Snapped distributor shaft? (1 Viewer)

[RicardoJM]

Have you ever had a distributor shaft snap? Typically, I've been able to find answers by searching through the forums, but I did not find any occurrence of a shaft snapping which has me thinking this is a very rare event.

I had a big cap electronic distributor shaft snap in two yesterday.

A bit of back ground, I just completed a swap (engine, 4 speed transmission) on my 71 FJ40 which included "upgrading" to a big cap electronic distributor from a small cap electronic distributor. I picked up the "new" engine from a friend who got it from someone else. It was rebuilt, low miles and pulled because the owner wanted to go in a different direction. When I got it, it was missing most of the accessories. I added accessories and replaced gaskets and seals. The linked thread has more details on the project; I did have some trouble getting the distributor to seat and checked the cam shaft gear for any movement, but did not find any.

For those that have snapped distributor shafts, what did you find (or think was) the underlying cause?

 

[RicardoJM]

I am bumping this back up as I broke the shaft on another big cap distributor.

After the first shaft snapped, I put in and have been running my small cap electronic distributor. The truck has been running great and not having any issues. I've put on over 1k miles in driving.

Last Friday night, I was helping a friend who needs to send his DUI distributor in for service, get his FJ40 running. He was able to get a Toyota big cap distributor, but did not have the dented side cover - so we put my small cap into his truck and the big cap into my truck. Putting the big cap into my truck took "he man strength" to stab, and within 60 miles the distributor shaft snapped. Because of the issue with stabbing the big cap distributor and the small cap goes right in, we took a micrometer to both to see if there were physical differences; the diameters of distributor shafts, gear and bottom blade were the same and I am stumped.

I believe there is an issue with the gear on the camshaft which makes it difficult to stab the distributor and because the mount for the big cap distributor is part of the distributor body when locked in place there is stress placed on the shaft. I believe because the small cap distributor uses a bracket, the stress is still there but because of the bracket it is not enough to cause the shaft to snap - yet. What other issue could be contributing/causing this?

 

[Poser]

Do you have a dented side cover on your engine?

 

[Pighead]

I want to hear the answer to this one too.

 

[RicardoJM]

Do you have a dented side cover on your engine?

I want to hear the answer to this one too.

Yes, I do have the dented side cover. The big cap would no fit without it.

 

[RicardoJM]

My friend reminded me that there is some additional info we need to share that could be critical clues:

1-The small cap distributor that I have that drops right into my motor and has worked fine for 1,000 miles without issue. It came with the motor when I got it.

2-We got another small cap distributor yesterday and tried to install it into my engine since my dizzy was in my friends truck. It went in just as hard as the big cap did, we would have had to whack it with a hammer to get it to drop in. We installed it (the new small cap) into my friends truck and it dropped in effortlessly. My small cap distributor was then put into my truck and it dropped right in to my engine.

 

[Rambrush]

Question
Does the big cap unit fit just fine with no shaft? wondering on tolerances also even though you have checked.
There is no way you should be forcing a distributor in they should slide in nicely. But if there has been force applied there should be marks where it is hanging up.
I have a long custom shaft I use for spinning up the oil pump for priming a new engine do you have anything like that for verifing the oil pump is ok nothing hanging up in there? wondering if the small fits fine it throws no load on pump but maybe the large does if the pump is slightly loose

 

[ColonelMustardFJ40]

According to the parts view @ SOR on page 022 the distributor drive gear is reversed between the two models of distributors. Could the shaft be bending because of this difference and fatiguing, eventually breaking?

 

[Poser]

Post up some pictures of your engine....

 

[RicardoJM]

Here are couple of photos just before I put it in.

I am also more active on the Rising Sun site and have a few photos of the swap process, well mostly of the old stuff, in my engine swap thread on that site.

 

[65swb45]

When I have run across this issue, there is ALWAYS a minor difference in tolerances that is not readily apparant. Sometimes it is the housing, sometimes it is the tip of the shaft, and sometimes it's the o-ring.

Once, and this was the hardest one to track down, it was a alignment deviation in the oil pump mounting block. Worked fine with one dizzy, but not another.

Best

Mark A.

 

[RicardoJM]

Question
Does the big cap unit fit just fine with no shaft? ...
I have a long custom shaft I use for spinning up the oil pump for priming a new engine do you have anything like that for verifing the oil pump is ok nothing hanging up in there?

With the shaft snapped, the big cap goes in and out just fine. The bottom end of the snapped shaft pulled right out both times, i.e. it what ever torque was in place that caused the stress is gone after the shaft snaps. I used a old flat blade in a drill to prime the oil pump. I do not have a distributor shaft that I use for this.

According to the parts view @ SOR on page 022 the distributor drive gear is reversed between the two models of distributors. Could the shaft be bending because of this difference and fatiguing, eventually breaking?

In my experience distributors for the F/2F series of engine are all interchangeable - so long as they are matched with the proper ignition system. In looking at page 22, I am not seeing a change in the gear direction.

When I have run across this issue, there is ALWAYS a minor difference in tolerances that is not readily apparant. Sometimes it is the housing, sometimes it is the tip of the shaft, and sometimes it's the o-ring.

Once, and this was the hardest one to track down, it was a alignment deviation in the oil pump mounting block. Worked fine with one dizzy, but not another.

