Adjustable Pulley pt2 a new belt design...

What dimensions do you need?
I may already have them in my cam lock design notes, or can get them from my '82 QV.

 

"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." Krowbar
TAG! LOL....
I missed that one Paul. Not having the cover off, I A.S.S.U.M.E.D. it was a 2:1 ratio. Good to know.

 

Scott~

Here is a site on belts.....
http://www.roymech.co.uk/Useful_Tables/Drive/Timing_belts.html

The trapazoidal belts we use, have a 3/8" pitch, which correlates to the 9.525mm you mentioned, but that pitch is not available in the HTD belt. This may be what threw off the lady at Gates. Our belts are called classical belts, and the belt we use is a "L" style belt, and is 1 inch wide. The HTD comes in pitches of 3,5,8,14, and 20 mm, but the widths are far away from what we are running, unless we choose a tighter pitch or go to a GT belt. If the pulley diameters are enlarged, between the increase in radius, and higher number of teeth, we should be fine with the current belt style we are using. If we were to move up to the 8M HTD belt, I would suggest ( if you want to use the HTD ) see if a 30mm wide belt is possible. That width belt, with the newer style belt technology and larger diameter pulleys should definetly make the belt drive a lot more robust.

 

Scott~

Just a thought, but I would guess that everyone who would be willing to upgrade the belt system, would still want the same width, or even a little extra, just to make darn sure the new system will be better. Changing the design, but narrowing the belt is going to make some people, including myself somewhat skittish. I think there is room for a 30mm wide belt, as its only another 6.5 mm. If we were to simply stay with the trapezoidal belt, with larger diameter sprockets we would again have a much stronger and more robust system. Add both together, wider belt, and larger sprockets and it would be almost bullet proof.

I just measured the actual running width of the bottom sprocket, and it is exactly 30 mm plus the flange. There is appoximately 10mm of space on the back side facing the cover, and probably some wiggle room on the front, so we could easily have 35mm wide sprockets.

Scott, if you could supply new sprockets that were equal in diamter, or larger, that would run the HTD 8mm pitch belt at 30mm width, I think you would find a lot more people ready to jump in. Add in your adjustable cam sprockets and make it all fit under a stock cover with a larger idler and I for one will help promote this thing. But remember, if it gets to expensive it wont go over so well either.

Did you get the measurements on the shaft centers you needed? I never got the time to dig stuff out yet.

 

Okay, I been putzin. I assembled a bunch of my parts and took a look at everything. One caveat up front, I didnt try to get dead nuts accurate as I dont have tooling that would accurately measure that kind of distance that way. But as an example, just using a decent rule, I came up with 139.7 mm between the camshaft centers. So seeing as the actual is 141mm I think I hit it pretty close. This is working only with the front bank.

So, here is what I get:

Bottom drive pulley sprocket center to intake cam sprocket center, 274.6mm

Center to center both cams, 139.7mm

Center to center exhaust cam sprocket to drive sprocket 269.8mm

The center of the idler is about 17mm outside the centerline between the drive and the exhaust cam.

The idler is 63mm

The belt has 101 teeth and is 1 inch wide with teeth centered at .375 inch. Because it is a "L" design belt, its in SAE measurements. But look at the belt number 101 R 254. 101 teeth 25.4 width, funny.

Now, I also set the harmonic balancer up there with the belt installed and looked at the clearance. We will run out of clearance at the cam sprockets long before we need to worry about the bottom pulley.

Inside the belt cover, I found a minimum of about 6mm clearance around the cam sprockets, and that was at the flange. The belt itself has a couple mm more clearance. There is a LOT of room around the idler, if we want to increase its size. You could easily increase its size 20mm with no trouble, as long as the belt wouldnt mind.

Looking at width, the current sprockets are already over 30mm wide, and there is plenty of room on both ends for a bit more. However, the belt should not ride farther back towards the motor, as the belt tensioner would need to be modified to clear the belt if it did. But I think by simply making the new sprokets say about 3mm longer, there would not be any trouble running a 30 mm wide belt.

If perhaps you were to stay with the present layout but use the HTD belt at 8mm pitch, you should have 4 more teeth on the lower sprocket, which would get two more in belt contact, and 6 more on the cam for roughly 3 more belt teeth there. If however, you want to run the pulleys out to just clear the belt cover, lets say you increase the cam sprockets 10mm. I only checked one belt cover, so I am only assuming simular clearance on the rear cover, and making the same assumption across the fleet. But I could foresee some having to grind some metal off the iside of your belt cover for added clearance. But there is a lot of "meat" in those covers so its not any trouble.

If the cam sprockets were increased 10mm in diameter, the overall size would allow 39 teeth with the HTD belt at 8 mm pitch. This would require a drive sprocket with 26 teeth. This would give us 3 more teeth in contact on the drive and almost 5 more teeth at the cam. These would clear everything with zero to minor modifications, and would fit under a stock cover. As I said, the cover may need some clearancing but minimally. The only other thing it needs is a better idler pulley. This would eleviate a lot of the belt issues for a lot of people and would allow some kind of increase in the maintainance schedule. One thing I think we should keep however is to leave the drive pulley made out of steel. I dont think I have ever seen a drive pulley made of aluminum. I'll keep this assembled for a day or so in case we need any further data.

 

BTW, the QV cams measue 101mm center-center. The 4V valve angle is less than the 2V, so the cams are closer together.

The drive ger centerline to the tensioner s/b the same for the 2V & 4V cars. I'm pretty sure that they used the same tooling setup for both blocks as they built them both on the same line for several years.

Doesn't look like I'll get a chance to get the other 4V meas'ts anytime soon.

