1973 85HP low comp/help finding gaskets

[jahughes]

The first one turned out so well I went and bought another for a spare!<br /><br />1973 Johnson 85HP, this one was overheated to the point it started melting the plug wires.<br /><br />Low compression (30 lbs), I've been looking for a head gasket set but I'm having trouble nailing down the Sierra number for this year.<br /><br />I have found Johnson part number 0318662 out at the BRP catalog at evinrude.com, but can't find the matching Sierra number.<br /><br />Neither iboats nor Boatfix.com seem to cross reference the Johnson number with the Sierra...<br /><br />I'd like to have a set on hand so when I pop the heads off, if the cylinders aren't all scored up I can just smooth the heads if necessary and change the gaskets and maybe get lucky and have a runner.<br /><br />Thx for any help you can offer,<br /><br />Jason

 

[DHPMARINE]

Re: 1973 85HP low comp/help finding gaskets

Jason,may luck be with you (and the force ).The number you list is a common part,and should be at your local Johnson/Evinrude Dealer.But pull your heads first,I think you need more than gaskets and sandpaper.<br /><br />DHP

 

[jahughes]

Re: 1973 85HP low comp/help finding gaskets

Thanks much DHP, yah, I know I may have much more on my hands that just a gasket problem, but at $40 for the whole motor I figure I can't go wrong with it for spare parts if nothing else.<br /><br />Can anyone provide the Sierra part number for this gasket? I can't seem to find it, and I really have looked/searched, honest! I'd like to buy it online if possible.<br /><br />Thx all,<br /><br />Jason

 

[BoatBuoy]

Re: 1973 85HP low comp/help finding gaskets

Checked several sites and Sierra. Evidently they don't make one for that engine.

 

[jahughes]

Re: 1973 85HP low comp/help finding gaskets

Thanks BB, appreciate the effort!

 

[jahughes]

Re: 1973 85HP low comp/help finding gaskets

OK, I popped the heads off and looked at the cylinders, I'm not experienced at judging cylinder wall appearance but they looked pretty good to me, one minor spot of scuffing on the wall of one cylinder about 3/4" across or so, not black, just less shiny than the rest of the wall.<br /><br />I found and bought the head gaskets, put them in today and I still have about 30 lbs. on all 4, reading with 2 different compression testers.<br /><br />1. Am I correct in thinking that enough damage to cause compression loss on all 4 cylinders would be pretty obvious in a visual inspection? Is even the minor scuffing I'm seeing enough to cause a serious problem with the one cylinder?<br /><br />2. Do I need to do anything other than just remove the plugs and crank it over to test compression?<br /><br />3. If the cylinders are OK, did I install the head gaskets properly by just blowing things off with compressed air, not using any sealant and just torquing them down in the clockwise bolt pattern?<br /><br />4. Is there another thing that could be causing a uniform loss of compression on all 4 cylinders, a blockage somewhere?<br /><br />5. Could the low readings be caused by the engine rotating pretty slowly rather than at "starting speed" for this motor? I mean pretty slowly as in just barely turning over, maybe 30 RPM or so.<br /><br />As always, thanks to all you experts for helping us rookies out!<br /><br />--Jason

 

[jahughes]

Re: 1973 85HP low comp/help finding gaskets

Bump...

 

[Basscat 1]

Re: 1973 85HP low comp/help finding gaskets

First thing you need is a service manual.<br />That will answer a lot of your questions.

 

[R.Johnson]

Re: 1973 85HP low comp/help finding gaskets

With compression readings that low, you probably have stuck rings, and scuffed pistons. Take off the intake by-pass covers on the sides of the block, this will give you a much better look at the problem.

 

[jahughes]

Re: 1973 85HP low comp/help finding gaskets

Thanks R. Johnson, I took off the most conveniently located cover and to my untrained eye it really doesn't look bad as far as any scoring/scuffing on the piston itself. Biggest problem I think is that I don't know if I'm looking for subtle, or dramatic damage. Subtle scratches I have, dramatic I don't.<br /><br />As for the rings, the one toward the top of the piston is thicker with more room in it's groove to move, and I do see it moving when I wiggle the flywheel just a little, so it doesn't appear stuck. The thinner one toward the bottom of the piston doesn't seem to have much play in it's groove so it's hard to tell, but I'm not seeing what looks like hardened carbon packed into the grooves, more like some oily crud that would blow out pretty easily with a decarb if I could get it to compress/run.<br /><br />Basscat, you caught me being one part impatient, one part lazy, I do have the book, I'm going to to "curl up" with that baby now and see if I can get some further guidance there.<br /><br />If anyone can tell me what a bad piston looks like though I'd appreciate it!<br /><br />Thx,<br /><br />--Jason

