1972 Evinrude 65 HIGH compression?

[crackedglass]

I picked up a boat today for parts, on it is a 72 65hp Evinrude which looks to have had some rather recent and extensive work done. All electrical components appear to be new, the motor has been apart, it's painted and super clean. The same goes for the lower unit, I found receipts for new shift coils from Feb. and a complete reseal and water pump job on the lower at that time.
As with any new to me motor, I gave this a compression check, what I get is 180 psi on all three cylinders? I was expecting closer to 140 psi or so tops as on my later 70hp. I hung the motor on an old boat and test ran it, it runs great, the shift buttons are junk, so I rigged up a toggle switch to shift the motor with for now.
It don't seem to do anything wrong but it cranks hard even with what appears to be a brand new starter. I ended up taking my group 27 trolling motor battery to start the engine. The thing runs super strong for a 65hp. Maybe too strong. I even tried several compression gauges and all were within a few pounds so I ruled out a bad tester. I also tested it before and after running it and it read the same. It may have gained pound or two when tested warm but not enough to matter.

Has anyone ever ran across one of these with such high compression readings? Will it survive like this or self destruct?

 

[JB]

Re: 1972 Evinrude 65 HIGH compression?

It's sort of like having too much money, CG.

Sounds like it was very well overhauled and perfectly broken in.

Count your blessings and enjoy.

 

[crackedglass]

Re: 1972 Evinrude 65 HIGH compression?

I'm not sure it is broken in yet, I got it only partially assembled and with no controls, the last owner never went past just hanging it on the boat. I hooked up the controls and a toggle switch to be able to water test it on the river.
More compression will add more power over stock, and it runs really well, but I can't help be be a little concerned about the electric shift lower unit and the fact that it will no doubt make more heat in the motor than an engine running at lower compression.
Will I need to run high test fuel?
It seemed to run fine on regular fuel at a slightly rich oil mix but it was only about 65 degrees outside and the water is still cold, I'm a little concerned that it'll need high test fuel and that it may run hot or detonate in hotter weather.

 

[wilde1j]

Re: 1972 Evinrude 65 HIGH compression?

Regular (87 octane) is fine. If breaking in, run double oil (25:1) for the first 10 hours.

 

[jbjennings]

Re: 1972 Evinrude 65 HIGH compression?

My '72 50hp johnson has 155psi on it, so I suspect the '72 motors may have a little higher compression than what we're accustomed to seeing. I was suprised at the 155psi on mine, too. I think you just have a really fine motor as mentioned. As to the starter, they can get weak but still function. It may just be a weak starter. I DO NOT recommend those brand new cheapo starters on ebay (made in china). I got one for my merc and they are not too sporty.
Good luck with yours,
JBJ

 

[crackedglass]

Re: 1972 Evinrude 65 HIGH compression?

The starter looks new. One local dealer told me it may need a recall done, something about adding a second head gasket to lower compression but he said it was before his time.

From what I was told there was a lot of work done by a local dealer, but the person giving away the boat wasn't the one that owned the boat or had the work done. I'm not sure if it was due to a death in the family or a divorce, she just wanted it gone, along with several other boats, trucks, cars, and tractors. (I'll be hauling junk out of that place for a month).

It starts fine with enough amps, it just won't turn over with a smaller battery. It don't sound like it would crank for long though. It's got enough compression that its nearly impossible to pull by hand with a rope and handle.

 

[dazk14]

Re: 1972 Evinrude 65 HIGH compression?

That compression is way too high. Yes, you will detonate and grenade the top end. A good new stock motor was 150psi and considered already pushing the limits.

There was a little secret OMC didn't advertise. At the time, the bigger motors were designed to run 1000hrs, yet the 3 cylinder was a 750hr motor.

It's possible, someone was trying to build a "race motor"(burning AV gas/racing fuel) where longevity is not a priority.

