The Marine Doctor - 1985 Evinrude Pullstart Shortshaft Motor Low Compression

boaternoob

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1985 Evinrude Pullstart Shortshaft Motor Low Compression
02/06/10 at 18:35:59

I have low compression in one of my cylinders; in the top it is 90 psi bottom is 40 psi. I realize there can be a number of things wrong, but I think it is a blown gasket or non-closing/broken reed because when I ran it last, I ran it an hour after I noticed the loss of power and it didn't Freeze, second there are no plooms of smoke or rattling in the power head indicating an issue with the cylinder or piston.

Nonetheless, my seloc book indicates to access the head or the manifold behind the carb (basically anything on the power head) I need to remove a number of items including the flywheel. I don't want to screw up the timing on the motor regardless how hard or easy it is to fix, or break anything in the flywheel or magneto.

Question: Below are pictures where I think the powerhead mounts to the casing. It's apparent the power head needs to be removed from the motor casing, since the bolts are very tightly hidden by the motor casing. Can I just remove the power head leaving the fly wheel on by unscrewing the bolts that fix the power head to the motor casing?

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boaternoob TMD's New People Offline TMD's gets you back on the water Posts: 6	Re: 1985 Evinrude Pullstart Shortshaft Motor Low Compression Reply #1 - 02/06/10 at 18:36:51 picture 2
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boaternoob TMD's New People Offline TMD's gets you back on the water Posts: 6	Re: 1985 Evinrude Pullstart Shortshaft Motor Low Compression Reply #2 - 02/06/10 at 18:37:19 Picture 3
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boaternoob TMD's New People Offline TMD's gets you back on the water Posts: 6	Re: 1985 Evinrude Pullstart Shortshaft Motor Low Compression Reply #3 - 02/06/10 at 18:39:25 Looking at picture 1, it just hit me that there is a lot of carbon there... Perhaps its a valve issue because there shouldn't be fuel coming through...
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The Marine Doctor YaBB Administrator Offline Posts: 21453 x1\|Sask\|Canada\| Gender:	Re: 1985 Evinrude Pullstart Shortshaft Motor Low Compression Reply #4 - 02/06/10 at 18:44:33 You can leave the flywheel on. I would pull the head though before yanking the powerhead off....a damaged piston or head gasket may not make any noise at all. TMD
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boaternoob

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Re: 1985 Evinrude Pullstart Shortshaft Motor Low Compression
Reply #5 - 02/06/10 at 21:24:28

Thank you for your response as I know you are very busy.

I was able to get the top two bolts off of the head. I proceeded to remove the two bolts below in the middle of the head, unfortunately the heads of the bolts sheared off upon removal. The bolts were seized or over torque in the past, oh well… The bolts are now flush with the head casing with no nub to torque on…

Any suggestions?

I read I can use an easy out kit, which drills a small hole in the bolt without destroying the mating threads and in return that extension made can be torque on. The bottom bolts can only be accessed with a wrench and not a ratchet so if those shear off, I wouldn’t be able to access them with a drill and history unfortunately always repeats it self haha

A friend suggested it’s probably a valve that’s staying open and suggested spraying wd-40 in the manifold behind the carb where the valves are located. With that he indicated that could potentially fix your low compression problem. Due to the sheared bolt head, that option is looking better especially since the bolt is still in place and won’t let air leak through.

It’s sad what happened, but it is what it is…

Your melancholy yet encouraged fan,

Boaternoob

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The Marine Doctor YaBB Administrator Offline Posts: 21453 x1\|Sask\|Canada\| Gender:	Re: 1985 Evinrude Pullstart Shortshaft Motor Low Compression Reply #6 - 02/07/10 at 01:51:41 The reed valve will not cause the drop in compression. The piston seals the cylinder from the reeds as it moves through the block You may have to pull the powerhead now to remove the rest of the head bolts. TMD
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boaternoob TMD's New People Offline TMD's gets you back on the water Posts: 6	Re: 1985 Evinrude Pullstart Shortshaft Motor Low Compression Reply #7 - 02/07/10 at 05:25:46 Thanks for the advice I will do that as soon as I remove the bolts with the easy out... Will keep informed... Thank you for this website and your expertise.
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The Marine Doctor YaBB Administrator Offline Posts: 21453 x1\|Sask\|Canada\| Gender:	Re: 1985 Evinrude Pullstart Shortshaft Motor Low Compression Reply #8 - 02/07/10 at 12:52:59 Your welcome and good luck. TMD
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Paul Moir

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Re: 1985 Evinrude Pullstart Shortshaft Motor Low Compression
Reply #9 - 02/10/10 at 04:34:12

No, no don't use an ez-out!

If you end up snapping one, you'll need to take it to a machine shop with an EDM drill. Normally these bolts are seized from corrosion and will need to be drilled out of they broke off flush. It's pretty easy to drill them and have a heli-coil installed or if you DIY and you're careful, you can preserve the original threads. But ez-outs are known for breaking when trying to remove these corrosion seized bolts (they work fine on over-torqued bolts) and removing a broken ez-out is not trivial.

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