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351W eats distributor
Well it did it again. This time I got about a 1/4 mile from the house when the engine went dead. The short story is that it sheared the dist. gear pin for no appearant reason. I am changing from a Mallory Unilite with a steel gear to a MSD with a brass gear in hopes of fixing. The Mallory is a self oiler that is way too tight, so I think it is heating up enough to weaken the pin. Last time the oil pump gave way and siezed with a tiny piece of the gear! Any thought on this problem are appreciated.
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Just a thought, but was your block decked? If so, how much was taken off? Is it possible that your distributor is now "too long" and bottoming out when you lock it down?
What kind of cam are you running? |
Your oil pump seized before? Do you have a mesh screen strainer? They should prevent peices big enough from seizing the pump to get through.
What about the length of the oil pump shaft or the dist body, if they were too long you might be able to tell when you tighten the dist clamp, can you get a feeler gage between the top of the block and the part of the dist that seats against it? Was you gear pressed on or was it loose on the shaft before you pinned it? |
All to common problem actually. There was a recent discussion on this very subject by the Gasholes. Brass gear may or may not solve it. MSD dist is subject to the same potential failure.
The basic problem is the clearance of the bottom bushing. Ask MSD how to measure to correct length to determine the clearance. IF it is not within specs (often the case on ANY dist) there are steps to take to correct it. Another possible failure scenario is high volume high pressure "race" oil pump. OR using heavy weight oil on a cold day. High pressure pumps are used on "race" engines because the internal clearance on all parts are "loose" compared to street engines. With the greater clearance you need higher pressure higher volume to keep adequate oil flow. On a street engine with tigthter clearance the pressure can go TO high and strain the dist gear and drive unit when using a high pressure pump. ANY dist is subject to this problem. ALL must be measured and checked for specs on clearance. Ernie |
MZHUN:
How long had the gear been installled on that particular distributor? Contact MSD and get the required measurement for installing subsequent gear. The thrust face of the gear is pulled down against the thrust surface that is machined in the block where bottom of the distributor shaft slips over the hex shaft for the pump. If it does not rest on the surface while installed the gears will not mesh properly. If the shear pin is shearing there are forces preventing the shaft from turning once engaged. As you have stated check the bushing inside the distributor and check the pump. It is possible to have a small piece of metal that has gotten on the outside of the gerotor inside the pump. This situation will continue until you actually find what is preventing the shaft from turning. The decking of the block with a 289/302/351 does not affect the meshing of the gears as stated above (sorry Chappy), The installed manifold hieght has no impact on the distributor fit. Rick |
Thanks for all of your feedback. Here are some of the answers to your questions:
Cam is a Comp Magnum cam 292 lift and 534 duration Oil pump is standard high volume replacement with mesh screen that gives me 50 psi at idle and 60 above 2000 rpm. I am running Castrol 5-30. Gear in this dist. has been on roughly 1500 miles and wear pattern is right in the middle of the gear. Dist. ktightens all the way down. Not sure if the block was decked, as it was built before I got the car and I am still trying to get the build sheet from the previous owner. Matt |
Quote:
Can you explain why this is so? If you deck the block, haven't you in effect lowered the height of the manifold, and then necessarily, shortened the distance between the pump and the manifold? I noticed you said that it is the case wth the SB, what about with FE or 385 series? Curious . . . . |
Another thing to consider..
If the cam is steel then a steel gear should be used. If the cam is iron then use an iron gear. Bronze can be used with either cam, but, wears quickly. Mike |
FE,,,,,, same kind of problem. All though more common with the small blocks for some reason. Virtually never heard of with Chev engines (I hate them). :D
Ernie |
This is very interesting. I had the EXACT same problem. Last summer, my mechanic had just finished installing my 351W. We had a brand new Mallory Unilite distributor. I took it to Pocono for open track running two days later. It never ran well all day, as we hadn't been able to fine tune the carb before I left. But on my third session, it sputtered badly, backfired then stopped. Turns out it had sheered the pin, just like MZHUN described. My mechanic and I were not able to figure out why. Everything else in the motor seemed fine. Still totally confused as to what happen. We put another stronger pin in it and I've had no problems since.
