1977 351W Power problem

[Galloping Ghost]

I have a 1977 351W I/O OMC engine - having a problem fixing this one. I have completely tuned it up, set the timing, and here is what I have: the engine starts and runs fine when not under a load. When under a load it will run fine at an idle, and when kicked up to 3500 rpm or more, it seems to have no power. The engine seems a bit "steemy" - steam will come out of the valve cover if a hole is unplugged - dont know if this is normal... - could this be a head gasket problem? It will overheat when under a heavy load and not on plane - the boat will no longer plane. floored, it will sometimes only go up to 3700 rpm - instead of 4400. any insight would be helpful! also, i have done two compression tests - the first one i did with the engine cold, and all the plugs out. all of the cylinders were at around 110 - 115 and #'s 4 and 5 were around 80. another test was done with the engine warm, and all the plugs in. this test showed all of the cylinders to be at about 95psi. in this test i added oil to the holes, and the compression stayed pretty much the same - they all went up maybe 4 lbs. help!!

 

[Galloping Ghost]

Re: 1977 351W Power problem

also - one more thing - the timing may not be advancing - it is set at about 10 btdc at an idle, and when i get it up to 3000 or so the timing does not advance much at all - it is not a vacuum advance, it is mechanical.

 

[ron7000]

Re: 1977 351W Power problem

1975 model 233 here, went new in 1993 with a factory new 351w.<br /><br />With that year, if you have the original prestolite distributor with mechanical advance, you need to pull the distr. cap, take off rotor, remove points mechanism and pull out the plate the points sit on. Underneath that are two springs, one on each side along with a set of weights. These control the timing advance. I bet it'll be all rusty, with one or two broken springs. you will have to call all over the place to find replacement springs. At worst, the whole distr. mechanism is worn and is best to buy a new distributor.<br /><br />A quick way to check if the distributor advance is working properly, but may be confusing to you if you don't have the experience, is with engine off and distr. cap off, turn the rotor by hand lightly in the advance direction (the way the rotor turns with engine running). Clockwise I believe. It should turn 20 to 30 degrees, then if the springs are working spring back when you let it go. The surefire way is with a timing light and engine running.<br /><br />If timing isn't advancing, then that'll definitely cause a loss of power at 3000+ rpms and you'll never get 4400 rpms.<br /><br />You're real problem is you definitely need a valve job. Had to do that on mine with the old '76 motor around 1985. So if you got 25 years, that's pretty darn good. Pull both heads, get them machined and get new valve seats, stainless valves, springs seats and retainers. You should see around 140psi compression all cylinders, and no less than 110psi. Then if you don't get good and consistent compression, then you will need new rings.<br /><br />With bad valvetrain, your carb will never work properly! You must get the heads worked! Don't waste your time or money doing anything else.<br /><br />After doing the heads, you will have new head gaskets and I think you'll find a lot of the other problems have gone away. The steam may be coming from a head gasket leak, but most likely leaking valve seats.<br /><br />For what it's worth, I spent ridiculous money and time on my '75 motor, fixing everything on it from fuel pump, carb, distributor, manifolds, before deciding to bite the bullet and buy a whole new motor. Best decision I ever made. Might want to think about that before investing into a '77 motor, unless you like working on motors.

 

[Galloping Ghost]

Re: 1977 351W Power problem

hey - thanks for the wise words!! i have just discovered that one of the springs is missing!! i will start with that. you are right - the springs are nasty to find, and it is even difficult to find a distributor for a '77. the engine only has about 650 hours on it, so even if it is a pain in the buttox i am gonna try and at least get it to work a little for the rest of the season. i know the valves need done, and am dreading doing that. if you don't mind me asking, how much did your new motor run?

 

[Wart T]

Re: 1977 351W Power problem

A missing spring wont cause that. The springs pull the weights back into position when the engine slows down. You havent found the problem. I suggest checking shutters.

 

[ron7000]

Re: 1977 351W Power problem

Originally posted by Galloping Ghost:<br /> if you don't mind me asking, how much did your new motor run?

from basicpower in NC, it was marine factory Ford brand new, $3200 I think, for the high output 285hp version. It has the GT40 heads. The regular 260hp 351w was $2800. These were 1993 prices. Motor came with everything ready to run except fuel pump, starter, alternator, and exhaust manifolds. I don't know if they still sell those packages.

