Number: 75
Registered: 11-2005
| | Posted on Thursday, May 22, 2008 - 09:31 pm: |
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To add to what Bt Doctur said, once a valve sticks open it will suck water into that cylinder. |
