The Break Down of a '69 Pontiac OHC inline six

Discussion in 'The "Other" Bench' started by TheSilverBuick, Dec 20, 2010.

  1. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    So I have about 95% of the engine pulled apart now and thought I'd bring some photos over for those who were interested in seeing something a bit different.

    The plan for this engine is to EFI and Turbo it. I'd like to get a ridiculous amount of rpm out of it too (by using the turbo as an airflow crutch), but I have to determine what parts I have to work with and cost. Then to drop the whole thing into a '69 Firebird, yet to be purchased.

    So to start, here is my fine working area. I managed to get the engine into the basement so I could keep warm and lay the parts where they will be until needed again. It's actually brighter in there than it appears.

    A few stock engine specs:
    250cid or 4.1L (I have a 292 crank, thinking of making a stroker, but the rod/stroke ratio goes to hell)
    3.875" Bore
    3.53" Stroke
    Rods 5.7" long
    1.92" Intake valves
    1.60" Exhaust valves
    ~8.5:1 Compression
    Forged Rods
    Cast Crank


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    Started with the belt cover and the intake/exhaust manifolds. For any of you that have Chevy 250 experience, you can see the differences.
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    I'm entirely too used to dealing with Big Blocks, these ports are tiny, no wonder they say there are flow problems :'( Looks like it definately sat for a while, some surface rust on the bottom of the intake manifold and in the ports. Engine still turns over easily.

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    Exhaust #1
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    Exhaust #2 & #3
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    Exhaust #4 & #5
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    Exhaust #6
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    Rusty two ports are Intake #1 & #2
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    Intake #3 & #4
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    Intake #5 & #6
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    Clean thermostat housing, the thermostat and housing were both quite clean.
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    The Manifolds.
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    Intake Manifold port.
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    Exhaust manifold port.
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    Check out what came with the engine.
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    Popped the water pump off, the water jackets are relatively clean. I've certainly seen worse.
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    The front of the engine with all the covers removed, as well as the belt and water pump.
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    Decided to slide the lower sprocket and balancer onto the 292 crank. Fits nicely.
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    Front of the 292 Crank with the balancer on there.
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    Interestingly enough, the distributor cap, rotor and points are brand spankin new. Never been ran new. Not even a hint of an electrical arc.
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    Plugs don't show anything special. Shows the same carboned up look as the ports, no wear on the electrodes.

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    I'm going to stop the post here to make sure it saves it, next post in a few minutes will be digging into the engine.
     
  2. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    The highlights of the inside are, cam lobe and cam follower on the #1 intake valve are worn flat, something is up with the valve keeper on the exhaust valve on #2 cylinder allowing the cam follower to rub the spring retainer and lastly, interestingly enough, it has two different types of pistons in it too, cylinders 2 & 5 are a matched set that don't match the rest.

    Took the accessory drive block off first. All looks good there.
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    A picture of the cam in the cam housing/valve cover. Notice the lubrication holes. I'm thinking this set up will really like the properties of synthetic oil. You can see the funny wear patter on the second lobe, I have a better picture coming up.
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    The cam follower arraignment on the head.
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    Here is a picture of the number one cam followers, you can see something wasn't working right.
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    Yup, wore down.
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    To show the lash adjusters under the cam followers. The valve springs and the lash adjusters push up and the cam pushes down.
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    Looks just like a lifter with an added piece to the top. The whole body of the thing does not move up and down, but it is fed by a hole in the side of the body like a lifter, then the top part hydraulically takes up the slack. I'll be taking one apart later.
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    The bottom side of one of the cam followers. It centers/locks itself onto the valve stem with that groove. Hench how the #2 exhaust started hitting the spring retainer.
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    Here is the #2 cylinder, the difference is obvious. At first I thought there was a valve tip height issue, but then realized the retainer is off...
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    You can see four spots were the cam follower was rubbing the spring retainer around the valve stem and lash adjuster side.
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    Here is the whole head. It had a steel shim head gasket. I didn't notice any issues with the valves from the bottom side.
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    Here are the two piston designs. Cylinders 1,3,4 &6 had the pistons on the right, and cylinders 2 & 5 had the ones on the left. 2 & 5 are a paired set, where one is on the compression stroke, the other is on the exhaust stroke.
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    None of the combustion chambers stood out as different from the others, so here is a picture of one. I checked the head numbers, and they match for a low compression '69 1bbl head.
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    Thought I'd take a picture of the rod cap and bolt through the accessory drive opening.
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    Think the 292 would need a shorter piston and rod?
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    Had to break this up into two post, hit the picture limit, lol.
     
