1995 2700 scr7.4L low rpm

[canada randy]

Making a deal on 1995 2700scr 7.4(454) bravo 2. When owner took me out first trip looked like 4000rpm(maxed) at 33mph.I test drove it by myself today and only got 3800rpm at 30mph(tried various trim and tab setting briefly,didn't want to run wide open too long). Prop is 17 3/4" by 21P. Less than half fuel and low water/waste tanks. No hour meter. 110-120psi on all 8 compression test. Oil pressure read 20-40 psi through-out test (fresh 30weight castrol HD)Guessing 2:1 ratio on the bravo2. Thought maybe overproped? Or is motor played out? Should i try smaller prop for now? Should i save$ for new 400-450hp engine or rebuild to 400hp+(later)? I have 19 foot 55 mph boat and would sure like to get max speed out of my new cruiser. Concern is this engine should hit 4200-4600rpm. Thanks for any advice.

[seapuppy]

welcome to the zoo...alot of things could be causing the boat to not perform to WOT..is the engine freshly tuned up??..the bottom clean??....is the gas good??..ie not going south on you from aging.??..several other items to concider...compression sounds low to me...how is the vacuum readings??..dwell ok..is it points?...
how many hrs on the engine??

Steve

[ss3964spd]

Agreed, compression does sound a little low, and since there's only a 10# difference across all 8 it could well be that the engine is a little tired. You might want to consider a leak down test. Also double check that when the throttle lever is at WO that the throttle blades in the carb are also completely open (that engine probably has a QuadraJet).

Could also be proped wrong.

Dan

[canada randy]

Thanks will check points etc tomorrow.Go from there.Should i switch to electronic ignition?Point system may have to do for now. Btw Clean water on intake from owner cleaning boat.Noticed tiny air bubbles from intake gasket at valve cover when doing compression test. Put wrench on intake bolts. 4 turned slightly to snug.Some rust at bolts. No water on plugs or in oil.Will check with soap and water to see if sealed for now. Will have to do intake gasket i guess. Was hoping to just pay and go boating. Owner didn't do much for maintanence.Changed fluids thats it.Saw it launched. Bottom looked good.Clean and solid w/bottom paint.Drive and prop a little dirty.Had new rear cap on upper drive.Old cap cracked at lower bolt says owner.Don't know why.Drive and engine sounds and runs good. Owner doesn't use much and doesn't know anything about running it or doing proper maintanence.

[canada randy]

Has anyone had 7.4 with 17 3/4"x21P aluminum quicksilver w/bravo 2? If so what was your max rpm and speed trimmed with light boat? From what i've read this was standard on bravo 2 for 1995 2700scr.

[ss3964spd]

The points are fine for now Randy, you won't notice any performance difference by switching to electronic. You might see slightly better mileage and maybe a little easier starting but don't count on it. You'd definitely see less maintenance though.

Bummer about the intake. Remember though that the intake runners are not pressurized - they run in a vacuum, so I be very curious as to why you are seeing air escaping at the manifold to head gasket. I'd seriously consider a leak down test. When you did the compression test was the engine close to operating temp and did you have the carb throttle blades open?

[canada randy]

Blades held open .Only warmed up slightly for couple minutes. Wasn't sure about working on hot engine.My auto mechanic can't figure air leak either. I'll do intake gasket myself. Have some experience with complete engine re-assembly . Have to finalize deal yet.Totalling the cost + tune-up to lower purchase price. Why should you consider leak down test? What differerences should i see? Thanks greatly.

[ss3964spd]

A leak down test offers a better representation of engine health, specifically how well the rings and valves are sealing, than does a compression test. Compression test is faster to perform, but leak down is more telling.

The air leak at the intake is weird. Was it bubbling above the intake runners or else where like the water passages or cross over?

[canada randy]

I have to look closer. I showed my auto mechanic on a car approx where coming from. He thinks possible cross over area. Is that exhaust cross over? Looked at cap and rotor earlier. Looks old and corroded. Couldn't even pull rotor off with bit of pressure. I got work to do. Should i pull out of water to do intake gaskets?

[ss3964spd]

If it's in the center of the manifold, left and/or right, then it's probably the exhaust cross over - which makes more sense because the cross overs are the only areas of an intake that could be subject to pressure instead of vacuum.

Don't think you need to pull it from the water. Tilt the drive up. Remove any water supply hose to the engine that is below the level of the cylinder heads, but above the water line - one from the engine mounted water pump for instance. Any water left in the engine should drain down to where that hose was removed. Big block Chevys have don't have water passages from the rear of the heads into the back of the manifold, all water exits from the block through the heads and into the manifold at the front of the engine. As a precaution, once drained, remove the t-stat housing. If there is still water in the manifold you'll see it.

Another quick health check you can do is to warm up the engine, let it idle, remove the oil fill cap, wipe the opening of oil, and place a piece of paper over the opening. If the paper (don't use tissue) is drawn onto the opening it means the PCV is working and the engine isn't producing a lot of blow-by past the rings. If the paper is pushed away then, well, something isn't right.

