7.4 454 Repower opinions needed.

[RogersJetboat454]

Re: 7.4 454 Repower opinions needed.

They didn't even start making Gen VI motors until '96.

Guessing it's a Gen 6 engine that will match the mechanical spec's of a Mark IV from that era.

I don't think the General has much to do with making Mark IV component's anymore, especially entire crate engines.

 

[sparky774]

Re: 7.4 454 Repower opinions needed.

Umm, if you have a need for speed you could drop a remanufactured (MARINE) 502 big block in for under $4000. http://remanufactured.com/Inboard_Marine_Engines.htm

You have experience buying from this place?

 

[RogersJetboat454]

Re: 7.4 454 Repower opinions needed.

To the OP;

Don't know if it's been said, but there may be something else going on that has been damning these engines. It may not necessarily be a engine build problem. Could be fuel delivery issue too. A fuel system with a leak/restriction could be leaning the engine out.

I would be checking the fuel system out with a fine tooth comb before turning the key on what ever engine you install.

 

[sparky774]

Re: 7.4 454 Repower opinions needed.

To the OP;

Don't know if it's been said, but there may be something else going on that has been damning these engines. It may not necessarily be a engine build problem. Could be fuel delivery issue too. A fuel system with a leak/restriction could be leaning the engine out.

I would be checking the fuel system out with a fine tooth comb before turning the key on what ever engine you install.

You know this is good advice, i plan on doing this and i was also thinking that i might consider replacing the fuel tank since this boat is a 79 and has the original tank still (aluminum). Fuel pressure was good though and the plugs are not white they are just the right color

 

[RogersJetboat454]

Re: 7.4 454 Repower opinions needed.

You know this is good advice, i plan on doing this and i was also thinking that i might consider replacing the fuel tank since this boat is a 79 and has the original tank still (aluminum). Fuel pressure was good though and the plugs are not white they are just the right color

I would also check fuel volume as well, but it sounds like you have the bases covered.

 

[sparky774]

Re: 7.4 454 Repower opinions needed.

How do i check fuel volume?

I am considering getting a air fuel ratio gauge i have seen a few kits out there. Is that the same idea?

I was wondering if a small amount of water in gas could cause detonation without causing other problems like bogging bad idle etc.. i really dont think it could though.

 

[sparky774]

Re: 7.4 454 Repower opinions needed.

Just called rapido marine. They are out of stock of bigblocks, and he says he is probably going to have to phase out completely because he cant find any cores out there.

Right now my top choice for REMAN is michiganmotorz

If any one has a good supplier for remans OR good prices on genuine GM marine longbocks (new) please let me know.

Has anyone had dealings with 1800runsnew.com??

A few over on offshoreonly have had good experiences BUT i have also heard from more than one that they do not stand behind their products 100% they actually told one guy he would have to sue them to get any warranty money out of them (maybe bs)

 

[RogersJetboat454]

Re: 7.4 454 Repower opinions needed.

How do i check fuel volume?

Store bought or home made graduated (measuring) container of some kind. Don't have any volumes to shoot for off the top of my head, but an unrestricted big block fuel pump should be able to pump a good amount of fuel in a short amount of time.

I am considering getting a air fuel ratio gage i have seen a few kits out there. Is that the same idea?

Nope. An air fuel ratio gage uses a wide-band O2 sensor placed in the exhaust stream to measure the O2 content of the exhaust exiting the engine. O2 sensors don't particularly like working in wet environments (water cooled exhaust).

I was wondering if a small amount of water in gas could cause detonation without causing other problems like bogging bad idle etc.. i really dont think it could though.

Nope. From what I've heard, some of the old time racers usta mist water into the engine to prevent detonation. Any amount of water in your fuel would probably be causing a running condition.

 

[sparky774]

Re: 7.4 454 Repower opinions needed.

Well after doing some research i have eliminated 1800runsnew from my possible list of suppliers... they do not sell new gm marine engines as they state on their website. Heres the proof:

http://www.offshoreonly.com/forums/...r-opinion-marine-engines-inc-1800runsnew.html

Also they have no warranty to speak of at all despite the fact that they claim to be covered under GM powertrain warranty... all lies.

