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Big hat's off to Anthony today for some very quick help. My new CB Performance alternator pulley finally arrived to day via USPS and Canada Post. The new pulley parts are just beautiful but I noticed from the get go that this CB pulley has a larger diameter than the pulley that was on there. My problem was that I needed advice on where / how to source a new belt of the correct length. It turns out that the existing belt is 840 mm and the replacement belt needs to be about 912 mm. Anthony made it easy and the local Napa will have one for me tomorrow at 8 am.  Thanks, Anthony...nice one !!

mppickett posted:

Hi David, I'm glad it's coming together. Just curious, do you have a power crank pulley or a regular size one?

Mike

Giday, Mike. I don't know much about my engine other than it was built 55,000 km ago by a fellow in Vancouver, Canada that had a good reputation. Here's a pic of the new CB Performance alt pulley just sitting on the shaft and my hand holding one half of the pulley that had gone bad. Full o.d of the new ( black pulley ) is 4 1/4" and the one I'm holding is 3 3/4"o.d. 

I don't know what a crank "power" pulley is, nor do I know the o.d. of a regular sized one. My crank pulley is shown in the second blurry pic. It is 5 3/4" o.d. 

Now  quick poll to help make a colour decision on a small plane I'm rebuilding. 5th pic is the type of plane....just a small single seat job but it needs to get painted in Military yellow or silver. Which colour do any of you like, please ? Yellow 3rd pic or silver 4th pic ? Thanks. 

 

 

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David Stroud IM Roadster D posted:
Giday, Mike. I don't know much about my engine other than it was built 55,000 km ago by a fellow in Vancouver, Canada that had a good reputation. Here's a pic of the new CB Performance alt pulley just sitting on the shaft and my hand holding one half of the pulley that had gone bad. Full o.d of the new ( black pulley ) is 4 1/4" and the one I'm holding is 3 3/4"o.d. 

I don't know what a crank "power" pulley is, nor do I know the o.d. of a regular sized one. My crank pulley is shown in the second blurry pic. It is 5 3/4" o.d. 

Now  quick poll to help make a colour decision on a small plane I'm rebuilding. 5th pic is the type of plane....just a small single seat job but it needs to get painted in Military yellow or silver. Which colour do any of you like, please ? Yellow 3rd pic or silver 4th pic ? Thanks. 

 

 

Hi David, The normal size of the alternator pulley is 4 1/4" so your bad one may have been an undersized pulley. Your crank pulley is a "power pulley." Normal size crank pulleys are around 6 3/4" and folks often switch to a smaller pulley to reduce the speed of the alt/fan to save power at high rpms.

Regarding paint color, I like the look of the silver with yellow trim (4th pic). The silver helps to set off the shape of the cockpit. Very nice looking plane!

Thanks,

Mike

David, your old pulley ratio is 1.53:1, you new one is 1.35:1. The new ratio with your larger pulley is 13% SLOWER than before. You might want to keep an eye on your head temps.

Stock fan ratio is 1.59:1, the stock fan is the fastest and flows the most air. Your new ratio is almost 18% slower than stock. I'd pay attention to oil temps. And buy a CHT gauge.

Or, the best solution? Buy a stock size(6.75") degree pulley and another even longer belt. Take the crank pulley off first to see if it's the stock threaded type or sand seal.

Last edited by DannyP
DannyP posted:

David, your old pulley ratio is 1.53:1, you new one is 1.35:1. The new ratio with your larger pulley is 13% SLOWER than before. You might want to keep an eye on your head temps.

Stock fan ratio is 1.59:1, the stock fan is the fastest and flows the most air. Your new ratio is almost 18% slower than stock. I'd pay attention to oil temps. And buy a CHT gauge.

Or, the best solution? Buy a stock size(6.75") degree pulley and another even longer belt. Take the crank pulley off first to see if it's the stock threaded type or sand seal.

I'll look at the crank pulley situation tomorrow. What are the implications of stock threaded type or sand seal ? 

I checked with CB Performance today because they sell two non stock pulleys. PN 1931 which is what I bought for about $75 and PN 1912 for about $45 and this one looks to be a smaller diameter on the website. In fact they are the same diameter at 4.25 ", just that the last one is made in Taiwan and the better one is made by CB Performance. 

So now I'm wondering why would they make one that would turn the cooling fan slower than stock ? 

David Stroud IM Roadster D posted:

I checked with CB Performance today because they sell two non stock pulleys. PN 1931 which is what I bought for about $75 and PN 1912 for about $45 and this one looks to be a smaller diameter on the website. In fact they are the same diameter at 4.25 ", just that the last one is made in Taiwan and the better one is made by CB Performance. 

So now I'm wondering why would they make one that would turn the cooling fan slower than stock ? 

My understanding  is that it’s the other way around. There is the stock diameter VW generator/alternator pulley and then they started using the Porsche 356 diameter pulley which is smaller to get the fan to turn faster.

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