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Sportster Motorcycle Motor - Top End Discuss Sportster Motorcycle Top End issues. Rockerboxes, Valves, Cylinders, Pistons, Rings, Lift Rods, etc...

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  #1  
Old 5th December 2020
Hank71 Hank71 is offline
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Sportster/Buell Model: xlh
Sportster/Buell Year: 1971
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Exclamation Rockerbox spacer ´71 XLH

Are there any of you performance/race guy´s of age who are familliar with Legendary Carl McClanahan´s ,,Handbook of Inexpensive Modifications for Harley Davidson Motorcycles V-Twin Thunder! ???
I am fortunate to have a copy and have successfully applied several of the inexpensive horsepoweradding improvements to my ´71 XLH.
On page 15 is a description of a rockerbox spacer which I am about to have on my bike. But none such is to be found as far as I know in any aftermarket place and manufacturing is...challenging...but offcourse possible BUT then I thought...Maybe some old racetrack mechanic or peformancefreak like myself have made too many once in the eighties and now have them lying on the rear shelves in the garage.... Well do ya????? If so please let me know or maybe direct me to someone who can produce a piece of medium hardness .090" thick aluminum sheet 6 by 6 inches . And have it send to Denmark Europe....
I am riding all year in all conditions but have heads off for restoring my (again) trashed valves, guides and even broke a spring this time... so as you might understand i´m in a hurry to get back on wheels
THNX Hank
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  #2  
Old 6th December 2020
kitabel kitabel is offline
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Never seen one.
Sounds like something easily made from eBay 6061-T6 scrap.
Take a look here: https://tinyurl.com/y3pglfrd
What did you do to modify the engine, and why .090"?
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  #3  
Old 6th December 2020
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bustert bustert is offline
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pictures say a lot also exactly what you want
a 6x6 piece of aluminum is easily found but what do you want with it. do you want it to shape to the box?? not a big deal and it does not have to be in one piece. the big issue is getting it to denmark from the usa.
if you take a gasket and make a pattern on the aluminum, you could do it all by hand.
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  #4  
Old 7th December 2020
needspeed needspeed is offline
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Hi Hank71,
I also have that book. McClanahan is saying that if you've done something that makes the valve stem protrusion exceed the maximum factory specification of 1.420" from the valve guide shoulder, the rocker geometry will be wrong. Sinking the valve deep in the chamber by grinding the seat or using longer stem XLR valves would do it.

He says raising the rocker cover up with a .090" shim will correct it. It might improve the rocker contact with the stem which is good but it may make the pushrod side worse.

Unless your valve protrusion is a lot more than maximum I suggest not doing this. And if it is and it's from sinking the valve deep and the goal is making more horsepower, then fixing that will be more of a benefit than raising the rockers.

He says to use a gasket on both sides of the shim so if gaskets are .030 thick then you're raising the rocker .120. He also says that it's OK to leave the center bolt out. I think that's a bad idea. If you put an extra .120 under the cover then you should put the same thickness under the center and use the bolt. And using the shims will make another potential place for oil to leak.

I've never seen these shims on the market. I made some years ago, all by hand. Drills, hack saw, files or whatever you have.
Sorry, I don't have them anymore.
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  #5  
Old 7th December 2020
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super +1 mr. speed
install new valve seats. i did so on my 74ch.
you will not make power with the valve shielded inside the pocket.
the old heads are prone to valve recession since the seats are the head material.
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  #6  
Old 8th December 2020
Hank71 Hank71 is offline
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Hi there ...
Thank you everybody for replying....
guess I´ll try to find a sheet of aluminum over here and try making some myself or maybe with help from friends.Actually I did put in new seats and still the guides were beaten sideways by the valvestem so now I´m restoring both heads with std. size valves/springs/guides...
Didn´t really do much yet to gain horsepower and have run but yet not raced or benched it.... but I put in Andrews Y cams with .045" lift the ones they say don´t need headwork and the S&S HI-4N ignitionmodule dualfire and the S&S super E carb. and 24 teeth main sprocket for higher topspeed (85 mph) and when on the street.... I keep surprising young and older bikers on new machines of any brand by either just hanging on to them or even takin´ them once i a while he he.. It is an old bike but it runs as if it doesn´t know. I´m very pleased....or maybe just too old ride like this... naaah .... never to old to ride hard and free..... Once again thank you all for your replies
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  #7  
Old 8th December 2020
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first rule of order is to make sure the guides are tip-top as the rest is relying on it for correct geometry.
if your compression is below 10, do not expect much from the y grind. and to double your trouble, the 24t counter sprocket will compound the problem. i put y in mine but the p was better all around. i need to drop tooth count to keep the y closer to the sweat spot, just haven't got there yet. the machine sits mostly.
btw: that sucker will run way past 85, up into the triple digits.
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