HELP!! Need Part for 1970 40 HP Johnson. Can't find anywhere.

[Hoochymama]

I stripped the threads testing the compression on my dad's motor I'm trying to restore. I don't need to purchase a whole new assembly just that plate that the two spark plugs screw into.

Anyone have one they are willing to part with, or have any ideas?

Thank you.

 

[Joe Reeves]

Re: HELP!! Need Part for 1970 40 HP Johnson. Can't find anywhere.

The spark plug threads are in the cylinder head, not in the thin plate that bolts to it.

The threads can be restored by simply having a 14mm Stainless Steel Heli Coil installed, the kits are available at auto parts stores, various hardware stores, etc.

The alternative is to install another cylinder head.

 

[Hoochymama]

Re: HELP!! Need Part for 1970 40 HP Johnson. Can't find anywhere.

On the 40esl70A motor there is a thin plate that screws onto the another plate that then bolts onto the main cylinder head. The "sandwiched" plate is the one I need; the one that has the spark plug threads on it.

But thanks for the other information.

 

[Joe Reeves]

Re: HELP!! Need Part for 1970 40 HP Johnson. Can't find anywhere.

The "thin" outer plate is the water jacket cover.

The "sandwiched" plate (the thick one) is the cylinder head.

The remaining item that you're calling a "cylinder head" is actually called the "cylinder & crankcase assembly, also called the crankcase, block, or powerhead.

 

[Hoochymama]

Re: HELP!! Need Part for 1970 40 HP Johnson. Can't find anywhere.

Gotcha. Thanks!

 

[Cofe]

Re: HELP!! Need Part for 1970 40 HP Johnson. Can't find anywhere.

If you stripped the plug holes doing a compression test, did the compression tester get hit with the pistons? Are the pistons damaged?

A long threaded compression tester will get hit by the pistons, damaging the threads on the tester, and when the test fitting is removed from the head the spark plug threads are then damaged.
As Joe said, installing helicoils is a good choice. You will have to get a head gasket, and remove the head to do the work. Hope this helps you.

 

[F_R]

Re: HELP!! Need Part for 1970 40 HP Johnson. Can't find anywhere.

Instead of buying a heli-coil kit, take the head to an automotive machine shop and have them install the heli-coil. Probably be cheaper and it will be done right.

 

[Tim Frank]

Re: HELP!! Need Part for 1970 40 HP Johnson. Can't find anywhere.

A new head is over $200- so FR's advice is worth reading twice.
(it always is, but especially this time...)