90, 90 HP Johnson RPM (long post)

[jeepers94]

I just recently had my engine repaired. All four cylinders were bored,new pistons, etc, etc. etc. <br />I have had an opportunity to take it out about half dozen times but all have been relatively short runs. All was working well. On my last trip out as we were heading back the rpm's dropped from about 4200 to 3000 all of sudden. I immediately backed off the throttle and let it idle, all sounded good, there was no alarm and water pump was shooting a good stream of water. I accelerated again and all seemed ok for about another 5 minutes then again, same problem. This time when I throttled back up, I could not get enought power to get the boat (16' Cajun Bass Boat) back on plane. The RPMS reached 3000. Luckily it was close to the ramp so we just cruised in. The mechanic is scheduled to take it look at it this week but I wanted some thougths as to what to expect. <br />The only thing different from this last trip was that this was the longest run. The boat was on plane for about 20 minutes before the problem started. <br /><br />Any thoughts would be appreciated.

 

[ob]

Re: 90, 90 HP Johnson RPM (long post)

Expect them to check for good spark on all four and eliminate any possibility of carb restrictons or fuel system fault.Insure fuel tank is venting .<br /> Hopefully your mechanic is planning on load checking situation with water check or dynomometer on propshaft through its full throttle operating range.

 

[Bob in Calif.]

Re: 90, 90 HP Johnson RPM (long post)

Remind the mechanic to do a compression check on all cylinders, this is paramont in your situation.<br />....Bob in Calif....

 

[jeepers94]

Re: 90, 90 HP Johnson RPM (long post)

Here is what the mechanic found. They pulled the spark plugs to do a compression check and found moisture in one plug. When investigated further it was determined that the lower powerhead gasket/seal failed and water infiltrated into one cylinder. I was told damage was limited to one piston only. Comments? Anything in particular I should be asking? It will covered under the warranty he provided for the overhaul work. I am not too concerned that I might not be getting the entire story, I just would like to know what to ask from people more experienced in this area. <br /><br />Thanks Again.

 

[Solittle]

Re: 90, 90 HP Johnson RPM (long post)

If you mean the head gasket failed that would make sense if it were not torqued properly. The head bolts should be re-torqued again after some period of operation (forget how long - make sure that this is done).<br /><br />If you mean exactly what you wrote about the powerhead gasket failed then it makes no sense to me as that brings to my mind the gasket, if any, below the block and I don't think water canget to a cyl from there.

 

[bonitoman]

Re: 90, 90 HP Johnson RPM (long post)

Water can get into the powerhead if the powerhead was not torqued properly or if a bolt broke off the the block was tapped and the person drilling went to far with the drill. I have seen this happen a few times. You could also have an exhaust plate corrode away and have the screw back out and take water in that way. It washes the cylinder and will eventually break.