Dan

[canada randy]

Its center manifold right side by carb , maybe inch back. If i pull boat out is there grease nipple on u-joint or gimble bearing behind 1995 Bravo 2 drive (should i pull off drive)?. A saw grease nipple back of engine. Coupler i believe. Is there gimble bearing nipple i havent seen yet behind engine? Is there grease nipple on U-joint? Thought i read coupler and gimble bearing serviced from engine compartment and sealed u-joint(no nipple). Will check paper trick. Much appreciated! Thanks
Randal

[canada randy]

Originally Posted by ss3964spd

If it's in the center of the manifold, left and/or right, then it's probably the exhaust cross over - which makes more sense because the cross overs are the only areas of an intake that could be subject to pressure instead of vacuum.

Don't think you need to pull it from the water. Tilt the drive up. Remove any water supply hose to the engine that is below the level of the cylinder heads, but above the water line - one from the engine mounted water pump for instance. Any water left in the engine should drain down to where that hose was removed. Big block Chevys have don't have water passages from the rear of the heads into the back of the manifold, all water exits from the block through the heads and into the manifold at the front of the engine. As a precaution, once drained, remove the t-stat housing. If there is still water in the manifold you'll see it.

Another quick health check you can do is to warm up the engine, let it idle, remove the oil fill cap, wipe the opening of oil, and place a piece of paper over the opening. If the paper (don't use tissue) is drawn onto the opening it means the PCV is working and the engine isn't producing a lot of blow-by past the rings. If the paper is pushed away then, well, something isn't right.

Dan

I tried with paper, then paper towel. Didn't suck.Had to hold over opening. Slight pressure pushing out. Almost neutral. Used soap on intake.Bubbles both sides of intake R&L at gasket at exhaust crossover.
Randal

[TonyA]

Hi randy: gee your having some fun, dont forget to set to timming position, because if you have to remove the intake manifold the distributor will have to come out. If yours has the ally manifold, below the exhaust cross over is a water cross over that has a lower pond in it so you will have some water trapped in it. have fun Tony

[canada randy]

Ya thanks. I haven't even bought the boat yet. So the fun hasn't even begun. I'm figuring what it needs to calculate puchase price. And what i need to do to get it up to par. I have some experience removing and tearing down engines and putting back together from long ago. Removing drive, etc. Have nessesary tools. If purchase successful. Put boat back on trailer. Pull off and service drive .Change intake gaskets. Impeller. Plugs,wires ,cap, rotor ,points, oils and filters ,etc.Complete tune-up. That looks like best case senerio. Don't want to think about worst. Just trying to cover all my bases. Boat looks good. Engine and drive at first glance seems to idle and run ok. Smooth. No nasty noises. But not maintained properly. Wish it had hour meter. Thought all boats did. Had it out a few times already. But needs work that i'm willing to do. If the price right. Was hoping to pay and go but that is kind of out the window right now. We'll see how it goes. Thanks for all everyones info
Randal
1995 2700scr 454 Bravo 2

[canada randy]

Another quick health check you can do is to warm up the engine, let it idle, remove the oil fill cap, wipe the opening of oil, and place a piece of paper over the opening. If the paper (don't use tissue) is drawn onto the opening it means the PCV is working and the engine isn't producing a lot of blow-by past the rings. If the paper is pushed away then, well, something isn't right.
Dan[/QUOTE]

Well if something isn't right, maybe its time to walk away. Or at least investigate further with leak down test. Sounds like good advice. Thanks Dan. Fun & Games eh Fun & games
Randal

Not to mention the Bravo internals. Wondering what thats like.

[ss3964spd]

Fun times 'eh Randal?

The paper test is very crude so I wouldn't base anything on that. Could easily be that the PCV is clogged or leaking. That the test was almost neutral isn' a bad sign.

Time for that leak down test. Ensure you find someone that has the tools and knows how to do it properly. But the first thing I'd do is find out what the static compression is supposed to be on that engine. 110-120 seems low.

Dan

[canada randy]

Just purchased leak down tester. Will either pull out boat and bring to shop or take portable compressor and genset to dock. Dock where its at right now has no electricity. Merc says compression should be 150. Fun times is right.

[canada randy]

I'm going to have to run engine to warm up at shop. I have muffs i used on the alpha. Will they work on the bravo 2 . Or is the raw water intake somewhere else? Thanks
Randal


added;
Should work.
Read through service manual which answered several questions. Thought it had points but it looks like it is electronic ignition.
More to read and more to do.

[canada randy]

Leak down test showed 8 % loss or less on all except #6 cyl. Which was 20%. Appears exhaust valve. Not sealing proper and possibly sticking. I may (should) pull that head off when i do intake gaskets. That #6 plug looked leaner than rest also. Not bad. Just others looked richer . Plugs and wires looked good. Cap and rotor look old and corroded. May cheap out and just change whats needed for now.

[ss3964spd]

Well done Randal, least now you know what you're dealing with.

If the engine seems to be running fine despite the weak cylinder and skanky cap and rotor, and given it's already July, I'd be inclined to sign up for a towing service and then do nothing at all and run it for the rest of the season. Pull it apart after the season to replace the intake gaskets and pull the head for inspection. You just know you'll find something else when you take it apart - like perhaps the exhaust manifolds/risers.

Dan