The Stovebolt Site Forums The Shop Area Engine Shop 1956 235 camshaft thrust plate

I ordered a new camshaft thrust plate and spacer. I noticed on the old one there are 4 small indentions on both side. What is the function of these indentions? I got the new one from Chevy’s of the 40’s and the picture they showed looked like my old on but what they sent was smooth on both side. Will this be a problem?

They held a bit of oil in the indentions. I'd suspect the camshaft would get enough, though. There's a nipple that squirts oil at the junction of the crank gear and cam gear and that slings a lot of oil around and oil will run out of the camshaft bearing also.

One comment...make sure when you install the new gear to get the clearance as close to .001" as possible (between the thrust plate and the camshaft gear.

Thank you sir!

The thrust plate itself can be installed either side to either side, lol. The grooves are to retain a little bit of oil.

For the 56 motors, you also need to use the ring spacer. If you look at the spacer, one side has a bevel.
The beveled side goes toward the can shaft (to accommodate the fillet on the cam from the machining). The spacer itself is designed so that the can gear is installed right to the spacer, no clearance needs to be checked. Install the gear firm against the ring spacer and you are done.

Feel free to put the little divots in your plate. Just don't go haywire. Dress them down nice and smooth.

If you are using an aluminum cam gear, don't press the gear on, hot or cold. Do a You Tube search for Tom Lowe's 12bolt.com video on installing the gear. Essentially you spray a little flat black paint on the back side of the gear, heat the gear up with a hand held torch to 475, put the gear on the cam and use a good size dead blow hammer to wack it on, let it fully cool.

Now, full disclosure, I just installed a gear this way a couple of weeks ago and it did not quite go all the way on, just a little smidgen short, so I put it in a press, still hot, reheated it to 475, and just nudged it down a tiny bit to firmly seat it on the spacer.

Jon G. What will be the consequence of having a clearance greater than .001” between the thrust plate and camshaft gear when you install a new gear?

You may get opposing views, but I think you have two things happening with the cam:
1. The angle of the cam gear is going to push the camshaft outward and into the thrust plate when the engine is running.
2. The angle of the cam lobes is going to make the camshaft want to travel backwards when the engine is running...the lobes running against the 12 lifters, that is. The cam gear will win the tug of war but evidently not all the time...

At idle (remember your cam is only turning at 1/2 the speed of the crankshaft) the helical gear won't have anywhere near the force it has at say 1000 rpm, so your crankshaft can move in/out by the amount of clearance present. If you're idling at 425 rpm, your camshaft is only turning at 212.5 rpm. See...I wasn't asleep in all of those math classes. That can cause your ignition timing to change and also may cause your valve timing to change. The more that plate wears the more low speed change might occur. If you look at a used thrust plate, you'll see a circular wear pattern. I've seen some of these worn to around .020". That allows a lot more camshaft movement than I think is good.

By coincidence I just replaced the camshaft, gear and thrust plate in my engine. I had been suffering a wonky idle (essentially persistent misfires at idle) for a few years. They went away over about 800 rpm but none of the typical problems would fix the idle misfires. The thrust plate had around .016" gap between the camshaft. Now it idles very smoothly...as it should. One lifter is resisting rotation, but that's either a matter of break-in or something else, and I haven't yet decided what to do about it.

Thank you for sharing. Your experiences and expertise are much appreciated. I will revisit my installation of the new gear to ensure the final location is acceptable.

Hope it is helpful. I've decided the .001" spec might be to buy a person the most time possible since all these plates will suffer wear. I think Dave mentioned they could be installed with either side facing the engine. And that's good information to have. If the one you have is worn, just flip it over and you'll have a new one.

Also...If .001" clearance can be had, then that's ideal but the range is .001" to .005", so there is some leeway.

Oh, one other thing. An important thing, I think...at least for those who are doing the work themselves. The cam gear is designed to go on one way only. But that doesn't mean it is impossible to flip it over and install it wrong side out if you get distracted or something. I mention this because like a big dimwit dumbo I did that a few weeks ago and walking back to my car realized something didn't look exactly right. What didn't look right was the fact the little dot that matches the dot on the crankshaft gear was not on the front side where it should have been. So I got to remove it and install it correctly.