Update: Adjustable cam pulley

OKay gents, here she is the much needed and anticepated adjustable cam pulley.

I spent the last two days going over fastners for proper torque and stress along with the vibrational issues they would indure. that was the biggest pain, the other pain was engineering around the small "real-estate". the neatest feature of all is that you no longer need to pull pins or jump teeth or even loosen the tension to adjust the cams.
these were designed based upon the cam adjustment pullies you'll find on hondas. however the similarity stops there. the honda based ones rely on tangs from the toothed wheel to transmitt torque to the cam. given the loads and speed of the 308 this wouldn't work. both parts of the pulley ride past each other at .001" across a .5" face on two sides. close for no axial movement but allows for degree adjustment.
the specs:
7075 aluminum, this is FAA certified aluminum; 95k tensile strength vs 45k for 6061-t6. Hard anodized
Custom spec'd ARP fastners M6x1.0 12point head, Helicoil inserts to negate shear.
Stainless Belleville washers double serrated DIN 6796

the pulley still retains the one pin that aligns the teeth and cam to 0*, the outer edge of both pieces are engraved with 1* increments from 0* to 10* for advance/retard to make adjustments easy to read. those marks don't show on the rendering, but would be found on the pad above the pin hole.
I'll have a physical part in 2-3wks.

now for the pic of the model....
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for those wondering the mass of the aluminum removed for the pin hole access is equal to the mass of the pad for the degree engraving. net result keeps it balanced to eliminate vibration. that was some fun calculating...thank god for computer engineering softeware...

 

NEAT!!!
This is long overdue. Closest we've had is Nick's cam gear with holes all around it.
Umm,
Is it that you kept the mass the same, or the rotational effects as the engraving mass is further from the center?

 

the pocket needed to get the pin into the cam removed a specific amount of material which would have the effect of an out of balance wheel, by adding the pad where the engraving is done that pad offsets the loss of material. it's hard to describe with out better pictures, i'll try with the model.

 

what's the projected cost?
Why stick with the stock belt design? Not to rain on your efforts, but you may find cost a resistance factor in marketing this jem. Don't get me wrong, I LOVE the concept. but IMO you would really clinch things if you went with a more modern belt design from the start, as being able to get away from the frequent belt changes would help sell it. All that would be required is to do a matching lower pulley, and the right length belt, and you would have it.
Good Luck.

If no one came with new ideas, we would still be driving model T's

 

ohh.. i'am planning on that also but that would drive up cost to the end user. sourcing the belt won't be hard but re-engineering the pullies will require some time. the current radius's between the parts has to be taken into account and the cam cover plate would also be changed. not to mention i would personlly feel better test bedding something like that first before droping in the publics hands. something like that would most likely be 6-9mnths out. but i do think we may see this from some other sources before i even get up to batt.

for now this would allow the replacement of the stock pulley while retaining the rest of the system. cost effective for those not wanting to spend $2k-2.5k on a complete swap. 'ballpark figure'

the current cost of this part would be somewhere between $200-$250 per pulley ready to install. the price of 7075 aluminum keeps going up.

 

I have been doing a lot of searching online, and I cant find anything that actually speaks about belt design. Some are "still" running a straight toothed belt. What I was wondering, instead of changing the actual belt design, why not try to fit a wider belt?

 

it's the radius the belt undegoes when traveling past lower pulley. sourcing a new longer belt i.e. another manufacture would be needed only to satisfy the larger pulley. the larger pulley would reduce the stress on the belt and allow for a larger berring.

but like dominos tip one over and more fall, a larger bottom pulley won't fit under the stock cover. new cover? or cut up the old one?

 

Good point! I have always suspected that the small diameter of the lower pulley is the most destructive of the actual belt drive design on the 3x8 motors. I note that other mfg's usually use a larger diameter system that the F-cars. Redesigning to upgrade would open up a WHOLE can of worms. Not a good trail to go IMO.
Instead of 7075, perhaps up the design strength, and go with 6061T6, or T651. You could anodise it for wear resistance. Should keep the costs down. The ARP fasteners are great, but they are right proud of them. try McMaster Carr. They stock a lot of fasteners, MIL spec, etc. and are a LOT better in price. They probably buy from the same source anyway, LOL.

 

7075 is much harder than 6061-t6 and anodizing. McMaster Carr does carry alot of fastners and is where i'll be sourcing the belleville washer. thier bolts however are std. ACME ASA where as ARP manufactures thier own bolts to a higher degree than the ACME ASA.
vibrational harmonics are a concern, the only ASA bolt to handle that would be a nylon patch/pellet bolt. but frequent use would remove the benefit of the nylon.

i tend to over engineer things, the last thing i want is for it to get loose at 7k rpm. better safe than sorry

 

Can changing the cam timing actually make more power, or does it just move the power band up or down?

 

yes, and yes

 

Well, I did some digging and found a site by Gates http://gates.com/facts/documents/Gf000282.pdf

It looks to me, from what I am reading, we should probably just stick with the belt we have. I dont even know if wider would be a benefit as they claim higher bearing loads. The only other possible idea would be some super tough belt made out of something like kevlar, but is anything like that even available??

 

here is a better rendering i just did adding the hardware and degrees for more clarity.
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as i sit here doing this i know why these parts in general are not done for these cars. i'm 40+hrs onto this already for just R&D still have the manufacturing process to handle. if i was to bill someone for this, it would be a quite a few sets of these before they turned a profit. if it wasn't for the few of us industrial types who find this fun, we'd be screwed...

