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1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics
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<blockquote data-quote="Edstrossner" data-source="post: 379026" data-attributes="member: 15774"><p>I took the intake manifold off the 25 last week with the thought of adding a pair of cone spacers to the reed assembly. After removing the reed plate I noticed that there is a large difference in the crankcase openings. Cylinder #1 has a larger opening than cylinder #2. So, I decided to tear down the power head and rework the block as follows:</p><p>Squared the ports with a 5/8" end mill. This did not square the ports that much. I just wanted to get all the ports set at the same height. They were off by .014.</p><p>I milled .062 off the exhaust port bottom to match the piston at BDC.</p><p>Milled .012 off the block deck</p><p>I did a lot of hand grinding in the crankcase area. My goal was to get the crankcase openings at the reed plate to be close to each other.</p><p>I also tapered the back of the cylinder wall as it leads up to the transfer ports and knife edged the transfer ports.</p><p>The biggest change will be the boost port. I followed the basic idea that Chrysler used in adding a 1" hole to the piston skirt on the intake side and putting a 1" hole into the cylinder wall at the transfer passage way. This should pump more fuel air mix up to the transfer ports.</p><p>I still need to match grind the exhaust tuner where it mates up to the block and also to plug the exhaust relief holes in the tuner.</p><p>I hope to get the power head re-assembled this week and try it out. </p><p>I'll post my results.</p></blockquote><p></p>
[QUOTE="Edstrossner, post: 379026, member: 15774"] I took the intake manifold off the 25 last week with the thought of adding a pair of cone spacers to the reed assembly. After removing the reed plate I noticed that there is a large difference in the crankcase openings. Cylinder #1 has a larger opening than cylinder #2. So, I decided to tear down the power head and rework the block as follows: Squared the ports with a 5/8" end mill. This did not square the ports that much. I just wanted to get all the ports set at the same height. They were off by .014. I milled .062 off the exhaust port bottom to match the piston at BDC. Milled .012 off the block deck I did a lot of hand grinding in the crankcase area. My goal was to get the crankcase openings at the reed plate to be close to each other. I also tapered the back of the cylinder wall as it leads up to the transfer ports and knife edged the transfer ports. The biggest change will be the boost port. I followed the basic idea that Chrysler used in adding a 1" hole to the piston skirt on the intake side and putting a 1" hole into the cylinder wall at the transfer passage way. This should pump more fuel air mix up to the transfer ports. I still need to match grind the exhaust tuner where it mates up to the block and also to plug the exhaust relief holes in the tuner. I hope to get the power head re-assembled this week and try it out. I'll post my results. [/QUOTE]
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1980's Johnson/Evinrude 20/25hp conversion to 30hp with pics
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