  3. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    The oil pan removed. The Pontiac's had a deeper skirt block from the chevy's to increase ridgity for higher rpm.
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    Some moisture definately got to the oil in the pan and the oil was a bit thick, but nothing shocking except I didn't expect the baffle.
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    The bearings looked pretty good.
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    I noticed all the flat surfaces had that hatch marking on it, and the curved bearing surfaces look like they've been cleaned up with something. Thoughts? OEM? Machine shop work? Dude at home? Also on the right, the bearing has a hole in it, that feeds a grove around the rod bolt. With the exception of the rod by the accessory drive block, they seem too low to be spraying the piston or cylinder wall. More thoughts?
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    The two styles of pistons. All and all I thought the pistons were shorter than I figured they'd be.
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    All the bearings looked really good. I still have to get the mic out to check their sizes.
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    All the rings looked good. No broken or stuck rings.
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    The mains pretty much all looked the same.
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    Seven, ha ha ha, seven mains.
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    The crank ready to come out.
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    The 292 crank on the left and the 250 crank on the right.
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    The 292 crank in the block.
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    It didn't hit or rub anywhere, but got dang close to some of the baffling, and probably would have issues with a rod/rod cap.
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    The main bearings I thought were interesting. I'm not entirely sure they are correct. I heard the chevy 250 bearings were different, makes me wonder if these are chevy 250 bearings....
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    The oil baffle for the oil filler and diptstick.
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    The oil baffle for the PCV port.
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    The window for the accessory drive and the oil pick up tube port.
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    Thought I'd take a picture down the mains.
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    The rear main/thrust bearing (the thrust was tight), showing the bearing ID.
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    The rear main, it's bearing shell had two holes in it.
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    Cylinders 2 and 5 has what appears a dingle ball hone job.
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    Cylinders 1,3,4 and 6 look like regular wear. No real ridge at the top of the cylinders that I can tell, just a bit of carbon near as I can tell.
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    Scratch that, three posts, lol.
     
  4. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    And for the last post for a while.

    And as the block sits now. I still need to remove the oil filler tube and a few other miscellaneous things.
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    And my pile of parts. All the bolts are in labelled bags in the postal box.
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    So that's the break down of a Pontiac OHC six cylinder. I still have to pull the head apart to see what's up with the valve keeper, and take the lash adjusters apart to check out the insides and either clean them or replace them. I need to track down some forged pistons, a new cam and at least one follower. I still have to measure the bore diameter to see if that holds any surprises. All and all I think I got a real good foundation to start with.

    If you want to see some comparison pictures with the Chevy 250 some people have posted some pictures on a thread I started on another forum. You can also see the redneck way I got the engine into the basement, lmao.
    http://www.bangshift.com/forum/index.php?topic=26281.0
     
  5. RAMKAT2

    RAMKAT2 Randy

    How much stroke do you gain from the 292 crank? Is the bore on that engine 3.875"? If so, you might be able to use 283 chevy pistons instead of looking for original pontiac parts. That would make a great engine in a late 30's Pontiac street rod.
    Can't wait to see the rest of the build. Later, Randy
     
  6. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    The pistons have some pretty good valve reliefs in them, so that's a concern. I intend to bolt the cam housing back on the head and on my bench see how far the valves stick below the head. I didn't measure, but the pistons sat in the hole by a fair amount (seemed like ~.050").

