Adjustable Pulley pt2 a new belt design...

Wouldnt Gates be a good source for engineering specifications to what thier belts are actually capable of? I would think of anyone on the planet, a big name timing belt manufacturer would have details on the various belt designs and what would be best.

 

Not in the Sacramento area, actually a bit east (Atlanta), but I do have an 84 QV sitting on a pallet in my garage that is fairly easily accsessable.

JD

 

Okay, do the guys at Gates see any inherent problem with the current design that makes it short lived, and in that context, can they offer an alternative that would out perform it?

I dont want to overburden you as I am sure this can get overwhelming. But right now we have a known quantity. I am all for an upgrade if its going to offer a marked improvement in performance, but it should be a known improvement, not a maybe. No offense, but if gates dont know the answer to that, and can offer some kind of real data to support it, we could be going back to that domino thing.

 

Only a 12" and a 4" caliper, a pocket machinists rule, a Stanley 25 ft. tape measure, a couple of plastic triangles, and a compass and protractor.

JD

 

Just saw your most recent posts. Are you in Irvine, or in El Dorado Hills near Sacramento. I live in Cameron Park and just picked up a 308 gt4. I am planning on doing all the belts and hoses before I drive it and will probably start tearing into it this weekend. Tried to send you a PM, but your box is full.

 

I just want to compliment smg2 on his efforts. The belt "issue" on these wonderful engines is truly one of the only negatives of these cars. There has to be something that can be done to upgrade the current belt system to make it more reliable. I applaud your effort and can't wait to hear what you come up with. I personally think that if a belt system could be employed that effectively doubled (for eg) the belt life I for one would purchase it even if it did require fabrication of larger or modified belt covers. Keep up the good work.

 

Looks like we have come full circle - or almost.

A belt (and matching pulleys) with the newer profile seems to be the cheapest, easiest solution to the problem. Option in the great design of the adjustable wheels, and we have an answer to what has long been a thorn in many sides, real or perceived.

Scott - you will be the toast of all of us (and the subject of a voodoo doll from the current belt maker). Keep up the awesome work!

Now, what is the story with 348s and 355s that they need 30K belt changes.....

 

I gotta second that post whole heartedly!
I am a bit familiar with the tremendous effort, time and money it takes to come up with a new design, or way of doing things.
I had read the new thread, and went down to the shop and measured the upper pulley on a 2 valve motor.
The measurement I came up with was 3.425" or 87mm, measured across the teeth. Please bear in mind it was a "stand on your head, push hoses out of the way" measurement, but I think it is quite close. The lower pulley should be 1/2 of that I would think.
The Honda belt would be ideal IMO, as they wind those motors up to some pretty crazy levels on a regular basis.
I wonder what the belt people would be able to say on the longevity arena based on the pulley diameters?
HTH!

 

Let me see if I am following all of this correctly. You have discussed the current design with Gates, and it is thier understanding that just changing the belt design to curvelinear, the belt life would increase? Further, you are attempting to calculate larger pulleys to increase the life even more. I would argue that at this point, the design fully requires a larger diameter idler pulley, to slow down its operating RPM.

Might I suggest, as long as you are willing to go to this trouble, you take a look at the 348 belt layout? If we are going to need a new cover, perhaps a single belt layout ala 348 would make more sense, and perhaps a 348 cover could be addapted to fit? I know the drive is totally different, as the 348 has a single drive pulley with two idlers, but perhaps a single idler directly above the two drive sprockets could be adapted.

I liked the initial idea of new cam pulleys that allowed a vernier scale to read advance/retard, and being adjustable. I wouldnt mind a larger idler pulley, just to make darn sure it would hold up between belt service. I wouldnt even mind the possiblity of increasing the size off all the belt pulleys, as it would allow the belts to live under less stress. From there I might get gun shy until I could see more data.

 

Thats what I was curious about Paul, and why I measured the pulley. I would think that before going a bunch further in the effort, it would be a wise move to contact them, with pulley diameters, and see what their engineers say on the increase in longevity a curvelinear design might offer. If it is a large enough margin, it may not be worth changing to a larger pulley system, with the added clearance issues.
I did dig thru my records and found the 2 valve pulley (cam shaft) CTC measurement:
141.065mm

 

I say if it aint broke dont fix it, but I am a purist....

 

Scott, I also wanted to thank you for looking into this, its great to have people out there willing to make something better, yet trying to work within the standard design so the car will still appear correct.

Some thoughts though. the bottom pulley currently has 20 grooves for belt teeth, and the upper ones have 30. I just counted. Kermit, we were forgetting the the gear reduction in the timing cover, as the bottom pulleys are not geared 1:1 with the crank, but would be geared 1 and a 1/3 so as to slow down the drive pulley, but perhaps more it was to allow more teeth in contact.

However larger you make the pulleys, the teeth will have to remain at a 1.5:1 factor. The next sequence in our tooth spacing would be 24/36, followed by 26/39. Obviously more teeth on larger diameter pulleys will reduce the strain on the belt, and increase its life remarkably. But how large can we go? I seen that 26 tooth bottom pulley and imagined that it was getting to the size of the top pulley. So I went and dug out my timing cover and cam pulleys and looked it over.

In the attached picture, you can see that a cam pulley, with 30 teeth, clears the oil seal my quite a margin. By the looks of it all, I would say Ferrari kept a small diameter pulley so you could get the belt off past the harmonic balancer. I dont know how much clearance is available under the belt cover, but if the bottom pulley were as large as a cam sprocket, the cam pulley would need 45 grooves. The cam pulley would grow in diameter from approximately 3.58 inches, to 5.37 inches, so basically we need .895 inches (roughly) of added clearance around the pulleys to operate pulleys that large. Other numbers that work are 28/42, 30/45. 32/48 works but its getting far to large.

Another idea I thought of, to allow a larger idler that would fit under the stock cover, would be to loop the belt down between the two cam sprockets and put the tensioner there. But they seem to always run the tensioner upstream of the cam sprockets, and that would seperate them.
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I would think that if it would fit under the stock timing cover, the 28/42 would make a good compromise, as it would leave some clearance around the harmonic balancer. 28/42 would give us pulleys approximately 3.342"/5.013". With an upper pulley just over 5" in diameter, we only need about 3/4 inch of clearance.

 

But not only do Hondas break belts when you beat the snot out of them, they are non interference engines, so who cares if the belt breaks?

I dont know the clearance of a 28 tooth pulley to the balancer. The pic I took is the stock cam pulley and it has 30 teeth. I can possibly dig further tomorrow and set up the harmonic on the timing cover and see how much room there is between the cam pulley with a belt installed. But it will only be a close guesstimate. But roughly, a 28 tooth bottom sprocket should be about .110" more clearance.

Just so everyone dont forget, belt the pulley arrangement on a Ferrari is not 2:1. Everyone knows the cam must turn at half speed to the crankshaft, on every 4 cycle engine made, and Ferrari is no exception. But Ferrari geared the small drive pulley off the crankshaft at 1.333333:1, and then the next step is 1.5:1 between the belt pulleys, for an overall ratio of 2:1. Thats why there are 20 teeth on the lower pulley, and 30 teeth on the cam pulley.

I could also, if I have time, measure the cam cover and try to see just how large we could go on the cam pulley and still have some air clearance. I think that is going to be more of a limiting factor than the size of the bottom pulley. And really, I think everyone wants to keep this stuff under a stock cover.