The interference numbers are a function of the hub material. For the steel ATI hub, the required intererence fit is 0.0007" - 0.0009". This is established by measuring the crank snout and the hub and if the hub is too tight honing until the correct interference is achieved. The Powerbond is slightly different but in the same general neighborhood of numbers. Most people don't measure and if you have too much interference it can be very hard to impossible to install/remove later. A slight amount of anti-seize is also recommended by ATI for installation. I think you will find the aluminum interference numbers will be larger.

 

I had the same difficulty believing this myself since most work I do the key is the driver. However, as explained to me, some of the new Fords don't even use a key for indexing and drive internal components completely by friction. I think this is a downright scary thought, but I guess in the long run it works and saves money. Not sure why else you would design something like this. In my world, its heavy, overdesigned and has a big safety factor!!!

 

Bingo... thats what I do. Its sounds funny but works like a charm.

 

Sounds like your in space hardware/testing, if I recall correctly the FS is like 10 to 1 for ground based applications.

 

Navy, everything is heavy and big.

 

The sprocket which drives the timing set and oil pump has to be keyed to keep the crank and cam in step with each other and to keep oil flowing. The balancer is an interference fit as it only drives parasitic devices such as the A/C compressor, power steering pump, alt. and water pump(unless you've gone electric). Those devices don't put nearly as big a load on the system nor do they have to be precisely timed as does your camshaft. I'd be willing to bet that you could install the crank pulley without the bolt and with a little luck the LS owner would be none the wiser unless the crank pulley started to "walk" off of the crank snout. I wouldn't try this myself, but after this discussion I think the only job of the bolt is to keep the crank pulley from "walking" and the interference fit is what keeps the pulley from spinning even when loaded down by the A/C, alt., PS pump and water pump. The bolt face and boss on the crank that the back of the pulley bucks up against when the pulley is fully home probably acts like a vise to "clamp" the pulley fixed, but I think the interference fit has more of an effect in keeping the pulley and crankshaft turning at the same speed.

 

I agree with most of what you said; however, in the stock set up the pully doesn't "buck up against" the boss on the crank. If this was the case not even GM would be dumb enough to tell you to hold the snout indentation between 0.094" to 0.176" in relationship to the pully hub face. If you were to "seat it fully home" against this boss you would be out of spec and under the 0.094 inch minimum and the pully/belt position would be out of alignment with the other belt routing points. Check out the hub installation proceedure in the Helms manual...

 

Now that I think about it a little more the sprocket(not the pulley) bucks up against the crank boss and the pulley bucks up against the sprocket. I will get my Helm manual out and check it out. I seem to remember that spec., but most people(myself included) push the pulley until it stops moving(fully home against the sprocket which is in turn already fully home against the crank boss). When the pulley stops moving I think you'll find that the crank snout is slightly indented whether it be by design(GM engineering) or luck. Once you are in the neighborhood of 250ft/lbs the pulley has long since stoppped moving because it has bucked up against the sprocket and the sprocket has bucked up against the boss on the crank. This is when the "clamping" (as in vise jaws) begins. My question is(and it's not something I can remember having come up before in the thousands of posting I've read on LS1Tech over the years)what do you do if the value is outside that spec.? Do you install shims if the value is too small or do you have to machine the back face of the pulley if it is too large? I would think that if the crank snout is slightly recessed inside the pulley face(by say between 0.094" and 0.176") the OEM GM bolt(which just happens to have a large flat washer which is an integral part of the bolt head) would "clamp" the pulley(and sprocket) against the crank boss.

 

I think GM put the numbers in there only as a check that the pulley has bottomed against the oil drive/crank sprocket. When I did my ATI, I had to measure and come up with new numbers to use as the stock numbers don't apply. The crank sprocket is supposed to have a chamfer that butts up against a chamfer in the crank.

 

As I've already stated: On stock applications the pully does not mount against the timing drive gear. There is a small gap between them. If you mount the pully too deep you have to get your pully puller and pull it out somewhat or the belts won't track correctly, if your not in far enough your supposed to re-install the old crank bolt and retorque to 240 ft lbs. The 240 ft lbs sequence is to be repeated (according to Helms) untill it is within the specified distance. GM evidently decided this was the best way to ensure the correct position of the pully. I have no idea about after market as each set up is somewhat different. That would depend on the design of the after market products and what the manufacturer recommends for mounting their design.