 

[joewithaboat]

Re: 7.4 454 Repower opinions needed.

lots of good info here and they have "NEW" GM

http://www.perfprotech.com/store/articles/7.4l_longblock_replacement.aspx

 

[Bondo]

Re: 7.4 454 Repower opinions needed.

I was wondering if a small amount of water in gas could cause detonation without causing other problems like bogging bad idle etc.. i really dont think it could though.

Nope. From what I've heard, some of the old time racers usta mist water into the engine to prevent detonation. Any amount of water in your fuel would probably be causing a running condition.

Ayuh,... Those ole Racers were mistin' water into the Intake, not in the Fuel....

I wouldn't discount Detonation til it's torn down...
Water don't burn like gas, 'n it's Replacin' the gas, not subsidizin' it...

I was gonna ask the same question, as to what's been killin' these motors...
'n I agree, it's probably not the builds...

 

[achris]

Re: 7.4 454 Repower opinions needed.

...
I was gonna ask the same question, as to what's been killin' these motors...
'n I agree, it's probably not the builds...

+1 for me too.

Fuel quantity and /or quality. Maybe a timing problem. From memory these use a mechanical advance inside the dissy. An old or broken spring might be causing the timing to advance too quickly, especially under load, which would account for dead engines.

just my 2c,

Chris.......

 

[joewithaboat]

Re: 7.4 454 Repower opinions needed.

hey Bond-o
I wonder if they have been changing the break in oil ??? LOL

 

[Bondo]

Re: 7.4 454 Repower opinions needed.

hey Bond-o
I wonder if they have been changing the break in oil ??? LOL

Ayuh,..... Donno,.... I'd call 10hrs. a 1/2 a break-in....

 

[joewithaboat]

Re: 7.4 454 Repower opinions needed.

Bond-o i know you think im nuts... But i didnt make it up
I get as much info as i can as i go, as to not have to learn everthing myself...
Thats why im here as well !
Dont you use a "new cam" in your "new/rebuilt" motors?
Please look here at Crane cams break in procedure as relates to oil ! You might have heard of them?

http://www.cranecams.com/uploads/instructions/214e.pdf

 

[Bondo]

Re: 7.4 454 Repower opinions needed.

Bond-o i know you think im nuts... But i didnt make it up
I get as much info as i can as i go, as to not have to learn everthing myself...
Thats why im here as well !
Dont you use a "new cam" in your "new/rebuilt" motors?
Please look here at Crane cams break in procedure as relates to oil ! You might have heard of them?

http://www.cranecams.com/uploads/instructions/214e.pdf

Nope, not at all,... We pretty much agree....

A cam is broken in, in 30 minutes...
A motor is broken in, in 20 hrs.... Under Load....

 

[joewithaboat]

Re: 7.4 454 Repower opinions needed.

Bondo im not arguing but to be clear... i know im carrying on from a previous post where i reminded a guy to change his first oil fill, often refured to as break in oil, and you disagreed.......
You run the first oil fill for 20 hrs ?

 

[achris]

Re: 7.4 454 Repower opinions needed.

Bondo im not arguing but to be clear... i know im carrying on from a previous post where i reminded a guy to change his first oil fill, often refured to as break in oil, and you disagreed.......
You run the first oil fill for 20 hrs ?

20 hrs is SOP... If the entire package is new, drive oil too....

And for me 'break-in oil' is just any cheap oil WITHOUT friction modifiers...

 

[joewithaboat]

Re: 7.4 454 Repower opinions needed.

20 hrs is SOP... If the entire package is new, drive oil too....

And for me 'break-in oil' is just any cheap oil WITHOUT friction modifiers...

Well it appears you are following mercruiser 20hour recomendations.... except they recommend
full synthetic,both of which i would tend to disagree with.
Im with you on the no friction modifiers. Amsoil has a special Break in oil, then on to full synthetic.
I bet mercruiser current procedures differ from old procedures based on late model stuff being roller vs flat tappet.

 

[achris]

Re: 7.4 454 Repower opinions needed.

...I bet Mercruiser current procedures differ from old procedures based on late model stuff being roller vs flat tappet.

Nope, still the same...