If the crank is in good shape then you may be able to shim the mains for less clearance, just make sure you don't block the oil passages, shim the cap side. I haven't personally done this but have read on here from Telriv(Tom Telesco) the resident Nailhead guru that it was an excepted practice back in the day. Worth a try anyway, shim the caps with the bearings in them and take a bore gauge measurement to see how much clearance went away. Shim stock @ .001" or .0015" or even .002" should get you where you need to be? You can even try the different size shim stock without taking engine apart to see which one gives the clearance you think you want using plasti-gauge to check size by just removing the caps, then put oil pan back on and check oil pressure. I would explain how to take the cap bottoms down as well if I didn't have to do so much typing to explain that. So probably not necessary to have the crank ground or the block line bored, different ways to tighten up clearances. GL
Knurl the crank. No, don't. (I shouldn't suggest this, but here goes...) You can lightly slide a fine file on the caps and registers as if you are finding the high spots, then same with a stone. If you found a few tenths on each side by just cleaning up the mating surfaces, that would help some. Please use a delicate touch and discretion. Even the old figure 8 with fine paper on a granite could do immense damage. Either way, I'd measure the main bore and assess it's condition before assuming to re-grind a crank. Maybe a bearing swap would do it? Not to open a can of worms, but main studs or stronger bolts changes dimensions too.
Those band-aids are... well, band aids. Shimming was done when engines lasted 60K miles. Hasn't been seen since they approached 100K. Squishing down the top and bottom isn't much of an improvement. Jim
I did cringe as I wrote it, thinking about how it might be taken with some naivety. Is the concern with the vertical clearance? I think both comments address that with honesty and insight from the machinists perspective. Is there any worry over bearing eccentricity? Personally, it would be in my interests to have suggested starting over and machining things with the end result pre-planned, as that would promote industry and make money. Reading how this project is where it's at and what he's dealing with, the suggestions are coming from the assumption that the OP doesn't want to ship this off for an entire re-do at considerable cost. It's quite frustrating to continually read about a non-suspecting customer send a crank off to be 'ground right this time' and then purchase a bearing to be surprised at the outcome yet again, instead of grinding the crank last I agree that a thou less clearance might not offer tremendous improvement in pressure, I can cite examples of double the clearance along with 'blueprinted' oiling systems pegging the pressure gauge in cases (different engine family)
All I can do is offer my own experiences, having made the same mistakes and then learned to do it right. SBB and BBB engines (Including BOPR and V6) all CAN give exceptional oiling, but all require particular attention to be paid to key areas. There are several ways to lose oil pressure and the only way to keep it is to be very particular about these key areas. Leave any one out when prepping your engine and pay the consequences in inadequate oil pressure. In order of importance then: Bearing clearances: .001-.0015max. You simply would not believe how much oil will spray out of a bearing with .0025" clearance. And you have a bunch of them. Rods and mains,, and cam bearings too. If you don't get those under control first you are wasting your time on the rest of it. I shoot for the tight side of that range. Keep the oil in, and keep the pressure. Oil pump clearances: If you let the oil leak around the gears you will never get the needed flow and pressure. You cannot do a damned thing about side clearance so set the end clearance as tight as you can get it without significant drag when assembled. Any more than that and you are throwing away the game. Feed the oil pump: It can't pump what it doesn't have. It sits above the oil level and needs all the help it can get. Hog out that suction hole. The factory eventually saw fit to go to 5/8", and you should too. The aluminum blocks have more meat than the iron ones, but even they should be able to go that big with a piloted bit. Radius the corners. Port the pump, the front cover, the booster plate and the filter housing. Can't get oil if it's all turbulent at every bend. If you get all that done, it's fine to look at the top end but that isn't where you are going to lose a lot of oil unless you just have a really crappy fitting set of lifters. Still, smaller losses do add up so it can only help. Jim
Thanks for that, I was hoping the detailed info would find the OP. The OP is past that point of having it 'done right the first time' and looking for solutions. I think what 300 sbb overkill and I were getting at was that the machinist, engineer or shop owner uses their skill set to decide what machining practices are appropriate for the various problems encountered. It sounds like blasphemy to run a stone across an imperfect surface to true it up, like the video on Youtube where a guy describes surfacing a head by dragging it on the sidewalk... Million dollar machines that hold much tighter tolerances than in these crude engines we discuss here occasionally need some attention by hand, as do certain engine bearings that seem to come right from the package with chips embedded into the the back side of the shells. That opens things up a few tenths. The main bores themselves can be as true as any machine can get them, but under load it distorts enough to need an eccentric bearing. This should be enough to suggest that the bore should be measured to assess the situation before arbitrarily line boring or grinding a crank for potentially no good reason. An engine assembler concerned with tolerances and oil pressure should be able to do this. 'If'...there were visible high spots on the mating surfaces or other related assembly issues found under closer scrutiny, the bearing would still be eccentric after the anomaly was corrected. It's more likely that a small ding or problem with a million dollar machine's turret or tool holder would be massaged by hand with a rock for ten seconds than sent to an automotive machine shop's crude version of a boring machine or spend half a day setting up a precision grinder. Coated bearings could be the easiest option. Typically, Polydyne bearings are .0005" smaller on diameter, possibly a different coating could be used or discussed with a vendor. Not having or following a plan is certainly more costly in the long run. Nobody has shimmed his engine or dragged his parts on the concrete yet. It's just open discussion intended to get the OP to think about solutions. Maybe single pattern knurling on his crank will have each of the journals acting like their own paddle-wheel oil pressure boosters...AS Seen On TV.
