1996 Four Winns Sundowner with 5.0 Cobra engine and drive

[Lou C]

Flappers are at the top of the Y pipe hidden by the rubber exhaust hoses. They will melt & fall down inside the Y pipe if you have an overheat. These are a hold over from the original OMC Cobra design. Volvo said that they felt they weren’t effective & could block the exhaust if melted. They dropped them after the ‘99 model year. I kept mine & have never had water in a cyl from the exhaust but that’s what VP said & did. I think if someone was going to remove them they might want to fit taller elbows or maybe a flapper over the outlet where the exhaust bellows normally fits.

 

[kenny nunez]

That rust leak is from the pieces of the exhaust manifold that have collected in the front of the drive. You can try digging out the pieces. That area is open to the exhaust and the drain hole is to completely remove any standing water when the drive is tilted. Being careful with a drill should help and even enlarging the hole slightly cannot hurt it.
After pulling the drive the rest is easy.
To pull he engine disconnect the battery, wire harness, throttle, fuel, water hoses, exhaust worm clamps, unbolt the plate where the shift control is located. Behind the engine there are 2 stainless 1/2“ 13 lock nuts with washers then on the stringers are 4 lag screws mounting the engine. Probably a 3/4” socket on your impact wrench, 5/16” socket on your battery impact drill for the worm clamps and pliers along with some screwdrivers the engine comes straight up and out. With your experience and equipment this will be what we over here call a “CAKE WALK”

 

[Scott Danforth]

I could probably muddle through but I'd rather admit I don't know what I'm doing and ask for advice / links

factory service manual. https://www.outboardbooks.com/

however with the boat on the hard (@Lou C can fill in some details on removing the drive)

• with gear selector in forwared remove 6 bolts and tilt ram nuts and pull drive from bellhousing
• inside boat, unplug electrical, disconnect battery cables, disconnect exhaust hoses, throttle cable, shift cable and fuel line (plug it)
• connect chain hoist to top of motor
• disconnect engine mounts
• lift motor out

to make it lighter, remove the manifolds and elbows before pulling

to lower the boat enough for larger engine hoists, pull the wheels and let the hubs ride right on the concrete

 

[Lou C]

I highly recommend the factory shop manual, the OMC ones were very good.

 

[Lpgc]

Thankyou very much @Lou C , @kenny nunez and @Scott Danforth , very much appreciated info!

I still have concerns about the height for lifting the engine, I understand I could remove the trailer wheels but that would only give me a extra few inches, I don't know if that would be enough. I'll maybe roll my engine crane out and see how high that will go and/or see if I could maybe modify/extend it's boom arm and front wheels.

But I think I might as well continue on my current track for now, maybe I won't need to pull the engine... Run a compression test, have a better look inside all the cylinders with my borescope, check valve clearances (maybe identify a problem like a bent pushrod or damaged follower etc), then maybe pull the inlet manifold to check followers.

 

[Lpgc]

Today I took the road cover back off the boat with intention of doing a compression test, I'd already removed the plugs and had also removed the air filter flame arrestor (just for a better view of the rear of the transom and components mounted on it).

We had a rain storm the other day and it seems the road cover had a bit of a leak.. I was working in the yard the other day and could hear the little bilge pump had turned on (makes sense that it will be connected directly to a battery, I had turned the battery isolator off). The pump was running but there was no water pumping out of the side of the boat so I expect the outlet pipe from the bilge pump is disconnected. I removed the bilge plug, around 10 gallons of water came out and the bilge pump turned itself off. The little bilge pump not pumping water out of the boat is the least of my concerns at the moment...!

Connected a battery charger so the battery(s) would be fully charged for the compression test (the bilge pump running for hours would have taken some charge) and turned the key to crank the engine... Loads of water spat out of the starboard side plug holes :-( . Now it could be that some rain water got into the carb through the road cover... The boat is leaning slightly to starboard in my yard so if water got into the inlet I might expect it to slosh in the inlet manifold to the starboard cylinder bank. But I think it's more likely that there's a problem with the starboard exhaust manifold, it looks like someone had tried to bodge it with some type of sealant on it's outside before, have to wonder if it's also cracked internally, probably due to freeze damage... And water getting into cylinders causing hydraulic lock would explain the 'pause' I previously mentioned during cranking when I repeatedly turned the engine off and restarted it (to remove plug leads in turn to check to test to see if the knock went away) when I had it on the water.