Size of the gap for stock applications? Really easy to figure, all that needs to be done is for someone currently installing a cam to depth mic the distance from the crank shaft face to the face edge of the drive sprocket, then subtract the center pully hub width (somewhere around 1 1/8") and add the minimum 0.094". This will give you the minimum gap distance for stock set up, want the max? Then add 0.176" instead of 0.094".

 

I have a stock hub on my bench, I am not seeing how you can achieve the 250 lb-ft with the bolt (prior to installing new bolt) without it bottoming against the oil drive/timing sprocket. There is nothing to prevent it from bottoming. What am I missing?

 

I too believe it bottoms. The next time I pull the front cover off of an LS I'm going to put the pulley on without the timing cover installed to see what happens. I will stop pushing the pulley when I reach the specified recess value and then verify if a gap exists or not. As has been mentioned there isn't anything to stop the pulley from bucking up against the sprocket. Most people torque the bolt to 250ft/lb if they have the strength to turn it that tight. By that time I think the pulley and sprocket have long since been kissing each other.

 

As I stated in an earlier post, the force developed by the bolt is used to help turn the timing chain as well as the serpentine belt. I didn't believe it at first either, but I spent a lot of time on the phone with Cloyes (their tech folks are very knowledgable) and Cloyes makes a lot of OEM setups as well as aftermarket.

 

The balancer hub absolutely bottoms against the crank gear timing sprocket. The factory service manual specifies .094 - .176 distance from the balancer hub to the end of the crank snout. This applies to stock balancer and timing set applications only. When I installed my Rollmaster single timing set and ATI balancer, I had to measure/compare both components to the stock components to ensure I was within the correct distance specification. The stack-up distance will be different when you introduce aftermarket components.



The line drawing from the service manual clearly shows the two pieces are 'pressed together' when installed.

 

For the sake of argument lets say there is a gap between the rear face of the balancer and the front face of the sprocket. If the interference fit doesn't provide sufficient purchase to rotate the A/C compressor, PS pump, alt. and water pump the balancer is eventually going to spin on the crank. This is because of the gap which negates the additional clamping force that would otherwise be provided by the bolt if there were no gap. Either the balancer hub is going to fail or the crank snout is going to get eaten up by the slipping balancer or they both will fail. Now if the balancer does actually buck up against the sprocket and in addition to the interference fit you add the clamping force of the bolt against the balancer which is against the sprocket which is against the crank boss you should have enough purchase to keep the balancer from spinning on the crank even with all of the parasitic devices putting full load on the pulley at the same time.

 

No it doesn't , you need to re-examine the top drawing, notice the cross hatched lines outlining the solid portion of the pully and then the sprocket. Even in the drawing it clearly shows a small gap between them.

 

In the drawing, the only reason the space is there is to differentiate between the two components. Why don't you measure all of the components and add the stack-up height together? If you did, you wouldn't be stating this INCORRECT information.

 

Better yet, there is a tool specifically made to install the harmonic balancer on the crank. It has a specific length bolt and spacer so it is not too short and won't bottom out in the crank either. The Chevy dealer let me use theirs but you can buy them. Scoggins Dickey has them. I used it on my 5.3 and it went on no sweat.

 

In actuality the upper drawing does NOT even illustrate the sprocket. It only shows the pulley and crankshaft in crosshatch. You are mistaking the crankshaft for the sprocket. The small gap shown is between the snout of the crank and the first step face of the pulley not the sprocket. The sprocket isn't even illustrated here.

 

Wrong, it shows three pieces, note the three different cross hatched sectional areas, it shows the front portion of the crank timing sprocket with the latter portion of the sprocket cut away - just as the rear portion of the crank is cut away. It shows the front poriton of the crank, the pulley, and the front portion of the crank sprocket.
If the sprocket wasn't included and it was all the crank as you think - then the cross hatch lines would match the same direction and orientation as is used to represent the front portion of the crank thus noting its part of the the same component.