 

[Galloping Ghost]

Re: 1977 351W Power problem

thanks for the info old bald fat guy! at the huge risk at sounding completely ignorant, what are shutters??

 

[xltier]

Re: 1977 351W Power problem

also check to see if the mechanism is rusted up so as it cant be turned a little like ron said.as old guy said that spring wont give lack of power.would be opposite if anything.u should be able to turn the shakt about 1/8 turn and watch the weights move out then back under spring tension.when u find a spring of course.hth

 

[danthern]

Re: 1977 351W Power problem

I had the exact same problem with the exact same motor. We pulled the points and the plate , sprayed a little WD-40 under there and worked the mechanism by hand back and forth to free it up. Haven't had a problem since. Hope your solution is as simple.

 

[Galloping Ghost]

Re: 1977 351W Power problem

hey thanks for all your wise words everyone! this forum is a great place. i replaced both springs on the distributor, and everything was much better. however, still not much power - compression - only about 95 lbs. on average. i ran it this weekend, and after having to get her up to 4400 to plane, she blew the head gasket after about a half hour. it was a nice tow in from 10 miles out! so now i am pulling the heads, and am about half way there. what a pain. one more question - can i get springs, seats, retainers, valves for a regular 351W, or are the marine mechanisms different?

 

[Boomyal]

Re: 1977 351W Power problem

Originally posted by Galloping Ghost:<br /> can i get springs, seats, retainers, valves for a regular 351W, or are the marine mechanisms different?

I'd let a reputable auto machine shop do it all. Components would be the same as auto but a shop would be able to select the proper parts as well as do the valve job and head surfacing. Then you can reinstall the heads and go for it.

 

[Galloping Ghost]

Re: 1977 351W Power problem

yes - thanks for that - i will be taking them to a shop my buddy knows well - now here is something else - has anyone ever blown a head gasket on the water? there was a decently loud "pop" and then the engine ran faster, no power at all, and interestingly enough it never stalled. it purred like a kitten at about 1100 - could this be just a head gasket, or could it be a busted cam shaft???

 

[Boomyal]

Re: 1977 351W Power problem

Not sure about the 'pop' but most head gaskets probably blow 'on the water'. Depending on the area of the blowout, you could have and air leak that would cause the motor to speed up from a lean condition. A 351w is pretty bulletproof, so I suspect there is an underlying cause for it to blow the gasket. It wouldn't be age. The camshaft is unlikely to be an issue here. Just check the contact surface of the lifters when you pull the heads. Don't mix them up and it's best to keep your pushrods in order as well.

 

[ron7000]

Re: 1977 351W Power problem

With my osco manifolds and risers, I had the gasket fail between one side a couple years ago and let water get into cylinders after shutdown. Went to start it one saturday morning, one cylinder fired and as the water filled cylinders compressed popped the head gasket.<br />This was only on a cold startup, and one cylinder had fired before the other cylinders hydrolocked. I don't remember any kind of loud pop, other than the abrupt stopping of the engine and assoiciated noise. What I did hear was a hiss for about a second- where the head gasket let go. After that I pulled plugs, turned engine over to expel tons of water from one bank of cylinders, and check compression to find 2 or 3 cylinder under 50psi. Then immediately pulled the heads.<br /><br />Had the heads rebuilt at a local shop with stainless valves, new seats and retainers, and felpro marine head gaskets. The only thing to look for I think are stainless valves. The rest (springs, retainer) if you don't reuse them, just have to fit the application.<br /><br />In my case, and apply this as appropriate, I checked for bent pushrods. Just find a clean piece of glass and roll them on there.<br /><br />If you have a bent pushrod, definitely check for a bent piston rod. I simply checked mine by rotating engine by hand with heads off and observing pistons at TDC. If a cyl. has a bent rod, then piston should not travel as high up. As for how much difference is too much, I can't tell you, maybe for than 0.030"? Compression check after reinstallation may show the problem.<br /><br />When I got my heads back from shop, all my lifters, pushrods, and rockers were in one box. I've also read (albeit mostly internet) that you should keep everything ordered. But the shop said don't worry about it, and I have over 100 hrs on the motor after that so I don't think it's something to worry about. It is, a very tough motor. If/when you reinstall the heads, let me know what you find out or do for the valve-lifter adjustment procedure.