In these pics it looks like someone has applied a thin layer of some type of sealant to a crack (the bottom rusty line running the length of the manifold).




I can buy another 'BARR' brand (the supplier says a premium US made brand?) manifold from a UK supplier for £312 + a bit for shipping. But that's just the manifold not including the riser. Is there potential for a problem in the riser too? Or I could buy a complete new set of BARR manifolds and risers for £1080 from the same supplier. Both deals are on this web page https://repowermarine.com/buy-omc-e...arts/omc-exhaust-system/manifolds-risers.html . I haven't checked to see how those prices compare to US supplier prices but I'd expect them to be more expensive this side of the Atlantic...

Anyone got any thoughts? Should I buy just the manifold or is there potential for a problem in the riser? Or would you buy the whole set in case there's a similar problem at the port side?

There's no water in the oil and the oil hasn't gone down, so I assume the block and heads are not cracked... Is that a safe assumption?

I might also assume that the knock is from either a bent pushrod / damaged follower or bent conrod / damaged big end bearing / damaged piston rings caused by hydraulic lock... Thoughts?

Obviously fixing a cooling system problem / water entering cylinders problem won't cure any damage caused to the engine by previous hydraulic lock (or rust due to water in cylinders left standing) but I've got both problems (cooling and knock) to fix anyway and if I buy the cooling system components I'll still have them when I've fixed the knock, just have to buy new gaskets if I remove and refit new cooling system components to fix the knock.

I might pull the inlet manifold to see if I can see any problem with cam followers... Assuming the inlet manifold on the carb engine is heated, is the gasket (valley gasket?) a special marine part or is it just the same as a standard inlet manifold gasket?

Simon

 

[Scott Danforth]

isnt freezing water wonderfull for cracking things

you need new manifolds and elbows. most likely new block as well because blocks dont usually survive either.

 

[Lou C]

this is the biggest problem with raw water cooled inboards, if you forget to drain it JUST ONCE, it's game over.
that's why any boat I buy in the future will be 4 stroke outboard powered. We have a little Suzuki DF 2.5 for our water taxi and it is a beautiful thing, yearly maintenance is like an hour, you do it all standing up, then just drain carb and gas tank and it gets put away for another season.

 

[kenny nunez]

2XS with SD on a complete manifold set. I still think a rocker arm stud has pulled up due to a stuck valve. I have in the past freed up stuck valves without taking off the head. I have used a brass drift and hammer to drive the valve down against the spring then tried prying up which worked many times. Drive the stud back down, replace the rocker arm. Good luck.
Another trick to pull the engine, strap your hoist in the pick up bed to reach over the transom.

 

[Bondo]

I might also assume that the knock is from either a bent pushrod / damaged follower or bent conrod / damaged big end bearing / damaged piston rings caused by hydraulic lock... Thoughts?

Ayuh,..... Before you spend any more money, do a thorough diagnosis of All it's problems, then a co$t benefit analysis, as I believe yer quickly approaching the bottomless money pit situation, on a less than desirable boat,.....

 

[Lpgc]

I had to finish looking at the boat soon after my last post, been out with extended family for a meal.

But I did complete the compression test...

Still not sure if Volvo / OMC use the same cylinder numbering system as Ford but until I know different I'm calling cylinders 1>4 starboard front to rear (so it follows I'm calling 5>8 port front to rear)...

Cyl / Psi
1 140
2 95
3 155
4 170
5 147
6 137
7 170
8 155

So cyl 2 is particularly low and there's quite a percentage spread on the others.

Maybe I should add a bit of oil to cyl 2 to test if it increases compression, which would point to rings or otherwise point to valves, head gasket or a crack.

I'll try again to use my borescope to look inside cyl 2.

If there's no evidence of any water ingress on the port side cylinders, why change the manifold on that side? If I filled the cooling system with water from a hose with the plugs out and no water entered cylinders wouldn't that show that the port side manifold must be OK, at least for now?

