New Guy Here with some questions Re: Chev 350 and Exhaust

[Galaxie_406]

Well here it goes, I have a 19.5 Hammond Eldorado that had the OMC 350 in it. When I purchased the boat it came with a cracked block, no problem it was a good deal. I rebuilt a 010 4bolt with all the goodies balanced and blueprinted with the addition of Vortec heads. Installed the engine 2 years ago, fired it up in a test tank to run in the cam and shut it down. It appears that I did not "winterize" the block but heck I live in Southern Califoolya and we had some below freezing temps, anyway busted the block. My problem besides getting another block is that upon tear down I noticed that water entered from my exhaust into the head and my question is: Could I have run too big or too much overlap on the cam (Thought it was pretty mild with the Vortec heads) or do I have a cracked exhaust manifold? is there a way to test the manifolds? test plate? if so how many pounds do I need to test to? seems to be mostly on port side. Called my local shop and they say "needs new manifolds $400" and never answered the question on testing. All help is appreciated.

[TerryKing]

>>Could I have run too big or too much overlap on the cam (Thought it was pretty mild with the Vortec heads) or do I have a cracked exhaust manifold?

Well, first answer the Exhaust Manifold issue! I'd just hook up my garden hose with some hose adapters and hose to that I could flow water in and out of the manifolds, one at a time. (Since you're going for an (ouch!) new block, the manifolds are (or can be) off and separate, right?)

With water running right thru the manifold passages, just put some restriction with your thumb on the outlet hose. As I recall, a tight thumb on a 1/2 inch hose end is about 10 or 15 PSI, uncalibrated!. Any manifold should hold tight with 30 to 50 PSI. Just look for leaks into the exhaust passages.

The cam overlap is another issue. Hmmm... A lot of overlap produces some negative-pressure pulses in the exhaust, (I THINK?).. DEpending on where/how your exhaust water enters the exhaust system it might be drawn back in.. You'd have to have a running engine to check that!.

I homebuilt manifolds on a flathead Mercury V8 (Yeah, I'm OLD!) that ran Offenhauser heads and a "3/4" cam. Originally I had the outlet water from the block going in at 90 degrees about 4" aft of the aftmost cylinder, and I did get a little water in that aft cylinder, as seen as some droplets on the spark plug. Later I redid that with the water aimed more out the exhaust and I think it was OK...

That engine looked nice in a homebuilt 17 footer with the 3 carburetors on top!

Hope you get it running again!

[Galaxie_406]

Thanks for the reply, the exhaust system is the stock cast iron water jacketed through the stern drive type, still cannot find my cam card but I believe my info is stored in my old computer which I will need to bring out of mothballs and check specs. Still need to pressure test the manifolds.

[Beech2000]

Hey Galaxy,

Find your cam specs yet?

You have me worried.

Here are the specs on mine.

http://www.compcams.com/Technical/Se...umber=08-417-8

I hope I don't have that problem.

My boat is 1998 SeaRay 190BR in final stages of 5.7 rebuild. Being a SBC 5.7 she sits kind of low in water. and exhaust is through sides instead of through transim.

I always worry about water getting up there and back down into manifolds or worse.

Let me know when able. Thanks

[TerryKing]

Looking at the specs:

Valve Timing At 0.006  	   	 
        Open          Close
Intake   25             65
Exhaust  72 	        24

I interpret that to mean the exhaust valve closes (24 degrees) just before the intake valve opens (25 degrees), meaning there is (just) no overlap.

So, there SHOULD be no negative-pressure pulses in the exhaust ports at low speed...

My knowledge on this is 50 years old and may have worn out by now

[Jango]

Intake timing - open @ 25 deg BTDC, close @ 65 deg ABDC

Exhaust timing - open @ 72 deg BBDC, close @ 24 deg ATDC

Lobe centers are 112 deg, with overlap of 49 deg - duration of 270 deg intake and 276 deg Exhaust.

Shouldn,t be a problem

[Galaxie_406]

As for me, no card as of yet but then again I have been preoccupied with the wife buying a newer motorhome for me to pull my boat to the river :-) If I cannot find my cam card, can I just set a dial indicator on the top of a lifter and rotate the crank to pick up my readings?

