Re: Mercury, 30hp thunderbolt, spark problems
Hi,<br /> First, let's figure out what you have. "Thunderbolt" was a name used on the 40hp motors of that era (Mark 55), while "Turbo-Four" was the trademark for their 30hp block (Mark 30). Makes a big difference in how you go about getting the magneto out. Your serial places it as about 1958 or so.<br /><br /> In either case, you'll have to pull the magneto out (held on by four bolts at base of magneto tower), clean the points, set them at .008", clean up the rotor and cap of all corrosion, check the condenser, etc. You can actually bench test for spark when you have the plastic caps removed. Holding the magneto housing against a vice, leave the copper contact that comes from the coil about 1/2" from the vice and spin the rotor. You should be able to get the spark to jump that gap. Once that's tested, assemble the cap and put the spark plugs in the boots, and then put the plugs in the vice. Again, holding the magneto body against the vice, spin the rotor and see if you've got a good spark. That'll save you the hassle of getting the magneto in place again.<br /><br /> I would also HIGHLY recommend acquiring a copy of the 1965 and Prior Service Manual, which your Mercury Dealer should be able to order. If they can't (or won't) try Grubb's at
www.oldmercs.com. The Mark 30s often require removal of several other parts to get the mag out. Mark 55s have a bit more room and the magneto should just drop out with a minimum of dissasembly.<br />- Scott
