Help with belt size for timing pulley

[borna]

Hello all,
I am building a 4 cycle engine that I want to use timing pulley instead of spur gear.
I already have these 2 pulleys that I'm planning to use
Crank
https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=59051&GroupID=217

CAM
https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=58689&GroupID=217

The center distance between the Cam and Crank is 7.26”

Can someone guide me through as what size belt I need to get?
They have a center distance calculator on their site, but not very sure if I am using it correctly.

Thanks
Borna

 

[steamer]

Hi Borna,

Usually, there is a tension idler in engine applications....Do you have a drawing you can share?

Dave

 

[Ogaryd]

hi Borna.

I came up with 16.98in. long, 208 teeth, you'll need extra length for tenstioner. What did you come up with?

Regards Gary

 

[firebird]

Hi

Follow this link and download the utility

http://www.colinusher.info/Software/Model Engineers Utilities.html

Its a brilliant little free programme and has a belt and pullley calculator that I have used.

Cheers

Rich

 

[borna]

Thank you all.
The calculator on the site came out with 209 teeth but that is not available, so I guess I can go with 208 teeth?
So I'm going to buy 3 belts
208 teeth
210 teeth
and one with 240 teeth so I can use tension idler?

Question on tension idler, does it have to pulley or I can make a roller?

And to answer Dave, as far as drawing, it only make sense for me and not a drawing to be used by other

The engine is like 95% completed, and here are some pictures that you can see so far as what I have.

http://www.homemodelenginemachinist.com/index.php?topic=19172.msg199554#msg199554

Thanks

Borna

 

[Ed T]

Tensioner would go on the outside of the belt (the smooth side) so it does not need to be a toothed pulley and it should go on the "slack" side of the belt. That's the side that is being pushed by the crank pulley up toward the cam pulley. Timing belts are really fussy about their shaft alignment being parallel so a small idler pulley with flanges may help to keep the belt tracking better. Not a cure for misaligned shafts, just some help. Also, just running the numbers in my head, a 240 tooth belt is almost 20% longer than you need and I'm not sure that you wouldn't be better off with something a bit shorter. You might want to do a test of reasonableness with a strip of paper just to see how things work out. Looking forward to seeing the finished project.

 

[Ogaryd]

Hi Borno

I agree with Edt about the 240 belt being to long, Your cam & crank pulleys are rather small dia. so the distance
between the belts dosent allow much adjustment. Useing all flanged pulleys is a good idea but it will be nessacary to
install belt and pulleys at the same time. My guess would be 210 teeth,
Maybe some other people can chime in with opinions.

PS. Your engine looks good
Regards Gary

 

[borna]

Belt arrived today. 208 teeth seems like a very good fit, but since I never worked with belts, not sure what the tension should be? How do I make sure the tension is good?

Thanks
Borna

 

[borna]

Belt seems just the right size. Don't think I need tensioner pully

Borna

 

[borna]

I almost there. Only thing left is ignition stuff.