1972 evinrude 4hp yahtwin

[drewmitch44]

Re: 1972 evinrude 4hp yahtwin

ok i tested the spark with a tool i made that looks similar to that wood tool above. Im getting good spark in fact more than a 3/8 spark. whyle i had the plugs out i stuck my thumb over the top cylender hole and as i turned the flywheel by hand i could feel inside the cylinder pulling in and pushing out air. From what im told that is what is supposed to happen. Well on the bottom cylinder there is nothing no air trying to get in or out. this might not be the best way to test compression but i think that nothing is happening in the bottom cylinder. If thats the case is the next step to rebuild the power head and if so what parts and where do i get em?

 

[Paul Moir]

Re: 1972 evinrude 4hp yahtwin

That's too bad. I think you can get +.030" pistons and rings fairly inexpensively from your local dealer. Perhaps you're lucky and it's just a blown head gasket or a couple stuck rings, but either way start by taking the head off.<br /><br />I'm putting together a 4hp teardown/reassemble project over at the shareaproject.com website. Here's a link to it (I've only just started, check back in a couple days):<br /> http://www.shareaproject.com/pages/imageDetail,p,182,i,2526,00.html

 

[drewmitch44]

Re: 1972 evinrude 4hp yahtwin

so if thats the case should i start a new topic for rebuilding the power head?

 

[drewmitch44]

Re: 1972 evinrude 4hp yahtwin

i just figure that man there is a new carb new coils and condencers and points new plugs new prop and new fuel screen, the motor will run on just one cylinder and everything is new why not rebuild the power head? Paul it looks like in your web sight you are tearing down the same motor just the johnson version. am i right by trying overhaul out and should i just bank on the 30 over pistons or should i just put it in the next weeks trash?

 

[Paul Moir]

Re: 1972 evinrude 4hp yahtwin

Still working on it - there's a little more now. <br /><br />It's up to you. If there's something seriously wrong with the bottom cylinder, you might want to opt for an ebay powerhead. There's a '79 going for $20 presently, but if you bide your time there will definitly be more. Use these search terms:<br />(4, 4hp) (evinrude, johnson) (powerhead, engine, block)<br /><br />Probably a rebore job isn't reasonable. I think you could probably get the pistons & rings for $100 or so, but then you'll need to have it bored. Probably $400 at best all told. <br /><br />But pull the head. Maybe it is just a blown head gasket. My 4hp had stuck rings on the bottom cyl (<50psi) and now has 100/95.

 

[lark2004]

Re: 1972 evinrude 4hp yahtwin

nice job on the shareaproject page Paul.<br /><br />Drew, pull the head off your motor first. As has been said several times, you may just have a blown head gasket, or stuck rings. Don't throw it out without looking first!

 

[drewmitch44]

Re: 1972 evinrude 4hp yahtwin

well broke it apart and the piston in not even moving not only that it seems like the piston is fried into place from only running on the one cylinder. cylinder wall seems to have chunks melted off of it. so i will be on the market for a new small outboard. Thanks for all your help guys and it was still fun finding the problem

 

[itstippy]

Re: 1972 evinrude 4hp yahtwin

You needn't shop for a new outboard, just a good powerhead to bolt all those good parts to. Anyway, don't junk what you've got. Put it on eBay if you're not interested in fixing it yourself. Let it live on!