1985 Evinrude 90 HP Compression readings?

[reelfishin]

I am in the process of swapping one of my motors over to another boat, it's a 1985 90 HP which I plan to add power tilt and trim to, a new prop, and a complete tune up. The motor has always run great with no issues but I figure now was the time to freshen up the tune up and add the tilt/trim unit since it's off already. Having bought a fancy new Snap On compression gage I figured I'd check that while I was at it. I checked several of my motors I have here, including a few I have stored for future use. What I found surprised me, the 90Hp has the lowest of all compression readings, I got 124/123/124/121.
I also checked a well used 1977 135 hp I have and got 139/131/134/132, and my 1985 70hp, which was 142/141/141.
I also checked another older early 70's V4 I have here and got 145/144/144/141, and a 1985 115 hp that reads 120/121/119/118.

I'm used to dealing with auto engines and seeing higher readings, as well as a few Mercury motors I have that have compression in the 145 to 150 range.
I realize that some of the smaller two strokes run with a lot lower compression, but what's normal on a 1985 90HP?

What should I expect to see on these? do some V4's have more compression than others? It seems that the lower hp motors all seam to have less compression. One local dealer said that the 85 through 115 motors always read lower than the 135/140 motors. For comparison sakes, I checked a buddies motors, a pair of 1984 115s and got between 121 and 125 on all cylinders, both of those motors have two fresh power heads last fall.

 

[5150abf]

Re: 1985 Evinrude 90 HP Compression readings?

All those look good to me, even the numbers on the 85 115 are aceptable.

Sounds like you have some pretty good motors there.

 

[ottertail]

Re: 1985 Evinrude 90 HP Compression readings?

The biggest thing I look for is the varience between the cylinders. you have a 3 lb difference from high to low on this engine. I would consider that very good.

 

[jonesg]

Re: 1985 Evinrude 90 HP Compression readings?

I thought my J150 was bad at 90 psi, then found out its a commercial outboard, some are designed to top out at 100psi.
The upside is I can use cheapo regular gas.

 

[reelfishin]

Re: 1985 Evinrude 90 HP Compression readings?

I did some checking to see that the difference was between various power heads and it looks like they used the same pistons on the 88, 90, 100, and 115 HP, and then different pistons on the larger motors. The carbs vary as do the block castings but I am thinking that that difference may be exhaust porting and various bolt bosses.
What I am thinking is that maybe there was a compression increase on the larger motors? It seems that most of the smaller V4s have lower compression than do the larger ones?
The lower readings really surprised me on the 90 HP since its probably the motor with the least use and appears to be in the best shape overall. On top of that, its one of the strongest running motors I've had in a while. It came from a freshwater only area and even still looks new.

How do you ID a 'commercial motor'? I have a V6 which I was told was a commercial motor with only 100 psi compression across the board. It was given to me on a boat. I haven't used it as of yet simply since I felt that the 140 V4 was a better choice as far as it's hp to weight ratio. The added weight didn't justify the additional 10 hp on a smaller boat.

 

[reelfishin]

Re: 1985 Evinrude 90 HP Compression readings?

All those look good to me, even the numbers on the 85 115 are aceptable.

Sounds like you have some pretty good motors there.

Does anyone know what the difference between acceptable and bad is?
What were these motors when they were brand new? I've always had used motors from this era, and most of my new motors were all Mercury and Mariner back then, which all ran about 150 psi per cylinder when new, some even higher.
The first time I tested an Evinrude I was shocked to see the lower readings.
It's probably got a lot to do with why they seam to run longer between overhauls.

 

[guy74]

Re: 1985 Evinrude 90 HP Compression readings?

On most Johnson/Evinrudes you want compression numbers that are within 10% of each other and preferably over 100lbs. Some smaller rope start motors will only give readings of around 80psi, but as long as the reading are even across the cylinders they run well. I hope this answers your question.

 

[emdsapmgr]

Re: 1985 Evinrude 90 HP Compression readings?

All the numbers are pretty normal for each type/year OMC engine you have checked. They all are pretty healthy blocks, with solid readings. The 85 and 115 are exactly the same short block, with same crank, pistons and rods. These typically read in the 125 range-brand new. Your numbers look just fine for the two. The older (high performance) 125/135 and early 140 blocks all had the same pistons, rods, cranks, but had higher compression heads and higher port timing. Numbers in the 135-145 range are normal for these engines. The piston and rod was redesigned in the 1973 timeframe, but as were later pistons/rods were used commonly across all V4 engines. OMC changed hp, by using different port timing, changing heads, special tuned exhaust, intake blocks, and by varying the carb throat sizes. These 2 strokes make high hp numbers with small displacements (99.6 cubic inches) because they fire every rpm. Actually, the larger OMC V6 crossflow engines actually run considerably lower compression than these V4 engines. Commercial engines have lower timing, and lower compression so that they can run on low-octane fuels in foreign countries, may have different lower unit ratios. These generally don't make good recreational engines.

 

[viking1978]

Re: 1985 Evinrude 90 HP Compression readings?

In answer to what is good or bad. Over a 100psi and within 10% of each other. the motor compression sounds very good.

 

[reelfishin]

Re: 1985 Evinrude 90 HP Compression readings?

I have to say, most of the problems I've had with all of the V4s have been wiring related, not internal motor problems. Being in NJ, it seams that nearly everyone of these has corroded wiring. I've replaced the wiring harness on all but two of my motors here.
I picked up another 1976 135 today which reads a dead even 126 psi on all 4, but it had what looks to be squirrel damage to the plug wires and a wasted tilt and trim setup.

I normally pick up motors when I can just for future use, it just so happens I've accumulated a number of V4s lately. Lots of free boats around with gas being so high. So far, none of the motors have been bad. I need to find a few good tilt and trim setups for the 1976 motors. Between the lot of these, I may have one good set up with some serious work. Most of the early tilt and trim units all look to have been dormant for many years, I guess when they stopped working, whoever owned them then just forgot about the tilt and trim function. The later V4s, after 1978 almost always are just wiring problems, usually rotted wires and bad rectifiers, with the wires completely rotted off. So far, no bad stators. Another common problem is damaged skeg fins or broken or cracked anti-cavitation plates. I've got a few dozen lower units that need to be welded up, but internally their fine.

I spent three hours Sat. removing frozen steering cables from rusty tilt tubes, I had four good motors which the previous owners had cut the old cable off flush and jury rigged new steering leaving the old cable in the tube. I got all but one out, that one may mean a new tube.