1989 johnson 175 one cyl low compression

[dryalls]

Hi there,
I have just bought a secondhand 1989 johnson 175, and it had one cylinder with low compression before i bought it.

I have compression tested it and 5 cylinders have readings between 92 and 100 psi the 6th has a reading of around 50psi, its the lower cylinder on the starboard side. Do I replace all the rings or just the rings on the cylinder in question?

Are the other cylinders within and acceptable range?

Engine was hard to turn over by hand when i first got it but seems to be better now, turns over and starts nicely with starter motor.

starboard head seems to get quite abit hotter than the port side, also the leg below the motor seems to get quite hot, is this a concern?

is it possible that the thermostat is stuffed on that side and that caused the low compression?

any thoughts on these matters will be greatly appreciated.

thanks
dan.

 

[tashasdaddy]

Re: 1989 johnson 175 one cyl low compression

could be just a head gasket, i would try that first, also change tstats, while out flush out the block.

 

[SparkieBoat]

Re: 1989 johnson 175 one cyl low compression

also do a decarb..details in the top secret files section at top of the forum.

 

[dryalls]

Re: 1989 johnson 175 one cyl low compression

ok thanks i will take these steps.

if it turns out to be a ring issue, do i do all the rings or just the ones on the problem cylinder? provided the others appear in good cond.

thanks
dan

 

[SparkieBoat]

Re: 1989 johnson 175 one cyl low compression

you can do just one cylinder, so long as your compression does not vary too much.

 

[bktheking]

Re: 1989 johnson 175 one cyl low compression

ok thanks i will take these steps.

if it turns out to be a ring issue, do i do all the rings or just the ones on the problem cylinder? provided the others appear in good cond.

thanks
dan

Do them all, if you have the motor apart and have to buy a gasket set and pull the powerhead, would you want to have to put in a new ring set when another cylinder drops out a year from now?

 

[emdsapmgr]

Re: 1989 johnson 175 one cyl low compression

You have to pull the whole engine down to do the one ringset (and maybe a piston if it is scuffed) so plan on new ringsets and a hone job on the other 5 holes. Those 175's have the low compression (bathtub) heads on them and your compression is normal at 95-100. You should find out what caused the low cylinder now, as an overhaul fixes the compression problem, but not the root cause of the failure. It could be the overheating, but probably not since is was only one lower cyl. I'd be suspect of the lower carb. Pull it apart and carefully inspect the jets on the carb side that feed the low compression cylinder. Possible dirt is lodged in the jet or a passage, causing that one cyl to run lean, creating the low compression problem. That year's model is underrated at 175 hp. It is closer to 192.

 

[dryalls]

Re: 1989 johnson 175 one cyl low compression

thanks for all the acvice so far.

looks like i have a major problem, the housing that holds the problem cylinder sleave in place has separated from the sleave and is rather corroded. i'll try put a pic up if i work out how.

this has cause the head gasket to go.

im guessing this problem has exsisted for a longtime time and its finally caused the head gasket to go.

cylinder and sleave appear to be in good condtion still, do you think i could put a new head gasket on and use it again or is it scrap? i did notice the head gasket will sit on the sleave so it should get a seal???

not sure if the problem was caused by this, but the pressure regulator at the top of this head had something blocking it, what exactly does the regulator do i've never dealt with this system where theres a pressure regulator and a thermostat?

again any advice will be great appreciated.

regards
dan

 

[dryalls]

Re: 1989 johnson 175 one cyl low compression

photos are hopfully attached.

they show the bottom starboard cylinder with the housing and the cylinder sleave separated from about the 9 o'clock position to the 2 o'clock position.

 

[dryalls]

Re: 1989 johnson 175 one cyl low compression

...

 

[ezeke]

Re: 1989 johnson 175 one cyl low compression

I would look for a replacement block. At least part of the problem was overheating caused by the water passage being blocked by the swollen water passage deflector.

 

[SparkieBoat]

Re: 1989 johnson 175 one cyl low compression

go ahead and upgrade to a 60 degree optical looper or and e-tec..I have seen people **** away so much money on old motors, the newer motors are so much better and more reliable, especially the bigger ones. I got a 96 150 rude that idles so smooth you could set a full cup of coffee on the cowl and not spill any. Cranks up fast even when real cold and gets better fuel mileage than the older ones too. also real easy to work on once you figure out how to trouble shoot it. I can have all 6 carbs off in under 5 mins...I have seen these for as low as 1500..just make sure you check it out good and run it on the water first if at all possible.

 

[emdsapmgr]

Re: 1989 johnson 175 one cyl low compression

Was this engine used in salt water? The pressure relief valve in the head thermostat housing opens about when the boat begins to plane. The increased boat speed increases internal water pressure and will push open this nylon valve, flooding that half of the engine with increased cooling water. It is closed at idle. A blockage in that valve could definitely heat that side of the head up when planing. Ezeke points out a major problem regarding the lack of circulation of water around that cylinder. I am suprised the blockage did not also affect the top two cylinders more. Either of these two cooling issues may have been enough to sound the control box hot horn. I'd check the head sensor on that (head) side for proper operation. This block is not economically salvable. If you do go with another block, some of your current internals may be reuseable.