'74 351W Engine Blow By
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=35681
Printed Date: November-17-2024 at 6:00am
Topic: '74 351W Engine Blow By
Posted By: bobcycleb
Subject: '74 351W Engine Blow By
Date Posted: April-01-2015 at 7:03pm
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Hi gang-- here we go-- rebuilt this engine twice in the last two years. Unfortunate rookie mistake is to run it without enough oil--fried some bearings and therefore the second rebuild. Latest round all new rings, pistons, valve items/seals, gaskets, exhaust manifolds, risers. We think the rings are sealing well--no oil leaks anywhere. Getting blow by (oil in to tube between breather cap and flame arrestor). It then drips down the arrestor, down the back of the carb, on to the intake manifold, and eventually down the back of the block and on to the bilge area. Broke it in nice-- about 10 hours at 2500 rpm max. Would get a couple of teaspoons of oil over a couple of hours. Took it up to 3300 rpm and got noticably more oil right away--couple of teaspoons within 15 minutes. I'm feeling like something is going on with the intake manifold itself (like rusting out--crossover is messed up maybe, etc.). Ideas?? Things to check? (Vacuum off carb is at steady 16#--no matter the rpm's). ------------- Bobcycleb |
Replies:
Posted By: tryathlete
Date Posted: April-04-2015 at 1:44pm
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If compression and leak down tests have not been done yet I'd do that first. Might be a single cylinder issue where rings did not seat properly or ring gaps were not offset. I'd consider the possibility of poor valve stem sealing or valve guides that might have been oversized to true them up when heads were done. If you're not fouling plugs, maybe best to just forget about the slight consumption and enjoy the boat. ------------- 2008 MasterCraft 197TT 1996 Nautique Super Sport 1988 Waterlogged Supra Mariah |
Posted By: JoeinNY
Date Posted: April-06-2015 at 10:24am
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It is possible you broke it in too nice. Once the cam is broken in as soon as the boat is up to temp I run it through approx. ten cycles of hard take-off to wide open throttle to hard deceleration back to idle. Let the gauges stabilize then repeat. If you have really put ten hours on without ever getting above 2500 rpm you were not doing the rings any favors. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: phatsat67
Date Posted: April-06-2015 at 10:32am
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Agreed, It needs a decent amount of WOT and varying rpms to properly seat a new set of rings. What was the ring material used? ------------- |
Posted By: bobcycleb
Date Posted: May-12-2015 at 2:18am
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Hi gang-- sorry it's been a while-- weather here in Northern Colorado has not been conducive lately. Here's the scoop--when we rebuilt the engine last fall we ran out of time and went straight to outside storage--must have firmed up the front main gasket--was leaking a bit--replaced last week (was hardened) and no more oil from that area. Also replaced the thermo gasket (had a slight leak)--now we have no more water. Oil leakage had been reduced about half.--looked like it was just the excess pushing out between breather and valve cover (has consistently been an issue). Installed a higher end oil/air separator (used older 351W valve cover with round hole (vs. original notched hole version for twist-ons) that was threaded and attached with locking collar between the baffle and valve cover itself.. Guess what--no more oil leaking from valve cover/breather area. FINALLY-- no water and no oil leaks--truly ready for season! Thanks for the ideas! ------------- Bobcycleb |
Posted By: Clew In
Date Posted: May-25-2015 at 11:49am
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Hey Bob, Could you post a picture or link to what you used and replaced? Thanks, Tom ------------- Clew In |
Posted By: bobcycleb
Date Posted: May-30-2015 at 1:48pm
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Hi guys-- here are a few pictures--finally getting back to some good weather north of Denver! Enjoy-- Bob!    ------------- Bobcycleb |
Posted By: jhersey29
Date Posted: May-30-2015 at 4:17pm
| I had some excess oil in the similar tube on my GT40 after rebuilding it this winter. It resolved after about 10 hours. I also had to torque the manifold again after a few hours. I did 3 - 4 rotations when I put it back together and after.a few hours of operation it need another 1/4 turn roughly per bolt. The rebuild has my idle a little lower than I want but getting it up has proven difficult on that efi motor but seems to be ok with out stalling. |
Posted By: MrMcD
Date Posted: May-30-2015 at 5:20pm
| Nice work, glad you got it ready for Summer. |
Posted By: gun-driver
Date Posted: May-30-2015 at 5:46pm
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[QUOTE=bobcycleb] [QUOTE] Looks good but that fuel line setup looks a little scary 
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Posted By: 8122pbrainard
Date Posted: May-30-2015 at 6:43pm
I sure agree. I missed seeing the potential bomb!!  I feel Bob should be worrying about other problems other than blow by!!  ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
gun-driver wrote:Posted By: bobcycleb
Date Posted: May-31-2015 at 12:25am
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What would you do different with the fuel line set up? ------------- Bobcycleb |
Posted By: 8122pbrainard
Date Posted: May-31-2015 at 8:18am
It MUST be steel with inverted flare fittings on the high pressure side from the pump to the carb. The alternate is a USCG approved hose assembly for that purpose. You need to think marine where any fuel leak is trapped in the bilge unlike automotive and is a potential problem. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |