Bubbacuda68
Member
Has anyone come up with a solution for the weak intermediate oil pump shaft on small block, 68-340 to be exact?
Oil pump intermediate shaft breaking
- Thread starter Bubbacuda68
- Start date
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Plymouth 65
I'll be in the shop
They make pinned/hardened intermediate shafts. MP or Melling. 65
Bubbacuda68
Member
One of the 2 that I snapped was a pinned Melling. I have checked for binding and there is none, brand new bushing. Still snapping
Where does it snap, near the oil pump end ?
Tommy
Tommy
How much pressure is the pump putting out,,,,,unless it’s over a 100 pounds , you shouldn’t be able to break a shaft,,,not a good one .
Tommy
Tommy
Inertia
Well-Known Member
I'd be scrutinizing the oil pump/gears for evidence of whatever is jamming the pump.
Once is an anomaly, twice is not.
Used oil pick-up?
Once is an anomaly, twice is not.
Used oil pick-up?
In addition to what has been said above, if it is snapping, make sure the pump is seated flush and the shaft is straight . If the shaft engagement to the pump is not straight, there will be excess stress applied to the shaft.
Also be sure there is the right clearance between the shaft and the bronze bushing as well as the mesh with the cam gear to avoid binding and excess heat build up for lack of clearance and oiling.
Also be sure the shaft length is correct. For example if the block and china wall has been machined, you may have to shim the distributed or shorten the distributor tang that engages the oil pump drive to be sure the engagement and mesh of the gears is correct.
See discussion in this recent thread starting at post #146.
www.forabodiesonly.com
Also be sure there is the right clearance between the shaft and the bronze bushing as well as the mesh with the cam gear to avoid binding and excess heat build up for lack of clearance and oiling.
Also be sure the shaft length is correct. For example if the block and china wall has been machined, you may have to shim the distributed or shorten the distributor tang that engages the oil pump drive to be sure the engagement and mesh of the gears is correct.
See discussion in this recent thread starting at post #146.
Old Race 340 Teardown
Crane is still around in a way . Key people spun off and started their own companies . For example Daytona Sensors is pretty much an extension of Crane Ignitions. Somebody else in the cam department runs another cam company ... I forget which one . Speed Talk has some threads about this .
www.forabodiesonly.com
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It's been argued that the pinned shafts are weaker than the pressed on and I can see some validity to it. The hole drilled through the shaft to accept the pin can certainly be a weak point.
Dan the man
Well-Known Member
Is it a high pressure pump? Camshaft turn freely?
Dan the man
Well-Known Member
I did investigate this same thing years ago and it was said then that pinned shafts are weaker.
Newbomb Turk
Well-Known Member
If that’s where the failure is. Most of the failures I’ve seen the drive fractured at the neck down to the hex drive.
I've seen that as well. That's why the "good" shafts don't have a hard "step" there. The goos ones look like this. Without the pin, of course. But you know that already.
Newbomb Turk
Well-Known Member
I should have asked RRR too (he can read this and answer too) how many of these failures have you seen at the drive gear end?
I know I’ve run as high as 125 pounds of oil pressure and never failed a drive.
I also gave a theory about bronze gear wear. IMO most of the bronze gear failures are because cam thrust is not verified and corrected.
If it’s not corrected the cam can move enough that rapid gear wear occurs.
I can’t count the number of times I’ve had to machine a cam gear to tighten up cam thrust. Almost half of the builds have the thrust too loose.
I've seen ONE break at the gear end where the pin is. It wasn't mine. It was on a big block. It had much the same shaft as the one I pictured above. That's the only one I've ever actually seen.
No pic on the op's break(s)?
Professor Fate
Push the button, Max...
OP hasn't been back since post 3.
No word on where the break actually is.
No word on where the break actually is.
Bubbacuda68
Member
Right where it goes from round to hex.
Bubbacuda68
Member
Yes, the oil pick up is used but the pump is a new HV pump
Bubbacuda68
Member
That is where both of my failures were, at the neck down where it goes to hex.
Newbomb Turk
Well-Known Member
Does the drives you are using look like the one in post 12 or does it have a machined edge where it goes into the hex?
If it’s the latter that’s why it’s failing. Although I can’t think of a drive I’ve seen that was pinned and not machined with a radius going to the hex.
I was talking with a friend of mine who is older than me a bit and he said when guys were running straight 50 and 60 grade oils were spinning the gear on the shaft on cold starts when the weather dropped below 50 degrees.
Evidently that’s where the pinning came from. No one should be running oil like that today.
Bubbacuda68
Member
It looks exactly like the post in 12
Inertia
Well-Known Member
Is this a fresh build, or a running engine.
You wouldn't believe the debris that'll come outta a used pickup while banging it on side of the solvent tank when cleaning .
A little background will help .
Newbomb Turk
Well-Known Member
Well damn. That’s a pretty thing. Maybe the new drives aren’t worth a crap.
Like I said earlier, I’ve run 125 psi on those drives and never failed one.
Unless some focknoid found its way into the pump and locked it up I’ve got nothing.
Try priming it with a hex shaft and drill. Put it on lock(slow speed) grab a beer and wait n watch.
Bubbacuda68
Member
I h
This is a fresh build, pick up is used but CLEANED through and through. New bushing, oil pump, etc.
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