1965 33hp oversized piston part numbers.

[Paul Moir]

I'm trying to decide whether to repair or scrap this engine (1965 33hp Johnson RX-13B). The expensive bits are in good shape, but I ended up having to tear down the engine to repair a crankcase leak. While I had it apart, I measured the piston-bore clearance at .015" (same on both cyls). I'm still getting better at using telescopic bore guages (cheap, click out type) but I seem to be measuring the bores at 0.007 - 0.009 oversize. A large ridge at the top of the jugs bear witness to the wear.<br /><br />So, I'm considering boring this out to 0.020 or 0.040" over depending on the price and availablility of oversized pistons and rings. To begin my hunt, I'm going to need the part number of the oversized pistons and rings. It should be in the first or second page of Section 2 in the OEM 33hp service manual along with the specifications. If someone has that manual ('65-'70 33hp should be the same part), would they mind posting it for me? <br /><br />Also, I'll be beginning my hunt with Twin City, partsforoutboards guy and Stone & Sons. Anyone else have suggestions?<br /><br />PS - The engine had 100psi compression on both cylinders before I tore it apart, yet the ring end-gaps were around 3/16"! I guess there's a good reason for three compression rings.

 

[DHPMARINE]

Re: 1965 33hp oversized piston part numbers.

Paul,<br /> I took a wrong turn getting the part numbers,but ....<br /><br />Rings--<br /><br />020 378437<br /><br />030 378438<br /><br />Just a suggestion,the ridge at the top of the cylinder will always be smaller than the rest of the bore.<br /><br />i don't know the ring end gap,but however you measured it 3/16 sounds large.did you measure by putting the ring into the bore (squarley)and measuring the gap that way?<br /><br />One other point .... 100PSI each....I don't think you have a problem<br /><br />DHP

 

[Paul Moir]

Re: 1965 33hp oversized piston part numbers.

Thanks DHPMarine! I really appriciate the help.<br /><br />I've got to say, I found the bore/ring wear pretty suprising considering the compression. Needless to say, the bores are pretty well free of any sort of scarring.<br />I did measure the end-gap correctly part way from the top of the ports to the top of the cylinder, using the butt end of a piston to set it in there squarely. The spec is supposed to be .007-.017" I tried a couple different rings at a few different depths since I found it so suprising. <br /><br /><br />My cheesy Seloc manual says the piston-cyl clearance is .045-.0030. I'm sure they mean .0045-.0030 since that would be the same as my '62 28hp (via the OEM manual I have for it). Am I correct in taking your meaning that a gap of .015" here isn't excessive and I should just doctor up a new set of rings?<br /><br />If not, do you happen to have the piston PNs there as well?<br /><br />Thanks again for being so helpful!

 

[alcan]

Re: 1965 33hp oversized piston part numbers.

Hi Paul<br />Standard bore for this motor is 3-1\16". Part# for std. piston is #380566 w\o rings. Part# 380557 for .020 over and part# 389558 for .040 over both w\o rings. My book lists these parts as N\A.

 

[Paul Moir]

Re: 1965 33hp oversized piston part numbers.

Thanks kindly alcan. I figured these parts were N/A but one can hope right? <br />Now I can begin my hunt in ernest!<br /><br />PS - A long time ago you suggested to another member to use socket head cap screws for engine hold down bolts. Thanks for the tip - they're pretty much the only type that would work for my old 28hp. And they look great!