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261 smoking from road draft tube

Discussion in 'The Hokey Ass Message Board' started by Mike in Tulsa, Nov 15, 2010.

  1. I just fired up my 261 for the first time after getting it in my truck and I'm getting white smoke from the road draft tube and the valve cover breather. A little history... 1958 Chevy 261 inline 6, I ran the motor before I pulled it out of the donor truck. I did 4 compressions tests - the highest number I had was 135 and the lowest was 120+. With oil and wide open throttle I got 150+ highest to 130 lowest. Seemed to be in decent shape. I pulled the pan for a visual inspection - everything seemed fine. I found a 235 head for it and had it completely rebuilt. New water pump, fuel pump, rebuilt carb, cleaned radiator... It stays at 180 degrees with just over 30 psi oil pressure. Got the valves adjusted and it runs nice and smooth and quiet. It doesn't have any smoke at all out of the exhaust. A little moisture but that's it. I did another compression test. My highest reading was 90 and my lowest was 60. What's going on here? The motor sounds fine and runs smooth. Any ideas? Thanks in advance.
  2. Oh, the oil is nice and clean too. I've ran it for probably 30 minutes total.
  3. Johnnyzoom
    Joined: Jun 23, 2006
    Posts: 319

    from Florida

    Can you test with a vacuum gauge for more clues? How does coolant look?
  4. cederholm
    Joined: May 6, 2006
    Posts: 1,621


    How much smoke are we talking? My 235 does that and since we have more redlights then cars, it was a real hassle. My understanding is a little air movement is needed for those vent pipes to create a little vacumme and pull the bypass gasses out.

    I added a simple PCV and all is well.

    ~ Carl

  5. It's enough to smoke you out of the garage. The coolant looks good too. Will the PCV take car of it? I had a 216 in a 52 Chevy that didn't smoke out of the road draft tube. Smoked pretty good out of the exhaust though.
  6. tommy
    Joined: Mar 3, 2001
    Posts: 14,757

    Member Emeritus

    If it was sitting for a while, give it some time.

    It's normal for road draft tube cars to have wisps of smoke coming out of the breather fill tube when idling in the garage. There is no road draft when it is sitting still. If it is huffing smoke out of the bottom road draft tube below while parked then it's got some excess blow by. If the engine has been sitting for a while, drive it with some Marvel Mystery oil or ATF to loosen up the sticky rings. It may take several trips for it to work but give it a shot. What do you have to lose?

    We have become so used to PCV systems sucking all the fumes away while parked that we get scared when we see the fumes on a parked road draft system car. Don't panic yet.

    My Studebaker engine sat for over 20 years and would kill all the mosquitos in PG county when I got it running again.
  7. K10
    Joined: Jul 16, 2006
    Posts: 57


    261's use a different head gasket than a 235. Steam holes are necessary for proper cooling.
    This was ripped from Chevytalk.
    "You shouldn't have any problem mounting the engine. All of the 58-62 blocks I have seen had the holes for the 55-57 type front mounts.

    The oil filter is critical. If your engine is set up for a full flow filter (the ports will be pretty big, like 3/8" or 1/2" pipe thread) you absolutely must not use the bypass filter from a 235, and you certainly can't plug the holes. Just get any remote filter kit sold for a V-8 and you will be fine.

    Lastly, there is a very good reason why the steam holes must be drilled in the head. The 261 block doesn't have any water circulation between the cylinders. Their outer walls actually touch. This means that a vapor pocket can build up on one side or the other of a cylinder and create a localized hot spot which could result in damage. The "steam holes" vent this vapor into the head, which has a continuous water passage and can carry the vapor away to where it won't cause a problem.


    And more;

    "You can use a 261 head gasket, positioned on the 235 head, to mark the location of the steam holes which will need to be drilled into the water jacket passages of the 235 head. My machine shop drilled mine when I had the valve job done."

    Head on over to Inliners. com for a full review. May I humbly suggest that you do not run the engine further until you fully understand it. The 261 is a different beast from the 235. The oil passages being plugged improperly will cause total failure. And if you didn't get the right head gasket and drill steam holes, you're also on your way to premature failure.
  8. Yes, I had the machine shop drill the steam holes and I used the 261 gasket. The motor hasn't been started in about 8 months and I don't know how long before that.
  9. Rickybop
    Joined: May 23, 2008
    Posts: 7,189

    from Michigan

    Strange that the compression-loss is in all cylinders. Did you maybe over-adjust the valves a little, and they're not seating completely?
  10. Curt B
    Joined: Oct 15, 2009
    Posts: 325

    Curt B

    And on the topic of the steam holes¬Ö.3 of the holes are unlikely to intersect the jacket and are useless if not drilled at an angle toward the manifold side. GM used 12 degrees as shown here:

    Attached Files:

  11. Von Rigg Fink
    Joined: Jun 11, 2007
    Posts: 13,426

    Von Rigg Fink
    from Garage

    with a hot compression drop like that i would be thinking your valves might be too tight.
  12. Thanks guys. I think I'll re-adjust the valves and try again. That compression is what really has me worried.

    K10 and Curt, I did a lot of research on putting the 235 head on a 261. I found out that not very many people know anything about it but when I took the heads - the 261 and the 235 - into the machine shop(Carbone's in Tulsa), they knew exactly what needed to be done. I learned a lot from the guys on Chevy Talk, the 49 to 54 site.
  13. Re-adjusted the valves. They were real close. Still has low compression. The only thing I can think of is while I had the head off I kept the cylinders lubed up with oil. Can't figure out the compression thing. I'm using a cheapo harbor freight tester. Maybe it's off?
  14. medicinal_marinara
    Joined: Nov 24, 2009
    Posts: 139

    from Oregon

    Are you holding the throttle open while testing?
  15. Atwater Mike
    Joined: May 31, 2002
    Posts: 10,635

    Atwater Mike

    On O.H.V. pushrod engines, the valve lash increases as the engine gets warm. (uninformed and inexperienced will deduce that valve lash tightens up with temp.)
    They are wrong.
  16. I'm holding the throttle wide open. I adjusted the valves according to the manual. I have solid lifters. The more I run the motor the more it seems to clear up. The compression is up to 100 to 110. Still low but getting better.
  17. Screamin' Metal
    Joined: Feb 1, 2009
    Posts: 506

    Screamin' Metal
    from Oklahoma

    The rings have probably become it some and it should calm down....but 90 is way lower than it should be....and 60, I won't even go there....

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