Bent Valve - 1994 5.0L Mercruiser Alpha

[gbarrett]

Bent a valve - heard it knock 3 or 4 times while running, took the valve cover off and found broken pushrod. I'm going to pull both heads tomorrow and take them to get them rebuilt at the local machine shop. I've built several car engines so the work doesn't intimidate me. Is there anything I should know apart from an ordinary Chevy small block? From what little info I can find online, it looks like the pushrods are the same length. I'll probably replace the timing chain and gears while I'm in there.

Anything else I should know?

Thanks!

Greg

 

[Bt Doctur]

Re: Bent Valve - 1994 5.0L Mercruiser Alpha

I would find out the how and why it happened. leaky riser rusting a valve guide?

 

[Scott Danforth]

Re: Bent Valve - 1994 5.0L Mercruiser Alpha

the difference between your 5.0 and one from a truck is the cam, gaskets, core plugs, and accessories. the block and heads are the same. my guess is like Bt Doctur mentioned. you have a leaky exhaust system and the valve stuck which lead to the failed pushrod. you should pull the manifolds and heads to do a full inspection.

 

[Volphin]

Re: Bent Valve - 1994 5.0L Mercruiser Alpha

Look for some late (98+) model Vortec heads if you want a nice upgrade. +1 on the manifolds! They are 17 years old... They should be pressure checked. Be careful not to tear the boots on removal. They will not go quietly.

V

 

[Scott Danforth]

Re: Bent Valve - 1994 5.0L Mercruiser Alpha

Look for some late (98+) model Vortec heads if you want a nice upgrade. +1 on the manifolds! They are 17 years old... They should be pressure checked. Be careful not to tear the boots on removal. They will not go quietly.

V

vortec heads came out in 96. the intake will need to be changed if you go with vortec heads

 

[Volphin]

Re: Bent Valve - 1994 5.0L Mercruiser Alpha

True but all did not have the kidney shaped combustion bowl. 98-on is safer bet.

V

 

[gbarrett]

Re: Bent Valve - 1994 5.0L Mercruiser Alpha

It's all apart. It looks like the riser one the port side may have a very small leak. No rust visible in the combustion chamber. I checked online and found a new set of cast iron risers & manifolds for $420. Does that sound about right? I assume there's no way to recondition the old risers. The local machine shop gave me a quote of $300 to rebuild the heads. So with new risers & manifolds, rebuilt heads and gaskets I guess I'm looking at $1000 or so.

Oh well, the boat was free and this is all I've had to put out on it since I got it in February.

 

[gbarrett]

Re: Bent Valve - 1994 5.0L Mercruiser Alpha

After looking at the manifolds, I don't see anything to make me think there's a crack in them. Do manifolds normally get replaced with the risers or are the risers the normal problem?