 

You got it!
Then add Marketing costs, etc, and what started out o be a fun project starts to look like it is going to barely break even on a good day. Then along comes the knock offs (pirates), who market the item shamelessly, and there you are.

 

belt info,
the Dayco belt we use is an 'S' profile, top of the page on the link.
http://62.110.184.188/dayco/en/products-belts-profiles.htm
interesting read, now to find out if another profile is better. a cross reference on size would be nice. more digging...

 

more info on the digging...
to redesign the belt system using larger pullies and a longer belt would take some good engineering. just increasing the pulley dia. and slapping on a longer belt isn't a good idea like i thought it would be.

the life of the belt has a few factors to consider, enviroment, tension (critical), construction.

the enviroment of a the timing belt on the 308 isn't that bad, no acids or steam. so a low factor here. the tension is a critcal piece, heres why. under the proper tension the belt will provide positive engagement with no slip or deformation. loosen the tension just a bit and the 'slap' will cause slipping, jumping and blisters. to tight and deformation with shearing will occur. construction is the pitch and depth of the teeth and design of engagement.

the Isoran belt is the 'bees knees' of belts, so we can factor out the belt material. the big issue we have figured out is the lower pulley bieng so small, we can get around the jumping a tooth with current setup by using a deeper profile however the current pullies are to shallow for that. so if one is to re-engineer the pullies you might as well go larger. next can-o-worms, going larger means we need to decide on a pitch profile and dia size of pully, then the tension needs to be factored to achieve the correct belt tension given the leangth etc. of the new belt.

so as we can see it is do-able, but it needs to be done right or we can make the situation worse. the time needed to re-design the set-up is huge! sure i could spend the time doing it, i figure it might take me a few months to get the number right and settle on a pitch design, each have thier comprimises. and lets say i can get an off the shelf belt that fits the design criteria. bringing it to market would cost me the materials and manufacture time. i'd have to negate the R&D becouse calculating that in would drive the cost up. and how many would i even sell to make the venture worth the time?

fear not i'll still be fidiling with the project, i don't see the light just yet. maybe i need new batteries

the majority of this information comes from Dayco and my old trusty machinery/engineering books. even a simple crown would keep the belt self centered and avoid wearing the edges, but that crown has to be exact or you'll 'break the back' of the belt.

for now i'm happy with my adjustable replacement pullies...

 

Great project. Don't be discouraged by economic claims.
BTW; I don't want to hijack your thread, but I'm curious. What design software do you use ?

Best Regards from Germany

Martin
'german engineering and italian passion'

 

Here was another site

http://www.roymech.co.uk/Useful_Tables/Drive/Timing_belts.html

I didnt take a lot of time to devulge it all, but its kind of interesting. From what I am seeing, and someone correct me if you see something differently, it looks like the trapozoidal belt is needed on small diameter pulleys with high speed and (relatively) high loads.

From what I can see ours is a "L" belt (3/8" or 9.525mm pitch) and 1 inch wide, but no L series belts are listed any wider that ours. There are some other links in there, one shows a speed chart, which indicates lighter and lighter belts as speed climbs. This could be the reason the belts are underdriven off the crank, so as to slow down the input drive.

 

the squishy pink stuff between my ears, har har i use Acad to draw up and model the parts. the rest is old school paper and pencil calculations.

 

Could you share the specifics about the Isoran belt that led to this statement (curious minds want to know)?

 

this is a strange answer but here goes, Isoran is a proprietory weave of 'fiberglass' and rubber boding agents. i'm using that word loosly becouse no-one will tell me what it is exactly, here is another wierd part to it. it is not made in the U.S. or used here other than bieng imported for our cars. Dayco uses Kevlar in the U.S.. it would seem that reading between the lines Kevlar and Isoran are near identical. I talked to the U.S. branch of Dayco and they have no information on the Isoran belts, not made nor marketed here. I ended up having to discuss this with the import manager for the European Market.
A call to MegaDyne even netted me some very paraniod people, who am I, why do I need to re-search the composition of belts?... etc. just trying to find the right belt for the application is going to take some convincing to get the info i need.

 

If I read correctly in some of these articles, Kevlar is only rated up to a 180 degree F temp operating range. I could see this belt area on the 308 easily exceeding that.

 

After gong over the material in the links, I note that the pulley diameter is not really addressed, as far as longevity is concerned at least.
The closest I could find was a referance warning to avoid pinching or damaging the belt by folding in a manner that would sharply bend the supportive fiber inside. I would think that the tighter the radius, the more the belt is in fact bent, and this sharp bending must contribute to early failure.
It would certainly stand to reason that the more a material is bent, in a repeated action, the more prone to failure it becomes.
I think it all boils down to we are stuck with the basic design, as a complete new system is not economically feasable, and changing belts has been and will continue to be a fact of ownership.
An adjustable pulley however, would certianly improve the search for performance gains. Being able to dail the cam to varied opening/closing events without the usual involved procedures would be a real benefit.
Once the cam is dialed in @ Zero, or base setting, an adjustment to the cams would simply mean removing the covers and dialing it in. If you decide that setting isn't what you were going for, simply dial in another, or reset to zero. I could see that it could be easily done trackside, sans bulky air conditioner.