15 HP Power head compatibility 1974 and 1984

[Calibra]

Hi

​A mate of mine has a 1974 and a 1984 15 HP engine.

​The 1974 engine is controlled by a tiller using cogs which is awful. The electrics on the 1974 is also the old style (Can't remember the name, begins with M)
​The 1984 has a crack in the powerhead but has a better electrical system.

​Can we take the powerhead from the 1974 and put the electrics from the 1984 version on it?

Thanks

James

 

[Calibra]

Thinking about it, maybe the question is easier understood by

Can we replace the magneto ​electrics on the 1974 engine with Capacitor Discharge Ignition from the 1984 engine?

 

[flyingscott]

Yes you will need all the parts from the 84. The complete ignition assembly under the flywheel cdi box/coils and the flywheel itself. What is wrong with the cog system for the tiller.

 

[Calibra]

In the UK, we struggle to get parts. My mate brought the engine and converted it to a tiller. Its never been right and has loads of slack.

​He has the 1984 engine which apart from a cracked powerhead looks really neat and tidy. We wanted to take the 1974 powerhead and put it in the 1984.

 

[flyingscott]

The cog system does have lots of slop pretty normal for those. Yes the 74 powerhead will fit on the 84 motor but I believe the exhaust tuner will be different between the 2 blocks. Go to http://www.leeroysramblings.com/Outb...0articles.html to get more info for modifying the 84 tuner to fit on the 74 block. The 84 block will have some updates on it that you may want to put on the 74. Or you can just drop the 74 block in as is, exhaust tuner and all.

 

[Chinewalker]

With some swapping of parts, you can make it work. In addition to the magneto and flywheel, you need to swap the exhaust cover to maintain the mounting points for the power pack. Also, I believe you can swap the cylinder heads, which gets you a better designed head, and the plugs will better clear the power pack (different angles). And, yes, you can swap the '84 tuner pipe, too. Come to think of it, the '84 recoil lockout bits are a little less finicky, too.

When it comes down to it, if you basically just swap the core or short block of the '74 onto the '84 chassis, and use all of the '84 bolt-ons, you should have a pretty decent little motor again.

 

[Calibra]

Thanks for the information.
The engine is a 1986, not 1984 - doh. But that should not be an issue

 

[flyingscott]

A 1986 model will have the cable tiller I believe.