Camshaft Belt drive

[TurboTom]

I have started work on a camshaft belt drive for the AMC 6. I have digitized the front cover and just about have the system planed out.
Looking for some market study
1) Would you pay $550 for this product?
2) See Above
3) How big of a market is there for hardcore Jeep 6 performance parts?

Please post any features wanted and what YOU think the market would be.
I am going to build at least 2 to start with, My turbo drag engine will have one and one for Sixpak if he is willing to trust my design

[John]

Are you willing to build 3, I would be very interested in one at that price. Wet or dry design?
John

[TurboTom]

Dry.
Once I get it sorted and dyno tested I will make as many as I can sell

[Mgardiner1]

Tom, i know its not hard to answer with out a working prototype, but what would one hope to achieve by choosing belt drive instead of chain?

[SilverXJ]

I would be interested, but I don't want my engine to be a guinea pig. $550 isn't a bad price. Would cam timing be able to be adjusted without removing the harmonic balancer and all the other fun stuff?

[Plechtan]

I was also working on a belt drive, things are pretty tight, you only have about 1 1/8 inches to fit the belt and the seal. If the block plate is 1/8" that leaves you only 1" for a 1" belt ! Usually the drive companies would like the pulley wider then the belt. So then you could go down to a 20mm belt (~3/4") but it would not be as strong.

The crank is 1.250 where the cam gear sits, this would now become the sealing surface, but it has a keyway in it. So you have to put a sleeve over it, so say 1/8" thick so now the shaft is 1.5" . A seal for a 1.5" shaft would be about 2" OD, now you need some material to hold the seal, so say that is 1/8" thick so now you have a 2 1/4" boss sticking out from your cover. The pulley would have to be cut out to clear the boss, so say you bore it out to 2.375 to clear everything. The pulley you would use would probably be about 3" in diameter. so 3" - 2 3/8 = 5/8 you have to divide this number by 2 to get the wall thickness of the palley, So you end up with 5/16 wall on your palley. then subtract out the depth of the tooth (1/8" ?) you end up with only a 3/16 wall on the end of the pulley. Seems a little thin to me.

The other issue is the cam gear. it would be nice to use the later design with the thrust plate, but the cam companies are not making cams for this. If you use the earlier cam design, you need some way to keep it from moving back and forth.

Just my 2 cents

[John]

Dry.
Once I get it sorted and dyno tested I will make as many as I can sell

Keep me posted.
John

[TurboTom]

Belt drives take less HP, Hold the timing stable and dare I say it, handle crankshaft harmonics better.

Yes it is tight but I believe doable. I plan on taking both cam designs in account, But will have a thrust bearing for the older design.
I machined a back cover prototype out of plastic I had here. I will use this material for designing the drive before I start with the aluminium.
Here are a few pics of the beginning stages...hot off the ShopBot

[Mgardiner1]

veeeeery interesting I love watching custom stuff like this come together.

What would you plan to use for a crankshaft seal? stock lip seal or something special?

[Plechtan]

TurboTom wrote:
Yes it is tight but I believe doable. I plan on taking both cam designs in account, But will have a thrust bearing for the older design.
I machined a back cover prototype out of plastic I had here. I will use this material for designing the drive before I start with the aluminium

It looks like the older blocks used a different bolt pattern on the timing cover, I think they changed in 92 or 99, not sure. If you buy a gasket kit, it comes with 2 gaskets.

What dimension did you get for the centerline of the cam to crank? I came up with X- 3.75 and Y + 3.375 using the crank centerline as the origin. This was just using calipers, maybe you have a better way to measure it. I could not find any standard belts or pulleys that would work with the center distance. You will probably have to use a roller to hold tension.

[SilverXJ]

I could not find any standard belts or pulleys that would work with the center distance. You will probably have to use a roller to hold tension.

What do you look for in a pulley to use, besides the thickness? I assume that the cam pulley has to be 2 times the size of the crank pulley? As long as that is constant could you use different size pulleys, or are you fixed using x size pulley?

[Plechtan]

Well, the cam pulley must be twice as large as the crank pulley, you have about 5" center to center from the cam to the crank. So the biggest pupulleysou could have would be about 3.25 X 6.5 the radius of the crank pulley would be 1.625 and the radius of the cam pulley would be 3.25, so 3.25 + 1.625 = 4.875 This would give you 1/8" clearance between the pulleys. You may be restricted by the lower part of the timing plate/ cover as well. Good numbers to use are 3" and 6" pulleys, this is close to the stock size. The bigger the pulley the more belt engagement you will and the more torque you can transmit, the actual speed of the belt will go up as measured in ft per minute.

[SIXPAK]

The entire deal is a compromise since the correct belt length does not exist. This is the reason for the idler.

It's been done allready on a 4.0 but not to the extent that it could be a drop in AND use existing stock balancers and the stock serpentine set up. There is alot more to dong a project like this than what it appears at first glance. The plastic mock up back plate is a great start.

[TurboTom]

On the final design the cam timing will be adjustable at the cam pulley.
Seals will be determined by the space available.
As for the pulley design, there are quite a few stock units out there as well as "pulley stock" a long piece with just the gear on the outside, you machine the center the way you want
The cam to crank distance is 5.045". There is a possibility not to use a tension roller, but a tension roller is not really a bad thing. It would make up for line bored blocks, make belt installation easier and help with general tolerance differences.
I must thank SixPak for his help on this project.

[Flash]

I'm just foaming at the mouth here.........and this would only apply to the 99+ 4.0L but, if you were to weld a retainer(for a Cam oil Seal) to the cam thrust plate, ........and then made a smaller plate, that attached to the bottom of the block, thru the crank(with the cranks seal being deeper in to the block now)and seals to the bottom of the oil pan................

Since the wideness of the belt, is at a premium, eliminating the backing plate would add that much more to it. You could have the cam sprocket Hub, recessed so the new seal wouldn't affect the depth of the cam sprocket......and still seal the oil out.......
[/quote]

If you could keep this idea, it would be better,........if its a bolt on piece, you would sell more............. but then again, if I'm looking to twist a 4.0L stroker above 5500++++ i would be willing to take my block to a machine shop to have this, that, or the other, machined slightly to make it all fit.............Like i said just foaming at the mouth!!!!!!!!!!


Flash