Paul Thompson 'Hooligan'
Admin
Hi all
I have come across a number of MSD distributors where the roll pin securing the drive gear has sheared, 3 of which were fitted to motors with high volume pumps.
The most recent 'owner', forwarded me the email below that may be of interest to others - Opinions / experience / comment also welcomed and encouraged...
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Subject: Re: [SCOF] DIRECT from M-S-D regarding DIST. GEARS & PINS
Date: Wed, 23 May 2007 20:37:17 EDT
RT... Thanks! Great explanation.
Seems like if a pin shears and the gear spins then the shaft ought to go in the trash and a new gear/shaft combo should be the order of business.
Herb
In a message dated 5/23/2007 4:05:54 P.M. Eastern daylight Time, [email protected] writes:
Ok, I really didn't have time for this today only a week after the Fel-Pro myth-busting endeavor, but once again I'm a tree shaker and fact taker, so it looks like it's another myth that needs busting.
I just called MSD and asked to be directed to an engineer in the Distributor division specifically associated with the distributor gear operations. Since everyone uses Email nowadays, there was no wait time and I got to a tech instantly. (what a sneaky tip, eh? to use the phone instead of Email!)
After explaining my background and expertise in the field, quite a few of the phone tech guys I was transferred to didn't want any part of this, and I was ultimately sent quite aways up the ladder to an engineer specific to this component, named Joe Lapelli at MSD.
After explaining the issue to him regarding the rumor that "MSD told a major engine builder and/or customer that any time one of MSD's "RACING" distributors were to used with a hi-volume oil pump or used in applications where higher than stock revs were experienced, their distributors had to have the gear pin drilled and enlarged in order to prevent the pressed on gear from rotating."
Well, at this point there was dead silence on the other end of the phone... probably because I was talking to an answering machine. So at 10:21am CST I stated my case and hung up while awaiting for Mr.Lapelli's return call.
At 2:02pm CST Joe called me back and had a lot to say. He very adamantly stated that "if we at MSD thought there was a need to use a larger pin in any of our distributors, we would have done so at the factory!" The reason they do not, is that is the only fusible link left in a High Performance distributor system using a stiff oil drive shaft as it is. If the gear can not spin, the resulting damage CAN take out the engine block, and has more than once! (more on that below).
And while they do have had their tech's suggested in the past that ONE solution to an already spinning gear would be to install a larger pin, that is not what they would recommend anyone else to do in advance. Joe confirms that he too would have to think that most
likely there is something else wrong that caused the gear to spin, and that should be sought out and addressed first before blaming the gear.
They understand that if the gear slipped once due to the existence of another problem, most likely the new gear will now not press on as tight as it should, and therefore the only option would be to drill for a larger pin... however, he did say a new distributor
shaft is really the right thing to do, and the larger pin is merely a bandaid to the problem. The reason they might advise a larger pin to be installed AFTER the gear spun once, is that otherwise they would have to say "get a new distributor or shaft". And while that may be the RIGHT thing to do, it is not what most unseasoned customers want to hear.
Joe confirmed that MSD distributors were designed with Hi-Volume oil pumps and hi-RPM's in mind and should never spin a gear in normal operations. However, he did clarify that significantly high oil pressures would include 100psi+... and "higher than normal revs" would be in the 9,000 rpm+ ranges... anything less would fall into what the distributor was intended for.
But, as the poorly fit gear relying only on the pin and some press fit to keep it from turning reaches a spike in oil temp, the resulting expanding dist gear may JUST have enough press fit lost to allow it to spin even with the larger pin. This is why it is considered as being just "Borrowed time" rather than a solution.
If anyone were to challenge your representation of these facts, just consider the following...
It is common knowledge that if the distributor gear pin was intended to hold the gear in place all by itself, it would have been a press fit SOLID pin with a retaining collar to prevent it from flying out during the centrifugal force of operation. There would be no fusible link at this point. And that could have catastrophic consequences.
Additionally, if there was sufficient force to break an extremely tight press fit AND shear a pin, the oil pump shaft itself would want to break or twist first at the small hex under the distributor, or more than likely, "splay" out the bottom of the now broken distributor shaft where the oil pump drive shaft fits into, resulting in the block being irreparably damaged in the process.
Keep in mind, if something were to get into the oil pump, like a piece of a valve seal or the like and that pump stops dead, and there is no fusible link in the distributor gear, something really, really bad is going to happen.
