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Topic: Chronic PT658 Engine problem |
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Jerry Gilmartin
TOP BOSS
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 Posted on: Dec 5, 2021 - 4:10pm
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Hello there! Last Thursday, on 12-2-21 the crew took the recently repaired PT658 out for a "shakedown cruise" of sorts. We tested the Port Engine, which had just had the supercharger drive shaft replaced.
We have had an unfortunate history of breaking supercharger drive shafts! This in itself is sort of mind blowing when you consider this shaft is a 1 inch diameter hardened steel shaft about 12 inches long and splines at both ends. The function of this shaft is to transmit the rotation of the crank shaft into the large central hub of the lower supercharger drive gear. There is an idler gear in between that and the supercharger gear itself which results in a gear ratio of ~6.25:1 for a speed increase of the supercharger wheel in relation to the engine crank shaft.
Our problems started a couple of years ago when we snapped the center engine super drive shaft during an apparent backfire of the engine while starting it. After we disassembled the gear set, we discovered a possible contributing factor (or root cause) of upper engine block internal drilled oil passages were clogged with 60 year old gunk, thus starving the supercharger bearings of lubricating oil. To fix this problem, we flushed the oil passages to remove the old gunk, and then upgraded the old style oil filters to a more modern 1 micron spin-on type oil filter to prevent that same problem from occurring on all 3 engines. OK so now we should be good. WRONG.
So fast forward to last year, and we snapped two more of these same drive shafts! One was for an unknown reason, and this latest one was apparently due to another oil supply issue. We are still trying to take some sort of corrective action but as for now all we can do is keep replacing these irreplaceable supercharger drive shafts! So we are currently in negotiation with a competent machine shop, who has our last remaining spare shaft to use as an example to copy. Does anyone have any ideas or recollections as to why this is happening? We spoke to one of our veterans who has since taken his last patrol on this subject and he said this was a well known "Achilles Heel" of the Packard engines. And before you ask Yes we contacted Randy Smith in New Orleans and he had never heard of this happening with his engines on PT305.
So hopefully somebody on this Forum will hear something or dig up some information about how to prevent this strange failure from happening again! Please let us at PT658 know if you have any solutions. Thanks! Jerry.
Below picture has supercharger drive shaft circled in red connecting the crank shaft to the drive gear.
Jerry Gilmartin
PT658 Crewman
Portland OR |
Total Posts: 1472 | Joined:
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Travis B
Advanced Member
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Posted on: Dec 5, 2021 - 7:55pm
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Jerry, I have several questions about the problem you are having. If you like we can discuss this over the phone or on the forum which ever you would like.
Where is the shaft breaking?
The replacement shafts are they original or from another v12 for a different application.
Has this happened to all engines or just one.
When you replace the shaft to you flush entire oil system to remove any debris and or metals from the broken shaft?
Do your Packard engines have a hydraulic gear change
arrangement of oil operated clutches to increase the superchargers RPMs kind of like a low and high speed for the supercharger?
Have you checked compression in each cylinder?
Your issue sounds like torsional Vibration.
I found this information about German Engineers looking at our V12 engines used during the war.......
The primary moving components within a V-12 engine power train include the propeller, reduction gears, crankshaft and supercharger drive. These components rotate at relatively high speeds and are driven by the considerable forces coming from combustion gasses via the
pistons and connecting rods. These forces cause intermittent loading and un-loading of the crankshaft journals, which results in non-uniform torsional inputs to the crankshaft, causing it to load-unload at a frequency proportional to the speed of the engine. This variation creates uneven torque impulses on the entire drive train, which being made of high strength steel, twists. This spring-like twisting and un-twisting induces a vibration within all of the
components of the system, which in turn manifests themselves as vibrations. Each of these modes has a natural frequency, determined by the stiffness, configuration and shapes of the materials of construction. Within the mode there are other events occurring, these are vibrations which are multiples of the fundamental natural frequency of the mode and occur at specific crankshaft speeds, or rpm. These orders start at ½ times the
fundamental, and increase in the series 1, 1½, 2, 2½, 3, 3½, 4, 4½, ... Many of these orders have very little energy in them and can be ignored. Some however, often the 4½, 6 and 7½ orders, can be very energetic, and if ignored, can produce stresses that will fatigue and ultimately fracture the metal in the crankshaft or drive element.
-Travis
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Stearman
Advanced Member
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Posted on: Dec 5, 2021 - 8:16pm
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This antidote might help! Back in the late 70s, one of the museums in England was restoring a prewar Autounion mid engine V16 supercharged Grand Prix car , the most advanced car in the world when it raced. So they sent a peace of the aluminum engine to Cambridge University for analysis. They sent back a simple note stating, "the sample has all the consistency of good quality lawn furniture!" I would think you could find one of the collages in your area, with a good engineering department, that would love to use one of your junk shafts to analyze and recommend a better material for a learning experience! You could probably get them to do it for free, as a non profit group.
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Jerry Gilmartin
TOP BOSS
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Posted on: Dec 5, 2021 - 8:24pm
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Thanks Travis I will list the answers to those questions below.
