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74" Knuckle Pistons

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BrentCross@Bronko's

Posts: 88

Joined: Thu Feb 01, 2007 8:20 pm

Post Wed Jun 18, 2008 10:15 am

74" Knuckle Pistons

What are list members using for standard replacement 74" Knuckle pistons? I don't see anything available from S&S or Wiseco. Any thoughts?
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47knuck

Posts: 530

Joined: Sat Apr 02, 2005 1:01 am

Location: Ogden, Utah, USA

Post Tue Jun 24, 2008 1:08 pm

Re: 74" Knuckle Pistons

Brent: I have run standard FLH pistons with no problems. But I have also got Pan cylinders with plates under them because they are shorter than Knuck cylinders. So I put clay on top of the pistons and measured the thickmess after turning slowly by hand. This is how I got the needed clearance to keep the valves from hitting the piston. A little arithmatick and I had plates made at 0.125" thick. This gave me 0.020" under the valve to the piston. never did worry too much about the compression ratio this gave me I just wanted to ride. Bike has run with this setup for 30 years and two sets of cylinders as well as a new set of flywheels. Others will have more exact numbers but this worked. Is there a big difference with the angle between the valves for a Pan? That would be the most important change cause it would move the valve relief on the piston some. Some one here must know. Steve
Steve H
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Lee W

Posts: 141

Joined: Sat Sep 23, 2006 8:58 pm

Location: Carver, MN

Post Thu Jun 26, 2008 11:56 am

Re: 74" Knuckle Pistons

I was surprised to see that most catalogs are listing pistons as "Pan/Shovel". Didn't they all used to list them as Knuckle/Pan/ Shovel? No matter, any piston listed for a 74" Pan or Shovel will work in a Knuck. Personally I have been using cheap imported pistons and having the skirts teflon coated for about the last 10 or 15 years. I have just started adding a ceramic coating to the domes. When you add the cost of the coatings you are still considerably under the price of a Wiseco or S&S, and in my opinion have a piston with a lot better chance of survival. Just my 2 cents worth.

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