1956 Evinrude Big Twin

[Hillbillywill]

I recently acquired another vintage outboard. A '56 Big Twin 30 hp. It looks rough on the outside. Put it up on the stand and did a compression check using an in expensive compression tester. Initially both cylinders were around 55lbs. I squirted a bit of WD-40 in both cylinders (not sure why I did this) and rechecked the numbers a week later. Top is now around 120lbs and the bottom is at 90lbs. does this make any sense? Did I just use a cheap compression tester? This engine is a bear to crank manually. I can barely crank it, so it seems like it has plenty of compression. I'm guessing it's been a long time since it's been ran.

Questions:
Should I ignore those numbers and press on?

I'd like to get this motor back up and running.

 

[kfa4303]

Re: 1956 Evinrude Big Twin

Hi Hillbilly. Great old motor you found there. What you described is actually pretty common. Motors can/do give different compression readings depending no their state of repair. It's not uncommon for an old motor that has been sitting to have low compression. The WD-40 is fine and actually a good idea and helps to free up the rings and get everything moving again after sitting so long. Products like Sea Foam and Deep Creep are also good to use. You'll also generally get higher compression numbers using an electric starter, rather than trying to pull that big 30 hp over by hand. No mean feat as I'm sure you've found. Even on perfectly good motors you'll generally get higher/better compression on a motor that's been warmed up and running or a bit vs. a cold motor. All that being said, the compression numbers are very important. In addition to requiring a certain minimum amount of compression to work (over 80 psi on that motor is good) the two cylinders need to be within 10% compression. So if one cylinder read 100 psi the other could read between 90-110 psi (i.e. +/- 10% of original 100 psi value) and still be ok. Unless there is major internal damage the compression issues can often be fixed by simply changing the head gasket, which is a pretty easy job and only costs about $20. Give these links a read and holler back. The good news is that you have a very well liked and reliable engine to start with that's well worth the effort. You can usually get these old vintage OMC's up an running for under $100.

http://www.duckworksmagazine.com/04/s/columns/max/24/index.cfm

http://forums.iboats.com/showthread.php?t=158086

http://forums.iboats.com/showthread.php?t=167352

 

[1946Zephyr]

Re: 1956 Evinrude Big Twin

Well, it looks like you still have some sticky rings. I would do what you can, to get it running. Run it for about an hour and re-take the copression test. Running some Sea Foam would probably help that too.

 

[Hillbillywill]

Re: 1956 Evinrude Big Twin

Thank you guys! This forum is great. I am going to press on and do my best to resurrect this beauty! I have a 57 and 58 Johnson 35 hp seahorse and this 56 will be a nice addition to the collection. Thank you for the recommendations.

 

[kfa4303]

Re: 1956 Evinrude Big Twin

you'll have the trifecta of cool motors! The 56, 57, 58 models are definitely the coolest. I love the reverse two-tone of the '58's. Good luck!

 

[HighTrim]

Re: 1956 Evinrude Big Twin

Pull the bypass covers and see if the rings are sticking. You simply press on them with a screwdriver to see if they "bounce". If the rings check out, time to pull the head, change the head gasket and dress the head. To dress the head, put a piece of emory cloth on a mirror or piece of glass, and move it in a figure 8 pattern until you can see the head being sanded evenly. I have a feeling the rings are sticking a little though, by the results of your wet compression test. The psi difference is too much to run, you should investigate further before proceeding.

I have most of the lineup as well for the 56, 57 and 58 years. The Golden Javelin is my favourite, followed by my 58 Super Quiet. Also love the 35hps in standard trim as well though........ah heck, I love em all!

 

[Mas]

Re: 1956 Evinrude Big Twin

Did you pull the spark plugs when doing the compression test? 120 psi is exactly where you want to be. The cylinders must be lubed since it sat a while, but adding the WD40 actually helps "seal" the rings and gives misleading higher results. Try the test again after getting the motor running.

Mas

 

[HighTrim]

Re: 1956 Evinrude Big Twin

He only had 120 psi on the top, only 90 on the bottom.

 

[Hillbillywill]

Re: 1956 Evinrude Big Twin

I did pull both plugs before checking the compression.

I bought the 56 Evinrude and 58 Johnson as a lot. The 58 is complete and looks almost new under the hood, but I haven't done a compression test on it yet. I'll do that this weekend. The Johnson have three rings per cylinder? The gentleman who sold these motors to me was very gracious. He gave me a bunch of parts including a Javelin power head. I put that away for a rainy day. Wondering if I should lube that power head for dry storage?

 

[HighTrim]

Re: 1956 Evinrude Big Twin

Yeah put fogging oil into it and keep the plugs in.

Yeah 3 rings per cylinder, part number 304712

 

[samo_ott]

Re: 1956 Evinrude Big Twin

You got 120 psi by pulling it? That's amazing!

I have dual matching '56 Evinrude 30's that I collected over time and hope to get them set up together on a boat this year

 

[kodibass]

Re: 1956 Evinrude Big Twin

Your engine has not been run in a while, Your numbers are nice and high, When I get one like this I spray the inside of the cylinders with light oil, let it soak over night, get my 6 gal 24-1 mix tank and try to start the engine, run it for 30min or more, then try a few re-starts run for a while longer let it cool down enuff to handle being worked on, re-do compression check your numbers will most likely even out and be just fine.