Timing Gear Cover question

[Conaway2]

What is the spec for the depth of the timing spring and plunger well ? And, is this constant over all years of model A production ?

The engine in my roadster - rebuilt as a short block by Schwalms 6300 miles ago. -has a timing gear knock. The knock disappears completely if I push against the timing gear with the timing pin.

I have replaced the timing gear several times, and also replaced the timing gear plunger and spring. But, the tension from the spring as i reinstall the timing gear cover seems less on this engine than on others I’ve owned. Did the depth of the longer well on the timing gear cover change over the years of production ?

Or, maybe I have a very worn timing gear cover.

Thanks very much,
Jim

[lrf]

My club had an engine rebuilt, we test ran it and it knocked. Figured it was the timing gear moving, tried a stronger spring and cracked the cover housing. Finally we were told that an oversized (.004) distributor drive gear was installed. We put in a used, standard size drive gear and the knock stopped. We figure the oversized was pushing or pulling on the cam. Aren't Model A's "fun" (and fussy). LRF

[Dan McEachern]

How much backlash did your timing gears have?

[nkaminar]

Since the knock disappears when you push on the gear with the pin, you are probably correct that the spring is not doing its job. I have seen covers where the boss where the spring and plunger go was tapped and a bolt and lock nut inserted to make the spring adjustable from the outside of the engine. In my case I had to add a big spacer to the spring.

[Conaway2]

Thanks for all responses. I plan to check a couple of spare timing gear covers I have to check for variation in the depth of the plunger well.

I’ll probably end up adding a spacer to increase the spring tension.

Dan, I haven’t measured the backlash, but will plan to when I have the timing cover off again.

Thanks - Jim

[katy]

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Les Andrews book gives a spec of 35-38 lbs for the spring. Problem is that he doesn't give a length for the spring pressure to be measured at.

[Bob C]

The prints show 29-32lb at 1 7/64.

[katy]

Service bulletins, page 574 says: Tension of spring, approximately 35 lbs.

Somewhere I read that: It is only necessary for the plunger to camshaft to have between .006" - .010" clearance before installing the plunger spring.

[nkaminar]

I would guess that the spring tension numbers are at the working compression. Careful measurements of where the end of the cam sits in relation to the face on the block where the cover mounts and the depth of the hole were the plunger sits in relation to the face of the cover will give the working compression. Then put the plunger and spring on a scale and compress it to the working height and read the force on the scale. A press can be used to compress the spring or a lever can be built to make it easy to compress the spring. I saw a mechanism like that on the Barn Forum a while back.

[katy]

A small bathroom scale on a drill press works good for testing springs.
If you're going to use spacers to increase the spring pressure, put them inside the plunger.

[Gene F]

Good idea Katy

[nkaminar]

I had to reset the timing on my modern car. The clock was still on daylight savings time. (drum roll)

[Conaway2]

I believe the problem is solved. I inserted a 3/16” spacer inside the camshaft plunger and reinstalled it with a new spring.

Before adding the spacer, the timing gear cover would fit right up against the block with no pressure from the spring pushing the cover off. Every Model A I’ve owned and worked on for 50+ hears always needed to have a few timing gear cover bolts tightened to pull the cover in. Not this engine !

Adding the spacer made the difference, and the engine is now quiet.

I also compared the depth of the plunger hole with that on another timing gear cover I have and see no difference between the two.

I can only conclude at this point that the new camshaft installed during the engine rebuild is a little shorter than a factory original.

Jim