Also, if there was SO much force to be able to break a super tight press fit and a pin, surely the distributor and cam gear would wear and gall sooner than later as a result. These small sized components simply are not designed to withstand these types of forces, and
therefore, are really not being subjected to them as some might think.
Finally, you yourself can take the hands on test. It takes almost the force of BREAKING a new gear trying to get it on to overcome the tight press fit on the shaft that's required... that's how it is supposed to be. Now, take a "loose gear" and slip it on and install the roll pin.
NOW try to press it off. It will take almost hardly ANY effort of the press to shear the roll pin and the gear will begin moving.
There is no comparison in the resistive forces involved and there is no way even a LARGER pin could even come close to the force a good and proper press fit can provide.
ON another note, in the past it was always a problem with "some" 351-C's for their STOCK dist. gears to shear the pins... usually due to the dist gear sitting right ON the pad inside the block and creating excessive friction rather than floating on the wear pad in the block. As the engine heated the metal would expand thus creating more friction, and heat, until the gear spun. They made dist shims for the 351-C's used for racing back in the 70's just for this problem. It as a block height variable that created this. However, as for this being a "common" problem amongst other Ford engines? In the grand scheme of things, not at all. Sure you may hear a couple dozen friends complain... but what about the couple MILLION others that do not have a problem or rave about it? Rarely do those unaffected folks remind others that their gear is doing fine. You only hear stories and repeats of the same stories that might otherwise give the false impression there is a problem larger than it really is.
Bottom line is, you should NOT have to re-drill for a larger pin if the gear presses on properly (ie: really tight). If the gear does not press on tight, well, THERE'S your problem! And most likely it will shear the pin, eventually. Other than getting a new shaft,
drilling for a larger pin is the only bandaid that might work.
I hope this once again puts some of these myths to rest. As always, when looking for a definitive answer, you reach for the top and talk to the people directly responsible for the product or concern, and NEVER the tech guy that might have just got this job after a short stint at the local Taco Bell. "Ask everyone, Trust no one, and seek the truth out for yourself". That's my motto.
MythBuster /rt1002
-------------------------------------------------------
Anyone...?
I have come across a number of MSD distributors where the roll pin securing the drive gear has sheared, 3 of which were fitted to motors with high volume pumps.
The most recent 'owner', forwarded me the email below that may be of interest to others - Opinions / experience / comment also welcomed and encouraged...
-------------------------------------------------
Subject: Re: [SCOF] DIRECT from M-S-D regarding DIST. GEARS & PINS
Date: Wed, 23 May 2007 20:37:17 EDT
RT... Thanks! Great explanation.
Seems like if a pin shears and the gear spins then the shaft ought to go in the trash and a new gear/shaft combo should be the order of business.
Herb
In a message dated 5/23/2007 4:05:54 P.M. Eastern daylight Time, [email protected] writes:
Ok, I really didn't have time for this today only a week after the Fel-Pro myth-busting endeavor, but once again I'm a tree shaker and fact taker, so it looks like it's another myth that needs busting.
I just called MSD and asked to be directed to an engineer in the Distributor division specifically associated with the distributor gear operations. Since everyone uses Email nowadays, there was no wait time and I got to a tech instantly. (what a sneaky tip, eh? to use the phone instead of Email!)
After explaining my background and expertise in the field, quite a few of the phone tech guys I was transferred to didn't want any part of this, and I was ultimately sent quite aways up the ladder to an engineer specific to this component, named Joe Lapelli at MSD.
After explaining the issue to him regarding the rumor that "MSD told a major engine builder and/or customer that any time one of MSD's "RACING" distributors were to used with a hi-volume oil pump or used in applications where higher than stock revs were experienced, their distributors had to have the gear pin drilled and enlarged in order to prevent the pressed on gear from rotating."
Well, at this point there was dead silence on the other end of the phone... probably because I was talking to an answering machine. So at 10:21am CST I stated my case and hung up while awaiting for Mr.Lapelli's return call.
At 2:02pm CST Joe called me back and had a lot to say. He very adamantly stated that "if we at MSD thought there was a need to use a larger pin in any of our distributors, we would have done so at the factory!" The reason they do not, is that is the only fusible link left in a High Performance distributor system using a stiff oil drive shaft as it is. If the gear can not spin, the resulting damage CAN take out the engine block, and has more than once! (more on that below).
