1959 35hp Compression Release

[scout-j-m]

I am waiting on a repair manual for this motor to come in before diving into any diagnostics/repairs but wanted to ask something regarding the compression release system. When looking over the powerhead, I noticed the head to have what seemed to be an oily residue on it. This motor is missing the bar which connects the compression release to the recoil starter also fwiw. Is that residue likely from poor, worn out seals on the compression release valves causing some fuel/oil mixture to leak out back when it was running? Will this effect the compression reading? The motor has also sat about 8 years on top of being extremely old to begin with. So I'm curious as to if I need to replace the compression release valves/seals before I begin the compression test.

 

[F_R]

If the valves are seating perfectly, there is no pressure applied to the seals while running. However, they rarely seat that well, so you may be right, the seals may be leaking. They are just o-rings, and deteriorate with age. As for them affecting compression readings, it depends on how badly the valves are not seating. Truthfully, I doubt they are that bad, unless something is holding them open (carbon??). It would be extremely rare for the valves themselves to need replacing.

 

[scout-j-m]

Thanks F_R. I figured the seals were just plain old o-rings but hadn't had a chance to to look into all that much aside from the exploded parts diagram online. I guess I will do a basic compression test first and then investigate those valves further if I need to. Maybe if it comes to that I can just replace the o-rings with some generic ones from the hardware store.

 

[HighTrim]

I have found carbon chunks jamming the valves as FR stated, but rarely, if ever, encounter faulty valves. Well, once, but that motor threw a rod! lol

Set them to 020 gap after cleaning them up.

I would test compression first before worrying about it though. Usually in the 90 to 125 psi range, depending on gauge.

 

[scout-j-m]

Thanks guys!

 

[scout-j-m]

Bumping this thread. I did a little work on the motor to clean it up but never really did much past that as I got caught up working on some other smaller motors for my HP restricted lakes. Finally now caught up on all of my other project motors so this is the last one I currently have available to work on. I'm going to do a basic gear lube and impeller service this evening after work and then a compression test and go from there.

Back to the subject of the compression release, does anyone have a picture or know of a good figure that illustrates how it works and what parts are required? My motor is missing all of it aside from the valves themselves. I know I need the cam that attaches to the head and the bar connecting to the recoil starter, but not sure what else. I'd like to go ahead and get some parts as I recall this motors electric starter having some issues back when it used to run.

 

[jimmbo]

http://boatinfo.no/lib/johnson/manua...nson.html#/326

Pages 313 - 317 have some pics and info regarding the Compression Relief

This book is the Service Manual for your engine, if you have an Evinrude, the Johnson equivalent is RD-21 or RDS-21

 

[scout-j-m]

http://boatinfo.no/lib/johnson/manua...nson.html#/326

Pages 313 - 317 have some pics and info regarding the Compression Relief

This book is the Service Manual for your engine, if you have an Evinrude, the Johnson equivalent is RD-21 or RDS-21

Thank you! That definitely is going to be helpful. Good to also now know that the valve clearance should be 0.015" - 0.025".

Hopefully I can source most of the necessary parts off online auction sites.

 

[F_R]

How strong are you? Will any women or kids be running the boat? Reason I ask is those parts usually are missing because somebody took them off because the motor will actually start easier without them...IF you can pull the rope.

 

[scout-j-m]

How strong are you? Will any women or kids be running the boat? Reason I ask is those parts usually are missing because somebody took them off because the motor will actually start easier without them...IF you can pull the rope.

No problem for me I would think. I do recall it being very hard to pull though back when I ran it some when I was in high school and college and in prime shape. Not sure if there was some other issue or if it was because the boat it was on required somewhat awkward positioning to pull it.

 

[scout-j-m]

Got the impeller changed over the weekend. I was very surprised at how good the old one looked considering the motor has sat for a dozen or so years. When removed it sprung back out to original shaped with no bent vanes. The exhaust and pump area was nasty though with a mixture of old unburnt fuel, dead bugs, and lots of dirt from dirt daubers so it was good to get that cleaned out. Under the exhaust leg housing was also an assortment of dauber and wasp nests, bugs, and remains of some mice nests which I will need to clean before reassembly.