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

[Idlespeedonly]

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

It wouldnt hurt to pull the pan like checkmate suggested. You already have it out. Now I wouldnt replace the cam if the lobes are good. Especially the one that had the bad lifter. As for the heads, if they check good, mainly guides and seals I would probably let them go. If you keep the boat, sooner or later it will be time for a rebuild or replacement. Alot of this is preference and what you feel comfortable doing. I think you will be ok no matter which way you go with this.

 

[coopin87]

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

Well he did a leak down test and cylinders 1,2, and 5 are leaking a bit. Would you worry about this or just have him put a new lifter in and let the heads run? I found a set of used 350 heads (4 bolt) for $500 at the machine shop for sale. Or they want $300 to do the valve job on both heads plust the cost of parts.

 

[joewithaboat]

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

Forgive me for not remembering, did we ever confirm that this was indeed a roller cam?

If so i would replace all of the lifters if the cam looks unharmed.

If it is a flat tappet it gets new cam and lifters if it were mine and i planed to keep it.

The valves get burned from the lifters being set too tight. The lifter pumps up at high rpm and effectively grows the pushrod length. This holds the valves open a bit and cuts off heat transfer across the seat. Causing the burn or tulip.
Running them tight is also hard on the internals of the lifter.

If I have the engine out and on the stand there is no way I'm not checking the bearing clearances, Rods and mains. Remember the low oil to the top. It could be the lifters but the bottom end could be well worn also.

keep us posted, good luck!

 

[Idlespeedonly]

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

500 for the used heads is way to high since you may not know the condition of them. They maybe no better than what you have. FYI there isnt any such thing as a 4 bolt head. Just blocks. I honestly would leave them alone. But again it is your preference. Maybe have them check the bottom end out and see how that looks. If everything looks great then the head job may be worth doing. Talk to the machinist, some will be very honest with you. Sometimes their opinion may be the best.

 

[joewithaboat]

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

I'm not reading back thru 7 pages...
If memory serves me you have aftermarket heads on this rig, right? Do the valve job if they need it.
Your saying it has burned valves based on what?

 

[Idlespeedonly]

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

I thought this was a roller. But if not, like Joe suggested a new cam is what you have to get.

 

[coopin87]

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

I was reffering to the four bolts that hold the valve cover on (vortec heads i believe. He checked out the rest of the motor and said it looks great for the age ect. No other found issues I did ask him to look at everything. Joe I think it is a roller cam but dont know for sure I will look into it. I will make sure if it is a roller that all of the lifters are replaced. if it is a flat tappet then I guess I will have him change the cam as well. So as for the heads the ones for sale at the machine shop have been tested there and are said to be good to go. as for my heads if I decide to keep them should I just go ahead and have them taken to the machine shop to do a full valve job or should i just leave them on and run the boat till they go completely? What issues will i have if the heads are not redone ect. The low oil at the top was because the lash was so tight. when adjusted properly there was ample oil flow.

 

[coopin87]

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

They are aftermarket heads ... the mechanic is saying it needs valve job. He performed the leakdown test apparently.

 

[Idlespeedonly]

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

Dont mean to pick at you, Just trying to teach to help you out. You need to know this. There is center bolt and perimeter bolt. Perimeter bolt is 85 and older (i believe). 86 and newer in center bolt. Now both styles are still 4 bolt. Not all center bolt are vortec. Just telling you this so you do buy somebodys 4 bolt heads thinking they are what you need. Joe may disagree, but I would just replace the bad lifter. Lifters generally will outlast an engine. If the mechanic says to do the heads, then you should. Now just because they fail leak down doesnt mean you have burnt valves either.

 

[tpenfield]

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

OK guys. I just got word from the mechanic. Motor is out and he said cam is good. One of the lifters was shot. And i have a few burnt valves. Cost me $600 just to have him pull diagnose and put motor back in now i have to decide if I want to put new heads on it or just have a valve job done on my current heads. Any sugestions? I would really like the boat done by this weekend. :/ not sure if that is going to happen though.

My $0.02 . . .

Just have the valve job done . . . (I figured that the mechanic would find a bad lifter) . . . I do not think you need to tear into the 'bottom end' unless issues are found once the pistons/cylinder walls are exposed. The valve job should take care of the leaky cylinders.

Once the mechanic pulls the heads, he/you will be able to determine if new heads are a better/cheaper way to go. So, if the existing heads needed all kinds of work to fix valve seats, etc., then new heads might be a less expensive way to go. If the valves & seats can be fixed up with a little grinding, then that might be the way to go.

Thanks for the update . . .

 

[81 Checkmate]

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

Like someone said..... You are gona have to do a rebild sooner or later...

If they are vortec heads have them done at $300 and then you have good heads for the next rebuild.

If you dont have the xtra money, Slap it back together with a new lifter and go boating!