All the distributors we have tried (2 big caps, 2 small caps) did/do not just drop in the first time. Even the small cap distributor that is in there now was a bit of challenge to get stabbed the first time I put it in. With a sample population of 4 distributors, I am inclined to suspect the alignment issue is in the engine.

 

[Rambrush]

I would have to agree there is a alignment gremlin. The only movable object that could possibly be off would be the oil pump. or

I am wondering out loud about putting gear paint like used for checking gear patterns. put some on the distributor shaft gear. wondering how deep the cam gear is on the dist gear and if its very tight then the bind and break would occur.
or just put the dist in minus the gear but have the shaft in. I would assume that would go in easy wo gear.
If so this would indicate a: the gear is to large diameter which would be strange if it fits just fine in the other engine.
The B: could be if its possible the cam is to far back? Were things all lined up in front?

 

[ColonelMustardFJ40]

When I look at the images on Specter Off-Road Land Cruiser Parts - Page 022 Land Cruiser Distributors the shoulder of the drive gear is up on the later model (part #40 Electronic Ignition - 9/77-8/92 FJ40, FJ55, FJ60 & FJ62) and on the earlier model (part #40 Semi Electronic Ignition - 9/73-9/77 FJ40 & FJ55) the shoulder is down. Just an observation.

 

[RicardoJM]

I pulled the small cap distributor last night and there is some play in the shaft. This is why it goes into the engine easily and likely why it's shaft has not snapped.

While it was out, I looked around to see if I could determine what is not lined up. Using the snapped end of the shaft, I know the blade slips into the oil pump with no binding. Using a different distributor, I know the binding starts when the gears begin mesh, just after the o-ring starts to go into the block. I removed the o-ring and there was no change.

I did not find the cause for the alignment issue and would be interested in tips/technique/recommendations on how to proceed in determining/isolating the cause of the alignment issue.

I know that to fixing the issue will involve some work. If it is the oil pump the oil pan needs to be dropped. If it is the camshaft, the work is a bit more involved. I'd like to not have to do both if I don't have to.

 

[RicardoJM]

When I look at the images on Specter Off-Road Land Cruiser Parts - Page 022 Land Cruiser Distributors the shoulder of the drive gear is up on the later model (part #40 Electronic Ignition - 9/77-8/92 FJ40, FJ55, FJ60 & FJ62) and on the earlier model (part #40 Semi Electronic Ignition - 9/73-9/77 FJ40 & FJ55) the shoulder is down. Just an observation.

I hear what you are saying. When I pulled my distributor last night I compared the gears between the two and they are the same.

 

[RicardoJM]

...
Once, and this was the hardest one to track down, it was a alignment deviation in the oil pump mounting block. Worked fine with one dizzy, but not another.

Best

Mark A.

Mark in the instance where the deviation was in the oil pump mounting block - were you able to correct the mounting block?

Even though the truck is running ok with the small cap distributor, I'd like to fix the root cause of the problem. Long story short, the small cap distributor that is in there now is a 78 vacuum retard so I'm unable to use the ported vacuum connection that you drilled for me last month until I can get a different distributor installed.

 

[Trollhole]

What I think Mark is referring to is the two bolts under the dizzy in your picture. Those two bolts hold the mounting block for the oil pump. If the mounting block is not correctly aligned it will cause your dizzy shaft to have stress.

When rebuilding an engine this block shouldn't be removed unless you have the proper tool to realign it.

For instance if it's moved to the left. When your dizzy is put in it may not have an issue dropping in since the slotted end can still fits in the oil pump when the slot is horizontal. It's only when you turn the motor over and the cam starts turning the dizzy shaft. At some point the slotted end cannot make up for the misalignment (if you were looking from the passenger side in the dizzy hole the slot would be pointing vertical). At this point the misalignment of the oil pump mounting block will cause the shaft to bend ever so slightly. Over time it will eventually break the shaft at the weakest point. The dizzy gear pin.

Your going to keep breaking dizzys until you fix the missalignment issue. One way you could try if your not going to use the SST is to loosen the mounting block bolts put the dizzy in with the slot being vertical then tighten the bolts. It might work or it might not. The SST would be the best bet.

 

[65swb45]

To test my theory you need to:

1. Mark the block at the pump mounting bolts WITH a distributor installed.
2. Loosen the bolts and see if they move.
3. Retighten.
4. Remove the dizzy and see if a second distributor will now install easier.

If it does, consider the problem solved. If it does not, move the bolts back where they were.

In short, I place a higher value on an SST than the FSM, but is still not the be-all, end-all.

Best

Mark A.

 

[RicardoJM]

An update on this issue.

It appears the block that the oil pump attaches to was indeed just a little off alignment. Fortunately the solution was very easy and didn't require the oil pan to be dropped. I loosened the two bolts that hold the block in place, removed my small cap distributor and then put in another distributor and then tightned the two bolts. I needed a long breaker bar to get them loose and I only loosened them a couple of turns. I was concerned that in loosening the bolts, I would create an oil leak so far there has not been any leak.

It took me a while to source another big cap distributor. Last week one of my local club members came through with another big cap distributor (bit dirty on the inside) which went into the truck Friday evening. I put on over 120 miles this weekend and so far it is all good.

Many thanks to all who posted up on this thread and helped me figure this out.