Method for pressure testing exhaust manifolds

[donmagicjuan]

Hello all. I have an 87-95 Merc 350 (4bbl) direct drive with the center riser style exhaust manifolds. I recently replaced the engine with a reman due to a cracked block (I was unable to winterize the boat last year, but I'll welcome your harrassment for it anyway), and I reused the exhaust manifolds from the original engine. I believe I tested them to be ok, but now I'm second guessing myself and would like to hear your thoughts.

In my mind, the ideal method for testing the manifolds would be a leakdown test by sealing off the water entrance/exits and filling the water side with compressed air. However, I was having trouble coming up with a way to seal off just the water exits. Instead, I hooked up a garden hose to the water inlet hose and ran water through the manifolds for an extended period of time until I was satisfied that nothing was making its way into the exhaust side. I've since installed them on the engine, and everything seems to be ok (new engine has 6.5 hrs), but as I said, I've started to second guess myself. The main reason is because of the additional smoke that's been coming from the valve cover breathers on the new engine.

Here are the specific questions I have:

1) Is the smoke from the valve cover breathers normal during engine break-in as the rings seat to the cylinder walls, or is this primarily an indication of water entering the cylinders?

2) Do you think the method I used to test the manifolds is sufficient, or would you recommend a different procedure (or a trip to the shop with them)?

Thanks,
Don

 

[jerryjerry05]

Re: Method for pressure testing exhaust manifolds

A new motor shouldn't have blow-by. Lots of smoke then do a comp test.Are the valves set right?If your block was cracked then it's VERY possible your manifold/risers are bad too.They usually go before the block.The only way to pressure test a riser is with big dowels in the exhaust riser boots.
Remove the man/riser ,then block off the exhaust with pieces of wood dowel 3- 3 1/2" pieces of wood.hook an airline to the inlet hose and only put in a few pounds of pressure . Check for leaks.Jerry

 

[donmagicjuan]

Re: Method for pressure testing exhaust manifolds

Jerry,

Thank you very much for your reply. I actually had another issue that prompted me to do a compression check already, which turned out to be a broken valve spring. The inherent risks of a remanufactured engine, I guess. I'm still waiting on the replacement, but the other 7 cylinders all tested at 165-175 psi. By the valves being set correctly do you mean the lash adjustment? I was considering doing that at the first oil change, but with the compression numbers I'm seeing, I don't think the smoke is related to the valve adjustment. I could be wrong though.

Regarding the pressure test, I don't quite follow what you're saying. Which port are you plugging with the dowels? It sounds like you're talking about the end of the hose that connects to the muffler, but that's after the exhaust and water recombine, and I can't see how that would allow me to pressurize the water side. Are you talking about testing the manifold and riser separately or assembled as one unit?

Don

 

[jerryjerry05]

Re: Method for pressure testing exhaust manifolds

As a unit.Jerry

 

[donmagicjuan]

Re: Method for pressure testing exhaust manifolds

I think I'll try to block off the exhaust section of the riser before the elbow with a dowel as you suggested, then reconnect the elbow/hose and seal the end of that as well with a PVC end cap and the hose clamp. Does that sound right or am I still not getting this?

 

[donmagicjuan]

Re: Method for pressure testing exhaust manifolds

Just a quick update:

I was never able to completely seal off the exhaust port of the riser using the above method due to its irregular shape, so the pressure test never happened for me. I did, however, retry the original garden hose test, but this time the results weren't so great. An interesting observation during this test was that the risers showed zero signs of leaking as long as I had the water running through them. It wasn't till I shut it off that a small amount trickled down into the exhaust manifold. I'm not thrilled about replacing them, but I am at least relieved to know they're probably what was causing my smoking problem (or steaming, as it were).

 

[Haut Medoc]

Re: Method for pressure testing exhaust manifolds

12 year old mans/risers with a new engine?.....
Replace them......​

 

[donmagicjuan]

Re: Method for pressure testing exhaust manifolds

Heh, well for what it's worth I don't run them in salt water, but I see your point.

 

[michigan353]

Re: Method for pressure testing exhaust manifolds

A little off topic but I was wondering a good place to get a 'new' engine block. Don't want to spend a ton of money, just something to get me a few more years. I currently have a 1987 Four Winns 190 Horizon Mercruiser 4.3L 175hp I/O. Any suggestions?