 

[MCM]

Re: 1973 85HP low comp/help finding gaskets

Jason, with a fully charged battery, good starter/solenoid, clean wires/connections you should be cranking at around 300 rpm's. If you're only at 30 rpm's as you say you have a serious charging system issue or something binding internally.<br /><br />I'm not sure just wiggling the flywheel will give a true indication of anything being stuck, you may want to try pulling the motor over using the rope on the flywheel, If you can't turn it freely with the head off well???

 

[jahughes]

Re: 1973 85HP low comp/help finding gaskets

Hi MCM, thanks for the note.<br /><br />Yah, it's just a low battery as far as the slow rotation goes. The motor is up on a sawhorse and the battery needs a charge.<br /><br />Motor isn't stuck, it turns freely, just has low (30ish) compression all around. Changed the head gaskets, didn't help, looking for further ideas.<br /><br />R. Johnson was thinking the rings might be stuck in the grooves (not sealing against the cylinder walls) but that doesn't appear to be the case...<br /><br />Basscat, I checked out the book, the Seloc has pictures of pretty ugly pistons compared to mine, I think mine are OK, anyone think the slow rotation might account for the low readings???<br /><br />--Jason

 

[MCM]

Re: 1973 85HP low comp/help finding gaskets

Well I just re-read your post and if the motor got as hot as you describe it its possible the rings have lost the ability to seat properly. As I recall as the motor reaches operating temp there's an expansion (heat expands cold contracts) which causes the rings to seat properly, which is why they reccommend doing comp. tests at operating temp. It's possible therefore that the overheating has caused the rings to loose they're tensile strength. IMO it might be something to investigate

 

[andy6374]

Re: 1973 85HP low comp/help finding gaskets

Might be worth the $6 to try a decarb to free any stuck rings before tearing her down.

 

[R.Johnson]

Re: 1973 85HP low comp/help finding gaskets

Compression reading's are generally taken with a fully charged battery. You said you only took off one by-pass cover, so you still don't have a very good over all look at thing'g. Piston's will also show most damage on the exhaust side, so you could take off the exhaust cover for a better look. Do I understand this correctly, the engine was barely turning over for the compression test? With that engine just hanging on a saw horse, be carefull. At least C clamp it if you have some clamps. If you only have $40.00 in this engine, and you could use it for part's, you're way ahead no matter how things go.

 

[Basscat 1]

Re: 1973 85HP low comp/help finding gaskets

1973 Johnson 85HP, this one was overheated to the point it started melting the plug wires.

Thats pretty hot.

 

[ledgefinder]

Re: 1973 85HP low comp/help finding gaskets

You can get the head gaskets at any NAPA. <br /><br />I suspect you're not spinning the motor fast enough at all, or your gauge is horked. Typical measurement on that motor would be around 125psi. It's HIGHLY unlikely all three would wear, score and/or have stuck rings equally, so that all three would be at 30psi. <br /><br />BTW, the starter solenoid on those OMCs can get cruddy inside, and mimic a low battery or failing starter. Also, you need to have REAL solid connections to get the starter to spin well - better than you typically need on a car.<br /><br />Make sure both heads are correctly torqued before the compression test.

 

[ledgefinder]

Re: 1973 85HP low comp/help finding gaskets

..."all four"...

 

[jahughes]

Re: 1973 85HP low comp/help finding gaskets

Thanks for the added input guys.<br /><br />R. Johnson, yep, I only took off the one but after having the heads off and looking down inside I just didn't see what looked like any really significant wear.<br /><br />I think I'll put the battery on the charger, clean up all the connections real well, load it up with decarb, strap it onto the (large and sturdy BTW) sawhorse a little tighter and see what happens.<br /><br />I'll report back, thanks all so much for the advice!<br /><br />--Jason

 

[SportfishermansSVC]

Re: 1973 85HP low comp/help finding gaskets

I have seen similar problems before with the v4's of that vintage. You may get lucky and the decarb will work. I have found that seafoams deep creep product does a nice job of cleaning out the carbon and lubing the rings up if they have been sitting dry for a long time. On the other hand if it has been over heated that badly I would think you will find that you end up doing some work, at the very least you should put a set of rings on it. Just my 2 cents.