Mercruiser FORD 351 loss of power and low WOT revs

[johnnymac59]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Hi Guys, thanks for the input. Compression tests ranged from 95-115psi dry and 105-125 wet, so low on compression but not pointing towards bad rings as the increase is minimal. So I started to think that the loss of compression is due to bad valve seating/corrosion. I now think there is no doubt the compression is the culprit of the lack of power at WOT, whats causing it? Steam from exhaust points towards blown head gasket, and this in conjunction with bad valves would give me the symptoms.

The boat is moored and has a little growth bu not much, I have a brand new carby on it and the problem still the same as with the old carby...so points towards engine. Will keep you informed of findings once I strip it down.

John

 

[Bondo]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Compression tests ranged from 95-115psi dry and 105-125 wet, so low on compression but not pointing towards bad rings as the increase is minimal. So I started to think that the loss of compression is due to bad valve seating/corrosion. I now think there is no doubt the compression is the culprit of the lack of power at WOT, whats causing it? Steam from exhaust points towards blown head gasket, and this in conjunction with bad valves would give me the symptoms.

Ayuh,.... She sounds pretty Tired.... I'd think pulling the Heads is the logical next step...
With steam involved, follow the rust trails in the exhaust path,+/ or the Really Clean areas of the combustion chamber...

Btw,... Alittle marine growth is Too much....

 

[Lyle29464]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Good call a70eliminator, I'm surely back!!! The timing did make a difference, will rev out to 3300rpm now and feels better but still not right....whats the chance that the timing chain has jumped? I keep reading people suggesting this and others saying it's bollocks and never happens. How can I check this? If I find TDC on no.1 cylinder then do I check to make sure the rotor arm is pointing directly at the no.1 position on the distributor or slightly past it? Its been a long time since I worked on engines so bear with me guys.

starboard engine most likely does not have a chain. If its a reverse turn it will have gears.

 

[johnnymac59]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Thanks Bond-o for the heads up. Will pay attention to that when I strip her down.

 

[johnnymac59]

Re: Mercruiser FORD 351 loss of power and low WOT revs

It is reverse rotation, and heard they were made with gears rather than a timing chain. Good call will check this out when I remove the cover. The rotor arm in the distributor rotates CCW the same as the standard rotation, so I guess the distributor has a reverse gear on the bottom of the shaft?

 

[muc]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Hi Guys,

Have been through the top ten list and ticked them off as I go. Fuel system fine, new carby, clean filters, clean hull, porps ok, tested coils, new plugs...etc..etc...

Timing! Was running at 23deg BTDC...so slackened dizzy and altered timing to 12deg BTDC. Had to adjust idle and mixture, sounding good. Will take it for a test ride tomorrow...fingers crossed!

might want to check mechanical advance in dist. might be frozen or springs broken, seeing as you had to change it that much=red flag
good luck muc

 

[johnnymac59]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Thanks Muc, I have looked at the mechanical advance and appears to work but not too sure how well or accurate, so I have decided to order two electronic ignition kits (something I was going to do anyway)...might reduce my fuel bill!!!! a little..

Took off coolant hoses in prep for stripping down the engine, and in one of the small heater sized hoses that comes off the thermostat housing there was a piece of wooden dowel about 8cms long lodged inside...what the f$#%??? I'm surprised there was any flow of coolant whatsoever, would this explain the steam coming out the exhaust? The temp gauge was a little on the high side (just over 3/4) but never in the red...gauge faulty?? I will keep strpping her down and look for more previous owner blunders!!!!

Buy secondhand and buy the previous owners IDIOCY!!

 

[johnnymac59]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Hi all, I also want to change distributors to electronic ignition and I am starting to find it extremely difficult to find what I need. So any advice welcomed. I have carburetor engines FORD351w one is a reverse rotation with a top to the left dizzy gear....this is the tricky part, trying to find good quality marine distributors with one reverse rotation. I was looking at Pertronix but they dont do a reverse rotation for FORDS, only Chevs. Any ideas guys?

 

[cr2k]

Re: Mercruiser FORD 351 loss of power and low WOT revs

no the reverse is taken care of by the timing gear. Only the crank turns backwards.

 

[johnnymac59]

Re: Mercruiser FORD 351 loss of power and low WOT revs

I meant to say I need a distributor with a reverse gear on it (I know they both turn CCW), I have taken them both out and the bottom shaft gear is opposite on the reverse rotation engine. Having difficulty trying to find electronic distributors one standard one with reverse gear. Apparently easy enough to find if you have a Chev engine but not a FORD (FORD351w)!

 

[johnnymac59]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Finally back to the forum! Well all, I stripped down the engine, heads ok (not great, slightly leaking valves) but bores are all glazed liked a well cooked ham!!! So she is tired and weary and needs a fixin! So I have decided to bite the bullet and have ordered two replacement engines, due in Feb. Have also acquired two Mallory electronic ignition systems too, she should be sweet soon. will keep ya informed.

Thanks guys

 

[Bondo]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Ayuh,... Glad to see ya back,+ Sad to hear she's Beat...

Good Luck with the Fresh Iron.....

 

[johnnymac59]

Re: Mercruiser FORD 351 loss of power and low WOT revs

Thanks Bond-O, cheers for all your suggestions and I will post once the beast is beating waves again just to let you all know if she finally made it....