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  1. F

    GP 200 Race Prep

    Was a toss up whether to try the Megacycle or put a stock cam in. I understand that the big cam has worked with the 57mm pistons so we’ll see. And we’ll see about that first turn. Very fancy with the light rockers. I’m about done with the build so will report on the dyno run.
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    GP 200 Race Prep

    I’ve had a lot of trouble it’s this engine. It never had any bottom or mid. Had to wring its neck and then it struggled to get back up out of turns. Tried a few carburetor/jet/manifold combos with no improvement. Had a very flat torque curve. Was producing 17.5 hp. Seemed to me that it just...
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    GP 200 Race Prep

    Four races, a bunch of carb tuning runs, and a Dyno run. In 90’s weather. I don’t think it was abused except it was very hot. New pistons are Arias forged, .002 on the money. I think the oil circuit was too much for that little pump although the camshaft bearings had plenty of oil in em...
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    GP 200 Race Prep

    I think I found a simple way to set up the cam shaft. It actually has a name - Equal Lobe Centering - and it looks like the way the factory intended. The O on the stock cam faces up with lobes symmetrical about the shaft. At TDC that would be the valve overlap zone - where exhaust and intake...
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    GP 200 Race Prep

    Teazer - would you be kind enough to help me with the cam set up? Megacycles card below. Do I set the crank at 20.8 degrees BTC and rotate the camshaft until I have .040 clearance at the intake valve? Then check exhaust? I believe the factory spec is 10 deg. but don't know the valve...
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    GP 200 Race Prep

    I’m with you. I’ll try the cam and see how it goes. Damn engines have too many variables to predict much. I’ve had good luck with similar pistons in the airheads with a similarly shaped head. We’ll see. The 57mm pistons displace the same volume as the stock pistons with a calculated CR of...
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    GP 200 Race Prep

    You think that scoring was from a cold start? Maybe so. I cleaned up the 200 pump - not much material left to mill so I left it. I think to be on the safe side I’ll use smaller diameter brake lines for the oil feeds and a smaller oil cooler - maybe the cappellini cooler - slick but expensive...
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    GP 200 Race Prep

    I'm also going to put in Cappellini's fat studs since the new pistons will come with a big jump in compression. The big studs will restrict the stud oil flow passage to the head - which has external lines so that shouldn't matter. I was thinking that the previous combination of the stud oil...
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    GP 200 Race Prep

    Teaser - thanks so much for the response. Here's a pic of the work. I didn't have an oil temp gauge set up but I definitely did not feel enough heat going through the oil cooler. You can see the new pistons in the pic. Piston head and oiling based on some similar successful experiments...
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    GP 200 Race Prep

    Getting back to racing post covid so I’m tearing down my CB175 to put some oversized pistons and cylinders in for GP 200. Got a surprise seeing the old pistons - both badly scored. Before I move on I‘ve gotta figure out why. Old pistons are stock with about .005 clearance. I have an oil...
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    CB160 Crankshaft Bearings

    I've just picked up a 65 CB160 to prep for racing and upon pulling the engine apart found that there was water in the crankcase and a lot of rust including on the crankshaft counterbalancers though the shaft and bearings look clean. There's only about 2200 miles on the bike and though it looks...
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