Q: Where is the shaft breaking?
A: I need to research this one and possibly provide photos of broken shafts. the break is happening in the smaller diameter middle section of the shaft not near the splines
Q: The replacement shafts are they original or from another v12 for a different application?
A: We took our replacement shafts from all of our spare engines. We have a collection of several 4M-2500 Packard V12 PT Boat engines obtained from various places.
Q: Has this happened to all engines or just one?
A: It has happened to the center engine twice and the port engine once
Q: When you replace the shaft to you flush entire oil system to remove any debris and or metals from the broken shaft?
A: Yes the entire oil system including the oil sump was flushed completely and the oil replaced with new oil after flushing old particles out.
Q: Do your Packard engines have a hydraulic gear change
arrangement of oil operated clutches to increase the superchargers RPMs kind of like a low and high speed for the supercharger?
A: No, the supercharger is driven by gears as pictured below. I am familiar with on high performance aircraft engines have multiple speed turbo superchargers on them, but we only have the single speed direct gear driven style. Also, the engine output transmission gears are the original "Joes Gears" (Snow Nabstedt) used on original PT Boats. For a very short time in 2004-2005 we had some pneumatically operated gear shifting cylinders but soon removed them because the Skipper was over shifting the engines and causing premature clutch wear and failure of the reverse gear. So the pneumatic shifters were removed in 2005.
Q: Have you checked compression in each cylinder?
A: I am sure they have checked the compression, and I can get you that info as well, and as I recall it was normal compression values.
Q: Your issue sounds like torsional Vibration.
A: I will relay these concerns to our motor macks!
Meanwhile here is another photo showing the shaft and its associated gear train.
Jerry Gilmartin
PT658 Crewman
Portland OR |
Total Posts: 1472 | Joined:
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Travis B
Advanced Member
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Posted on: Dec 6, 2021 - 9:09am
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Also another thought check and inspect the supercharger, if the engine backfired hard enough the supercharger can sustain damage from such event. Please send me pictures of this broken shaft when you have a chance. I do have connections with several Packard engine builders who work on everything Packard including Jay Leno's cars. Hoping to get some more answers to your problem in the coming days.
-Travis
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Travis B
Advanced Member
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Posted on: Dec 6, 2021 - 9:26am
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I also reached out to a Restoration shop out here in NJ that works on Packards and also has a parts department for Packards. I am hoping they can locate some more of the supercharger driveshafts for you guys. Worst case I have someone who can reverse engineer a original to make copies.
-Travis
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Jeff H
Full Member
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Posted on: Dec 7, 2021 - 5:49am
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Jerry
What I noticed is the geared hub with the springs in it. You guys probably already checked this but if those springs loose tension they will stack up solid at a lower maximum torque/RPM and that may allow the connecting shaft to see a higher torque value than it was designed for. The shaft is designed to break if the engine revs too quick or the supercharger has a mechanical failure or for some reason is producing more drag/boost than it was designed for. I have noticed the same problems in high RPM engines with a manual transmission. The clutch disc has a sprung hub design similar to that on your gear. If the springs get week in the hub you loose the cushioning effect and higher shock loads are transmitted to the drivetrain. Just a thought. Good Luck!!
Thanks!
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Jerry Gilmartin |
TOP BOSS
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Posted on: Dec 7, 2021 - 9:34am
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Thanks Stearman, Jeff and Travis! I will be going down to the PT Boat house on this Thursday and will discuss these ideas with our crew. I think we have already sent the metal of the shaft out for analysis and it came back as good quality HSS, hardened on outside with core being able to "spring" like it was designed. I appreciate all of your fresh insight! We are open to any ideas that you guys may have, since the problem is sort of unusual and most of the guys who worked on these engines during WW2 have taken their "Last Patrol"
Jerry
Jerry Gilmartin
PT658 Crewman
Portland OR |
Total Posts: 1472 | Joined:
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Jerry Gilmartin
TOP BOSS
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Posted on: Dec 7, 2021 - 3:26pm
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Here is a photo from our latest newsletter of the most recent broken shaft next to our last unbroken spare. You can see just how much force would be required to snap this 1 inch diameter shaft like it was a twig.
Jerry Gilmartin
PT658 Crewman
Portland OR |
Total Posts: 1472 | Joined:
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Jeff H
Full Member
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Posted on: Dec 7, 2021 - 4:46pm
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Jerry
From the pictures you posted it looks like the shaft end that goes into the sprung gear has an extension that fits into a bushing or bearing to locate it. On that end the splines look like they have more wear than the motor end splines. This looks like the problem is coming from the supercharger end. I would check the bearing/bushing wear on all of the gears and look for anything that has caused the gear to gear mesh to open up and cause more vibration or misalignment. From what I can see in the photo that gear looks like it is seeing a lot of vibration or back and forth speed changes. I still would check that sprung gear closely since the springs are there to dampen those type of harmonics out. My assumption is this housing is filled with gear oil for lubrication. I know this is a pain for you guys like it was for the 39 years I worked in industrial maintenance but since I retired I kind of miss it a little. Good Luck!!
Thanks!
Jeff |
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