Cracked manifold questions

[lcmains1]

Hi everyone,

I just bought a boat that has an 89 mercruiser 5.0, I didn't even notice, but the guy who sold it to me had some jb weld on each of the exhaust manifolds (I called him back and he said it was like that for years). One is leaking very slowly and the other not at all. I have backed the boat down the ramp and ran the engine for about 5 minutes on the trailer. The engine starts excellent, shifts great and the oil seemed to be fine after the 5 minutes. I have decided to replace the manifolds as it just seems cheaper than taking a chance that they are leaking internally.

I have looked very close and the block seems to be fine, no visible cracks. Do I need to replace the risers also? I was planning to inspect them and use the same ones if they looked ok.

Any advice would be much appreciated!

Thanks,

 

[300sflyer]

Re: Cracked manifold questions

First thing I would do, is back the boat down the ramp again, and take it out for a 15-20 minute run. Then check the oil again to confirm the block is not cracked. Then if there is no water in the oil, replace the manifolds and risers.

 

[Fishermark]

Re: Cracked manifold questions

I would certainly check the risers well - and replace if there is any doubt. They are cheaper than manifolds and more prone to fail. You might even find a good deal with a manifold riser combination.

 

[HT32BSX115]

Re: Cracked manifold questions

Howdy,

Welcome to iBoats!

Well, you didn't say salt or fresh water but I'm with Fishermark........I would just get a "kit" (available right here on iBoats too)

If the engine is in otherwise good condition, new manifolds and risers will give you a measure of confidence.


Cheers,


Rick

 

[lcmains1]

Re: Cracked manifold questions

Ok, So i got the manifolds off last night. It appears the guy may have been honest with me.... I could not see any cracks on the inside of the manifolds. The risers look to be in good shape. The new manifolds should be here today! I plan to put these suckers on and be on the water for Memorial Day.

My question is.... When putting this back together, should I use any gasket sealer to seal things up good?

Thanks for your help, it is appreciated

 

[Bondo]

Re: Cracked manifold questions

My question is.... When putting this back together, should I use any gasket sealer to seal things up good?

Nope,... Fresh gaskets on CLEAN surfaces is usually the way to go...

 

[Fishermark]

Re: Cracked manifold questions

Just to add to what Bond-o writes - be sure to use good gaskets - especially between the manifold and riser. If your manifold came with the green paper gaskets, go ahead and throw those away and get the OEM gasket. It will be a grey - graphite type of gasket which goes on dry.

 

[lcmains1]

Re: Cracked manifold questions

Will do, what is the issue with the green ones? I have noticed that mentioned a couple times. I want to do it right, I really don't want to have have to take it all apart agian.

 

[Fishermark]

Re: Cracked manifold questions

what is the issue with the green ones?

They are simply cheap, aftermarket gaskets that do not work well. I am usually a big believer and user of aftermarket stuff. But some things just aren't worth the aggravation - and this is one area where a leak can cause big problems. And that means more money and problems down the road.

 

[Flysfloatsor]

Re: Cracked manifold questions

You did the right thing replacing them. Now you wont have to worry about it for a long time. (all cast manifolds wear out eventually)

 

[lcmains1]

Re: Cracked manifold questions

I will beinstalling the new ones tonight!
Does anyone know that torque or where can i find it? I need it for the manifold bolts and the riser bolts also. I have seen 25 for the manifolds and 35 for the risers, is this correct. I found this from a google search.

Thanks for all the help, I will let you know the outcome.

 

[Bondo]

Re: Cracked manifold questions

Ayuh,... I use my calibrated elbow, but 35ft.lbs. is about right...

 

[lcmains1]

Re: Cracked manifold questions

So i got these off last night and have the new manifolds on. I replaced theplugs while they were out of the way also, much easier to do that with the manifold off!

I have one more question though, why is one side of the riser mostly blocked from water flow with the gasket. (it just has 2 small pinholes in it) I know that it is correct as that is what came off, I was just curious if anyone knew why?

Thanks, I am going to fire this bad boy up tonight!!!
WOO HOO

 

[Bondo]

Re: Cracked manifold questions

why is one side of the riser mostly blocked from water flow with the gasket.

Ayuh,... To regulate the flows...

 

[brhodes]

Re: Cracked manifold questions

I have this project coming up in the near future. If you don't mind me asking, what type of manifolds did ya order/put on. Please report back after you crank it up with the good news.

 

[lcmains1]

Re: Cracked manifold questions

Ok, So I got the rest of the parts on and went to fire this thing up...... It started up without any issues, ran it up to temp and looked for leaks, notiiced nothing! It runs like new and no leaks, no water in the oil. Looks like it will be a good boating season for us!

I bought the parts from wholesale marine. They were Sierria brand, they came with the crappy gaskets but I bought different ones (OEM)
A few suggestions if you do this on your boat...

1. Plan to replace the plugs with the manifolds are off, they are very easy to get to.
2. Plan to replace the hoses that need to come off. They are very difficult to get off without tearing.
3. Plan more time than you think, I planned about 5 hours and ended up with about 8.

It was a fairly easy project, I would say that if you are mehanically inclined at all you can save yourself about $600 in labor from a shop doing this.
Thanks for all the help guys!

 

[Ancloter]

Re: Cracked manifold questions

Having done this repair in a different context I will offer a word of caution. The OEM elbow riser gaskets are unsat! They will come back to bite you ITA. They are paper. Water will eventually work its way through them and end up draining into the rear cylinders at shutdown. Then the head, piston or block blows -as you can frequently read about on these forums. My advice is to pull the gaskets and replace them with siliconed versions which prevent water intrusion into the gasket. I use Permatex RTV Blue and completely saturate the gaskets, including the edges, particularly around water jacket ports. Do this and you'll save the engine from blowing one day. Otherwise be wary of the start-knock from water in the rear cylinders because it will eventually happen when the (paper) elbow riser gasket fails.

The elbow risers have more metal to the outside then from the water jacket to the inside so gasket failures will occur inside first and won't be visible.

Also, did you use the same freeze plugs as the old manifolds? Prior Owner likely neglected to drain the engine before a freeze causing the cracked manifold in the water jacket section (you mentioned water leak). In this case that = freeze plug failure.

JB Weld for a cracked exhaust manifold water jacket is a legitimate repair. Old freeze plugs and paper elbow riser gaskets are not legitimate repairs. Both will contribute to future failures.

 

[Don S]

Re: Cracked manifold questions

The OEM elbow riser gaskets are unsat! They will come back to bite you ITA. They are paper.

The old ones were paper, but that changed in 99 with new types of gaskets. You DO NOT use RTV on them, they go on dry as per this Mercruiser service bulletin.
The OEM elbow riser gaskets are unsat! They will come back to bite you ITA. They are paper.