Mercury 400 improvement program

[Rapier]

When I got my '71 400 years ago - it was mint and obviously had had an easy life. It has proved reliable ever since, (bar rotten wiring). The '70 and '71 Mercury 400s were prone to fail due to the new design of the ignition system which relies on disty and rotor & stator (stuffed under the flywheel), rather than the 66 to 69 Mercury 350 which was a more conventional points and coils system.

It wasn't a success, the disty was prone to cracking (and it seems the stator and clearances are an issue..) warranty claims were high and when the new 402 pitched up in 1972 I think a line was drawn under the whole episode with the new 402. Rumour has it though, Carl K wanted to scrap the entire production run (2874704 to 3336257).

The 400/402 was also lumped with the 'crankbuster' moniker, which is unfair, as all the intelligence we have on that points to cranks failing only when excessively loaded. Anyway to cut a long story short..I had been keeping an eye out for a spare disty, on the assumption that if mine were to fail I'd not have a useless motor for long and this arrived via ebay US today for next to nothing. I thought it would contain only the disty and rotor and plug caps shown, but is comes with destructions below and powerhead to mid-section and bottom tray gaskets.

What's interesting that it's a retrofit pack to fix the initial problems and that by October 1970 it possibly was no longer an issue, i.e. that the entire production run had not been affected, which is what I assumed. Follow on from 4. says motors of serial number 2877943 and below 'should be test run 1st to determine if motor idles properly' If they don't, then the exhaust extension holes (3/16") need to be enlarged out to 5/16" (8mm) drill....

[Rapier]

Took my motor apart today to check if the intermittent miss I thought I heard at Ivy lake was distributor related.

- Don't use generic bolts to remove the flyhweel - these were too long....

- If the stator is green it's the modified version, black the troublesome one.

- The plug leads are crimped into a copper collar with a threaded end...do not pull them, they unscrew conventionally, their boots are also filled with a waterproof grease.