    The stroke is 4.12" on the 292 crank, or a tad over .60", so longer rod and shorter piston needed. If I were to get another rod I noticed the new Hemi 5.7 has a similar bore with a shorter compression height. But they all appear to be domed too. The Mopar 318 bore is close too, looking at info on them too.
     
  7. Big Matt

    Big Matt Well-Known Member

    Why would you need a longer rod? I thought you could use your stock length rods as long as you adjust the compression height of the piston???
     
  8. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    Good point. I haven't given it too much thought, just the quick look. Thanks!
     
  9. Hector

    Hector '79 Buick Limited

    The hatching on the flat surfaces is from the machining operation.The main bearing that you showed looks to be a Federal Mogul part,altough standard in size I don't think that is a factory part,I'm just guessing.

    The engine looks nice and clean,cool project.Thanks for the pics.
     
  10. RAMKAT2

    RAMKAT2 Randy

    Here's the math: 4.12"-3.53"=0.59"/2=.295" shorter rod to use the same piston with the 292 crank. I doubt you are ever going to get an ideal rod ratio out of this engine, but you probably aren't going to be turning 9000rpm with this motor anyway, and you might see a small increase in torque using a shorter than stock rod combination. John Kaase has made some huge power in the engine masters challenge competition using short rod motors.
    If it is an issue, have the cylinder walls checked to see if there was much core shift when the block was cast. As long as the cylinder wall thickness is consistent, you should be safe.
    My concern would be camshaft/follower/lifter/timing belt & timing gear availability. I am sure there is a following for this motor in the Pontiac community, so they should be of some help finding parts. Have you found any suppliers for those parts yet?
    It looks like there is alot of room to open up the ports to get more flow out of the heads. You might not need it with the turbo. Have you considered a small supercharger like the ones used on the late 90's 3800 Buick motors?

    Geez...I have to start looking at the pictures a little closer...there is a 3800 supercharger & intake sitting on the shelf behind the motor!
     
    Last edited: Dec 21, 2010
  11. TheSilverBuick

    TheSilverBuick In the Middle of No Where


    Have you seen this picture :Brow:

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    I did that as a joke. The intake on the bench is for my 4.0L '87 Jeep, and I intend on using the supercharger on the Jeep. This engine is going turbo.
     
  12. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    My basement entrance is currently under a few feet of snow, so I'm not going to tear into disassembling the head until I can get back in there :( Maybe I'll dig it out after Christmas.

    Talked to Jerry Woodland, of OHC Pontiac parts fame, yesterday for a bit. Nice guy, he should have all the parts I need for the head (cam, follower, etc.) in stock and he is looking to see if he has an old set of pistons he pulled out of a low miles race engine years ago that may be forged. :TU:
     
  13. tlivingd

    tlivingd BIG BLOCK, THE ANTI PRIUS

    so... what is this going into?

    i've been wanting to build a lotus 7 clone. This would be a neat power plant for it.
     
  14. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    I used to own a 1969 Firebird with a 400 Pontiac in it. Due to an uninsured/unlicensed driver running a red light in a 3/4 ton Dodge taking it out, I've been casually looking for one (for the right price, I'm not in a hurry), and since I own two big block Buick's and a 428 powered T-bird, I figured I could go with a smaller more unique engine. Then turbo it for my Big Block HP/Torque appetite :3gears: and EFI to keep the tune in check when I drive from my work at 7500ft, to anywhere lower (like now where I'm sitting at 900ft elevation at my parent's house for Christmas).
     
  15. goatless

    goatless Well-Known Member

    That would be super cool... the only problem is the Pontiac OHC6 would weigh as much as the rest of the car!:shock:
     
  16. jay3000

    jay3000 Well-Known Member

    I like watching someone do something outside the box.. :TU:
     
  17. N360LL

    N360LL milehi71Stage1

    Turbocharged/EFI Pontiac OHC stroked I-6 in a Lotus Super 7 will go how fast at SilverState????? Can your Big-block car make it from the start line to the finish line on one tank of fuel?
     
