Destroyed my Distributor gear

[Dave Erickson]

Are brass timing gears sold by reputable VW houses the same as those sold by Porsche places? MASSIVE price differences.

Gregg, they are identical. The steel timing gears for the cam are not the same for vw 40 hp and Porsche, but the brass distributor drive gears are the same.

[David Baugh]

No problem, Vic. I can be pretty stubborn, too .... especially when it involves something that I've seen, felt, and heard.

I would describe it as a "progressive bind". It starts out kind of "mushy", then progresses to a firm bind. That makes sense, though, as the driveshaft/gear begins to chew its way into the brass gear. Since I was checking for rod/case interference when I discovered it, I was going slowly and cautiously, and didn't force it past the bind. What was odd was that when I rotated the crank back to relieve the bind, I could hear and feel a faint "plop", which I presume was the driveshaft/gear dropping back into position. It took a lot of thinkin' to figure out what was goin' on. But, I wasn't gonna complete the build with the possibility of a rod/case collision. I even posted on it, and received several suggestions regarding relieving the crankcase for clearance.

I'm sure a lot of guys have gotten away with forcing the issue, with nothing worse to show for it than grooved teeth on the brass gear, and never knew anything had happened. We've all seen those gears, right? But, then there are guys like Gregg who, from his description, suffer a catastrophic failure.

Anyway, that's my story, and I'm stickin' to it!

Dave

[Albert Tiedemann]

The brass gear can be damaged another way unrelated to rotating the engine anticlockwise with the distributor removed. You can damage the gear by removing the third piece without first removing the distributor drive gear. When this maneuver is performed, there will be tell tale "broach" marks on the brass gear.

Sorry, Ab; I can't agree with that. I have NEVER removed the driven gear before removing the timing cover.
I suppose if things were partially seized from lack of use, that might happen, but otherwise; NO.

Yes, this is true Vic. If all things are free and not bound up for any reason, the gear will just rotate as the timing cover is withdrawn evenly. When there is a possibility of skewed removal and/or movement impairment of the meshing gears for any reason or both, damage will result and I have seen this in many engines. Perhaps this was done by others lacking knowledge or skill/experience in disassembly tasks or both or they were just in a hurry to get it apart. For me, I always remove the distributor drive gear before trying to withdraw the third piece. And, if you drop the washer on the way out, it is easily recovered. Removal of the gear first just eliminates a possible poor outcome if you are removing the third piece with little or no prior knowledge of the engine's history. For now let's just leave it as you do it your way and I will do it mine.

[Ron LaDow]

Ron; sounds like you're as stubborn as I am. Be sure to pull the fuel pump so its operating shaft does not hold the gear down because of the fuel pump drive.
David; thanks for the back-up.

Maybe stubborn, but when something acts opposite of what logic says, I'd like to know why.

[gregg hake]

Ron, and everybody else who is looking at the gears and thinking that the driven gear cannot ride up when turning the engine backwards:
Go ahead and remove your distributor; then turn the engine backwards; now pull the timing cover and replace the damaged brass gear.
Go ahead; try it.

Hey...I took one for the team on that one. The Distributor gear does a pretty neat job of shaving the timing gear brass threads off.

BTW...new timing gears are 20 - 30 bucks on the VW sites. Over 100 on the Porsche sites. That Porsche label must be expensive to print.

[Alan Hall]

I have seen some aftermarket brass gears from some of the VW parts places that looked to be pretty poor quality compared to originals. There may be more than one source of these gears with different quality.

[Albert Tiedemann]

Ron; sounds like you're as stubborn as I am. Be sure to pull the fuel pump so its operating shaft does not hold the gear down because of the fuel pump drive.
David; thanks for the back-up.

Maybe stubborn, but when something acts opposite of what logic says, I'd like to know why.

Well, it seems like I am doing things differently then most. Here is a try on the explanation of "why" the distributor gear moves upward if not restrained.

