I have often wondered why Cam Manufacturers drill and tap the Camshaft timing sprocket bolt holes to accept a 5/16-18 bolt instead of using 5/16-24 hardware.

The tensil strength of a 5/16-18 grade 8 Bolt is 7800 lbs.

The tensil strength of a 5/16-24 grade 8 Bolt is 8700 lbs., (an increase of 900 lbs.).

With the increase of spring tension, cam lift and the use of throttle stops (off-on-off) the load is ridiculously high, yet everyone continues to use lower strength hardware in their Camshafts. So far the only answer I get is that, “We have always done it that way”. The fact is that the load has substantially increased over the years and it’s not the same requirement.

Having seen high quality (no names here) grade 8 5/16-18 bolts sheared in two engines, maybe it’s time to ask them to tap the cam bolt holes to accept 5/16-24 hardware. Additionally the increase torque strength of the 5/16-24 bolt increases the clamping load of the timing sprocket to the face of the Camshaft, (and that’s also a good thing).

In both failure events the hardware was installed correctly and torqued correctly with red Locktite, separate quality torque wrenches at two different shops. Both engines had spring seat pressures at 360 lbs. Both cams were .800 + lift and both broke with less than 80 runs. Both engines used timing chains although a gear drive would not have made a difference.

Just wondering, but not going to use 5/16-18 hardware with the next Camshaft I purchase. I’ll pay the difference in manufacturing cost it can’t be as expensive as fixing the damage the bolt failures created.

Bob

There is relatively little tension in the fore/aft direction, other than that caused by the pull of the oil pump drive. That directional force has not changed. The rotating stress would be in the "shearing" force applied to the dowel pin and the3 bolts. While that force has surely increased, I haven't heard of anyone having that problem, so long as the bolts are tight. It would be some feat to shear all 3 bolts and the dowel pin. I had a massive failure years ago where the rod was jammed into the cam, and the cam snapped.

RIP

Is there room to put an insert like a keensert of a bigger size or just re-tap to a larger bolt?

I guess I never paid that much attention to it.

There is no shearing force until the clamp load is exceeded. Just like wheel studs. It’s the clamping load that holds the wheel in place not the shear strength of the stud itself. In my experience the hardened locating pin will shear pretty easy from a side hit compared to the more malleable bolts. There is no doubt that the 5/16-24 bolts would be a better choice but as with all production manufacturing there has to be a certain amount of failures to drive the change and obviously that number hasn’t been reached.

Curtis

a fine thread has less inclined plane,therefore more likely to stay tight and not be subject to loosening from vibration.correct???

Had a problem last year sorta related to this- hexadjust bushing was moving around in its little slot. Used good hardware, red loctite, and so on. Cam bolts were still tight, I figured it was just a fluke deal since we’ve used that same part numbers for years with no problems.
Put a used hexadjust off another bbc on it, new bolts, new bottle of red loctite, and it stayed in place this time. These are baby valve springs too, like 265-270 on the seat.
Figured with what spring pressures are nowadays, etc., etc. someone would figured out a better way than three coarse thread 5/16” bolts, always wondered why GM didn’t use 3/8-24 bolts at least on big blocks.

Im gonna have to go with crap bolts.
While at proper torque the bolt has stretched.
They are only 25-30 ft lbs.
Shear is the enemy here, and if the bolt is not properly heat treated they will fail upon stretch, leaving only the dowel to fend for itself.
Grade 8 is not in the china dictonary, they just have to look like gr8 not perform.

Also measure the tolerance of the gearset you are working with, if the holes are too big it will allow the gear to walk, especially if the dowel hole is large. It does not take much, just a few.000 and it just gets bigger.
Look for signs of brinelling on the back of the gear and face of the cam.
Check check check. Trust nothing to be true or correct.

If an interferance issue was not present you could always try studs. ARP may have something the right length.

Something else to consider. Anything with potential shear or rocking action needs a bolt or stud where it rests against a smooth surface and not the threads. That may be where most of the issue may start. Not a lot of surface area on the threads.

In the case of the last failure, the three ARP (not Chinese Junk) 5/16-18 grade 8 (7800 #) 12 Point bolts and the pin sheared flush with the face of the cam. Crower (by the way not their Camshaft) were kind enough to removed the broken items then re-machined the face of the cam so it was dead flat. There was evidence on the face of the cam and the back of the cam sprocket that as the bolts stretched the cam sprocket (chain drive) was slightly moving around. That in turn retarded the cam far enough to lose noticeable power. The sheared bolt studs were still locktited in the cam, if it had not been for the Enderle front fuel pump drive assembly holding the sprocket in place this would have been a major catastrophe, the engine died at a low rpm in the H2O box.

My point has been that using 5/16-24 (8700#) hardware makes better sense. Just because “We have always done it that way” is hardly reason to continue doing it “That way” particularly when it has proven on more than one occasion to be a failure point. The current application requires a serious “Re-think”.

I am hoping that the Cam Manufacturers spend a moment and give this consideration. This is a simple inexpensive up-grade.

Bob

quote:

Is there room to put an insert like a keensert of a bigger size or just re-tap to a larger bolt?

That might be real challenge dealing with a heat treated cam core.

In our case one of the problems is the base width of the front Pump Drive adaptor that bolts to the face of the cam. The width limits the size of the timing gear/sprocket retention hardware. The only hardware that will fit is either a allen bolt or a 12 Point 5/16 bolt. The flange diameter limit is .475 or less for the Allen bolt or .350 base diameter for the 12 point bolt. Anything larger doesn’t allow you to get a socket to fit over (or in the case of an Allen bolt into) the bolt head.