LOL. But seriously... some things really can't be band-aided. I'm not saying you can't shim bearings and all that other messing around, but if you're in there anyway what is stopping you from getting a set of +.010 main shells and having the crank touched up to get the right clearance? Jim
What if his main bores are jacked out of shape already or if using ARP studs, a little bit more torque used does the trick? What about a different shell? Even if 300sbb and I don't see eye to eye on some things, I'm backing up his suggestion. I don't shim bearings either. I posted that in humor but to get the OP thinking around the problem. It's not even my money and I'm irritated thinking about how he has to pay for it again when the shop should have ground the crank last (I know there's a ton of assumptions here. Just saying it was entirely preventable. There might not even be any lack of communication or carelessness by the shop, but they should push this one on the customer and decide it for him)
I'm guessing that's what the crank polished out at and the builder just went with it. Not hard to fix if you have it opened up. Jim
I have read everything you have written. I've not had any oil pressure problems on other motors. Normally it's just send it to the machine shop, assemble, check the clearances with Plasigage, wrap it up and go. This shop did over cut the crank and other dumb stuff; but as they said,"why are you worried about .0025". I assembled the motor. In any case, I have some shells and crank has gone to a highly recommended shop and will be re- ground to achieve .001 mains and rods. The 1961 factory manual shows rod bearing clearance of .0002-.0022. That .0002 seems way too tight but that's what the book shows. Don't think I'd dare to do it . Taking you gentlemen's advice, I am checking the main bore roundness(even though I was told that it checked out good) and the bearing ID before grinding the crank. TA booster plate on order and will set it up for .001 as I think you advised. The original oil pump cover has a semi circular wear pattern under the drive gear which is caused by the gear jacking under load because of slight wear to the hole in which the drive gear shaft runs. Shaft movement is slight and that steel booster plate will provide a surface that can be properly set for clearance. Oil pump gear to side wall clearance is .004-.005; TA tech did not think this was too serious. TA currently has a client with a "pro" built aluminum V8 that has less oil pressure than mine. V6 oil pickup tube is here and the oil feed will be 9/16. The comment about dragging the head on concrete is not far off. A local shop, "surfaced" my 401 heads by dragging them over a rotating stone on a steel table and yes, they leaked when I assembled the motor.
(For clarification purposes, not defending anyone) Checking the main bores isn't just for roundness. There's a range on that dimension. It might be near the high limit, leaving too much clearance when it's all added together. The crank might be entirely within the book spec range also. The new shells you have need to be measured installed in their home to determine what size to grind the crank to. That's why the crank is ground last. .0002" too tight? Scary indeed. A Subaru I machined had a -.0002" ? ( negative!) piston fit on the low end of the range. Hypereutectic piston that doesn't expand much and an aluminum block that does. That spinning stone 'should' produce better flatness if properly dressed and maintained than the slightly tilted spindle of a large diameter milling cutter, depending on which machine it is. Another thing too is that the cutter head can deflect based on whether the tool path is plowing down the center, giving 'confused cutting forces' or if biased to one side. That being said, (Subaru turbo) heads having a really tight tolerance for flatness turn out better on a spinning stone flywheel grinder than some mills. (point of this is to illustrate that a non-machinist customer would have a really tough time determining the cause of error or if it was from machining practices or equipment type) So far as it's written, no error has been described in why the mains are too loose for the liking, nor was a plan described that ensures that it will be different next time. Comment on the pro built aluminum engine also sharing oil pressure values...oil flow can be more important than pressure (resistance to flow). I'd follow their advice on why their's is how it is.
