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

[riptorn]

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

Ok so basically next step is pull intake manifold pull lifter out and inspect for cupping ect and shine light to see what the cam lobe looks like. If cam lobe looks ok and lifter looks ok replace lifter. (cant a lifter be cupped or wear down without the cam lobe going bad?)

Lets see the #5 cam lobe

 

[Pete104]

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

Pete,

the pushrod seems to be moving the same as other but rocker dosnt seem to be pushing the valve down that is the issue. only reason i threw in thread count was because it shows that all are properly adjusted everywhere else. not sure what you are talking about blind person can accomplish. Lash is done I got that but there is an issue with what seems to be the #5 intake valve not opening up enough. Maybe i didnt explain myself well enough. I will post another video soon so you guys can see exactally what im talking about.

It's very difficult to see the pushrod/rocker move @ any engine speed, and take it for granted. It's merely a "start". You are either going to have to measure it with a dial indicator or physically inspect it.

The point I was trying to make was, you don't need to look at what your doing, YOU need to listen.
Let's see the video.

 

[joewithaboat]

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

It is not that bad of a job if you can get your seat out. Give us a video of the rocker in question and view of the seat. I'm sure it comes out.

Something else you can do is hook up your timing light and use it kinda like a strobe light. Shine it on the pushrods and valvetrain you will notice inconsistent movement, pushrods should actually spin. They usually are not when the lifter is going flat. It will also help see if the rocker is not moving as much.

If you have adjusted the lash it wont sound any different, especially if it is an intake lobe.

 

[Don S]

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

Cant say im very happy about this but with my luck I believe you guys are prolly right. Im going to go ahead and start pricing cams anything else i should go ahead and replace since im going to be in there anyway.

You don't need to be pricing anything right now, you need to find out what the problem is, and what all else you may need. If the lobe is gone as I suspect, where do you think all that metal went ??????? Into the pan and off to the oil pump. Guess what that means.

 

[FreeBeeTony]

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

My son and I just tore down an old Corvette block that was recently rebuilt........
It was really for a learning experience for him....to se the inards of a SBC.

Found 2 rounded lobes from opposing cylinders, lifters mushroomed.
Removed pistons, bearings seemed fine.
Removed main bearing caps.......all destroyed!!

This is what Dons is getting at.....the metal from the cam lobes gets distributed through the rest of the engine.

If the cam is shot.....I'd pull the engine, you'll find alot of metal in the pan.

 

[joewithaboat]

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

You don't need to be pricing anything right now, you need to find out what the problem is, and what all else you may need. If the lobe is gone as I suspect, where do you think all that metal went ??????? Into the pan and off to the oil pump. Guess what that means.

My son and I just tore down an old Corvette block that was recently rebuilt........
It was really for a learning experience for him....to se the inards of a SBC.

Found 2 rounded lobes from opposing cylinders, lifters mushroomed.
Removed pistons, bearings seemed fine.
Removed main bearing caps.......all destroyed!!

This is what Dons is getting at.....the metal from the cam lobes gets distributed through the rest of the engine.

If the cam is shot.....I'd pull the engine, you'll find alot of metal in the pan.

Guys,

I completely agree that the metal going through the engine is not good. Lets remember that is does have a filter.

I have changed several flat cams in engines that I personally owned, and dozens for friends, family and friends of friends. All of these engines ran for many thousands of miles (or hundreds of hours in boats) with absolutely no problems what so ever.

If his engine is otherwise healthy there is absolutely nothing wrong with just changing the cam and lifters.

 

[Don S]

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

If his engine is otherwise healthy there is absolutely nothing wrong with just changing the cam and lifters.

That might be your opinion, but not mine. And he doesn't know if the rest of the engine is healthy or not.

 

[joewithaboat]

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

That might be your opinion, but not mine. And he doesn't know if the rest of the engine is healthy or not.

So do you normally recommend to customers that an engine be pulled and torn down because it might have other problems? :facepalm: That would be thousands of dollars, if he pays someone to do it, and we have no indication of any bearing problems.
A cam kit, if it is a flat tappet, and gaskets are only $200.00-$300.00 max.

 

[FreeBeeTony]

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

So do you normally recommend to customers that an engine be pulled and torn down because it might have other problems?

After seeing what I saw this w/e on this Corvette block.........I'd pull it if it were my boat, maybe not a car........but being stuck on the water is a bit different.

 

[Don S]

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

So do you normally recommend to customers that an engine be pulled and torn down because it might have other problems?

When a cam lobe is missing, I tell them about it, and yes I even recommend an engine be pulled and the pan dropped and checked for metal. I also tell them that many have replaced the cam and lifters without pulling the pan. Then I let them make the money decision.

 

[joewithaboat]

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

After seeing what I saw this w/e on this Corvette block.........I'd pull it if it were my boat, maybe not a car........but being stuck on the water is a bit different.

No offense but what does worn mains on your corvette engine have to do with a flat cam lobe on the o/p's engine?

