October 2000 News
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 OHV Top Ends
   By Rocky
I am working on reproducing the Koslo OHV heads I have - with a few twists. I plan to make them in a version to fit Chiefs and one for Sport Scouts, 101s and Warpaths.

In the pictures you see the rear head and mock-up on Scout motor and Chief motor. I went to the casting shop today and visited the front head. It appears that we will be using a core box sand to use as a pattern. The front head box is now in the oven being baked for 3 hours to cure the red sand. We have a perfect fin pattern and the combustion chamber looks real good shrunk down to 3 1/4 inches as Indian motors will need, the Scout for sure, the Chief motor may take 3 1/2 combustion chamber as the original Koslo heads I have. This was used on a Harley motor and could have been used on the Excelsior also. 

I am basing the cylinder on a Powerplus design. While at the casting shop today, we were planning the best course for a cylinder. We will need to make more fins for the top to transition to the head or just leave it like it is. The Scout motor will require moving the cylinder stud holes out board. Current thoughts are on using thru studs machined from 4130 chrome-moly. I have used these before on a hybrid fuel motor with XR-750 heads and it worked just fine on a stroker. I am still planning the cylinders. 

Hopefully in a few days I should have the first front head in hand. This will require a visit back to work on second shift to do some machine work. By the way, I saw the first pour on the 38-42 Indian-4 valve adjustment covers today. Boy that Aluminum gets hot. Fire is everywhere. Back to the heads. I will be making the first batch in Aluminum but current thoughts are leaning to doing them in cast iron.This will require a new foundry but the head would be original as  cast them for Excelsior. The valves would use the cast iron as their seat. My thoughts on aluminum heads go to weight saving and the thought of welding up the intake port and moving them around to make the heads dual carburetor. This would not require changing the cam rotation and you would have dual carbs like the Altoona motors. Pistons are going to be another area of concern for Scout motors but I am going to use some old nitro burning tricks to make it real simple. 

The rockers are currently at work, waiting for a break in the inspection department's Cord-AX machine schedule to generate a blueprint of the original rocker geometry. The original used a bronze bushing for wear on the fixed rocker shaft. I am leaning towards using a needle bearing on the rocker shafts and instead of a fixed contact end on the valve, I intend to use a tool steel roller on the valve. The valves haven't been given much thought yet but they appear to be an easy match to something that is available today. The original valves were flat across the seat area but to take advantage of the hemi combustion chamber the valves should be tulip shaped like the hemi car motors. The Chief rockers will be available in a 1 to 1 ratio and should be easy to manufacture. 

The Scout rockers are going to take a different rocker because of smaller case size leading to clearance problems with push rods and cylinder and head. The head problem is an easy fix with a different rocker and the lifter hole moved over 1/4 inch. I may have to leave push rod covers off all together. Which is no big deal. I kind of like all the moving parts exposed. There are no valve covers on the originals and these will not have any either. The rockers will lend themselves to changing the ratios up to 1.5 to 1 without any other work you will now get another 50% lift in cam action.  I have looked at Panhead rockers and they are out. A good compromise may be VW rockers which could be cut and welded to a section of tubing to fit over a 4130 shaft which bolts to the rocker side plates, I have also looked at Triumph motorcycle rockers as a candidate also. This area needs more thought after I have heads in hand.  At present I have no thoughts on porting I just know these heads look awesome.

The original spark plug used was an early one with about 7/8 inch thread. I will be changing this over to a modern plug size. Current thoughts are leaning to selling a complete head or a bare machined casting for Scout or Chief. 

Next month: Freshly cast front heads, the story behind the Koslo heads, rockers and more...

Click on pictures for full size

Twin exhaust port OHV head and Powerplus-based cylinder. Single port heads were in many cases found to run better, so the core box might be modified for single exhaust port

Top view

Hemispherical combustion chamber

Rear head mock-up on Scout cases

Rear head mock-up on Chief cases

Check out Rocky's Iron Wigwam website for HD & Indian Racing Parts.

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