I have this idea for a cam button and I was wondering what the slant six 'Pros' think.

While researching ideas for a cam button for the slant six, I came across this interesting item used on the Jeep engines.

It is Mopar p/n 83502890. It is basically a bolt with a center hole drilled part way down from the bolt head for a spring and pin. The idea is that the pin pushes against the timing cover, applying pressure to keep the cam centered.
The main problem with this particular part is that it is ½-20 threaded bolt. The slant six cam uses a 7/16-14 threaded bolt. I was originally thinking of drilling a center hole in the stock slant six bolt but was concerned about the strength of the bolt after drilling a ¼ inch hole in it. The alternative is to drill and tap the cam. This is a relatively simple procedure. Drill the cam hole larger with a 29/64 drill bit and then tap it with a ½-20 bottoming tap. This is easily done with basic hand tools.

Now that the ‘new’ cam bolt fits the cam, it can be bolted up and checked for clearance. In stock form, the new cam button only sticks out about ¼ inch. The clearance between the cover and the cam bolt is nearly ½ inch (0.42). To make up the difference, I added a thicker washer (a mag wheel washer is perfect) and also added a couple of small ball bearings inside the bolt itself.

The assembled unit is shown in the next photo.


The bolt is long enough that even two additional washers leave plenty of threads in the cam.
With the washers and bearings added, there is ample tension to keep the cam in its place.
If more ‘spring’ is needed, you can add more ball bearings (or metal rod) or just add another thick washer. From my measurements, I don’t think more than two additional washers would be needed. Another idea would be to weld a metal pad onto the timing cover itself, but I was trying to make this as simple as possible.

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-MattMan
LEANED & MEAN

Interesting idea! I know the racers have been making home-brewed cam buttons for a while, but that involves welding and other fabrication. Yours is simpler, it seems. Hopefully someone who is running a cam stop will chime in.

I have a welder, but not everyone has access to one. That is the beauty of this. I am going to look for pieces to use to modify the factory cam bolt for this type of setup. That way, you wouldn't have to drill and tap the camshaft (some may find that a little un-nerving). I am thinking of drilling all the way through the slant cam bolt and tapping the hole for a set screw. This will enable adjusting the spring tension without resorting to adding ball bearings. I am still working on the idea and would appreciate any feedback on this idea.
-Matt

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-MattMan
LEANED & MEAN

He may still have to weld a stiffener to the thin gauge timing cover... I've done Doc's mod on 2 timing covers and without something to stiffen or gusset across the face of the cover I have had the cover "pucker" or flex during hard acceleration during 1000-5000 rpm driveway test in idle, as the cam wanted to push forward and becomes limited by the allowance of the double roller timing set.... My "mild" 9:1 engine without the stop "beat' the cam gear enough to allow the bushing to fall out and stall the engine due to the timing change, I was lucky that it didn't walk and claim the oil pump teeth too...

Depending on the hardness of the pin it may wear away the metal of the timing cover, so tacking a wafer to the sweet spot may be needed to keep the cover intact.

This also makes for a good case to get a better timing cover that is thicker and stiffer, and would be nice to have a window that will allow cam timing changes to occur without tearing the front off the motor and leaks at the oil pan interface.(Which also brings up the problem, if you need to add ball bearings later with this mod, you'll have to take the timing cover off...with Doc's mod, a quick tweak of the wrench and the cam bolt comes back to clearance....


Just sayin'

Because its spring loaded, it doesn't really eliminate cam walk totally. A rigid button with a reinforced stop plate is the most effective method.

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There's no such thing as too much cam....only not enough engine!

Does anyone know what forces are moving the cam forward? Interaction with the oil pump and distributor gear tends to move the cam rearward.
I am wondering if you have a stiff enough spring (and reinforced cover) then you would have something that prevented or reduced cam walk and was auto adjusting.
I was looking for cam buttons but found that most of them are made for the three bolt cam gears. Actually, all of them were for the three bolt gears. This spring loaded one is interesting and is a Mopar part.

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-MattMan
LEANED & MEAN

The biggest contributor to the cam walking is the crankshafts natural forward movement. Since the cam is connected to it via the timing chain, it can't help by being pulled forward as well since there is really nothing to hold it back. I have also seen the Buick 231 engines have a spring loaded cam button, but it isn't very effective either. The gear to gear meshing between the distributor and oil pump probably contributes also to some degree. A lot of inline engines also use thrust plates to eliminate cam walk as do many "V" engines.

Don't get me wrong, i'm sure the spring loaded one you showed is better than nothing, but I think it still needs a reinforcing plate to push against because it will spend a lot of time rubbing it.

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There's no such thing as too much cam....only not enough engine!

i wonder if oil pressure in the rear Journal Gallery can push it forward as well?
I have the :"doc" Cam Stop in my engines - It will Move the Timing cover as it is thin gauge Steel.

The Ruster Race car is a bit better as I built a 2 piece cover and the Metal "Sandwich" part is very near the middle of the cover Just near 1/2 way so that seems to add a lot of ridgidity.


Greg

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http://www.youtube.com/hyperpack

I know I have had a fair amount of oil "puke" out of the rear journal and plug area when I remove the cam from a hi-po slant engine after race season. I think part of it also is that the cam journals decrease in size from the front of the block to the back of the block so if something doesn't hold it in place, a small amount of lube on the correct clearanced bearings will allow it to just slide out the front of the block under gravity+viscosity.

Yes they are different sizes to allow for the cam to be installed.


I don't think that has any effect on the cam sliding forward, as if the engine was tilted rearward and there was no timing gear on the front of the cam it would also slide rearward to produce the same effect.

Greg

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http://www.youtube.com/hyperpack

That is an interesting thought, about the rear cavity. I'll have to check it out.
Also, I guess I will have to reinforce the timing cover if the cam can push it with the cam stop mod.
Good info.
Thanks.

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-MattMan
LEANED & MEAN

The cam really should not move forward in a non-roller lifer application. That is why most older engines don't have anything to stop that from happening, nonetheless it is a good precaution in a race engine. Some cam billets do not have the horizontal hole drilled to relieve oil pressure at the back of the cam. Some don't even have the intersecting holes in the journal that oil the valve gear. Always inspect a new cam to see that all holes are there and that the oil holes line up with the holes in the rear cam bearing.

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If you didn't drive it there, it's not a street car.

All good points to consider.


Greg

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http://www.youtube.com/hyperpack

I installed the Doc-type cam stop on my latest engine build (13.90s in a 2950 lb car). Before that I have run 13s and 14s with several engines and cars and never had a cam stop. I have run a few of these engines for 30 min stints (1000s of miles) around road courses with 5500-6000 RPM redline and WOT for 1/3+ of the time. Our 24hrs of LeMons car (9 hrs straight endurance) has no cam stop. No cam problems. I really don't think the cam stop is necessary with a proper cam arrangement (holes drilled, etc).

I will also say that with a couple of exceptions (late 80s/early 90s builds), I have only used stock reground cams with stock (not rebuilt) oil pumps. At or near the world record HP Slant Six engines (Tilley in Oz) also have used this arrangement. He has made more HP with regrind cams than anything else.

Just some food for thought,

Lou

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Home of Slant6-powered fun machines

I have two Oregon Grind cams to use, I plan to try the milder one first.
I have #1395 and #1313. I am not very trusting of things, so I always check everything out before I use it.
It is for a drag racing application, which is why I have questions about the cam stop.
I am working on the block mods now.

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-MattMan
LEANED & MEAN