johnson 175 piston dead

[seacat69]

Hi guys<br /><br />I just bought a 5.5 meter seacat with a 1978 175 johnson, took the kids out today and the top left piston died (looking at the motor from the rear)I ran a compression test prior and all cylinders were on 100. It went well then i heard a scraping sound and it lost a little power.<br />I have removed the head and the cylinder appears a little scorched and the piston has some pitting. I am assuming it got a little hot.<br />my question is, <br />1/ can i easily remove the piston without removing the powerhead?<br />2/ what may have caused this?<br />3/ is there anything on the net that explains how to remove the piston/rings or powerhead<br />thanks<br />George

 

[rodbolt]

Re: johnson 175 piston dead

hello many things can cause that. without looking at it I cant tell why it died. most usual cases are insufficient lubrication and overheat followed closly by clogged main jets in the carb. could have been t-stats,waterpump, a clogged water inlet a clogged carb, the list goes on. the block Must be compleatly dissasembled and the cyl bored and an oversized piston used. if you go cheap and patch it it will die again. what part of the world do you live in?

 

[seacat69]

Re: johnson 175 piston dead

Hi Rodbolt,<br /><br />Im in Australia, I have worked on 2 strokes bikes and know how to rebuild a top end but in this case I have no idea, im not sure how complex it is to remove the powerhead but I was hoping that I can remove the piston without having to dismantle or remove the entire powerhead and then have someone hone it whilst its still on the boat. i have searched the net for diagrams info to no avail. <br />When i took it out today it was missing on low rpm and half to full throttle it hit 70kms/h with 2 adults and 2 teenagers (was very impressed until it died once on high rpm (5600) for 2 minutes. The water seems to cycle and no obvious signs of heating, it still ran good with 5 cylinders. thanks for your time

 

[Solittle]

Re: johnson 175 piston dead

seacat69 - Sorry but the powerhead has to come off and the block dissasembled. You can just have the one cylinder bored. Be sure you know why it failed or you are looking for it to fail again. Also I wouldn't run the motor unitl you get it fixed as you risk further damage.<br /><br />If you decide to do this yourself be sure that you have the OMC shop manual.