Timing cover resto

Discussion in 'Small Block Tech' started by Tripple7, Nov 19, 2020.

  1. MrSony

    MrSony Well-Known Member

    I will say my last engine that had .0025-.0027 clearances (worn stock components) had less pressure overall. Then it exploded.
     
  2. Tripple7

    Tripple7 Well-Known Member

    Based on the input here and what I've been reading about timing covers and oil pumps, I will give it a try and rebuild the original timing cover keeping an eye on all the clearances and add a TA booster plate.
    I started polishing the bottom of the gear pockets and was able to eliminate most of the scoring. Now the surface of the left one is smooth again, won't touch the pocket walls however to prevent pressure loss due to thermal expantion.
    I used 1200 grid sanding paper which I put to the gear with double sided tape and turned it with a drill. 20201215_161811.jpg 20201215_161743.jpg
    20201215_160910.jpg
     
  3. alec296

    alec296 i need another buick

    Be cautious about taking metal out of the pocket. Your are changing clearance to the housing. Which will ultimately leave you with the same problem. you will probably want to take a .0001 off the gasket surface now.
     

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  4. alec296

    alec296 i need another buick

    This is my ported cover.with large passages
     

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  5. Tripple7

    Tripple7 Well-Known Member

    Yes that Was my plan! Thank
    you for the advice
     
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  6. Jim Nichols

    Jim Nichols Well-Known Member

    You probably need to take a couple thousands off. The gears should stick up above the gasket surface. .001-.002 with the booster plate. Note the extra hole in Andy's pic. I go a little larger there and bevel the big hole with a Dremel.
     
  7. Jim Blackwood

    Jim Blackwood Well-Known Member

    Scoring in the pocket won't do much unless it is really deep. Polishing the scores out is fine but you can get more by setting the end play tight. Closing that up by .oo1" will do much more. Getting it down to under .001" all but eliminates leakage past the ends of the gears and since the housing expands more than the gears binding is not a concern.

    The best and most important thing you can do is control your bearing clearances. I specify .0008-.0012" and any machinist worth using can hold that. You'd be amazed what just that one thing does for your oil pressure. It should allow you to run thinner oil as well.

    Jim
     
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  8. Tripple7

    Tripple7 Well-Known Member

    Thanks Jim,
    As changing bearing clearances is not an option I will make sure to have a well working oil pump with an end play as tight as possible and upgrade it with the TA booster plate.
    Hope this improves my pressure so I can get rid of the HV pump.
     
  9. 72gs4spd

    72gs4spd Well-Known Member

    I’ve had numerous discussions about bearing clearance with my machinist. His take on the tight clearances is to make up for the poor oiling system design. With all the mods that he made the .0023 clearances will have no issues with oil pressure. With his 50+ years of building race engines I trust his judgment and he stands behind his work.
     
  10. Tripple7

    Tripple7 Well-Known Member

    Yeah, thats an interesting topic. I did not ask my builder why he chose those "loose" clearances.. might be because over here in germany they are not aware of the buick oil system issues.. maybe they went the GM/ chevy way, I don't know and asking about it won't change it. I mean, it works and oil pressure is there when I need it most: in the high RPM range.
     
  11. 72gs4spd

    72gs4spd Well-Known Member

    As my machinist puts it oil pressure is the measure of resistance in the oiling system. What you want is volume not pressure he says. The oiling mods reduce restrictions and increase flow. He told me you’d be surprised how low pressure is in the pro stock race motors he used to build spinning at high rpm.
     
  12. Tripple7

    Tripple7 Well-Known Member

    Of course it depends which type of application you run..for me as a weekend driver, longevity has priority. I am done with removing the scoring in the pokets and will start working the gasket surface and do the mods that were mentioned
     
  13. alec296

    alec296 i need another buick

    Looks like you will be running a thicker oil.
     
  14. Tripple7

    Tripple7 Well-Known Member

    I will start with the 20/50 I've been using and see where it gets me..
     
  15. alec296

    alec296 i need another buick

    Try 15-40. It’s slightly less strain on a tight oil pump. If pressure is good, then leave it. 20-50 is thick in colder weather.
     
