1957 JW12 3hp Johnson Peak Cylinder Pressure; Drive Shaft Stuck

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  1957 JW12 3hp Johnson Peak Cylinder Pressure; Drive Shaft Stuck

search | FAQ | profile | register | author help

Author Topic:   1957 JW12 3hp Johnson Peak Cylinder Pressure; Drive Shaft Stuck

forest813 posted 08-22-2015 12:27 PM ET (US)
[In a prior discussion about a 1957 Johnson 3-HP outboard engine model JW12] the peak cylinder pressure was mentioned as being 60-PSI, and higher was ok. I have the same motor and the peak cylinder pressure is 50-PSI for each cylinder. Is that sufficient to warrant a full engine tune up?
Also, when I dismantled the lower unit, the drive shaft stayed in the power head rather than coming out with the gear case. Is that normal?
jimh posted 08-22-2015 02:41 PM ET (US)
I would not worry too much about the reading your are getting for peak cylinder pressure in a test. The difference between a reading of 50-PSI and 60-PSI is not too great, and it could be due to factors such as the calibration of your gauge or the method of testing. You are asking about an outboard engine that is 58-years-old and only produces perhaps 2-HP by today's rating method. Take a chance with it. How many cylinders does that 3-HP engine have?
forest813 posted 08-23-2015 11:14 AM ET (US)
Thanks for your reply. It is 2 cylinder.
jimh posted 08-23-2015 02:32 PM ET (US)
Rather than look for a particular absolute peak cylinder pressure reading, look for the match between the two cylinders. If the peak pressure measured in tests is similar between the two cylinders, typically not more than 10-PSI difference, then the engine is probably in good condition.
forest813 posted 08-24-2015 08:56 AM ET (US)
Thanks for your help.
forest813 posted 09-17-2015 10:23 PM ET (US)
I need to inspect and possibly change the impeller but I cannot separate the upper from the lower gear case after removing the 4 gear case bolts. Am I missing anything? What do you suggest I do? Usually the drive shaft just slides away from the power head.
jimh posted 09-18-2015 09:40 AM ET (US)
Metal components that have been fastened together for 58-years may require some persuasion to become unattached. I suggest use of a solvent formulated to release stuck metal parts.

Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: 1957 JW12 3hp Johnson Peak Cylinder Pressure; Drive Shaft Stuck
forest813	posted 08-22-2015 12:27 PM ET (US) [In a prior discussion about a 1957 Johnson 3-HP outboard engine model JW12] the peak cylinder pressure was mentioned as being 60-PSI, and higher was ok. I have the same motor and the peak cylinder pressure is 50-PSI for each cylinder. Is that sufficient to warrant a full engine tune up? Also, when I dismantled the lower unit, the drive shaft stayed in the power head rather than coming out with the gear case. Is that normal?
jimh	posted 08-22-2015 02:41 PM ET (US) I would not worry too much about the reading your are getting for peak cylinder pressure in a test. The difference between a reading of 50-PSI and 60-PSI is not too great, and it could be due to factors such as the calibration of your gauge or the method of testing. You are asking about an outboard engine that is 58-years-old and only produces perhaps 2-HP by today's rating method. Take a chance with it. How many cylinders does that 3-HP engine have?
forest813	posted 08-23-2015 11:14 AM ET (US) Thanks for your reply. It is 2 cylinder.
jimh	posted 08-23-2015 02:32 PM ET (US) Rather than look for a particular absolute peak cylinder pressure reading, look for the match between the two cylinders. If the peak pressure measured in tests is similar between the two cylinders, typically not more than 10-PSI difference, then the engine is probably in good condition.
forest813	posted 08-24-2015 08:56 AM ET (US) Thanks for your help.
forest813	posted 09-17-2015 10:23 PM ET (US) I need to inspect and possibly change the impeller but I cannot separate the upper from the lower gear case after removing the 4 gear case bolts. Am I missing anything? What do you suggest I do? Usually the drive shaft just slides away from the power head.
jimh	posted 09-18-2015 09:40 AM ET (US) Metal components that have been fastened together for 58-years may require some persuasion to become unattached. I suggest use of a solvent formulated to release stuck metal parts.