Consider the gear set as helical gears with shafts at any angle, ratio other than 1 and center distances exact or approximate. If you work with gears regularly, then much has been committed to memory; but, if you don't, then you can find with a little searching that the sum of the helix angles of the two gears equals the shaft angle and the gears are of the same hand if each angle is less than the shaft angle. If you find by measurement or calculation that one of the helix angles is greater than the shaft angle, then the difference between the helix angles must equal the shaft angle and the gears are of opposite hand.

In either case, the hand of the helix is selected depending on direction of rotation and the direction in which thrust is to be received.

The direction of normal engine rotation is clockwise as viewed from the pulley end as is the distributor shaft [ as view from the rotor end or check little arrow on id plate or engraved into distributor housing] This is only possible if the brass gear helix is LH. Given this condition, Ron, logic would suggest that the helix of the distributor gear is also LH. Where is Larry when you need more engineering input? The steel washer that is placed under the distributor shaft is likely there to offer protection for the supporting surface in the third piece as this is the direction that the thrust vector is to be resisted. This means that with the directions noted and the added comment that the brass gear is the driver gear, the driven gear [distributor drive gear] would want to move downward in normal rotation of the engine.

If restrained with the distributor in place and the little die like spring interface in place [likely the compressed/installed length is much greater than the thrust vector mentioned above] the distributor gear cannot "move up" if rotation is other than normal. Other contributors to resistance to movement as mentioned by Vic above could keep the gear in place with the distributor removed and only a force resolution of the fuel pump rod loading contrasted with the trust vector would prove or disprove otherwise.

The manual states to turn the engine over backwards to adjust the valves as this will sequentially put the adjustment sequence 1 2 3 4. They did not caution that damage to the brass gear could/would result because they did not expect this procedure to be conducted with the distributor removed because of the initial starting position referenced aligning the notch in the distributor housing with the rotor when OT on the pulley aligned with the vertical line in the third piece or on the crankcase half.

There is also no cautionary statements in the manual that I could find that would guard against a possible and according to this topic, a near certainty of damage to the brass gear if you were to rotate the engine opposite of normal with the distributor and fuel pump removed.

[David Baugh]

Holy Moley, Ab!
And at first I thought it was a simple connecting rod/crankcase collision.
Now it seems I've opened Pandora's Box.

Dave

[Jens Hansen]

I'm in the progress of assembling the engine. Got the 3rd peace on!
When should I install the distributor gear so I can avoid these problems with damaging the distributor gear?

Jens

[Dave Erickson]

I'm in the progress of assembling the engine. Got the 3rd peace on!
When should I install the distributor gear so I can avoid these problems with damaging the distributor gear?

Jens

When you are ready to install the distributor. As long as the distributor is in place there is no risk, assuming it is installed correctly. You can rotate the crank in either direction without damage to the brass gear.

[Richard Shilling]

Unless I missed it, did anyone mention the thrust washer? You have to install the thrust washer before dropping the gear in. Putting the thrust washer on the gear and then installing it is a no-no, it will chew up the gear. Put a dab of grease on the bottom of the thrust washer, slide it on a screwdriver, put the screw driver in the hole, slide the washer dow and use the screwdriver to center it on the hole. Then put in the drive gear.

[Jens Hansen]

Dave and Richard, Thanks for the advice.
I will wait until I have got the distributor refurbished.
Got many other things to do before I need to get that done.

Jens

[David Baugh]

Yes, Richard, the thrust washer was in place. I think your scenario would occur during correct rotation direction. Don't know. Never left one out.

This thing only shows up during counter-rotation. The "plop" I heard when I relieved the bind seemed to eminate from within the timing cover. That's what led me to it.

Dave

[David Baugh]

In addition to the factory instructions that Ab mentioned concerning counter-rotating the engine while adjusting valves (with the distributor installed, of course), consider this.

Some more than others, but all internal combustion engines routinely counter-rotate their crankshafts (even if very briefly) when you shut them off or they fail to start. In consideration of this, the factory found it prudent to install a rather stiff spring between the distributor and its driveshaft/gear to hold the gear in position and prevent lifting and consequential damage to the brass worm gear during these episodes.

Dave

[Dave Erickson]

In order for damage to occur, the distributor drive gear has to lift far enough to disengage from the crank gear. That cannot happen if the distributor is in place and everything is correctly installed.