The ARP 2000 part number for the 5/16-18 X 1 1/4 12 Point is 3AG 1.250-2S. This will allow for the Drive thickness, depth shims and sprocket thickness. I can‘t speak to the thickness of the various gear drive cam gears each one is probably different. That ARP 12 Point bolt number is the only one they offer. I would not use a local Hardware Store Allen bolt because I have been unable to confirm that they are a quality grade 8 bolt, most of what I have found is highly (Chiness Junk) questionable, regardless of who re-packages and sells the bolt.

In any event for the time being a quality ARP 5/16-24 grade 8 is a step forward. Unfortunately larger (3/8) hardware will not fit for a variety of reasons.

Bob

Just my opinion, I think if there is enough spring pressure or cylinder pressure to cause the bolts and pin to shear, the key in the bottom gear on the crank would break first. I think there is something else going on to cause the failures. I may be wrong.

First thing that comes to my mind is I don’t think any of the companies engineer around the facts of bolting a pump to the front of it.

quote:

Originally posted by RPROGAS:
In our case one of the problems is the base width of the front Pump Drive adaptor that bolts to the face of the cam. The width limits the size of the timing gear/sprocket retention hardware. The only hardware that will fit is either a allen bolt or a 12 Point 5/16 bolt. The flange diameter limit is .475 or less for the Allen bolt or .350 base diameter for the 12 point bolt. Anything larger doesn’t allow you to get a socket to fit over (or in the case of an Allen bolt into) the bolt head.

The ARP 2000 part number for the 5/16-18 X 1 1/4 12 Point is 3AG 1.250-2S. This will allow for the Drive thickness, depth shims and sprocket thickness. I can‘t speak to the thickness of the various gear drive cam gears each one is probably different. That ARP 12 Point bolt number is the only one they offer. I would not use a local Hardware Store Allen bolt because I have been unable to confirm that they are a quality grade 8 bolt, most of what I have found is highly (Chiness Junk) questionable, regardless of who re-packages and sells the bolt.

In any event for the time being a quality ARP 5/16-24 grade 8 is a step forward. Unfortunately larger (3/8) hardware will not fit for a variety of reasons.

Bob

So are you saying you didn't use the hardware that came with the timing chain and gears, maybe the problem is the fuel pump drive not the bolts that was used? Just a thought.

Y'all must be talking about Chevrolet style engines. Ford uses ONE bolt to hold the sprocket to the cam, and it's been all too common to shear the dowel pin off in even mild solid roller applications. ARP makes a bolt specifically for Ford engines that works well, MUCH better than any grade 8 bolt that you can buy off the shelf at your local hardware stores....and also better (obviously) than the factory bolt. Lot of guys are putting dual dowel pins in them to make 'em live longer. I haven't but my stuff ain't as wild as most everyone else's. I think some of the 385 series aftermarket cams are now coming with 7/16-14 threads instead of the factory 3/8-16. And yes I, too, have wondered why a NF thread wasn't used. Seems like at a given torque, the NF threaded bolt would pull the two parts together tighter no?

I know this. After busting one dowel off last year, I ordered/installed an ARP cam bolt. When torquing that ARP bolt, you can literally feel a huge difference. It just feels completely different than the factory bolt even at the same torque. The factory and grade 8 stuff, you can feel it stretch. The ARP bolt not so much. Come to think of it, I did a cleveland at one point and the cam I ordered came with 7/16-20 threads in it. I used an old ARP rod bolt. Nary an issue-ever-with that part of the engine. Everything else was a different story, and a lot of it my own fault for cutting corners.

Thought BBC's had 3/8" NC, just like my BB Mopar, which I torque 35 ft. lbs. (grade 8), with loctite.

Went thru this several years ago, turns out holes in cam were not drilled deep enough or bolts were too long and were bottoming out. Always check since then

quote:

Originally posted by Dave Koehler:
Anything with potential shear or rocking action needs a bolt or stud where it rests against a smooth surface and not the threads. That may be where most of the issue may start. Not a lot of surface area on the threads.

I agree with Dave on this point. Thinking a shoulder bolt or stud with a smooth shank in the gear area would help minimize shear movement if the clamping load gives way.
Just a thought here, but aren't grade 8 bolts known to be more brittle than Grade 5? Perhaps a bit more malleability would be a good tradeoff, since the increased tensile strength of a Grade 8 fastener does not improve shear resistance, might even be worse? (No, I didn't sleep at a Holiday Inn Express last night, and I am not a metallurgist, but I do know there are many applications where a grade 5 bolt is preferable to a Grade 8)...

Having more dowel pins would increase the shear strength. Increasing tension will increase the clamping force but may not do as much for shear.

I to have seen the cam bolts just a little too long and so the clamping force was not as good as it should have been.

quote:

Originally posted by CURTIS REED:
There is no shearing force until the clamp load is exceeded. Just like wheel studs. It’s the clamping load that holds the wheel in place not the shear strength of the stud itself. In my experience the hardened locating pin will shear pretty easy from a side hit compared to the more malleable bolts. There is no doubt that the 5/16-24 bolts would be a better choice but as with all production manufacturing there has to be a certain amount of failures to drive the change and obviously that number hasn’t been reached.

Curtis

Curtis

This connection was not designed to carry this load through friction that would be developed from the clamping load of the bolts between the cam and gear. Ya there is some load carrying capacity there but not even close to what's needed so if there is any play in this connection it moves quickly and therefore shear becomes the main load path. Changing the bolts to fine thread will do little or nothing to strengthen this connection also.

Bottom line here is to torque the bolts properly and use red Loctite. If you have issues then, you need to find out why cuz something else is wrong.