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  #1  
Old 4 Weeks Ago
motorhedmike's Avatar
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Default Valve Lengths?

In my quest (obsession?) to get one of my bikes running, I've accumulated multiple sets of heads. I noticed there are at least a couple of different Intake valve lengths- 3.690" and 3.620". What are the applications for each? Also, measuring the valve stem protrusion from the guide shoulder seems less consistent than say, from the bottom of the spring pocket-? I'm just thinking is it possible for a valve guide- no matter where you get it from, could have a consistent enough shoulder to measure from. Thanks in advance...
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needspeed needspeed is offline
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For 1-15/16 diameter intakes the 3.620 is a stock length. The 3.690 is considered an "R" valve and is used with stronger than stock springs and/or higher lift cams that need more travel.

The guide shoulder thickness will probably be .075" +/- .005. Consistent enough to make the stem protrusion measurement.
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Okay, so if I add .075" to my measurements I would be basically eliminating the guide from the equation right. Bottom of valve spring pocket (where guide seats) to top of valve stem 1.45" minimum. The reason I'm asking is because I measured the shoulder/flange thickness on some of the guides I have, and they are all over the place- .064, .067, .070.....
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I see what you're saying. The .075 number I posted came from dimensions given in an aftermarket catalog (Kibblewhite) and from 2 guides I have that I know to be OEM, that measured .073 and .075. Aftermarket guides I have , source unknown, measure between .070 and .080.

The manual gives 1.325 min. to 1.420 maximum protrusion dimensions. If we assume the mean dimension of the guide flange to be .075 and you choose to measure to the spring pocket then the dimensions change to 1.400 min and 1.495 max.

You may be over thinking this a little but do what you think is best. The manual is giving a range of .095 for the protrusion spec. A few thousands variation shouldn't be a deal breaker. If it was it would be very hard to use the .080 longer,3.690 valve.
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I guess what all of this leads to is The heads I have for the '81 (measured the Harley way) are: 1.464" on the intake with the 3.690" valve, and 1.451" on the exhaust with the 3.510" valve. I just want to know if I'm going to be installing seats or if I can get by without. Stock 1000 with P cams.
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Any valvetrain gurus out there?
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So I found some good info on the AV&V site-

On heads with oversize valves and modified camshafts, you may need to sink the valve seats deeper for valve to valve clearance and this may result in a higher protrusion. The engine builder needs to decide what minimum spacing he needs between the intake and exhaust valve and then he may have to sink the seats to get the correct valve to valve clearance at TDC lift.
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oversize valves are one solution to correct excess valve stem protrusion.
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