  18. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    My Buick's should/could effortlessly make the course at ~100mph on a tank of fuel, probably could do it at 140mph. It's only 120 miles from gas station to gas station.

    I should be updating this today, I did a bit more last night.
     
  19. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    Did some more work/inspecting last night. Popped the valve cover back on and checked the lift on the valves to see how important the valve reliefs are in the pistons. Then I removed the cam from the housing and cleaned off the top of two pistons for inspection.
    I wanted to check how far the valves stuck below the deck. Though only the .035" is shown, the valve sticks about .070" below the deck. I determined this is the small cam, so the larger lift OEM cam would likely stick about .108" below the deck. Important to know to see if chevy 250 pistons have enough clearance.
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    The exhaust valve did not stick below the deck, it's just about right at it though.
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    Then I removed the cam from the cam housing. It comes out the back of the housing. The rear of the cam is on the right. The plate spins freely with that bolt keeping it in place. Looks like the plate has a tab that locks into the housing and the cam spins in the center of the plate. The plate also prevents the cam from walking forward. Then on the front side of the cam the sprocket bolts up and keeps the cam from walking backwards.
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    The cam journals look good. I haven't measured them out to see if they are oversized or anything, but they look and feel like they are in good shape.
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    This cam weighs a ton :p The cam has pressurized oil flow in through the journals and out on the holes in the lobes.
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    Running the numbers has verified that this cam is a base engine "C" cam, 1bbl cam in '68 & '69, so factory rating is 175HP on the low compression engine. Looks like the Camaro 250 in '69 had 155HP. I have a thread on the OHC forum going seeing what cam options are available out there.

    Here are the cam spec's, not that it matters since it's wiped.
    Then I decided to clean off the tops of two pistons to see if there were any oversized stampings on them. I half expected the two odd cylinders to be oversized and the rest standard :p
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    But nope, looks like this engine had some work done to it, as both pistons have a .030 stamp on them, so looks like the engine has at least had an overbore, doesn't appear to have been hot tanked though, or at least not enough to bake the original paint off it. Still has the two different piston mystery... Supply issue maybe? Of course I should actually use the dial caliper and measure the piston diameter :p Maybe next time.
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    I also double checked a few of the bearings looking for a date stamped on them, but alas none of them have any date stamp on them. Unless Federal Mogul just used the last two digits of the year, as they do have "00" on them, but that's it.

    I still need to remove the valves/springs and see what's up with the one keeper that isn't set right. I am also thinking of this weekend of bolting the crank back in the block with some plasti-gage and seeing what all the bearing clearances are as is.

    Then to top it all off, after I got in last night I got an email from a guy that has a set of forged pistons for the pontiac 250, but they are in standard size :Dou: I'll be measuring these pistons just to make sure they are actually oversized for this engine and not just a mixed set of pistons actually meant for another engine that conviently fit the standard bore of this engine (yeah right, I know it's a long long stretch..).
     
  20. TheSilverBuick

    TheSilverBuick In the Middle of No Where

    A small update.

    I had to go to the basement so while I was down there I thought I'd make a good effort to pop out the oil restrictor tube. Looks like the little hole is what feeds the lash adjusters, where as the remainder of the oil goes up and into the cam. Because the lighter load on the lash adjusters (as compared to conventional lifters, supposibly 33% less load) and the fact they don't pass oil up a push rod to a rocker assembly, they are very sensitive to having too much oil pressure and loading up the cam. Pontiac set the oil pump pressure relief valve to 30psi :Dou: and added this restrictor tube to keep the lash adjusters from pumping up. I'm wondering if I can get the oil pressure to a more conventional 60psi at the mains (then up to the cam), and get a pressure regulated 15-20psi external line to just the lash adjusters.

    The Mysterious Tube.
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    Where it sets in the head.
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    The backside of the head, there is the oil galley plug I'm considering getting rid of the small hole in the restrictor tube that feeds the lash adjusters and running a pressure regulated oil line to the oil galley behind that plug.
    [​IMG]
     

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