Sportwin rebuilding powerhead

[iwombat]

Given the low compression on my sportwin (65-65) I'm considering rebuilding the powerhead over the winter.

Horror stories, things to watch for, and any other useful advise would be good to hear before the whole procedure begins to take shape. I'll probably use the cases from the powerhead off the parts motor if the cylinders mic out as standard bore.

Anyone been sent screaming into the night by one of these?

 

[iwombat]

Re: Sportwin rebuilding powerhead

Oops - that's a '67 sportwin to be more precise.

 

[F_R]

Re: Sportwin rebuilding powerhead

They are intimidating, to say the least, to the uninitiated.:% After you've done 30 or 40, they are a piece of cake. Well tougher than most cake. More like mincemeat pie:/ I tore into so many of those things at the boat rental place to replace broken mounts that I could do it under the shade tree.

 

[iwombat]

Re: Sportwin rebuilding powerhead

I've done gobs of antique motorcycle and car engines, as well as the odd 2-stroke here and there. I do most of my own machining also. Although these days I let the laser-guided-water-jetted-honers do the cylinder boring for me. Those machines are just wicked-precise.

Speaking of which, if I do need a bore job, do the cases need a torque plate? Seems like there isn't enough torque from the headbolts to take the cylinders out of round.

 

[Chinewalker]

Re: Sportwin rebuilding powerhead

The biggest pain in the behind with those mushroom motors is simply getting them apart. The sandwich construction of the lower cowling/shrouding, along with the myriad of hidden screws, linkages, springs, etc. that hold it all together make for an interesting adventure. Once you have the powerhead seperated from the other junque it's pretty straightforward - until you're ready to put it all back together inside its shell... Take notes, take pics. You'll need them...
- Scott

 

[iwombat]

Re: Sportwin rebuilding powerhead

That's the reason I'm going to use the parts motor. It was a real pain to crack it all apart. If I have a complete power unit I can remove the old one and put in the new one in the same sitting before losing or forgetting where all the stuff goes back in. Digital cameras sure help a bunch too.

 

[ezeke]

Re: Sportwin rebuilding powerhead

I like the 9.5 because it just will not quit, which is why I am stuck with 6 of them.

If you run into a problem, post it here, I am sure that it will receive plenty of attention.

If you want to know where I found the stuff to keep them all alive for 40+/- years, click my user name and use the email.

 

[iwombat]

Re: Sportwin rebuilding powerhead

I hear you on that. I'm sure the plucky little thing has two sets of stuck rings. It still puts out decent power on the top end though. I'd like to be able to put down a slow troll with it though, which is why I'm considering rebuilding a powerhead.

Still curious about needing a torque plate for a rebore job though. Anyone?

 

[Chinewalker]

Re: Sportwin rebuilding powerhead

Do not even consider a rebore unless you can track down some oversize pistons - a very scarce item 40 years after the fact. More than likely your motor will benefit greatly from a simple deglazing with a hone and installing some new rings. Cleaning out of all carbon build-up in the exhaust side is a must-do, too...
If you were to bore it, you would be going in from the cylinder head side, so no plate necessary...
- Scott

 

[iwombat]

Re: Sportwin rebuilding powerhead

Thanks for that.

I'm avoiding a rebore at all costs, but you never know. Between two powerheads I'm sure one is still in spec. The torque plate question was borne more out of curiosity than necessity.

If you couldn't tell already, I prefer to get all the predictable questions out of the way _before_ starting the job. I'm just weird that way.