[Jango]

Yes, In addition you'll need an accurate Degree Wheel.

[Galaxie_406]

Here's what the card says. Mfg: Predator Cams
Duration at .050 Intake 214 Exhaust 224
Lobe Lift Intake .295 Exhaust .310
Lobe Separation Intake 107 Exhaust 117

Seat Duration 280 290

Degree #1 Intake Lobe to 107 ATDC

Also picked up a rebuilt GM 350 that had reverse rotation (Gear Drive) with a cam that had the numbers 201264 which seems to cross over to an Isky with the following specs:

Lift .450
Duration 264 Deg
Duration at .050 214
Lobe Separation? 108

Hopefully we can shed some light on the water entering into the wet exhaust after shut down, if the cams check out then maybe I have cracked exhaust.
Thanks Gary

[RMSOSF]

Are you running a roller cam? if so, I have one out of a 2005 Merc 5.7. It's a roller cam for use with Vortec heads.....stoack mercruiser cam. It's yours for the cost of shipping from Fla.

[Galaxie_406]

No not a roller motor, I went ahead and used the new Isky cam (Part # 201264) that cam with a rebuilt engine that I had picked up (Reverse Rotation Engine) removed the gear drive and used my new gears and roller chain from the broken engine. I am considering going with the roller engine for my next build unless I come across a cheap 4 bolt early block and will use that. Thanks for the offer on the cam but I have no idea which way I will end up in the future, as for now I have completed my temp 350 for this summers fun. Now I am onto finding out WHY water entered back into the exhaust, I still think it was originally a poor design on my part for the camshaft which may have had an overlap situation. I bead blasted the insides of my exhaust manifold and riser (one side today) to remove and soot carbon or rust and they look fine so far, I made a test plate to give them a pressure test tomorrow. The exhaust had been replaced at one time or another with later style Barr manifolds and very little use on them from what I can tell.

[RMSOSF]

Take pictures of the Manifold and riser mating surfaces and of the riser outlet and post them here, might be able to point out some things for you to watch out for.

[Galaxie_406]

Finished checking the exhaust manifolds today, bead blasted the manifolds and the risers. Took a real good look inside and they looked fine no signs at all of cracking, risers looked great too. Installed them with new gaskets. I believe the water problem was because of the cam profile and design, may have been ok for for a wet exhaust but not this type of exhaust. Cam has been change for a different profile and we will see how it goes.

Do people fire there engines after the boat is out of water just to make sure there is no way for water to get sucked back into the exhaust?

[Beech2000]

Originally Posted by Galaxie_406

Do people fire there engines after the boat is out of water just to make sure there is no way for water to get sucked back into the exhaust?

No. I only see the jet ski nats dry out after pulling out. Like to have gun when they do though. This can be done with jet drives but not mercruiser sterndrives since the water pump in lower unit would melt with lack of water. Not sure about OMC drives though.

In fact after salt water use it is manditory that the engine be run with muffs and fresh water be allowed to flush seawater out.

I always open the water valves in manifolds and block to remove following use.


Comparing your cam card to mine it appears my cam has more lift with less duration. I am unfamilure with OMC but ask if it is possiable that the wrong riser gasket was installed?

I know if cracks or leaks in manifold to riser on mercruisers; water would be allowed to enter exhaust. However it wouldn't single out one cylinder. though. Hmm....

[RMSOSF]

One question that was never asked of you in this thread and should have been the first..... How old are the manifolds and risers?


Just by beadblasting and inspecting, you will not find all the cracks. You can still have a crack that only opens and leaks when the manifold gets hot. You will need to do a good pressure testing complete with a block off plate, city water and a propane torch to determine if there are any cracks in the manifolds. The risers are tougher to do. You also need to take a very close look at the riser/manifold mating surface. Chek them with a straight edge and look for any permiation along the bridges. Permiation will look black compared to the rest of the metal. If you find some, the part is junk.

If those manifolds/risers are more than 4 years old, I'd replace them. To me, I'd rather replace the manifolds every few years than the engine......it's a lot cheaper that way.