 

[TilliamWe]

Re: Method for pressure testing exhaust manifolds

Just a quick update:
An interesting observation during this test was that the risers showed zero signs of leaking as long as I had the water running through them. It wasn't till I shut it off that a small amount trickled down into the exhaust manifold.

And that is exactly what happens when you turn off your boat. The water remaining in them leaks into the exhaust ports and into any cylinder with an open exhaust valve. You're lucky you didn't hydrolock or rust up a piston in your "brand new" remanufactured engine.

 

[bamadave]

Re: Method for pressure testing exhaust manifolds

Michigan, start a new thread. You won't get any responce asking a question unrelated to other thread.

 

[donmagicjuan]

Re: Method for pressure testing exhaust manifolds

And that is exactly what happens when you turn off your boat. The water remaining in them leaks into the exhaust ports and into any cylinder with an open exhaust valve. You're lucky you didn't hydrolock or rust up a piston in your "brand new" remanufactured engine.

Right. I get the rusted piston issue, and I agree with it, but I'm not sure I subscribe to the "hydraulic lock caused by a cracked manifold" theory. An open exhaust valve indicates the piston is on the exhaust stroke, meaning as soon as you begin to turn over the engine, the water in the cylinder will be immediately forced out. Unless you're "unlucky" enough to have an exhaust valve open in the overlap portion of the intake stroke, the hydro-lock concern just doesn't seem as valid as all the fearmongering would suggest.

 

[bruceb58]

Re: Method for pressure testing exhaust manifolds

When you take your risers off and put them back together again are you using a new riser gasket everytime? You should. Are the mating surfaces between the riser and the manifold both checked for flatness?

The ideal way to pressure test is to get a plate that covers the riser joint connection and pressurize from the water inlet.

Is this smoke you are seeing or steam? If water gets into the cylinder because of the leaking manifold, some may leak past the rings over time and get into the oil which could explain steam coming out. Of course, you oil would also probably appear milky if this was happening

 

[bruceb58]

Re: Method for pressure testing exhaust manifolds

Right. I get the rusted piston issue, and I agree with it, but I'm not sure I subscribe to the "hydraulic lock caused by a cracked manifold" theory. An open exhaust valve indicates the piston is on the exhaust stroke, meaning as soon as you begin to turn over the engine, the water in the cylinder will be immediately forced out. Unless you're "unlucky" enough to have an exhaust valve open in the overlap portion of the intake stroke, the hydro-lock concern just doesn't seem as valid as all the fearmongering would suggest.

I believe you are assuming ALL the water would be expelled during the exhaust stroke. I don't think you can assume that.

How would you explain all the people that have hydrolocked with getting water in by shutting their engine while the boat is moving? The water that enters is of course entering when the exhaust valve is open. If the engine really could expell all the water during the subsequent exhaust stroke, we wouldn't have these issues but we do.

 

[donmagicjuan]

Re: Method for pressure testing exhaust manifolds

I believe you are assuming ALL the water would be expelled during the exhaust stroke. I don't think you can assume that.

How would you explain all the people that have hydrolocked with getting water in by shutting their engine while the boat is moving? The water that enters is of course entering when the exhaust valve is open. If the engine really could expell all the water during the subsequent exhaust stroke, we wouldn't have these issues but we do.

No, I was assuming enough water would be expelled as to not cause hydraulic lock, but I'm not up for arguing semantics.

I didn't realize so many people were ruining their engines in this fashion. I guess because I don't ever kill the engine while the boat is still moving I hadn't thought of that scenario. I'm not trying to discount the potential for a cracked manifold to wreck an engine. I was really just reacting to TilliamWe's soapbox post.

Thanks for your advice on testing the manifolds. I'll definitely keep that in mind when the new ones near their life expectancy.

On a positive note, I've since replaced the manifolds and changed the oil, and the valve cover breathers are smoke/steam-free. Live and learn.

Don

 

[chiefalen]

Re: Method for pressure testing exhaust manifolds

You did good getting 12 years from those manifolds. Someone maintained the boat good. Florida boats get used alot more than northern boats.

 

[donmagicjuan]

Re: Method for pressure testing exhaust manifolds

I actually just moved here from Washington state, so until now it probably hasn't gotten as much use as you might think.