47-55.1 Eliminate draft tube options

[TX3100Guy]

One step forward, two steps back.......

Engine runs on the new distributor, but I very quickly noticed no oil pressure. Checked all wiring to oil pressure sensor and gauge. Since all was well with wiring, I had a very bad feeling......

After considerable measurements and testing. The new distributor does not engage with the oil pump drive. It seems that while the measurement from the tip of the distributor shaft to the cam gear is correct and since the shaft has no collar on it preventing the shaft from dropping in, the shape of the shaft directly above the gear prevents the cam gear from fully seating, thus the oil pump drive never even touches. The old magneto shaft has a spacer above the cam gear that is smaller in circumference allowing the cam gear to fully seat and then permitting the oil shaft drive to be engaged.

I can use an old distributor shaft in my power drill and get both oil pressure and weeping along the length of the valve train, but with the distributor - nothing.

OLD SHAFT AND SPACING ABOVE CAM GEAR


NEW SHAFT AND LACK OF SPACING ABOVE CAM GEAR

[TX3100Guy]

I tapped out the pin holding the cam gear and with the cam gear removed, the shaft fits all the way down to the oil pump drive, but the top of the shaft tapers out and the hold down clamp isn't wide enough to accommodate the width of the shaft.

I'm a bit confused how without the cam gear the shaft is long enough, although unable to be held by the hold down clamp. Could it be the incorrect cam gear refusing to mesh with the oil pump gear?

[leegreen]

The slot in pump has to be lined up just right, the cam gear turns the shaft a bit as you insert it, is it possible that it is the end of the shaft hitting the top of the oil pump that is stopping it going further and not the spacer above the gear? The way I remember doing this....note relation between rotor and flat end of shaft, insert into block, note the angle of rotor with a felt pen on block, pull distributor out and use screwdriver to turn pump to match, put distributor back in and hopefully it drops into place.

The tang may not fully bottom into the oil pump, does lifting back up the thickness of the clamp leave enough overlap of pump and shaft?

the measurement to check is the distance from oil pump slot to cam gear on both engine and distributor.

[TX3100Guy]

Originally Posted by leegreen

The slot in pump has to be lined up just right, the cam gear turns the shaft a bit as you insert it, is it possible that it is the end of the shaft hitting the top of the oil pump that is stopping it going further and not the spacer above the gear? The way I remember doing this....note relation between rotor and flat end of shaft, insert into block, note the angle of rotor with a felt pen on block, pull distributor out and use screwdriver to turn pump to match, put distributor back in and hopefully it drops into place.

The tang may not fully bottom into the oil pump, does lifting back up the thickness of the clamp leave enough overlap of pump and shaft?

the measurement to check is the distance from oil pump slot to cam gear on both engine and distributor.

Thanks for all this, but I've put a number of distributors in a few engines and never had this issue. If I purposely misalign the oil pump tang on the distributor from the slot on the oil pump itself, the distributor will set in at exactly the same point as if I align them perfectly (I used a Sharpie to mark the depth of the shaft in the block)

Incidentally, witness marks on the cam gear seem to indicate that it is only seating about 1/8 of an inch of its 5/8 inch width.

If I align the oil pump drive shaft on the distributor with the oil pump slot, it will not seat any further. When I removed the cam gear from the shaft, the shaft went a full 1/2 inch deeper in the block and was clearly engaged with the oil pump. Using the

[TX3100Guy]

Here is a picture of the distributor shaft with Sharpie markings at the depth it drops in with the cam gear installed and a second line at the depth it will drop with the cam gear removed from the shaft. Also notice the slight witness marks on the cam gear at its bottom 1/8 of an inch.

[leegreen]

the marks you point out on the gear and looking at the two earlier pictures; maybe the teeth on new gear are not cut as deep as on the old gear?

[1project2many]

I believe I would check the OD of the lower portion of the distributor gear and try to locate specs or a known good part to confirm it is correct.

[dsraven]

if you could source an original dizzy, with the shaft and gear still on it, you could do a comparison and ensure everything is right before setting it back down in the hole. that way you're not as apt to wipe the crank bearings from lack of oil when testing. the shop doing your magneto may also appreciate the old dizzy for dimension checking.
maybe somebody on the site has a dizzy laying around that could do a gear OD and count the number of teeth on the gear and also the direction the gear is cut, just as a quick comparison check.

[TX3100Guy]

Originally Posted by dsraven

if you could source an original dizzy, with the shaft and gear still on it, you could do a comparison and ensure everything is right before setting it back down in the hole. that way you're not as apt to wipe the crank bearings from lack of oil when testing. the shop doing your magneto may also appreciate the old dizzy for dimension checking.
maybe somebody on the site has a dizzy laying around that could do a gear OD and count the number of teeth on the gear and also the direction the gear is cut, just as a quick comparison check.

I'm going to a huge automotive swap meet on Friday, hundreds of vendors and oodles of old car and old car guys. I will be on the lookout for an old distributor and/or shaft with gear intact for measurement purposes.

I'm convinced that the gear is the problem. When the magneto with the collar on the shaft was not dropping in because of the collar, I did extensive measuring using an old dizzy shaft (with no gear on it) that I used to run the oil pump with a drill. At that time, I came up with a total depth required from the bottom of the oil pump slot to the top of the block of 5 1/8 inches. Of course that collar on the magneto shaft was 1/2 inch too short, thus keeping the oil pump shaft from making contact.

Yesterday, after I took the cam gear off the new distributor shaft an was able to fully seat it, I marked the top of the shaft where it become wider (top Sharpie mark on the photo above), it measures at 5 1/8 inches. When I reinstall the cam gear and carefully insert the dizzy, it is 1/2 inch too short.

The mag failed to seat due to the collar on the shaft, I feel certain that the distributor isn't seating due to a cam gear mis-match. The mag is supposed to be worked on tomorrow, which means I might get it back late next week. I think I will have to wait until then to resolve the mystery.

I will search for a distributor Friday at the swap meet, but in the meantime if anyone has a distributor on the shelf, I would love to know the diameter of the gear, the depth of the gear splines, and the number of gear teeth.

[TX3100Guy]

Just for grins, I went out to the shop and measured the gear on the "compatible" distributor that I bought. Here are the details of the cam gear that doesn't seem to fit -

Gear diameter = 1 3/64"
Gear height = 5/8"
Gear depth = 7/64"
Number of gear teeth = 13

[1project2many]

I believe you are chasing the correct component. There are other tools that can help determine what's going on. If the angle or width of the teeth aren't correct you will see telltales on both sides of the distributor gear (blue arrows). If the depth of the teeth do not match you will see telltales between the distributor teeth (green arrow). If the diameter of the non-toothed portion of the gear is not correct you may see telltales at the bottom of the gear (red arrows).

White lithium grease can be used as a gear marking compound to aid in understanding gear contact. Brushing this compound in a fairly thin film on the gear then installing the distributor will cause contact marks to show on the distributor. It may be helpful to turn over the engine once or twice without starting it to get a better pattern.

I look at the marks on the mag shaft and gear and wonder what's happened to make them (red circles). They may not tell a story related to this problem though. When I enlarge both pictures it looks like the mag gear teeth may be narrower. Maybe it's a trick of the lighting?

[dsraven]

it would be interesting to compare an original, used and not rebuilt, dizzy to your mag and your dizzy to see if there are differences and if the old one fits the engine you have. possibly something internal to the engine is not exactly the same. was the cam or the oil pump replaced during the rebuild?