Purely by coincidence a guy I've known many years on 'LPGforum' but only ever spoke to once on the phone brought up the subject of buying a boat himself, a Bayliner bowrider with a blown 4.3 Vortec engine. We've only discussed boats once before and that was years ago. I replied on his thread telling him about buying a boat myself and the problems I'm having with it. Turns out he has a good 351W head and he's willing to let me have it.

So let's say I get this head from my friend and get a port side exhaust manifold from the firm I linked to in my last post. Start out at least expecting to change the manifold, when the manifold is off it's easier to remove the rocker cover and check valve clearances etc, could also remove the inlet manifold and check for bent pushrods etc. With the manifold(s) off I could change the head. If there were a bent conrod the piston on that cylinder wouldn't reach the same height as other pistons? I might be able to identify play in a big end bearing by turning each piston to TDC and turning the crank a bit further until the piston is on it's down stroke, then tap the piston with a rubber mallet... If there's a dull knock there's play in the big end bearing?

Or I could buy a '96 351W long engine less ancillaries, no inlet manifold or carb for £1500, supposedly a good engine, never been in a boat. Re-use my Holley 2barrel but need to buy an inlet manifold?

Someone said a 302 dizzy won't fit a 351... Is that a physical fit difference or rpm advance? Rpm advance can be changed by changing bob weights? Even if the 302 and 351 have different firing order that just means having to swap plug leads around... And the boat 302 has 351heads, cam and firing order anyway?

 

[Lpgc]

2XS with SD on a complete manifold set. I still think a rocker arm stud has pulled up due to a stuck valve. I have in the past freed up stuck valves without taking off the head. I have used a brass drift and hammer to drive the valve down against the spring then tried prying up which worked many times. Drive the stud back down, replace the rocker arm. Good luck.
Another trick to pull the engine, strap your hoist in the pick up bed to reach over the transom.

It'd make for better peace of mind to replace all marine manifold parts but it's also a lot more expensive than just changing the part I'm pretty sure is broken.

Judging by the compression readings a valve can't be stuck far open and it does run on all 8 cylinders so there must be some valve movement but there's still potential for a valve or rocker problem like you say.

Thanks for the tips. I don't own a pickup, could borrow one I suppose. The guy on the other forum I mentioned said he hired a cherry picker to fit an AC system and 'killed 2 birds with one stone' by using the cherry picker to lift the engine out of his boat during the same hire period... Might not be a bad idea to hire a cherry picker hehe!

 

[kenny nunez]

The oil pump drive rod on 351s is larger than the 302. It just might be a loose rocker arm with a pulled stud on #2 cylinder. No need to to remove the intake to inspect for a bent pushrod, you just need to remove the valve cover to replace them. If your engine has a flat tappet cam it could be a worn lobe. You need to pull the valve cover to find the problem.

 

[Lpgc]

The oil pump drive rod on 351s is larger than the 302. It just might be a loose rocker arm with a pulled stud on #2 cylinder. No need to to remove the intake to inspect for a bent pushrod, you just need to remove the valve cover to replace them. If your engine has a flat tappet cam it could be a worn lobe. You need to pull the valve cover to find the problem.

Thanks, will do. It might not be tomorrow but that's the next thing I'll do.

I once helicoiled a pulled rocker arm stud on a 2.5 VM diesel engine. Strange engine, straight 4 but with 4 separate heads.

 

[Lpgc]

Today I removed the suspect exhaust manifold and riser, removed the rocker cover, removed the rockers and pushrods for number 2 cylinder to inspect. There's no obvious crack between the exhaust and water jacket as far as I can see. There was no gasket between the riser and the manifold or between the manifold and head, looks like someone has tried to make gaskets from RTV (silicone sealant), I wouldn't expect that to work too well when exposed to hot exhaust gas... Maybe water got into the cylinders through a leak between the exhaust and water jacket where the riser mates to the manifold?









I only did a quick straightness test (rolled them on a flat area of the boat), both pushrods seem straight.. **But there's some light scoring towards the bottom (cam) end of the inlet valve pushrod (not on the end of the rod but along it's shank). I'm not sure if the scoring points to anything, a lifter problem etc...?





