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

Discussion in 'Sterndrives' started by Galaxie_406, Mar 14, 2007.

  1. Galaxie_406
    Joined: Mar 2007
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    Location: Apple Valley - Sunny California

    Galaxie_406 Junior Member

    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.
     
  2. TerryKing
    Joined: Feb 2007
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    Location: Topsham, Vermont

    TerryKing On The Water SOON

    Testing Exhaust Manifolds??

    >>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!
     
  3. Galaxie_406
    Joined: Mar 2007
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    Galaxie_406 Junior Member

    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.
     
  4. Beech2000
    Joined: Jul 2006
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    Beech2000 Senior Member

    Find cam specs yet?

    Hey Galaxy,

    Find your cam specs yet?

    You have me worried.

    Here are the specs on mine.

    http://www.compcams.com/Technical/Search/CamDetails.asp?PartNumber=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
     
  5. TerryKing
    Joined: Feb 2007
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    Location: Topsham, Vermont

    TerryKing On The Water SOON

    Cam worries

    Looking at the specs:
    Code:
    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 :D
     
  6. Jango
    Joined: Aug 2005
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    Jango Senior Enthusiast

    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
     
  7. Galaxie_406
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    Galaxie_406 Junior Member

    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?
     
  8. Jango
    Joined: Aug 2005
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    Jango Senior Enthusiast

    Yes, In addition you'll need an accurate Degree Wheel.
     
  9. Galaxie_406
    Joined: Mar 2007
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    Location: Apple Valley - Sunny California

    Galaxie_406 Junior Member

    Found the cam card!

    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
     
  10. RMSOSF
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    RMSOSF Junior Member

    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.
     
  11. Galaxie_406
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    Galaxie_406 Junior Member

    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.
     
  12. RMSOSF
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    RMSOSF Junior Member

    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.
     
  13. Galaxie_406
    Joined: Mar 2007
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    Location: Apple Valley - Sunny California

    Galaxie_406 Junior Member

    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?
     
  14. Beech2000
    Joined: Jul 2006
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    Beech2000 Senior Member

    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....
     

  15. RMSOSF
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    RMSOSF Junior Member

    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.
     
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