Steve |
Chaplin:
On the 289/302/351 blocks the distributor does not attach to the intake manifold as in an FE. The seat that the distributor bottoms out on is not "Cut" when the block is decked nor does the new (lower) position of the manifold have any impact on the distributors vertical register placement. If you look at a bare block you can visualize this. Rick |
When I had the gear on my MSD distributor changed to be compatable with the roller cam, the guy said the gear fit was too tight. He reamed it out (for a "light press fit") and pressed it on and installed a new pin.
I was not comfortable with this so I called the MSD tech line. After talking to the tech guy he told me that FORDs must have the gear PRESSED on. A tight fit is required. I sent the distributor to MSD and they replaced the shaft and installed a new steel gear for me for free !! I think the tight press fit is needed becouse the pin alone isn't strong enough. |
Rick-
I just looked at a windsor manifold. I see what you mean. Thanks for correcting my error.:rolleyes: :) |
MSD
Have you contacted the manufacturer? If not, do so and speak with one of their tech people.
I'm using an MSD and when I built my 351W last Summer, I recall that in the MSD Distributor box there was a memo indicating that the gear might have to be changed, depending on what cam I was using. I called MSD and spoke with one of the tech guys and when I gave him the cam specs, i.e. part number, he said I was good to go with the gear that came with the distributor. Before doing anything else, I would call the manufacturer. Tony |
I contacted MSD and tech told me not to buy a new dist., and that the oil pump is the problem. I called Mallory and tech had no idea what to do other than drill it out and put in a bigger pin! I'm going to try the Brass gear on this Unilite and see how it works.
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I hate to diasgree with you Rick,
But the installed distributor gear height on windsors is something that needs to be checked. I have seen many distributor gear failures (in windsors) because the gear was too low on the shaft, so the distributor doesn't drop all the way down in the hole, it's flange sits a hair above the intake manifold's corresponding flange, this goes unnoticed by the installer, and when the distributor clamp is tightened, that forces the distributor gear down into a heavy preload situation. |
Mr Fixit
Wooooowhhhhhhhhhh! I did not say that this dimension is not critical, in fact it is crucial! It is one of the problems often created by the unkowing when a gear is replaced. I stated thet decking the block did not affect the installed hieght. The dimension to use for gear installation is published, printed and available from MSD, (and other sources) it may be included in the packaging with the gear from MSD. I would also agreee with the earlier post stating that the press fit of the gear on the shaft is very important to retention. The roll pin size can be increased to 3/16ths but the press fit is probably more responsible for its retention and torque capacity. Once this fit is right, it is pretty much bullitproof. Rick |
Andy Dunn,,,,, the Butcher. EXPERT in,,,,, well,,,, just about everything!
The Butcher KNOWS distributors and CC members concerning DIST GEAR PROBLEMS (yes, even Mr. Fixit). READ ALL ABOUT IT HERE: http://www.cobralads.com/butcher63.html Quoting Mr. Butcher: It was a dark and stormy night. Deep in his lair, the Butcher performed the last of his subtle distributor installation experiments. Suddenly the truth appeared before his eyes. He now believed he held the secret of the unexplained Ford distributor gear failures. It wasn't the high volume oil pump, it wasn't the alignment of gear teeth, and it wasn't oil starvation. The mysterious gear death was most likely caused by diabolical.... http://www.cobralads.com/mystery/DSC00129.JPG |
Rick,
I have seen the problem on distributors right out of the box from MSD, where the installed height is right where the spec says it should be, but the motor it went into disagreed. The broached hex in the shaft for the oil pump drive can cause a severe binding as well, if not deep enough. I have seen that on a couple of MSD pro-billet distributors. The oil pump drive puts a huge thrust preoad on the oil pump, and the distributor gear acts like the weak link and wears itself down to knife edged teeth, or the pin shears. ANyhow, paying carefull attention during assembly should catch any of these problems, before they become a problem. I made an early moring mistake when I mentioned the intake manifold flange, as we all know, the Winsor's distutor doesn't go through the intake, and you are correct that decking the block won't affect the Windsor's distributor height, unlike say a chevy. I ought to have my first cup of coffee before even reading CC. Do'h |
Matt, how about checking for "end" play. With the distributor mounted on the motor and the dist cap off, see if you can move the shaft up and down any amount. That along with visable wear on the bottom of the gear would tell you if you have outright binding.
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