I agree that flow can be more important than pressure, EXCEPT IN A CASE WHERE a potential buyer offers you a fair price for your car and backs out when he looks at the oil pressure gauge and sees 25psi @5000rpm.
If that's what you picked up from all of my post, please understand that I agree with you as the car's owner and you are perfectly justified for that. I was attempting to opine neutrally to that particular aspect... leaving it to TA, any experts of this engine design, or the Buick team that created it to offer any contrary thoughts. My posts on the subject was meant to assist the planning and machining process used to correct the condition. Hopefully this isn't out of context...if you were putting this together with intent to sell and somehow come out ahead, then the best advice would have been to pay whatever it cost for a specialist the first time, rather than to assemble it yourself using local shops chosen for price over end product and have the forum's contributions serve as 'proofs' to add value to your sale. I'm more curious about the machine shops opinions at this point, and why would you not go with what they recommended? I'm not accusing you of doing any of that, more like hoping you get to enjoy your cool car for years to come and that your comment was a wise thought meant for some time in the distant future.
I don't know how far I would trust a machinist who asked me why I had a problem with 0.0025" clearance in the mains. Especially if I had already given him the desired clearance numbers and that was what he gave me. Maybe that wasn't the case here, but if it was I'd be checking his work very carefully, and be extremely hesitant to give him anything he could screw up badly. Jim
I don't recall having read anything that suggests the machinist went outside published specs or acted against customer communications suggesting to deviate from that. IIRC, the OP learned of the preferred range long after the fact.
I I am condemning the poor results. My comments were made after discovering that the main journal diameters were at the small end."Legally" the machinist is not "at fault" in this specific area. At the time, i did not realize that .0025 would be a problem, although I unjustifiably expected a conservative mid range .0015. These loose journals (.0025)are partly responsible for the extreme low pressure according to forum members who responded. My previous experience with sb Chevy and Ford and Nailheads and other motors with iron oil pumps mounted inside the crank case (and no problem with low oil pressure at 4000 rpm), did not equip me to foresee the potential problems with an aluminum pump mounted a total of 20 inches from the oil entry point and supplying oil to that pump thru a 7/16 passage and other contributing factors such as lifters bleeding push rod oil where original equipment passed no oil. Your incisive comments caused me to reevaluate my methods. I and the machinist assumed that the desired clearance could be achieved by grinding to the upper or lower end of the factory specs minus the .010 under size. Not happening!! This time the block is at the shop with the new under size bearings installed; the machinist will measure the ID and grind each journal to achieve .001 clearance. The shop I am using this time comes highly recommended. As for the previous shop, they ground this 4.6 Rover stroker crank with NO fillet radii on the journals, installed the oil gallery plugs without cleaning out the residual metal, and installed ARP high strength bolts in 7 connecting rods leaving me to discover one rod with the old bolts(the ARP's were in the garbage can).
Wow! (Rod bolts, etc.) Thank you for addressing this in a responsible way. Your response has you looking like a stand up guy in my eyes. Hopefully no inference of neglect was taken on anyone's part here, in this thread or connected. This is one of those things that slips past so many builds, especially with the many strategies and areas of responsibilities. Best of luck to you.
In the past ,I have counted on luck (haven't got any with car stuff), and hoped for the desired outcome. I should recall advice that I gave to a friend who put money into stocks and "hoped" for a positive result: "Hope isn't a strategy". None of the machine shops I visited suggested actually measuring the main bearing ID and grinding appropriately. I took forum advice instead. Re the head surfacing; I have seen the special head surfacing tool you described; but the stone surfacing tool I saw being used was about 10" wide and looked like a wood planing tool. The operator hand held the head and moved it back and forth across the stone. (NO JOKE) Re selling the car: Money, time and energy are considerations that we senior citizens give much thought to. My "story" about the interested buyer was semi-hypothetical. I have received inquiries about selling, but haven't pursued it. Honestly, I regretted not selling it when the rebuilt Roto Hydramatic died. Rebuilt Roto's don't have new parts as there aren't many left and they were a problem when new. The 700R4 and one-piece drive shaft we installed required a complete revamp of the tunnel from the engine to the rear axle. This 61 Cutlass gets a lot of attention due to it's rarity. MAV TV did an interview at the Nashville Good Guys event and the Good Guys Gazette printed a photo of it the first time I took it to a show. (Pathetic, seeking of a cheap ego boost) Check out the newer thread " Oil Pressure 1965 V8" same ol' stuff. Thanks to all for generously given advice.