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  16. Jim Blackwood

    Jim Blackwood Well-Known Member

    Buick specified tight bearing clearances. If you want to open them up like an old school SBC and re-engineer the entire oiling system that's your privilege but it was never the way the engine was designed to work so don't be surprised when odd results appear. Here's a real life experiment for you: find a bushing, anything smooth will do, and turn a rod to fit it with .001" clearance and another step with .002" clearance. Drill each journal so you can thread in a fitting to supply oil to the bushing. Then get out your speedy sprayer, put a quart of your favorite oil in it, pressurize to 40psi, and try it on each journal to see how fast the oil passes through the bearing. The results will make a believer out of you. Now recall that you have 22 of those leakers in the engine, plus lifters and maybe rocker bushings too. With your open clearances you are going to need that extra 1/4" of gear length and maybe then some. And that's going to take a toll on the drive gears.

    Also, the purpose of the oil is to prevent metal to metal contact, and the more you spread out the force pushing the bearing sideways the easier that is. The tighter the clearance, the larger the potential point of contact is and therefore the smaller the pressure per unit of area and the less strength in the oil film and pressure in the supply needs to be to resist it. In other words the journal has a lighter footprint, kind of like balloon tires vs skinneys. As you open up the clearance the journal can go farther off center and as it does it presents a smaller area to the bearing and unit pressure goes up, making it more likely that contact will occur. What clearances do you see in modern engines? Answer me that. For all intents and purposes they ARE racing engines compared to this old iron, and we can benefit from following their examples in many cases.

    It is axiomatic in engineering circles that a fit with tighter clearances, regardless of the application or lubrication method is going to last longer than one with loose clearances. Why? Because wear accelerates as the clearance increases due to the increase in unit pressure, until it reaches the point that the journal can begin impacting the bushing, at which point it will quickly hammer it's way through the softer metal.

    Quit listening to people stuck in the past and do your own research.

    Jim
     
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  17. Buick#455

    Buick#455 Well-Known Member

    Well said Jim, well said....
     
  18. Tripple7

    Tripple7 Well-Known Member

    Hey Jim,
    Good and detailed explanation.
    My intention never was to open up clearances and won't be to re-engeneer the oiling system, I'm not questioning tighter clearances at all. I am trying to deal with this issue as good as I can and will use any advice I can get.
    Tearing an assembled engine apart which has been running pretty well for half a year is not only time but also money consuming.
     
    Last edited: Dec 22, 2020
  19. Mart

    Mart Gold level member

    Sound info. I used to rebuild bronze bearing machine tool spindles, big ones, 3"- 5" dia. Those had very tight clearances also. Used thin weight spindle oil, & same principal. Distribute the load over more area.
    The hand scraping of the bronze bearings kept the oil in pockets,
    tight clearances were the norm.
    Those o.d. grinding machines held super exact tolerances with those tight clearances. Grinding Chatter would develope if the bearings needed to be rebuilt. Hand scraping is a lost art now a days. Those bronze bearings were also 3-5 " wide, and would run 8 hour shifts every day.
     
  20. Jim Blackwood

    Jim Blackwood Well-Known Member

    I agree on the reluctance to tear it down. But that does mean that you are stuck with band-aids. Some of which are reasonably good, fortunately. Start with heavier oil. Now unfortunately this means extra stress on the drive gears and you may have to end up replacing the distributor gear but that can be put off. Next, you can do the oiling mods, all of which can be accomplished without pulling the engine. It's a bit of work but it'll both lighten the load on the pump and increase the oil flow/pressure. And you can use the high flow pump as a last resort. But beyond that it's really down to bearing clearances. By the time you are done you may quite possibly be up to straight 50 wt racing oil or even higher. At that point it's just a struggle to attempt to get a little more life out of the bearings and make them last as long as the rings, which in the Buick is really by this point a lost cause. At that point you might as well pull the engine, yank out the crank, and fit tighter bearings before you develop a rod knock and possibly even destroy the engine.

    But as a guide, provided the usage is street driving and you can resist the urge to hammer it, you don't need the recommended 15psi at idle and 10psi/1000rpm for the engine to live a long life. I think sensors for idiot lights were often in the 5-7psi range and if you have 30psi or better most of the time and aren't racing you should be OK.

    Jim
     
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