1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

[joewithaboat]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Ok that makes a little more sense to me. So basically what your telling me is when I do need to have everything redone I should just buy a new long block instead of having the one I have now refreshed.

Correct, 350 blocks are plentiful enough that most of the time it is smart to start with a fresh one as to not have to sonic check the wall thickness.

If we have a block that we have spent money on in other areas... line hone & fitted with aftermarket caps, zero decked, lifter bore mods etc. We will go to .060 after checking wall thickness. Most of the time the walls will become pitted from the sand casting before they get too thin.

 

[coopin87]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Well just got back from running to the machine shop and dropping heads off at the shop. Hopefully everything will be all put back together at the end of the day tomorrow. For anyone interested in the cost here it is ... $350 for valve job/resurfacing heads ... $600 to pull and replace motor ... $600 additional labor to fix all the issues ... $650 in parts to include exhaust butterflies, outdrive seals, all new lifters, head gaskets, all other top end gaskets, oil ect. bringing the grand total to about $2200 not including my new ignition system. But on the bright side I will be back on the water and have some peice of mind (I guess) lol.

 

[coopin87]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Well got some really irritating news today ... Got a call from the shop saying it does need a cam. Mechanic did not check it in the first place like I asked so needless to say It will not be done this weekend. Any way since it is not going to be ready this weekend I went ahead and decided to put a little bit larger cam in it (two sizes up from stock), new intake manifold and a four barrel carb. Couldnt pass it up for $175 for the lot. Just figured you guys would want to know that the cam was bad like origonally suspected. Maybe I will go boating next weekend if im lucky :/

 

[QC]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Absolutely confirm that cam is marine!!!! If you or they don't understand, search "reversion". You cannot use street mod cams in a boat with wet exhaust. I don't believe that has been discussed in this thread.

 

[coopin87]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

What is the difference between a marine cam and a auto cam?

 

[QC]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

The difference is in the overlap of Intake and Exhaust. A radical Auto cam will suck water in the exhaust back into the intake (reversion) and it can only happen with wet exhaust as in a boat. Not an issue with cars. It's a big deal, and you need to confirm what you're getting meets marine specs.

 

[coopin87]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

The difference is in the overlap of Intake and Exhaust. A radical Auto cam will suck water in the exhaust back into the intake (reversion) and it can only happen with wet exhaust as in a boat. Not an issue with cars. It's a big deal, and you need to confirm what you're getting meets marine specs.

I will make sure first thing tuesday morning. Thanks for letting me know I had no idea that could happen. Does make sense though.

 

[QC]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Actually, I misstated that, the water is sucked back into the cylinder, not back into the intake. Same result = bad.

 

[joewithaboat]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Well got some really irritating news today ... Got a call from the shop saying it does need a cam. Mechanic did not check it in the first place like I asked so needless to say It will not be done this weekend. Any way since it is not going to be ready this weekend I went ahead and decided to put a little bit larger cam in it (two sizes up from stock), new intake manifold and a four barrel carb. Couldnt pass it up for $175 for the lot. Just figured you guys would want to know that the cam was bad like origonally suspected. Maybe I will go boating next weekend if im lucky :/

I figured the cam would be bad. Sorry!

How are you getting a new intake, cam, and carb for $175.00? I'm always suspicious if it sounds too good to be true, which that does. It must all be used parts?

 

[coopin87]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Just intake, and 4 barrel for $175. The cam cost me $130 with lifters but the one i bought I believe it is automotive.

 

[coopin87]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Intake and carb are used

 

[joewithaboat]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Just intake, and 4 barrel for $175. The cam cost me $130 with lifters but the one i bought I believe it is automotive.

Intake and carb are used

Just a reminder... carb needs to be "marine" also.

Get the part number for the cam & lifter kit and post it if you can.

 

[coopin87]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Ok so I did a little more checking on the cam. The one i bought is actually an RV cam. I called around to a reputable marine engine builder and he said that cam will be fine. The Carb and intake are coming off of another engine that the block is bad on (head gasket blew and they kept driving the boat) it is a quadrajet and the intake is a high rise cast intake. Im also taking the circulating pump off of the other motor because mine is shot.

 

[QC]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Yes, what are typically called RV/Truck cams are a good match.

 

[coopin87]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Well everything is back together and I'm going to get the boat tonight as long as it passes the mechanics water test. Ended up putting a new starter on it as well since the old one was hanging up a bit. total work done
pull and replace motor ... $600
Other labor .... $600
4 barrel carb, high rise intake, circulation pump ... $200
Cam and lifters ... $150
Starter ... $200
Gaskets ect ... $250ish
extra prop ... $30
Exhaust butterflies ... $200
Head work $350
Outdrive parts ... $250
Drain plug hose kit (will be nice to get everything out) ... $50
After everything is said and done im into the drivetrain for about $3000 just in case any of you were wondering

 

[joewithaboat]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Well everything is back together and I'm going to get the boat tonight as long as it passes the mechanics water test. Ended up putting a new starter on it as well since the old one was hanging up a bit. total work done
pull and replace motor ... $600
Other labor .... $600
4 barrel carb, high rise intake, circulation pump ... $200
Cam and lifters ... $150
Starter ... $200
Gaskets ect ... $250ish
extra prop ... $30
Exhaust butterflies ... $200
Head work $350
Outdrive parts ... $250
Drain plug hose kit (will be nice to get everything out) ... $50
After everything is said and done im into the drivetrain for about $3000 just in case any of you were wondering

Im glad someone can afford to stimulate the economy. LOL

Sounds like they covered a lot of areas,
Good luck with everything!

 

[riptorn]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

For 3gs, if you can get three years trouble free your laughing. Just take is easy on the motor till all the seals and gaskets mate.
Good luck.

 

[tmurphy1602]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

ok i need to chime in here, i just rebuilt a motor for my boat, i used a 79 vet block and was planning on reworking the marine parts from the cruiser 260 that the block cracked.. i was totally convinced that auto engines are different than marine.... Wrong!! maybe today they are but not 15 years ago, there was no s/s crank in my block, bearings .. all the same as a stock 350, i still have all the parts.. so i don't care what people spout!! back then they are the same... minus carb, had some venting so they don't explode, even now most differences in marine and auto engine are if the the boat is a salty... this is when corrision is an issue, ive done my home work and now have a 400hp 350 in my boat to prove it.. if you need advice just pm me, there are a few mods you need to be aware of but nothing that will cause shortened engine life or performance!

 

[tmurphy1602]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

Ok so I did a little more checking on the cam. The one i bought is actually an RV cam. I called around to a reputable marine engine builder and he said that cam will be fine. The Carb and intake are coming off of another engine that the block is bad on (head gasket blew and they kept driving the boat) it is a quadrajet and the intake is a high rise cast intake. Im also taking the circulating pump off of the other motor because mine is shot.

RV stands for recreational vehicle, as in Motor home, it will make more pulling power at lower RPM, which should be great for marine use , due to the longer duration of an RV cam it does give them a nice throaty timbre, but its far from a race cam designed for high RPM.

as for inversion or sucking water just because its a AUTOMOTIVE cam.... lol like 99.9 percent of the rest of marine engines dosent mean it will be a problem,


with cams you need to know a few things, mostly for our purpose, there are 3 MAIN breeds of cam,

1, 60s -70s cams, single pattern,

2, split duration cam recommended for most marine uses, exhaust having a longer duration and higher lift, makes up for how restrictive most marine exhausts are, more gases going out means no water coming in!!

3, The equal duration/equal lift cams are for higher rpm uses, like a performance 350, now these do have a risk of sucking water IF you dont do your home work, so with that been said, i guess thats why we have thru-hull exhaust ehh??


if half the guys out there understood THE minor differences in auto/marine applications, instead of just pointing out obvious things like " oh is that a marine cam" as if they know what there talking about, maybe you would have a few Gs back in your pocket,

 

[riptorn]

Re: 1996 mercruiser 5.7 with thunderbolt ignition ... Top End knock Please Help

No comment.