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Technical I Need some flathead expertise

Discussion in 'The Hokey Ass Message Board' started by ciscokid, Oct 15, 2020.

  1. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    I adopted my uncle's 49 merc. It was sitting in his shop for approximately 20 years. It ran great when he parked it. After doing the usual to get it fired up up again after 20 years it didn't run quite right. I did a compression test and #6 only had 55 lbs. All other cylinders had between 115-120 lbs. I blasted a couple squirts of oil in #6, and it only came up a few extra lbs on the compression gauge. I pulled the intake off and all the valves seem to be moving freely from what I can see. Any ideas from the flathead pros out there? Thanks!
     
  2. Budget36
    Joined: Nov 29, 2014
    Posts: 13,173

    Budget36
    Member

    Let it run for a bit. Might just be a sticky valve.

    BTW, how did you determine the valves were moving freely?
     
  3. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    Thanks for the reply Budget! I've had the car running for some time now since I acquired it. That #6 is being stubborn. I was turning the engine over while the intake was off and watched all the valves move up and down. Not sure if that validates much tho?
     
    Last edited: Oct 15, 2020
  4. Budget36
    Joined: Nov 29, 2014
    Posts: 13,173

    Budget36
    Member

    That pretty much does. Since it’s been running for awhile, and wet test didn’t bring the compression up, I’d be thinking a valve isn’t sealing. Going to have to pull the intake again, pull the head and pull those valves. I’ve heard talk of doing the valves while in the car, but makes me squeamish where the metal and debris go.
     
    stillrunners likes this.

  5. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    I figured pulling the head was going to be my next step. I put some marvel mystery oil in that cylinder a few hours ago. I'll let it sit over night and check it again tomorrow before I decide to pull the head. Nothing to lose at this point. Thanks again for the advise. I'm a newbie with flatheads.
     
  6. alchemy
    Joined: Sep 27, 2002
    Posts: 20,405

    alchemy
    Member

    How many hours and miles have you recently put on the car? Throw some MMO in the oil and the gas and run a tank full through it. Then see how it runs.
     
  7. Petejoe
    Joined: Nov 27, 2002
    Posts: 12,263

    Petejoe
    Member
    from Zoar, Ohio

    I agree with alchemy.
    Don’t tear that apart just yet.
    I’ve seen low compression cylinders in flatheads that run just fine.
    Get it running smoothly and drive it with some MMO.
     
  8. v8flat44
    Joined: Nov 13, 2017
    Posts: 1,211

    v8flat44

    What alchemy said. Even though #6 is low, make sure everything in the ignition is GOOD too; will help over all performance. For some reason, flatheads like to confuse us as to what going wrong. Fuel or spark.
     
  9. stubbsrodandcustom
    Joined: Dec 28, 2010
    Posts: 2,273

    stubbsrodandcustom
    ALLIANCE MEMBER
    from Spring tx

    oK... so I acquired this car in august, got it home, heads were off, had a sticking valve that was broke free already, so What we did was LAP the valves. Every damn one of em, after finding compression on a few in the 50s to 30s. We lapped the valves, bolted back together lowest was 70 then going in the right direction..., mind you this motor hadnt been ran in years, made it fire off, 1 minute run time, compression test once cooled down lowest 95, little oil pushed it to 150. So my personal take, pull the keepers, get some valve lapping compound from the parts house, and get to lapping some valves, sometimes rust can happen in the seats and make that thing not want to seat. Its a cheap easy valve job that is easy enough to do.

    Hopefully this helps bud.. After doing mine, I am a firm believer in it for resurrecting flattys that have been sitting for a long time.
     

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  10. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,856

    Mike51Merc
    Member

    If your valves are freely moving, I'd suspect a crack in the block that runs into the valve seat.
     
  11. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    20191103_091001.jpg Thank you everyone for the great advise and guidance! I'm going to get busy on it today! Please keep sending any suggestions! I'm like a sponge right now! Here's some pics of the car and engine. 20200724_203250.jpg 20191103_090240.jpg
     
    Stogy, waxhead, Petejoe and 3 others like this.
  12. Sculptive Design Co.
    Joined: Jul 23, 2018
    Posts: 80

    Sculptive Design Co.
    Member

    Right on, sounds like progress! Nice looking Merc!
     
  13. tubman
    Joined: May 16, 2007
    Posts: 6,913

    tubman
    ALLIANCE MEMBER

    Looks like that engine has all the required exterior goodies (Offy heads, a Mallory dual point, and what appears to be an Edmunds "Racing" manifold with two four-bolt carbs). If the internals match what we can see, it probably has an aftermarket cam with adjustable lifters. If so, one of the valves might be out of adjustment. When you had the intake off, did you notice if the lifters had what looked like bolts on top?

    The car looks very well done and I would expect that no expense was spared. Can you confirm what brand the carbs and manifold are?
     