 

Ive been looking at this now for years and it never made a connection until now. Ferrari claims that the belt should not be retensioned. So why is there a cutout in the belt cover to access the tensioner hold down bolt? If it was truely designed never to be adjusted after installation, there would be no need for a hole in the cover. Anyone have any idea??

 

Here are 3 thoughts which may or may not be or any interest.

First, it's very common on race engines to simply remove the cover, I don't see a problem there. The problem is clearance on the lower pulley. There is about .150" between the belt and the timing cove. You can't make the clearance zero, so practically, you could make the lower pulley/belt about .200 larger diameter, no more...unless you stick the pulleys out away from the engine a bit, then you could go bigger.

The second thing is belt life. The new design belt will run way more hours between changes, so say you go from 30k mile to 100k miles...that seems like a good thing. The problem is that there are 2 numbers on the belt service interval, mileage and years. The old belts needs to be changes at 30k or 5 years, the new belt will be 100k or 5 years. To more ferrari owners, that meas changine the belt every 5 years even with the 30k mileage limit, so bumping up to 100k doesn't yield any gain. Maybe there is a lower chance of failure...I'm not sure about that.

The final though is that in the old archive somewhere Ed Gualt (sp?) had a conversion kit he mades up to go to a moddern, I think honda, timing belt. It migth be worth an archive search to see what he was doing...but I think he found of the self pulleys to do the job...I might have that wrong though, seem worht the search though.
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I commend your efforts. Couple of contributions:

First, I too approached Ed Gault a year or more ago trying to buy one of his belt systems or a list of parts so I could replicate it. Ed declined (liability).

Second, I talked with the techs at one of the dealerships about a Michellotto built 308. 342 BHP, 2v car. Engine was rebuilt by a well regarded race engine builder in the Midwest. They found one issue with high RPM running (dynoed to 8700 I think) was belt flex as the engine heated up. Caused some (less than optimal) change in cam timing.

Third, Bill at GT Car Parts sells aluminum 308 cam pulleys (I used them, better and a lot cheaper than the $1600 OEM plastic ones). He may have a source as I assume they were being made from blank stock.

Last a question. The 308 was one of the first Ferraris to use a belt (Boxer was first if I remember correctly). So this was late 60s/early 70s design. 355 is presumably 25 years later and there's 25 years more knowledge. What's the belt profile on a 355 and if it is still a block pattern, thoughts on why? Is anyone using the HID design on a high revving interference design engine?

Philip

 

I spoke with Ed back in 2001, & exchanged eMAIL with him last March when I tried to obtain his design drawings as I wanted to mfg a set & investigate the feasability of mfg. it. Ed had a machine shop with a gear hob cut the gears & press the flanges on with a 100 ton press.

His belt was a Gates T-212.

Here's a link to the 1st post in the series about his system:
http://www.ferrarichat.com/discus/messages/256120/2273.html
Unfortunately, the pictures were lost in the infamous Fchat hard drive crash a couple of years back. Possibly someone has downloaded them.

Ed had 10 systems made up. Was selling them for $1200/set. He ended up selling the last 2 or 3 systems on eBAY. Had just bought my car & couldn't scrape up the $ for his system back then. Funny thing is that I haven't heard about anyone actually running his system. However, there are 10 out there somewhere!

I asked the same question when I did my 1st major just after getting my car. Have asked several factory techs since then.

So far, No one has ever come up with an authoative answer.

My SWAG is so you can verify that the tensioner is indeed locked down after reassembly.

The WSMs are very very clear about not re-tensioning even once!

 

I think this has become a very interesting thread, I think we all learned something. I find it very interesting that Gates supports the original Ferrari design layout even after all of these years. Okay, so we stay with the same size pulleys, but change to the modern HTD belt profile, what about the tensioner? Fine as it is, or go bigger? Scott, are you still able to incorporate adjustability into the cam sprockets? Can you make the bottom pulley from steel? Can we go 30mm wide on the belt? Lets go!

Liability? Scott is simply doing this as a service, I don't think he's trying to really make anything except to pay for his time. I dont see how anyone could afford liability and still be able to do this. So you either except the engineering is equal to or better than what we have now, and take a risk, or you wait and see. But to hold Scott responsible is totally unfair. There are some smart people here who could easily look at this, and when he makes a few sprockets get some into some other hands and let them inspect them. If they pass muster, run em. If they need a change, do it. But then the risk has to fall on the buyer.

 

Probably right, exposing fingers to the belt is a concern too. If Gates says the original pulley size is in spec for the new belt, then it would seem there is no reason to even think abot bigger.

Ask...my 2002 jetta just got a belt change because it had to come apart to replace a waterpump and they said it was due next year (5 years) anyway, so $50 now or $800 next year. Generally anything rubber under the hood has a 5 year service life.

Your plan seems quite sound..particularly since the belt fits a common application.

 

This is one of the most informative, serious and important threads I've read on Fchat. Many thanks to all those participating. Here's my contribution/query.
I'm about to treat myself to one of Erik Buell's new 2006 XB12Scg motorcycles for my birthday. The bike, a 1200 cc V-twin, has as its main driveline a toothed belt that is described as "a 14 mm pitch, aramid reinforced, GoodYear Hibrex belt with Flexten technology." Now comes the best part, this belt has NO service life replacement intervals prescribed, in other words, it is expected to last the life of the motorcycle. That such an extraordinary claim can be made for a belt that is exposed to road grime, the pulsating torque of a V-twin engine, heat, oil and other debris (the belt runs out in the open, with only a guard to keep legs, feet or riding gear from getting caught), is amazing to me. NO REPLACEMENT necessary for the life of the motorcycle (even if it isn't true and it has to be replaced every 10/15 years) and we 3#8 F owners fret and worry about keeping our well protected cam belts from self destructing before 5/30 is absolutely preposterous and should be totally unacceptable-IMHO.
Ric