9.5 compression

[vanman250]

I have an Evinrude 9.5hp 1968 I checked the compression and it is 70 on both cylinders what should it be?<br /><br />Thanks<br />Bill

 

[Paul Moir]

Re: 9.5 compression

Around 100+psi is ideal, around 90+ is operable. 70 is pretty low and getting into the non-running range for a 9.5.<br /><br />Have you tried decarbing to free stuck rings? Is your compression at all close to even? How exactly did you perform your test (number of pulls, throttle & choke positions)? How much faith do you have in your guage?<br />Does it run?<br /><br />Hope this helps!

 

[alcan]

Re: 9.5 compression

Hi Vanman<br />There really is no set number. This is due to the fact that different gauges tend to read different. One gauge may read 100LBS while the next will read 85lbs on the same test. The thing to look for is the difference between readings with the same gauge. Now 70lbs may sound low and may very well be low. How ever if you motor is running good I would say 70lbs is good enough. If your having problems or one hole is lower than another, then you may need to worry. I have had many motors that ran well and for a long time with what I would consider low compression. Unless your going racing or something, let the motor tell you when it wants to be repaired (in a case like this).

 

[R.Johnson]

Re: 9.5 compression

If you have equal compression on both cylinders, and both read low, I would suspect the guage. I have found a considerable differce in guages, even by the "so called' best of makers. One thing I have never seen addressed is the stem valve in the compression guage. This alone can make a considerable difference in readings as it becomes clogged or dirty. The best test is to pull the cylinder head. I constantly see post's to decarb, clean carbs, sync & link, and etc.Pulling the head is fast, it's cheap, saves time, and money! tells you what you want to know, and only takes a wrench. Yes! I have compression guages, leak down tester, but my best tester is a wrench.

 

[CFronzek]

Re: 9.5 compression

Vanman,<br />I'm not an outboard pro but I have rebuilt numerous two-stroke bike motors. <br />For good power output in a two-stroke motor the piston to cylinder wall clearence and the piston ring to cylinder wall seal are critical. In a four-stroke motor only what goes on on top of the piston is important. In a two stroke the underside of the piston is used to pump the incoming mixture into the combustion chamber. Combustion gases that get by the piston and rings dilute the incoming charge, lean the mixture out,cause the motor to run hotter and drop power output.<br />As long as you have enough cylinder pressure to start the motor you can continue to run it. But low cylinder pressures mean the motor is going to need attention. <br />Make sure you take your oars.<br />Charlie

 

[vanman250]

Re: 9.5 compression

I have 70 on both cylinders no matter how many times I pull. The compression gauge is new, not the top of the line compression gauge but not low end, middle of the road I guess. The motor was running ok smooth no missing but did seem to lack power. My fuel pump went bad so I thought this might be the reason for the lack of power before it went bad. So I thought that if I was going to replace the fuel pump I would also do a major tune up. but I'm thinking I may need more then a tune up. I did pull the head, very little carbon and a very very small scuff mark on the top cylinder just past the exhaust port other then that they look ok.

 

[G DANE]

Re: 9.5 compression

I've had a scuff mark on mine, that didnt affect performance. It was at the same place, only feelable close to porthole. If you have the possibility, try the comp. tester on another motor. I think the bad fuel pump can easily be the reason for loosing your power. I would put it together again, adjust carb and give it a try. Be sure your ignition is up to the mark, if pionts/condensers, that can steal a lot of power too. I think they should be set at 0.020

 

[wayne h]

Re: 9.5 compression

i have a few of these engine 1 has 100 psi the other has 75 and they both run very well.as long as you are + - 10 psi you should be good. i would do a decarb even know the head looks clean there might be carbon in the exhuast and in the ring grooves.check your timimg and make sure your throttle linkage is adjusted right there are makes on the pionts plate where the throttle follower makes contact. if its not set right you will not get the power you want.also people like to play with the props in these smaller motors thinking that a bigger prop will work better but thats not really the case on these engines bigger props will not let the engine get to max RPM and you will have a power loss. i played around with about 6 props before i found the 1 that worked for my and my style of boat. if you dont have a shop manual i would get 1. u can find them on ebay just for that motor i would stay away from the manuals that cover all kinda of engines and hp ratings they just dont tell you enough about these engines there are alot of little things that make a big diffrence in the linkage adjustments. good luck and hope this helps you

 

[vanman250]

Re: 9.5 compression

I did a compression check on my 6hp chrysler that has very little use to see what type of readings I get and the chrysler has 120 on each cylinder so it seems like the compression gauge is ok. This 6hp Chrysler moves my boat faster then the 9.5hp evinrude.<br /><br />Bill

 

[vanman250]

Re: 9.5 compression

If I want to bring the compression back up what should I replace, should i just do a ring job and a tune up or should I replace more then that?<br /><br />Bill

 

[alumistar]

Re: 9.5 compression

vanman,<br /><br /> i have a 1965 9.5 so,i looked through my SELOC/Chilton 1956-70 1.5hp-40hp johnson/evinrude book. as far as i could see, they were so much more concerned that the compression results were within 5lbs. of each other, that they don't even list what the compression test should read. from my 2cycle dirt-bike days, i remember a 70 some year old motorcycle mechanic tell me that if your cylinder pressure was anywhere between 80-120lbs. you were fine. and he stated that it didn't matter what two cycle motor you ran. in most cases, cleaning it up real nice, cleaning piston heads off, new rings, bearings, and gaskets do the trick real nice. just don't forget to lube everything that has metal to metal contact while spinning, and use the right tools, don't "backyard" it. they're old motors. with a bit of care they'll run forever.<br /><br />hope it helps.

 

[henning_dt85]

Re: 9.5 compression

You can try to change piston-rings/headgasket. A 6hp Chrysler beats it?? Then it has to bee something rong. These ar good engines that should beat a 6hp.

 

[vanman250]

Re: 9.5 compression

Yes the 6hp Chrysler moves my 14' starcraft faster then my 9.5 Evinrude. When the fuel pump went bad on my 9.5 Evinrude I pulled out my Chrysler until I had time to repair my Evinrude that when I found out it was faster so I'm thinking there is more wrong with my Evinrude then just the fuel pump. I am going to decarb the motor and check the compression again. This motor has very little use for it's age and is in good shape. My Chrysler is a 1978 but was still new in the box until 8 years ago and I have only put about 15 hours on it since.<br /><br />Bill

 

[alumistar]

Re: 9.5 compression

vanman,<br /> 70 psi. is a bit low. try using another compression tester. if the reading is still the same, do rings and gaskets, and clean up the internal parts. after that, do these things: 1)rebuild the carbuerator 2)rebuild/replace the fuel pump 3)replace your points, condensers, coils and plugwires <br />4) change the water pump. all this will caost about 100-150 dollars. once done, it'll smoke your 6hp. try that, you'll be happy!!