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Well, with all the talk about the need for new motors, combined with all the controversy surrounding motor availability in mod, I thought I would post a step by step budget build up of a D-modified Mercury.
For this build I have chosen a 40ci motor as different groups (APBA AOF NBRA) have different rules and the 40 looks to fit them all. The motor I am using was an early 4 port cover Thunderbolt that was a very clean and will allow some shortcuts to keep the price down.
This is in no way an attempt to build an all out motor, but rather show how easy it is to put together a race-able D-mod. Many times I have seen a stocker win in D-mod so my thought is, if I could just get 2-3mph on a good stocker that would be good enough. Not to mention if you put a 50hp motor on one of those little boats it certainly should haul a$$.
This is a motor that I bought on craigslist for 100.00, the guy thought it was a 30hp but just the front cover was MK30 so I could sell that cover on eBay and get almost half my money back. These motors come with the small carbs so it's off to the pile to find a pair of the common KA carbs and a front engine cover as the small carbs use a smaller bolt pattern. While digging in the pile I also found a later (60s) magneto and tower as I feel the tower is stronger and it saves the rare Morse Fairbanks mag and early tower.
The first thing I do is pull the external parts off like the carbs, fuel pump and ignition. Then straight to the flywheel. These early ones can be tricky, first zap the nut off with an air impact then get a good puller with good grade 8 bolts, check the threads to be clean. mound the puller well and cross your fingers as some of these are stuck. once the puller is tightened as tight as bearable sometimes a tap with a hammer on the end of the puller often does the trick. With the flywheel and alternator removed remove the crankcase and end cap bolts, then remove the 3bolts with the lock tabs on the front cover. The front cover should come off. With the cover off grab the crank and pull the rotating assembly pistons and all out. Immediately find the three alignment pins as they have fallen or will fall out. I try to keep this assembly clean in hopes of just reinstalling it later.
After removing the water jacket cover (head cover) and intake port and exhaust covers and that little hose and fittings on the side you should be down to the bare block. At this point I run a tap through all the bolt holes. I also check my end bearings and cut the ends of the end caps off with a hack saw using rags and tape to keep the bearing clean finishing them off with a belt sander for that ever popular factory look.
Now onto the block, I first inspect the bores, One would be surprised how bad a scratch in the cylinder can be and still be just fine, due to the three ring pistons. once It's determined that the bores will live, it's time for some preliminary porting. This is a job best done on a mill but using a Myers (milled) motor as an example I just break out the die grinder and go at it. The general rule here is do not cut the bottoms or tops of the intakes just square off the corners on the tops. So first I knife edge the aluminum on the intake side for better flow then I square off the ports a little with a 1/4 bit, do not cut the bottom outside corners of the ports. Then it is onto the exhaust, Same plan as the intake with a little more of an eye towards opening thing up. First the aluminum to de-shroud the ports then the steel to shape the ports while cutting the port windows I slide an old ring down the bore to the top of the port to use as a guide then while looking down the bore I cut the windows to shape, do not cut the bottom outside edges. Once I have the ports cut to shape I then using my ring guide and measuring from the block mating surface I then slide the ring down and raise the ports about 20 thousandths.
Well, the place is a mess now so It's time to clean up, clean the block, and move onto phase two.
For this build I have chosen a 40ci motor as different groups (APBA AOF NBRA) have different rules and the 40 looks to fit them all. The motor I am using was an early 4 port cover Thunderbolt that was a very clean and will allow some shortcuts to keep the price down.
This is in no way an attempt to build an all out motor, but rather show how easy it is to put together a race-able D-mod. Many times I have seen a stocker win in D-mod so my thought is, if I could just get 2-3mph on a good stocker that would be good enough. Not to mention if you put a 50hp motor on one of those little boats it certainly should haul a$$.
This is a motor that I bought on craigslist for 100.00, the guy thought it was a 30hp but just the front cover was MK30 so I could sell that cover on eBay and get almost half my money back. These motors come with the small carbs so it's off to the pile to find a pair of the common KA carbs and a front engine cover as the small carbs use a smaller bolt pattern. While digging in the pile I also found a later (60s) magneto and tower as I feel the tower is stronger and it saves the rare Morse Fairbanks mag and early tower.
The first thing I do is pull the external parts off like the carbs, fuel pump and ignition. Then straight to the flywheel. These early ones can be tricky, first zap the nut off with an air impact then get a good puller with good grade 8 bolts, check the threads to be clean. mound the puller well and cross your fingers as some of these are stuck. once the puller is tightened as tight as bearable sometimes a tap with a hammer on the end of the puller often does the trick. With the flywheel and alternator removed remove the crankcase and end cap bolts, then remove the 3bolts with the lock tabs on the front cover. The front cover should come off. With the cover off grab the crank and pull the rotating assembly pistons and all out. Immediately find the three alignment pins as they have fallen or will fall out. I try to keep this assembly clean in hopes of just reinstalling it later.
After removing the water jacket cover (head cover) and intake port and exhaust covers and that little hose and fittings on the side you should be down to the bare block. At this point I run a tap through all the bolt holes. I also check my end bearings and cut the ends of the end caps off with a hack saw using rags and tape to keep the bearing clean finishing them off with a belt sander for that ever popular factory look.
Now onto the block, I first inspect the bores, One would be surprised how bad a scratch in the cylinder can be and still be just fine, due to the three ring pistons. once It's determined that the bores will live, it's time for some preliminary porting. This is a job best done on a mill but using a Myers (milled) motor as an example I just break out the die grinder and go at it. The general rule here is do not cut the bottoms or tops of the intakes just square off the corners on the tops. So first I knife edge the aluminum on the intake side for better flow then I square off the ports a little with a 1/4 bit, do not cut the bottom outside corners of the ports. Then it is onto the exhaust, Same plan as the intake with a little more of an eye towards opening thing up. First the aluminum to de-shroud the ports then the steel to shape the ports while cutting the port windows I slide an old ring down the bore to the top of the port to use as a guide then while looking down the bore I cut the windows to shape, do not cut the bottom outside edges. Once I have the ports cut to shape I then using my ring guide and measuring from the block mating surface I then slide the ring down and raise the ports about 20 thousandths.
Well, the place is a mess now so It's time to clean up, clean the block, and move onto phase two.
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