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big bore pan

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Post Sun Feb 17, 2008 7:27 am

Posts: 3
Location: Junction City KY.
I'm going to build a new motor with 3 5/8 cylinders and stock stroke of 3 31/32 will this be a good combo?

Post Sun Feb 17, 2008 9:38 am

Posts: 2684
Location: Los Angeles, CA
bikerwilly wrote:
I'm going to build a new motor with 3 5/8 cylinders and stock stroke of 3 31/32 will this be a good combo?


Why not just build the Square Motor? 4" x 4".

Post Sun Feb 17, 2008 11:20 am
panic

The big-bore, short-stroke combination has been invented every 10 years as a new idea.
Since re-balancing is required anyway, it offers no advantage over the same displacement (81.9") achieved through stroke increase (4-3/8" is about the same at 81.2"), which is more effective.
More stroke will eventually limit engine life and maximum RPM, but not near where you are now.
You might get a better squish band - but only if you actually machine the parts yourself, they won't come like that.
The flywheels also offer you a choice of at least 3 weights.

What is it you're trying to do?

Post Mon Feb 18, 2008 6:05 am

Posts: 3
Location: Junction City KY.
I have flywheels out of a 56 74in was going to use them with std 3 5/8 bore cases . just though i'd use the wheels i have as it in good shapr and has rods on them.

Post Mon Feb 18, 2008 8:00 am

Posts: 3061
Location: Central Illinois, USA
I have no experience with such a combination in a Pan, but a big-bore stock-stroke Chubble turned out to be a delightful torque machine, able to pull a fully-loaded sidecar faster than anyone should, for several round trips to Sturgis from Illinois.

The owner insisted upon an overhaul at ~25,000 miles, as he had never gotten that out of a motor before.
I found nothing to fix, leading me to conclude that it is a very durable formula.

....Cotten
Note: It was originally an 80", but that is still a 'short stroke' to a lot of us.

Post Tue Feb 19, 2008 11:18 am
panic

Certainly preferable to stock bore, needs smaller compression dome for the same ratio, no down-side except that it's slightly more knock-prone than a std. bore if the quench is too large, but has better quench than stock if the quench is properly limited.
You're going to rebalance it, yes?

Post Tue Feb 19, 2008 11:40 am

Posts: 79
Location: No. Andover, Mass. USA
Someone mentioned 4 inch bore. Were would you find heads to accomodate this?

Dick


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