'85 Johnson 185hp V6 all cylnders low compression

[crazyfish180]

I recently purchased an 1985 185hp Johnson. The motor was rebuilt in 2002(not sure of how or who rebuilt it) First trip out motor started and idled great. Coughed and spit out of the hole but ran great mid and top end (5600rpm)15in prop. <br />Tried to de-carb to help the poor accelration, did not help one bit. After changing plugs and cleaning carbs did nothing I decided to do a compression check before I took it to a mechanic.<br />Compression on six cylinders between 69lbs-71lbs.<br /><br />Also noticed a water leak under the base close to stering arm (could be base gasket) understand no relation to compression issue...<br /><br />Pulled the heads, cylinder walls look excellent, still have honing criss cross marks. Pistons look great. Head and gaskets show no sign of leaks. <br />Did notice play in pistons, not sure what the tolerance should be but seem to more than a 2 stroke should be.<br /><br />Before I dump $2500 into a rebuilt powerhead...<br /><br />Any ideas would be greatly appreciated.<br /><br />Thanks again for the site.<br /><br /><br />Any ideas. Could it be just rings?

 

[Goodoleboy]

Re: '85 Johnson 185hp V6 all cylnders low compression

Welcome to the forum!<br /><br />Could be the way you did compression test. Or your gage.<br /><br />Dont seem likley you could turn 5600 RPM'S with numbers that low. Or even get it started for that matter. <br /><br />First warm motor up on the muffs. Then pull all the plugs out. then run a compression test.<br /><br />Turn it for 5 seconds or so. Treat all cylinders the same....."Good hot battery"<br /><br />If you still get numbers that low. Try another gage.<br /><br />Post results....well go from their!<br /><br />Good luck!

 

[R.Johnson]

Re: '85 Johnson 185hp V6 all cylnders low compression

You are only showing a 2-3 lb. difference, That does't sound right for a strong running engine at that low of pressure. There is an example of a compression guage, and a two cycle engine. I just did a compression test on a 55 HP twin. High compression, leak-down test showed it leaked like a basket. But! it did'nt run well either.

 

[crazyfish180]

Re: '85 Johnson 185hp V6 all cylnders low compression

Lee,<br /><br />Thanks for the reply and the welcome. Great site...<br /><br />I know, things just dont line up...<br /><br />I had done the proper steps on the compression check as you pointed out and then for reasurance I took it to a local marine shop and paid them to perform and document the compression on each cylinder.<br /><br />I am stumped... I am going to have a mechanic check the bore to make sure the wrong pistons were not accidently put in.<br /><br />Once again thanks for the reply. Any other suggestions would be greatly appreciated.

 

[crazyfish180]

Re: '85 Johnson 185hp V6 all cylnders low compression

Mechanic said looks like rebuilder had a few too many... Preliminary measurements show .00040 bore with .00020 pistons. He is going to measure again with high-end equipment. <br /><br />If this is true, of course I will replace the pistons and rings. <br />Any suggestions if what else I should look for as far as were and tear.

 

[Goodoleboy]

Re: '85 Johnson 185hp V6 all cylnders low compression

CF....I think you are trying to say ..... .040 overbore and .020 over pistons. Those pistons should only be something like .003 under bore size.<br /><br />But be sure to check service manual for proper clerance.<br /><br />Make sure cylinder walls arent scratched up. May need to be honed to slickem up uh mite.<br /><br />Good luck!

 

[crazyfish180]

Re: '85 Johnson 185hp V6 all cylnders low compression

All cylynders walls are in perfect condition, all <br />bores measure stock 3.5 execpt top right wich has a .020 piston in it. <br /><br />Does any know why I would have NO damage to any cyinders, run great at top end yet all cylinders are 68lbs to 71lbs compression<br />Could I have bad rings only?<br /><br />Yes I have done compression correctly and used three different gauges<br /><br />HELP...

 

[CFronzek]

Re: '85 Johnson 185hp V6 all cylnders low compression

 

[david18]

Re: '85 Johnson 185hp V6 all cylnders low compression

You probably have the low compression cylinder heads. If you do then about 80 psi is normal. You can tell the low comp heads by looking at the compression area and you will see about an 1/8" edge to the face. Go find a V-6 made in the late 70's and these will give you 100 plus psi and a few more horses.