Compression values for 1964 75hp starflite

[heryrg2711]

Hey guys, got a quick question for you. What should the compression be on a 1964 75hp evinrude starflite?

I just did the test and got some low values, 55 55 55 50(on cylinder 2). Are these values ok or are they too low?

Thanks.

 

[wilde1j]

Re: Compression values for 1964 75hp starflite

Did you test w/ all plugs out and good cranking battery? They're even, which is good. There are no published numbers for outboards.

 

[194269]

Re: Compression values for 1964 75hp starflite

When I worked at OMC back in the sixtys, between 90 & 105 are good numbers.

 

[heryrg2711]

Re: Compression values for 1964 75hp starflite

I took out 1 spark plug at a time. I also took off the spark plug wires off all plugs.

 

[wilde1j]

Re: Compression values for 1964 75hp starflite

Try again with all plugs all plugs out. Numbers are likely going to be somewhat higher.

 

[JB]

Re: Compression values for 1964 75hp starflite

You probably used very flawed technique, heryrg. But. . .I believe that your engine is healthy, because you got nearly equal readings on all cylinders.

Go to the Top Secret File ^^^ and redo the test correctly. I would wager you will get much higher psi, and they will all be close, as they are now.

 

[boobie]

Re: Compression values for 1964 75hp starflite

Don't forget compression gauges also vary from one to the other on readings.

 

[heryrg2711]

Re: Compression values for 1964 75hp starflite

I took all the spark plugs and re-did the test. I got lower numbers, like 35lbs.

I thought about it, how can i get higher compression with all spark plugs out?
Creating more places where air can leak does not seem like it would raise compression.

Could timing bog up the motor, make it feel underpowered and have low compression?

 

[JB]

Re: Compression values for 1964 75hp starflite

You are still doing something wrong. Pulling all plugs allows the starter to spin the engine faster and should result in higher psi.

Did you do the test exactly as described in the Top Secret File??

 

[wilde1j]

Re: Compression values for 1964 75hp starflite

If you did test correctly, there's no way you could get lower numbers.

Also, does the motor run?

 

[heryrg2711]

Re: Compression values for 1964 75hp starflite

The motor does run. When out in the water seems it is under powered. It also misfires more then should, i think might be running too lean. Also trouble starting cold, i think inherent problem with such an engine.
I think the battery might have been at fault, it was not fully charged. I will try to re-test once i get the tool again.
I'm also gonna change the sparks plugs and check the timing once i get the tools.

 

[wilde1j]

Re: Compression values for 1964 75hp starflite

If you got a 'real' 35 psig the motor would not run, period.

 

[boobie]

Re: Compression values for 1964 75hp starflite

Was the mtr spinning over fast enough when you did the test??

 

[yorab]

Re: Compression values for 1964 75hp starflite

Make sure that the spark plug hole seats are clean before screwing in the tester. When you clean them, be sure that you don't knock all of the gunk into the cylinders. Also, be sure that the threads in the heads are in good shape.

I thought about it, how can i get higher compression with all spark plugs out?
Creating more places where air can leak does not seem like it would raise compression.

Once the piston inside of a particular cylinder has covered the intake and exhaust ports, the cylinder should be completely isolated. In a healthy system, no air would leak out of the cylinder in question, regardless of what is happening at the other cylinders. Therefore, removing the plugs in the cylinders that are not under test will not cause air leaks in the cylinder under test. In fact, as JB pointed out, removing the plugs creates less pressure in the system as a whole, thereby allowing the starter to spin faster, which more closely replicates the conditions that the engine experiences while operating.

The Seloc repair manual for your motor talks about these basic principles of two-stroke operation. Although many slam the book as being useless when compared to the authentic Factory Service Manual (FSM), it provides a very good tutorial for the beginning outboard mechanic. It is available at many public libraries and is worth scanning through. If you plan to keep the motor for some time, you should probably also pick up the FSM.

 

[194269]

Re: Compression values for 1964 75hp starflite

I hate to say it, take it apart if you plan on keeping the engine. Over my long years of working on outboards, I have never seen an early 89.9 cu/in (75 80, 85, 90, and 100hp) OMC V-4 when pulled apart that didn't have at least one scored piston and cylinder . And your's sounds like it has four bad cylinders. Just my .03 worth, good luck.

 

[JB]

Re: Compression values for 1964 75hp starflite

Well, taking it apart might be the right thing to do but only after you have valid evidence that it is needed.

This problem is one of doing a correct compression test and interpreting the result correctly.

The odds that all four cylinders would go bad at the same time and the same amount are about as good as Charles Manson winning the Nobel Peace prize.

 

[194269]

Re: Compression values for 1964 75hp starflite

Instead of fighting the compression gauge after several trys, I would just pull the cylinder heads and have a look see. Just five mins. a side. I have had several engine come to me with all four cylinder scored.

 

[wilde1j]

Re: Compression values for 1964 75hp starflite

Agree with JB. Make sure there's a real need before taking stuff apart. If you pull the heads, you need new head gaskets. For what?

 

[JB]

Re: Compression values for 1964 75hp starflite

I think this engine is okay, compression wise. His first attempt, with 3 plugs in and a weak battery produced 55psi +/- 5psi. I think that is pretty good, given the conditions and technique.

I have no idea what else is wrong with the second test, but I am quite certain the engine didn't have a 4 cylinder failure between tests.

His outboard runs, so I would quit wasting time trying to prove that it can't, and focus on the symptoms he does have, which are pretty vague.

heryrg, from your posts I think you don't understand how your engine works well enough to be trying to service it. Get a factory Service Manual, study it, and you will be better prepared. www.outboardbooks.com

Good luck, and keep us up with progress.

 

[194269]

Re: Compression values for 1964 75hp starflite

With all due respect to you JB, he did mention that he got 55# on three out of the four cylinders. He also mention that he felt that it was low on power and hard starting when cold. Nothing was said about about a low battery when that test was done. He also has been talking about this for the last 7 days and has not come up with an answer. As I mention before normal compression readings should be 90 to 105 #'s. The problem could also be blown head gaskets in that case he would need new head gaskets, pull the heads and settle it.