right compression

87 200hp johnson<br /><br />I performed a compression test.<br />cyl 1 80lbs cyl 2 95lbs<br />cyl 3 70lbs cyl 4 90lbs <br />cyl 5 80lbs cyl 6 90lbs<br /> <br />I called johnson outboards and the person I talked to said 75 to 90 would be a good range but I felt it was a little low. I pulled off the gasket and found the #3 cyl to be very loose almost like there was no rings left but all of the other cyl were fine. The gasket on that side was almost gone. The question I have is can you replace the rings without having to bore the cyl. The pistons look very good and the walls have a very little shine to them. Also does anyone know what the correct compression should be for this type of engine. <br /><br />thanks

Re: right compression

Did you have the throttle wide open? You will get a lower reading if you crank with the throttle closed.

Re: right compression

YES <br /><br />2 test had been done. one with the engine warm and the other with the engine cold. Both seem to have the same results. The dealer also got the same results he was the one that suggested that I check the #3 cyl because of the large # difference. I had a problem with the engine stalling when going back to idle and from the diagnosis the #3 cyl was not working right seemed to be running on 5 instead of 6 cyl. The engine runs great in forward and reverse only when returning to idle.

Re: right compression

mako<br /><br />Looking over your previous posts it looks as if you've been thru the ringer on this one. Those compression #'s do seem a little low. I would think 100+ would be acceptable but the Johnson guy knows best I guess. Do you think the rings could be sticking due to carbon build up. What about the much ballyhooed decarb. I had a stuck ring on a cylinder on my '85 Merc 150 and it saved the day for me.

Re: right compression

Mako.... If any of the cylinder walls have the slightest amount of scoring, those particular cylinders will require boring oversize.<br /><br />However, if there is no scoring, you could simply have the cylinder walls deglazed by honing them slightly.... create a criss cross honing pattern to the walls. If this isn't done, the new rings would not be able to seat properly.<br /><br />If memory serves me right, the 1987 V/6 loopers compression on the starboard bank was slightly higher then the port bank due to it's internal design. However, also relying on memory, I believe that the normal compression on that engine was up around 125 psi, and that the compression was lowered to approximately 90 psi starting with the 1988 design. I may be in error on that point.<br /><br />At any rate, the compression difference between the highest and lowest reading of 25 psi indicates that the engine is due for an overhaul. I strongly suggest you do not run the engine any more until this is done.<br /><br />Keep in mind that powerheads do not fail by themselves, something caused it.... usually faulty ignition or/and fouled lean running carburetors. Good luck.

Re: right compression

Joe <br /><br />You are correct the engine does need an over haul. I pulled the engine apart and did notice it was bored 20 over. The problem is there is alot of play on the #3 cyl but no scoring of the walls. The only question I have is what type of socket do you use to take the piston rods off with. It looks like a spline drive socket but not sure. I don't want to put a 12point and strip the nut.<br /><br />thanks.

Re: right compression

5/16 - 12 point<br /><br />c/6<br /><br />Hooty

Re: right compression

Hi mako 2578<br /><br />Get ( borrow ) a new set of rings, put in top of cylinder and mesure gap. You will know something about cylinder wear then. Someone else here must have similar motor, and tell you correct compression. Different models are released with different compression. Compared to other Johnsons i know, normal compression on a good motor is within 120 - 150, but some were designed with low compression, especially some larger models like maybe yours. Maybe honing, one new piston and a set of rings could do it ? Saying this, to probably make you save work and $$

Re: right compression

Forgot to add:<br /><br />Guys like Joe and Hooty that worked on lots of motors will know.

Re: right compression

Just got the engine back had to bore 44 over. Put all new gaskets and put back together but it seems like the engine is coughing almost like <br />mis-firing. I rebuilt everything even the carbs before this thing went back together. Is this a common problem with the coughing till the engine breaks itself in. Someone told me it is just the rings trying to find themselves.