1986 johnson 10 horse rebuild

[MWG2600]

Ive started putting my powerhead back together, The block was bored and decked. new wiseco pistons. The crank and pistons went together without trouble, i got the engine cases bolted up . When i went to test fit the head and gasket, the tips of the dome are hitting the head with the head only pulled down not torqued .
I put Prussian blue on one of the pistons and here are the pics. Im thinking file it down to fit and clay check the clearance. You can how the factory piston is more rounded at that part of the dome.

 

[raczekp1]

Re: 1986 johnson 10 horse rebuild

i think you can file down this piece of top piston,
but you didnt mention if you have put head gasket between head and surface block

 

[1946Zephyr]

Re: 1986 johnson 10 horse rebuild

Is the steepest side of the crown on the intake side?

 

[jasper60103]

Re: 1986 johnson 10 horse rebuild

I'm no expert, but that cylinder head (first pic) has been cut down for sure. It's down in the keep out area. Maybe too far?

 

[MWG2600]

Re: 1986 johnson 10 horse rebuild

I used the new head gasket, with only the 4 head bolts on the cylinder i was checking, the pistons are facing the correct direction.
The block has been decked, i dont know how much. The cylinder head has not been machined on. Jasper what makes you think it has? keep out area? im not following. Im planning to file it down and check it with clay like i would on a domed piston auto racing engine.

 

[raczekp1]

Re: 1986 johnson 10 horse rebuild

in my motor i had to file 0.4 mm of block surface and 0.3 mm of head surface,
but i order new head gasket 0.5 mm thicker then standard one.
after reasembling motor runs good

 

[MWG2600]

Re: 1986 johnson 10 horse rebuild

ive started to file down the offending spots, how much clearance should i be looking for?

 

[MWG2600]

Re: 1986 johnson 10 horse rebuild

Ive been told .030 by one mechanic Dose that sound about right?

 

[raczekp1]

Re: 1986 johnson 10 horse rebuild

will run fine.dont wory

 

[tosoutherncars]

Re: 1986 johnson 10 horse rebuild

1) How many thou did they shave off the block? and;

2) do your new pistons match up with the old ones? Particularly, gudgeon pin center to piston crown? (What I'm saying here is, don't go by skirt length, just sitting them on a flat surface and seeing that they are the same overall height; measure pin-to-crown.)

 

[Haffiman]

Re: 1986 johnson 10 horse rebuild

Just round off the edges. Sharp corners will just start 'glowing'. This is a common problem on cast pistons on cross flow engines.

 

[MWG2600]

Re: 1986 johnson 10 horse rebuild

The piston pin location is identical on the new pistons, The tops of the dome were a little wider where they were hitting. Going to get some clay today to confirm how much clearance i have.

Next on the list is getting a piece of glass and emery cloth to surface the read plate. I have new boysen reed valves to install and that's one of the steps they have to get the read plate as flat as possible.

and i forgot to order a new thermostat when i got the rest of the parts, Anybody know what auto parts stores sell sierra parts?

 

[tosoutherncars]

Re: 1986 johnson 10 horse rebuild

Napa sometimes does; but your local JonnyRude dealer will stock the tstats, they are common across a bazillion models. Probably not worth spending a lot of time comparison shopping for a $15 part...