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#21
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#22
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#23
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The OP is in the UK, it's very difficult to find anyone over here that can be trusted to do any Pontiac high performance mods or machine work. The reason I built my own mains girdle was because I didn't trust any UK shop to machine/fit 4 bolt splayed caps.
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#24
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Oil pump drive shaft
This seems like an opportunity for someone brilliant to come up with “something better”. The problem is the tang on the pump. That dictates the necessity of a fork in the shaft. There is a property called modulus of elasticity. It's basically the same for all steel alloys. It controls the stiffness of the material. So it doesn't matter what alloy is used. The forks will bend the same amount. Strength is different than bending. Alloys can take more abuse before reaching the breaking point. But you need both properties working for you or you reach a "zipper point" and the fork will fail. So you need a different pump shaft and drive shaft interface design. Not just a stronger fork. My guess is that something like a splined end would be much stronger, think along the lines of a manual trans input shaft. You don’t see axles and transmissions driven by cheesy “tangs”.
Sent from my iPhone using Tapatalk Last edited by Vid; 06-02-2021 at 12:35 PM. |
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#25
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Except for Ford Model A rear axles with a key to attach the axle to the hub.
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My Pontiac is a '57 GMC with its original 347" Pontiac V8 and dual-range Hydra-Matic. |
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#26
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But how hard can it be to get a crank cut on your side of the Pond?
I mean Gez , in terms of bring down a counter weight some that’s done off the crank center line so it can be done in a big enough lathe, you don’t even need a crank grinder!
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#27
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Will Rivera '69 Firebird 400/461, 290+ E D-Ports, HR 230/236, 4l80E, 8.5 Rear, 3.55 gears ‘66 Lemans, 455, KRE D-Ports, TH350, 12 bolt 3.90 gears '69 LeMans Vert, 350, #47 heads: work in progress |
#28
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Just an observation: If the Pontiac oil pump drive looks Mickey Mouse to you compare that to the 1/4" Allen Wrench a Ford uses to drive their pump! It's 7 1/2 inches long too. I may be the luckiest man alive but I have never broken a Pontiac oil pump drive shaft from basic street engines to the 1500 HP Grocery Getter replica we ran with a stock Melling M54 pump for almost 20 years. May break one tomorrow, but so far, no blems in hundreds of builds over 40 + years. I have used some of the Nightmare Performance parts over the years. The Camshaft thrust plates in particular. Their products are top notch and may provide some extra insurance if worried about shaft failure. |
#29
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The Nitemare shaft seems like a must for those of us who've broken one or don't care about an extra $50 for an important part to not brake and destroy $15k.
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69 GTO Convertible, 4000lbs 462ci, 606tq/569hp - 93 oct @ 34 deg (207psi) 11.7:1, KRE H Ports, Lunati HR 282/290 w Johnson Lifters & 1.65 Scorp, E30, EFI, Holley HP + Dual Sync, 12-1 Crank Trig, 120lb Inj & 1000cfm TB, Torker II EFI Int & Rails, PTC 10", Ricks SS Gas Tank, Magna 4303, Aerom EFI Reg, Aero Front & Wilwood Rear Disc Brakes, Dougs 1 7/8" & Borla Pro XS 3", Alum Rad & Dual Fans, 12:1 Box, UMI Arms & Viking Berz Fr + Rear CO Shocks, Hella UP28 Vac Pump, 12 Bolt, 3.73, 33 Spline |
#30
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I have never busted one also, but that being said I have had a few stock ones showing near a 1/8th of a turn twist in them.
Race motors are not as hard on them as a every day street car that has to start up in the dead of winter when it’s -10 to -15 out without the chill factor!
__________________
Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs! And he was not talking about 1/8 or 1/4 mile ETs! 1) 1940s 100% silver 4 cup tea server set. Two dry rotted 14 x 10 Micky Thompson slicks. 1) un-mailed in gift coupon from a 1972 box of corn flakes. Two pairs of brown leather flip flops, never seen more then 2 mph. Education is what your left with once you forget things! |
#31
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There's probably only one small spot at the largest diameter of the counterweight that will be close, I would grind a small flat at that spot - just enough to give .050" clearance. As Mgarblik said it's probably around a gram, doubt you or the engine would ever notice.
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#32
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My hunch is that Batson was likely correct and the pump shaft was not quite aligned right when the distributer was bolted down. It isn’t all that uncommon, and it can happen with other non pontiacs that have similar drive set ups. The couplings can get a bur on the coupling and will not seat quite correct, then when it is tightened down it puts a bind on the shaft and misalign’s it. It then splits the yoke on the shaft.
If you put it together and it breaks again, you better be looking at the counter weight clearance. I agree with taff2, I think the area would likely be small and not effect the balancing. I know of many of Pontiac engines running around with neutral balanced rotating assemblies and the oem flywheels that are not quite neutral with no issues. I have heard of some Butler rotating assemblies rebalanced found to be not all that dead to on and never heard of complaints either. My opinion anyway, I would clearance it an put it together if it is an issue. I design/engineer a lot of drive lines. Sometimes you can over design the drive and it makes the smallest misalignment a big problem. My opinion is Pontiac engineers did fine on there design efforts on the shaft drive, for the most part it is not where the short coming are. My guess is the HD melling shaft was case hardened more to address the wear down at the drive points than shear on the shaft. I don’t think the weak spot on a oil pump drive for a Pontiac is pump drive shaft. We have never sheared a shaft or split the shaft at the unions. What we have done is shear the key up on the cam on the timing chain. We have sheared a couple of them, they were race engines with oil restrictors on the galleys, heavy weight oil and a 80 psi pump. They would run fine to about 95 psi, then key on the timing chain would shear, engine quickly stopped and proceed to bend several valves. That was with just and ordinary std pump shaft. Would have thought if the pump shaft was the weak link it would have sheared it instead. 60 psi pumps and those issues went away. Could have saved your self some trouble and piece of mind by measure the counter weight clearance with some feeler gauges. But I have my doubt that there is an issue there, make sure the coupling seat together correctly before you clamp the dizzy down. Last edited by Jay S; 06-02-2021 at 07:49 PM. Reason: Add |
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#33
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It shouldn't be an issue to turn down an oil pump driveshaft .050. It's the recommended procedure by AP to correct clearance issues. The drive in the picture came out of a World record setting Pontiac that made close to 1,000 horsepower and was spun past 8,000 rpm on every pass.
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#34
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Sent from my iPhone using Tapatalk |
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#35
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#36
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#37
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Yeah, I know it won't. It's gotta go back in the engine, break a thousand horsepower and win more races.
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#38
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That shaft is still bigger than Fords with those pencil ends and they can make more power than any Pontiac. |
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#39
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You guys really need to study metallurgy and heat treating. As long as the base alloy isn’t brought past its quench point( very unlikely in a normal lathe cutting operation) turning .050 off of it isn’t a cause for alarm. If it makes you sleep better at night, re-heat treat the shaft. The ONLY Pontiac oil pump drive shaft I have ever had fail was one I bought from H-O years ago. It didn’t break, but it was certainly interesting getting that steel “pretzel” out of the block. FYI....incorrect installation .
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“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
#40
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“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
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Closed Thread |
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