Then I re-installed the pushrods and rockers and cranked the engine while watching the 8 rockers to see if they all seemed to rock to the same extent, they did. But what I wish I'd done is crank the engine to watch the rockers before I removed them or the pushrods because now I don't know if the inlet valve pushrod had somehow become misplaced at the bottom end before I dismantled anything or if I accidentally effected a fix by removing and refitting those parts.

The motor must have hydraulic lifters because when not cranking it's obvious that lifters are bleeding down, none of the valves are left open much when the engine isn't turning.

**Could there be a problem at the cam end of the inlet pushrod for number 2 cylinder? Something that both caused scoring on the pushrod and would cause the knocking sound?

I used my borescope to have another look inside number 2 cylinder, it only does monochrome pictures. Difficult to tell of the piston crown looks steam cleaned or not but it does look very clean, I can make the numbers out on top of the piston very easily. There's a bit of a scuff mark on the cylinder wall. I did try to get a look at the valves using the borescope but I'm struggling to turn the scope to point to the valves. I did manage to see the bottom part of one of the valves but not a great view. I'll try to find the mirror attachment, seems less chance of it becoming detached and lost inside the cylinder now I have easier access to the plug hole with the manifold removed. I took a few pictures but I need to find a memory card reader before I can upload them to the laptop and post them here.

Need to do another compression test on cyl2 now I've removed and refitted the rockers and pushrods.

 

[kenny nunez]

Hopefully your engine has a roller cam which will rule out a worn cam lobe.
With the rocker arms off #2 you can put compressed air into the cylinder. Most likely the exhaust valve face is rusted. You may just have to pull that head for a valve resurface.

 

[Bondo]

There was no gasket between the riser and the manifold or

Ayuh,..... That is a serious problem, 'n no doubt where the water was coming from,......
Post pictures of these gasket faces,....

 

[Lpgc]

Ayuh,..... That is a serious problem, 'n no doubt where the water was coming from,......
Post pictures of these gasket faces,....

I tend to agree, wouldn't expect the RTV to stand up to exhaust gas flow even if the exhaust is water cooled. But I can't be sure that the manifold or riser isn't cracked, I haven't seen a crack but that's hardly a thorough test. Been wondering if I could do a more thorough test by filling either the outer coolant channel or the interior exhaust channel with water and seeing if it leaks through the cast, test the manifold and riser separately.

I already bought a new exhaust manifold, it comes with gaskets, I could fit those gaskets whether I fit the new or old manifold but I think it makes more sense to fit the new one even if I convince myself that the old one isn't cracked. It's 1230 Tuesday morning here, the new manifold should be arriving today but I won't be fitting it today, need to fix the knock and compression issue first.

Will post pics of the mating faces tomorrow.

Hopefully your engine has a roller cam which will rule out a worn cam lobe.
With the rocker arms off #2 you can put compressed air into the cylinder. Most likely the exhaust valve face is rusted. You may just have to pull that head for a valve resurface.

My big compressor broke years ago, didn't bother to fix it, bought it for spraying then only used it occasionally to run small pneumatic drills etc from. The only other compressors I have are 12V tyre inflators hehe, not sure if they'd put air into the cylinder quickly enough to build pressure if there's even a bit of ring blowby (and we'd expect there to be a bit of blowby) even if the valves are OK so it'd either prove no problem with rings or valves or if there is a problem it wouldn't tell me which was the problem?

Not sure whether I'd prefer a cam issue or a head issue. I'd prefer either rather than a bottom end issue...

Nearly forgot about the borescope pics, couldn't find the memory card reader so just bought another from Amazon that'll arrive today.

Out of interest how much would a known good 302W or 351W cost in the US? I phoned one of my LPG conversion customers today, he likes American vehicles, owns 3 x SRT8 vehicles including a Jeep he's added a supercharger to and a 90's Mustang. He might be able to put me in touch with someone selling a 302W or 351W in the UK.

If you were going to do an engine swap but keep the same drive and marine bits would you go with a 302W or 351W? Volvo Penta / OMC rate this spec 302 as only 190hp, rate the 351 at around 250hp.. I'd like the extra power ;-)

 

[Lpgc]

Also - should I have seen any flappers so far? I haven't seen any.

 

[Horigan]

There was a service bulletin released to remove the flappers. My '95 didn't have them when I got the boat seven years ago.