And while they do have had their tech's suggested in the past that ONE solution to an already spinning gear would be to install a larger pin, that is not what they would recommend anyone else to do in advance. Joe confirms that he too would have to think that most
likely there is something else wrong that caused the gear to spin, and that should be sought out and addressed first before blaming the gear.
They understand that if the gear slipped once due to the existence of another problem, most likely the new gear will now not press on as tight as it should, and therefore the only option would be to drill for a larger pin... however, he did say a new distributor
shaft is really the right thing to do, and the larger pin is merely a bandaid to the problem. The reason they might advise a larger pin to be installed AFTER the gear spun once, is that otherwise they would have to say "get a new distributor or shaft". And while that may be the RIGHT thing to do, it is not what most unseasoned customers want to hear.
Joe confirmed that MSD distributors were designed with Hi-Volume oil pumps and hi-RPM's in mind and should never spin a gear in normal operations. However, he did clarify that significantly high oil pressures would include 100psi+... and "higher than normal revs" would be in the 9,000 rpm+ ranges... anything less would fall into what the distributor was intended for.
But, as the poorly fit gear relying only on the pin and some press fit to keep it from turning reaches a spike in oil temp, the resulting expanding dist gear may JUST have enough press fit lost to allow it to spin even with the larger pin. This is why it is considered as being just "Borrowed time" rather than a solution.
If anyone were to challenge your representation of these facts, just consider the following...
It is common knowledge that if the distributor gear pin was intended to hold the gear in place all by itself, it would have been a press fit SOLID pin with a retaining collar to prevent it from flying out during the centrifugal force of operation. There would be no fusible link at this point. And that could have catastrophic consequences.
Additionally, if there was sufficient force to break an extremely tight press fit AND shear a pin, the oil pump shaft itself would want to break or twist first at the small hex under the distributor, or more than likely, "splay" out the bottom of the now broken distributor shaft where the oil pump drive shaft fits into, resulting in the block being irreparably damaged in the process.
Keep in mind, if something were to get into the oil pump, like a piece of a valve seal or the like and that pump stops dead, and there is no fusible link in the distributor gear, something really, really bad is going to happen.
Also, if there was SO much force to be able to break a super tight press fit and a pin, surely the distributor and cam gear would wear and gall sooner than later as a result. These small sized components simply are not designed to withstand these types of forces, and
therefore, are really not being subjected to them as some might think.
Finally, you yourself can take the hands on test. It takes almost the force of BREAKING a new gear trying to get it on to overcome the tight press fit on the shaft that's required... that's how it is supposed to be. Now, take a "loose gear" and slip it on and install the roll pin.
NOW try to press it off. It will take almost hardly ANY effort of the press to shear the roll pin and the gear will begin moving.
There is no comparison in the resistive forces involved and there is no way even a LARGER pin could even come close to the force a good and proper press fit can provide.
ON another note, in the past it was always a problem with "some" 351-C's for their STOCK dist. gears to shear the pins... usually due to the dist gear sitting right ON the pad inside the block and creating excessive friction rather than floating on the wear pad in the block. As the engine heated the metal would expand thus creating more friction, and heat, until the gear spun. They made dist shims for the 351-C's used for racing back in the 70's just for this problem. It as a block height variable that created this. However, as for this being a "common" problem amongst other Ford engines? In the grand scheme of things, not at all. Sure you may hear a couple dozen friends complain... but what about the couple MILLION others that do not have a problem or rave about it? Rarely do those unaffected folks remind others that their gear is doing fine. You only hear stories and repeats of the same stories that might otherwise give the false impression there is a problem larger than it really is.
Bottom line is, you should NOT have to re-drill for a larger pin if the gear presses on properly (ie: really tight). If the gear does not press on tight, well, THERE'S your problem! And most likely it will shear the pin, eventually. Other than getting a new shaft,
drilling for a larger pin is the only bandaid that might work.
I hope this once again puts some of these myths to rest. As always, when looking for a definitive answer, you reach for the top and talk to the people directly responsible for the product or concern, and NEVER the tech guy that might have just got this job after a short stint at the local Taco Bell. "Ask everyone, Trust no one, and seek the truth out for yourself". That's my motto.
MythBuster /rt1002
-------------------------------------------------------
Anyone...?