 

[joewithaboat]

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

When a cam lobe is missing, I tell them about it, and yes I even recommend an engine be pulled and the pan dropped and checked for metal. I also tell them that many have replaced the cam and lifters without pulling the pan. Then I let them make the money decision.

That's good advice... to those that choose not to do the tear down, sell them a big magnetic drain plug. Might extend there run time.

 

[coopin87]

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

Ok guys so work has picked up and I dont have time to do everything myself. Took the boat to a reputable shop today to have them verify the problem so I can go from there. If it is the cam what else do you guys recomend me to replace while the motor is pulled apart. I will update you guys again tomorrow when the shop calls me. To be honest I want to make sure that while everything is apart I do as much as possible to make sure its good to go for this summer. Not sure if the motor will need to come out yet or not seat looks like it can be removed and if it can be the pan can be dropped with it sitting in there or so it would seem (lots of room underneath the motor).

 

[Bondo]

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

Ok guys so work has picked up and I dont have time to do everything myself. Took the boat to a reputable shop today to have them verify the problem so I can go from there. If it is the cam what else do you guys recomend me to replace while the motor is pulled apart. I will update you guys again tomorrow when the shop calls me. To be honest I want to make sure that while everything is apart I do as much as possible to make sure its good to go for this summer. Not sure if the motor will need to come out yet or not seat looks like it can be removed and if it can be the pan can be dropped with it sitting in there or so it would seem (lots of room underneath the motor).

Ayuh,.... I think ya wanta quit thinkin' 'bout doin' Anything, In the boat....

If the cam is Wiped out, the motor's Gotta come Out....
Even if ya got the base off, how ya gonna flip the motor over to look at Anything,..??

Yank it, 'n bolt it on a stand...

 

[joewithaboat]

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

Ayuh,.... I think ya wanta quit thinkin' 'bout doin' Anything, In the boat....

If the cam is Wiped out, the motor's Gotta come Out....
Even if ya got the base off, how ya gonna flip the motor over to look at Anything,..??

Yank it, 'n bolt it on a stand...

Why do you have to pull an engine to replace a cam with a flat lobe?

 

[Don S]

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

Why do you have to pull an engine to replace a cam with a flat lobe?

Not again :facepalm: Ever get the feeling that most people think pulling the engine due to a wiped lobe on the cam is a good idea? What happened to all that missing metal ?
You made your statement, is it really necessary to cross examine everyone that says pull the engine ???????

 

[Bondo]

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

Why do you have to pull an engine to replace a cam with a flat lobe?

Well,.... The timing cover is comin' off, so the base is comin' off,...

For that alone, it's Easier to do on a stand....

Pullin' a boat motor Ain't a Big Deal,...
'ell,... There's Alota barges out there that pullin' the motor is step #1, if ya wanta change the Spark plugs, muchless the Starter....

It's a fact of life,.. If ya wanta play a Boat Mechanic, it takes Tools to do the job....

 

[joewithaboat]

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

Not again :facepalm: Ever get the feeling that most people think pulling the engine due to a wiped lobe on the cam is a good idea? What happened to all that missing metal ?
You made your statement, is it really necessary to cross examine everyone that says pull the engine ???????

I am assuming that the two of you are boat mechanics based on reading your posts for months now... You guys share lots great insight on boat specific things that not many folks learn about from just owning/maintaining a boat. The two of you often pinpoint problems quickly and offer sound solutions and that's great. That's why i originally came here to gain info without having to go through it myself.

Now i know a ton about automotive engines, which is all a in/out boat engine is. When a cam lobe goes flat it does so over many millions of rotations it doesn't just happen. The metal from this will be very fine. The oil pump flow in a small block chevy can be measured in gpm, the oil is filtered many times over and this fine metal is removed by the filter. If there was a piece of metal banging around getting tossed up repeatedly against the bottom of the piston skirts or cylinder walls that wont be held down by a magnetic plug (if you smart enough to be using one) you would be smart to go after it. There wont be anything to find from a flat lobe. You guys are being "salesmen mechanics" and advocating much money to be spent unnecessarily.

As i said previously i have replaced countless flat tappet cams with worn or completely flat lobes in engines that gave many miles or hours of service afterward.

 

[joewithaboat]

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

Well,.... The timing cover is comin' off, so the base is comin' off,...

For that alone, it's Easier to do on a stand....

Pullin' a boat motor Ain't a Big Deal,...
'ell,... There's Alota barges out there that pullin' the motor is step #1, if ya wanta change the Spark plugs, muchless the Starter....

It's a fact of life,.. If ya wanta play a Boat Mechanic, it takes Tools to do the job....

So because i drop the engine to change spark plugs on Turbo Porsche now i tell everyone they need to drop there engine to change plugs.... your logic is a little messed up.

Just because you would rather be paid to pull an engine doesn't mean it must come out for a DIY guy to swap a camshaft.

 

[joewithaboat]

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

What do you guys charge to swap a cam, pulling the engine and putting it back????