Camshaft knocking problem

[Bob from Northport]

We have been in the process of installing a new engine into a 1928 Fire engine. The engine was purchased from a rebuilder, unnamed for the present, not showing much concern about this problem. The final assembly was completed yesterday, and the engine started very nicely. But the loudest knocking noise we have ever heard also appeared upon starting. The underside of the engine was taken apart today and checked-no problems with bearings or torque. We disconnected every item on the engine attempting to locate the problem. We finally located the problem with the camshaft. We removed the side cover plate, and ran the engine, and watched the camshaft move in and out toward the front of the engine. Suspecting the spring and plunger inside the timing cover, we removed and replaced it with new ones twice, only to see the same movement and noise appear. When hand cranking/moving the cam and crank, the camshaft moves outward toward the front of the enigne .035 on one side, then moved back against the engine casing. This is with movement VERY SLOWLY!
1. Can anyone offer reasons why the camshaft would move that much when barely moving?
2. The plunger/spring is not strong enough to stop the movement-why?
3. Is this a problem with the camshaft regrind?
4. Since the only thing that comes in contact with the cam is the oil pump-distributor shaft gear set up-could this be causing the problem.
We don't believe another spring/plunger will do any better.
Any thoughts Mr Endy? How about the rest out there. This is a totally free job to the village that owns the truck. We could use the help.
Thanks!!
Bob's Model A Ford Garage Bob Campbell

[Tom Wesenberg]

Check the crank gear to cam gear clearance. You should be able to feel freeplay by moving the cam gear back and forth (not in and out). Turn the crank 90 degrees and try it again. Check for freeplay in at least 8 places on the cam gear.

Did the distributor shaft turn freely?

[Glenn C.]

The plunger to cover side clearance fit is very important to start with. Try to find a gear cover that will give you a minimum side clearance as posible. You may have to have a custom plunger machined to fit the cover correctly. Plunger should be hardened. We install machined spacer washers under the plunger (without a spring to start) untill we obtain .006" - .010" clearance. Install spring and plunger using lots of assemblers lube (Lubriplate)

[california dean]

If the above checks don't find the problem, you might try removing the oil pan and checking the crank assembly to cam lobe clearance, especially when the engine is at the point of rotation where the forward movement of the cam is observed. Anything changed on the crank assembly, like added counter weights, different rods, bolts, nuts, etc. could be contacting the side of the cam lobe, pushing it forward a slight amount with each rotation. Some engines have very little clearance between parts in this area. A suggestion anyway. Let us know what you find please.

[James Rogers]

I had one do this once. I changed the oil pump and camshaft and solved the problem. I used the cam in another engine and had no problems with it so, I believe the oil pump was the problem. I added a gasket to the bottom plate of that pump and used it with no problem.

[Patrick L.]

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I recently installed an after-market oil pump/distributor drive that is quite noisy.. The cam gear and drive gear are getting to know each other better so the noise is getting better with time, I figure in another 20 yrs the noise should be gone..

[Del in NE Ohio]

I encountered the same problem last summer with the installation of a newly rebuilt short block. I can't say for sure but I suspect the NEW pump drive gear was a factor. I left it in place and put a couple of thin washers behind the new plunger spring and it went away. 1500 miles later all is okay.

[Greg Jones]

Bob-

I did a search and found your posting on the camshaft movement problem. I am very interested in what you might have done to fix this problem, as I have the exact same thing going on. Now I know why I come across those timing covers with a bolt installed in the plunger spring recess-suddenly it seems like a good idea. I have the cam movement issue in an inserted, relatively low mileage engine with metal timing gears. I have done everything except pull the dang motor and fit a different cam, something I would like to avoid if possible. Any insight you might share? I want to quiet down this old thrashing machine! (My knock is on acceleration and at high speed-otherwise runs great at 55+ mph with ease)

[MikeK]

Following up on what Tom W said, uneven timing gear engagement is often caused by errant crank grinding which leaves the first journal on a slightly different centerline than the slightly reduced diameter the crank gear rides on.

The result is an eccentric rotation of that little gear, causing the helixed gears to feed the cam in and out. Just 0.002" off centerline will cause this, easy to do if you use a crank grinder with a "self-centering" three jaw chuck to hold the nose of the crank. That gear seat needs to be indicated to within 0.0005", something nobody does with a crank grinder unless you EXPLAIN prior to grinding.

For car cranks that drive a chain sprocket or belt cog wheel rather than a gear, several thousanths slop there makes no difference. Not so with direct helical gears.

I'd suggest checking the runout on the small crank gear if the cam gear play varies. If that checks out perfect you may have a cam gear that is off-center, an easier fix.