    Stogy likes this.
  14. Glenn Thoreson
    Joined: Aug 13, 2010
    Posts: 926

    Glenn Thoreson
    Member
    from SW Wyoming

    Nice car! You either have a leaking valve or a leaking head gasket. Before you pull the heads try running a torque check on the head bolts. Aluminum heads take less tightness than cast iron. After sitting so long the gasket may have shrunk a bit and could leak between cylinders. you can check that by hooking an air hose to the cylinder in question and listen for air escaping into the adjoining cylinders. Don't over tighten them. If it still doesn't run right you will need to lap, grind or replace the valves on that cylinder. Head off, look for signs of leakage on the head and block. Unusual black discoloration between cylinders indicates a leak. Check the head for flatness. Use a new head gasket properly torqued. Usually 10 to 15 lbs less than factory specs. Be sure to use flat washers on the head bolts. The engine in my avatar car had been in a barn for 30 years and requires a complete valve job on the entire left bank while the right side was perfect. Good luck with your project..........
     
  15. Run it and let it get hot couple time in hope the rings will free up .
     
  16. rusty valley
    Joined: Oct 25, 2014
    Posts: 3,883

    rusty valley
    Member

    use some grease on the intake gasket, then they can be reused several times. nice merc
     
  17. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    Thanks for the advise and the comments Tubman! My uncle definitely put his heart and soul in this car. It has an isky cam with adjustable tappets. The intake is Fenton and the carbs are holley.
     
  18. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    Funny you say that! The gasket came off pretty easy considering how old it is and was in decent shape! Thanks for the reply
     
  19. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    Awesome advise Glenn! Thanks for the help!
     
  20. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    Thanks for the reply! I ran the car around a hand full of times and brought it up to temp prior to pulling the intake off with the hopes that it would "loosen up". Hopefully after this lil bit of work, it'll do the trick.....
    Thanks again!
     
  21. tubman
    Joined: May 16, 2007
    Posts: 6,913

    tubman
    ALLIANCE MEMBER

    Excuse me for being nosy, but they sure look like later model Holley 4 bolt carbs, and at closer scrutiny, the manifold is a Fenton. Are they bolted directly to the manifold or are they on adapters? I ask because Edmunds was the only intake manifold that I know of that had mounts for 4 bolt carburetors.

    I am a big fan of more modern larger two barrel carburetors on street flatheads (with hoods) and am vary curious how the car performed with two of the buggers. I think they flow about 350 CFM each; that probably means a big inch engine.:eek:
     
  22. Mike51Merc
    Joined: Dec 5, 2008
    Posts: 3,856

    Mike51Merc
    Member

    Nice car!
    The intake manifold mounts to a flat surface so it should free up easily. Some guys actually grease the intake gaskets so they can be easily removed and reused.

    As for my valve seat comment, make sure you clean and check the whole valve seat for cracks. They often crack on the middle cylinders into the shared exhaust ports.
     
  23. 4ty
    Joined: Jan 1, 2009
    Posts: 272

    4ty

    Try adding Marvel Mystery Oil to the gas tank (glug, glug, glug) and drive it.
    Paul in CT
     
  24. tubman
    Joined: May 16, 2007
    Posts: 6,913

    tubman
    ALLIANCE MEMBER

    Looks like Fenton cast iron headers as well! First class all the way!

    May be too much carburetion for it, especially if the carbs are dirty and not in top notch condition.
     
  25. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    Good observation Tubman! Yes Fenton intake with adapters....
     
  26. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    Thank you Paul! The engine oil will get a dose as well!
     
  27. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    Yes, original Fenton headers as well. My uncle said he bought those for 15 bucks at a swap meet back in the day! He said there was a time when no one wanted any of that stuff, so he snatched it all up! I re-kitted both carbs. Those pictures of the engine are from when I drug it out from his storage barn. It looks a lil better now, minus the acorns!
     
  28. ciscokid
    Joined: Jan 29, 2011
    Posts: 149

    ciscokid

    Thank you!
     
  29. adam401
    Joined: Dec 27, 2007
    Posts: 2,856

    adam401
    Member

    I'm not a cautious guy at all haha and certainly no expert but I dont like the idea of marvel mystery oil in the engine oil in flatheads. I know its done but I've had old timers tell me not to so Ive always headed the warning. Could certainly be old wives tales. I know they recommend that you put it in the oil like a few hundred miles before an oil change. Well in the flathead I change the oil like every 500 miles so I dunno. Go with your gut feeling I guess.
    I do use 4 oz of MM oil in every tank of gas in both my model A 4 cylinder, my 41 Ford 9n tractor and my 8ba flathead coupe to keep the valves from sticking.

    I dont know if this was answered but the question had been raised about wether your engine has adjustable lifters. Seeing all the cool bolt on speed equipment thats there it wouldnt be suprising.
     
  30. tubman
    Joined: May 16, 2007
    Posts: 6,913

    tubman
    ALLIANCE MEMBER

    Does your uncle have any idea of how big the engine is (cubic inches) and what Isky cam it has? There is a possibility that the engine may be over-carbureted with those Holley's.

    I have to say that I am very interested in how that carburetor setup worked. If it worked well, it opens up a lot of possibilities for me.

    Everything I've seen so far tells me it was a top of the line build.
     

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