Just a thought!

 

[bugging57]

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

You have aftermarket heads that are a performance upgrade over stock. Don't buy a set of stock heads and rebuild them. Fix the heads you have. Recut the valves and seats, put guides in if necessary, put in new valve seals and go with them. As far as the rest of the engines goes....I would go through the shortblock and replace the cam and lifters. You already have it out and will be taking of the heads. The labor and gasket cost will have to be paid out again when you rebuild it if you dont do it now. $600 plus gaskets will go a long ways towards refreshing this block.

1. Hone and re-ring the cylinders if they are still round and within spec. Otherwise, bore them and put in new hyperetic pistons.
2. Check the main and rod bearings with a plastigage, replace if not within spec.
3. Replace the cam bearings.
4. Replace the oil pump and clean out the oil pan and oil pick up.
5. Have the Starter and Alternator tested by an auto electric shop while you have it out. They can check the brushes and armatures on a bench without taking them apart. If they cant do that then you didn't take it to the right place.
6. Did you replace the whole ignition system? If not have the coil tested and replace the dizzy. New plugs and wires.
7. Put it all together with new, quality gaskets and call it good.
8. Enjoy this boating season and many more knowing you have a reliable engine and not one that will leave you stranded because you saved a few bucks back in May of 2012....

Glen

 

[joewithaboat]

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

Leak-down can show bad for several reasons.

Vortec heads will likely outflow your very good s/r torquer's.

Its very hard to diagnose an engine from the internet. If you have found a good mechanic than I would go with his recommendations until he gives us a reason not to. LOL.

My method of thinking is usually 1 of 2.

1- Do as little as reasonably possible and cross your fingers. Budget friendly.

2- Check everything and spend what ever is necessary.

I find that an awful lot of roller cams that have lifter problems, are shot and will have problems soon again if not properly diagnosed.

 

[coopin87]

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

Ok guys so here is a little update I went out this afternoon to look at everything. Good news is it is a remanned block with low hours on it based on the carbon deposits around the tops of the cylinders. Bad news is it is bored 40 over. I took the heads to the machine shop this afternoon and they should be done sometime Friday (fingers crossed) for about $350. Im going to have the guy go ahead and put a new gimble berring in it while he has the outdrive off. He is also replacing exhaust flappers because they are shot. It is a good thing I had him pull the heads because the head gaskets were not great looked like there was some blow by happening in the middle of the block on both sides. Cam is good so im going to leave it alone. All lifters are being replaced and hopefully I will have the boat on the water by saturday evening or sunday morning.

 

[joewithaboat]

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

Ok guys so here is a little update I went out this afternoon to look at everything. Good news is it is a remanned block with low hours on it based on the carbon deposits around the tops of the cylinders. Bad news is it is bored 40 over. I took the heads to the machine shop this afternoon and they should be done sometime Friday (fingers crossed) for about $350. Im going to have the guy go ahead and put a new gimble berring in it while he has the outdrive off. He is also replacing exhaust flappers because they are shot. It is a good thing I had him pull the heads because the head gaskets were not great looked like there was some blow by happening in the middle of the block on both sides. Cam is good so im going to leave it alone. All lifters are being replaced and hopefully I will have the boat on the water by saturday evening or sunday morning.

Nothing wrong with .040 over

If the head gaskets were not sealing well i would make sure and surface the heads while you have them off.

Id go with the good Felpro perma torque stainless based "blue" head gaskets to make the best of not being able to surface the deck.

Use good sealer on the head bolts.

Have fun on the water!

 

[81 Checkmate]

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

Glad to here the good news Coppin!

Looks like we are going to have some great boaten weather this weekend.....

 

[coopin87]

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

Yeah weather is looking great for this weekend just hope it all comes together so I can enjoy it on my own rig and not have to bum a ride lol.

 

[coopin87]

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

Nothing wrong with .040 over

If the head gaskets were not sealing well i would make sure and surface the heads while you have them off.

Id go with the good Felpro perma torque stainless based "blue" head gaskets to make the best of not being able to surface the deck.

Use good sealer on the head bolts.

Have fun on the water!

I thought .040 was a little much when dealing with a boat motor. Guess it will be all good as long as it is properly winterized in time every year. The machine shop is going to make sure the heads are true I made sure to ask them before I left. Im not sure what gaskets the mechanic is using but I will be sure to ask him. Thanks for all the input joe.

 

[joewithaboat]

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

The difference between .030 and .040 is .005 per side.... which is less than the thickness of of two sheets of printer paper.

Most 350 blocks are OK to .060 over but you should start really paying attention to core shift after .040.

 

[coopin87]

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

The difference between .030 and .040 is .005 per side.... which is less than the thickness of of two sheets of printer paper.

Most 350 blocks are OK to .060 over but you should start really paying attention to core shift after .040.

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.