You'll want to start by measuring the head to see how much was machined from it. It could also be in combination with cylinder decking (machining the block deck).

It is also not uncommon for different brand head gaskets to vary - quite a bit -in thickness and that is not in comparison to designed low compression gaskets.

A VERY general rule of thumb for your ballpark size motor is ~.001 removed per 1psi increase.

Start by ordering a low compression(octane) head gasket). OMC part#0332816 Boatsdotnet or Sierra part#18-3895 iboatsdotcom, or GLM Part # 35830...$50bucks.

When you have the head off, measure it and someone on this board should have a stock dimension for that. I may, but I don't receive notifications from iboats.

I consider 150psi for a 3 cylinder of that vintage 89 octane MINIMUM for casual cruising. 91(or so), if you like to get after it. Once broken in, use good oil. I believe most people are happy(cost/performance) with the Pennzoil synthetic from Wal-mart. I'm currently having a love affair with BRP xd-100, but it is pricey.

This should get you started

 

[crackedglass]

Re: 1972 Evinrude 65 HIGH compression?

I picked up a second parts motor today for free, it's the same motor but in not so mint shape. It was free so I loaded it up and took it. Its got a new prop and it is a running engine so if nothing else it's a spare lower unit and some misc. parts.

The one thing I noticed is that there's a decal on this motor stating something about a recall being completed and to use 89 Octane fuel.
The one thing I noticed is that the head gasket on this thing is more than three times the thickness viewed from the edge than on the good motor. The compression on the parts motor is only 141-132-155 top to bottom checked with the same gauge.
Another thing I noticed was how easy this motor cranks over, it don't labor to turn over and spins at a higher RPM when cranking. I swapped the starters and both starters acted the same on either motor. The higher compression motor just needs more power to crank it over.

I don't think the motor was built with any performance in mind but I don't doubt that maybe there's a difference in head gasket thickness issue going on here. If this were a car engine, I'd be seriously concerned as to where I'd find fuel for it to drive it everyday. Especially with race fuel selling for upwards of $10/gal. or more.

The one thing that has me puzzled is that it don't run bad or sound odd on regular gas, but of course it's not been very warm out yet either. It does run strong power wise, a bit stronger than I expected I suppose but nothing extreme.

 

[dazk14]

Re: 1972 Evinrude 65 HIGH compression?

I believe this has all been covered.

It will idle great, never load up, and will grenade when you start putting rpm's/time into it. Tuners use VERY expensive knock sensors (that don't like getting wet) to note detonation that can't be heard - and most of it can't be heard. It is already a high strung motor, high stress motor - which I believe I covered before regarding the 750 hrs vs. 1,000.

Those low displacement 3 bangers were great on gas, good top end and very crappy bottom end. OMC has already maxed out the compression to try to maximize the acceleration and it was still weak.

 

[crackedglass]

Re: 1972 Evinrude 65 HIGH compression?

I've always considered the OMC three cylinder motors pretty much as good as it gets, with the bigger twins running a close second.
I've never really thought of them as good on gas though, of all my motors the threes are the hardest on gas, but I'm sure that's mostly due to engine size over the 60hp twins.
I ran a 55hp electric shift triple for over 10 years almost daily, it ran flawlessly from the time I bought it used till when I sold it with the boat. It no doubt had high hours, I ran it for no less than an hour 4 months of every year for at least 9 years and it was used when I got it. Its still being used today with no major work ever being done. My 70hp, a much newer 1985 model had a new power head installed when I bought it 7 years ago and has been great every since but it gets far less use these days due to how hard it is on gas. I will most likely pull that motor off and hang a smaller twin cylinder on that boat to save some gas and gain some freeboard.

It's probably not worth too much aggravation to try to lower the compression on the 65hp, if a head gasket change don't do it, I'll either run it and see what happens or use it for parts. I've got nothing invested at this point. I agree that 180psi is too high for regular gas, and probably too high for the lower end to withstand it for long.