Does This sound Right ?? Compresion

[Alpinegold]

I took my 79 115 Johnson to the shop today. It is a convenient boat repair but I have heard some stories....? The motor had a powerhead replaced in 2001. I have ownen the motor for 1 year. Over the last 6 months about 1 out of 3 trips, I would plane up on the initial take off and then it would surge down to 2 cylinders. I would put it in nretral rev the motor and it would take off like a spotted tail ape. Yesterday it did the same and I could never get it to bang on 4 cylinders. In the responses I received from the forum, it was suggested that the problem might be wiring issue or bad power pack and possible ignition coil.

This shop told me I had 2 bad cylinders. Is this right? The day before yesterday , the boat ran excellent. Why would a boat run like a super champ on Saterday and then Sunday it has 2 bad cylinders.

 

[jbjennings]

Re: Does This sound Right ?? Compresion

I don't think you have two "bad" cylinders. Like suggested, you're losing spark on 2 cylinders. Do the suspect cylinders run off the same coil or powerpack?
Why don't you buy a 20 dollar compression guage at the autoparts store or better yet, borrow the neighbors, and check for bad cylinders yourself. Did you ask what the mechanic meant by "2 bad cylinders" ? He may have just had other things on his mind and didn't make himself clear. That's what I figure. Cylinders with bad pistons or compression and such don't work one day and then not the next, then work again. That really sounds electrical to me.
just my opinion (Keep in mind I don't know crap about big motors like your's)
JBJ

 

[iwombat]

Re: Does This sound Right ?? Compresion

As suggested, you need to get clarification on the term "bad cylinders". That could mean just about anything.

Your problem certainly sounds electrical, but could also be fuel related. If the latter, and you were running lean in one carb, it could certainly toast a couple of cylinders from running w/o proper lubrication.

Find out what your mechanic means first though.

 

[ezeke]

Re: Does This sound Right ?? Compresion

Pretty easy to see 2 bad cylinders on a crossflow; just pull the cylinder heads and bypass plates. I doubt if any wrench would try to bluff on that.

With the problems you reported, it should have shown up on your compression test a long time ago.

 

[Alpinegold]

Re: Does This sound Right ?? Compresion

I'm just sick about it cause this motor has ran great. The thing that bugs me is it didnt completely shut down. On a couple occasions it would just give me a small bump which would cause a very slight loss of power, I would cut back on the throttle slightly and it would go away and never have the proble occur the rest if the day. I would start and stop the motor 5 maybe 7 times and it would never have another problem. It just felt electrial in the way it would cut out and then resume like nothing happened.

 

[tashasdaddy]

Re: Does This sound Right ?? Compresion

as said clarification, of what they say is the problem. watch them do a compression check, to show you they are bad. they motor has 2 power pack that run 2 cylinders each. and they sometimes do crazy things when they go bad.

 

[emdsapmgr]

Re: Does This sound Right ?? Compresion

It is also possible you have a weak fuel pump. The engine may be consuming more fuel than the pump can supply. Try squeezing the primer bulb when it starts to miss and see what happens. If it picks up and runs well while the bulb is being primed, the pump is suspect.

 

[Alpinegold]

Re: Does This sound Right ?? Compresion

I tried the pumping the bulb but it didn't do anything.

I am going to see them this afternoon. Can anyone tell me what the compression should read on a 79 115 Johnson and an estimated tollerence ?

When I say estimated tollerence, I mean how far off the compression should be before a cylinder goes completely bad and shuts down.

 

[JB]

Re: Does This sound Right ?? Compresion

They should be over 100psi and within 10% of each other, Alpinegold.

I don't think you have bad cylinders. I think you have a bad (intermittent)powerpack or a bad carb. If side by side cylinders quit it is a carb, if cylinders on the same bank quit it is a powerpack.

If a cylinder loses compression it doesn't cut in and out. . .it loses power or just quits. You are describing cylinders cutting in and out with full power when they are in.

Identify which cylinders are cutting out, switch the powerpacks and see if the problem switches.

Humph. Bad cylinders my foot.

 

[Dhadley]

Re: Does This sound Right ?? Compresion

If it is low compression wanna bet it's the 2 starboard cylinders? Why did the powerhead have to be replaced before? Broken rings?

 

[Alpinegold]

Re: Does This sound Right ?? Compresion

I really want to thank everyone for the information. I will post what I find out from the repair shop tomorrow.

Alpinegold

 

[iwombat]

Re: Does This sound Right ?? Compresion

I'm not going to take that bet, DHadley.

I'm willing to bet "bad" means "not firing" in this case though. Did the '79 have two power packs, or was that year still using one? What year was the switch?

 

[Alpinegold]

Re: Does This sound Right ?? Compresion

I did not get off work in time before the shop closed so it will be tomorrow before I get over there to see what is up.

On the replacement head, I don't know why it had to be replaced. I know the gentleman who bought the boat before he sold it to me because he is my best friend. He had the head replaced about 2 weeks after he bought it. He used the motor a total of 12 times over 5 years. At the time he was out of town for months at a time with verizon.

The 79 115 that I have has 2 power packs and 4 ignition coils.

 

[jbjennings]

Re: Does This sound Right ?? Compresion

So what's the word? Was it ruined cylinders or bad powerpack? I'm suspicious of and hoping for a bad powerpack....CURIOUS!
JBJ

 

[jay_merrill]

Re: Does This sound Right ?? Compresion

I'll put my money on a bad timer base.

 

[emdsapmgr]

Re: Does This sound Right ?? Compresion

FYI-for comparison, a stock 1979 85 should have 125 lbs compression after an overhaul.

 

[Alpinegold]

Re: Does This sound Right ?? Compresion

Finally got with the repair shop. Seems they changed thier mind about what was wrong withg the boat. Here is my compression numbers.

140 140 140 140

Not bad for a 1979 motor with a rebuilt head in 2001. It was the powerpack that was causing the problem.

 

[jbjennings]

Re: Does This sound Right ?? Compresion

Sounds like you've got a good ol' motor with compression #'s like that!
Good to hear you didn't have a bad engine.
Good luck,
JBJ

 

[jay_merrill]

Re: Does This sound Right ?? Compresion

Glad that you got the problem sorted out. I agree with the others, sounds like you found a good one!

 

[Benny1963]

Re: Does This sound Right ?? Compresion

hoipe ypu watched them 140 is high wich is good but i can get 150 out of my six cyl cross flow with a little twc 3
in cyls and to be exact across the board that high
and my 150 has 2 scored cyls
maybe they should run leakdowntest.
but ihope there right .sounds like ya might be in good shape
bennyb