200 blackmax low compression after winter storage

dwmmatt23 · May 25, 2012

I recently pulled my boat out of winter storage, it was not starting and after checking all cylinders were reporting low compression @50. Motor is a 1978 mercury blackmax 200hp. Curious what could cause this as it was running fine all last summer when it was stored, now low compression in all cylinders to the point it wont start. It also seems really tight and hard to crank over. Could rings be sticking, there was no fogging oil used when stored. Any input or advice on where to go to from here would be appreciated, thanks

1961glastron · May 25, 2012

Re: 200 blackmax low compression after winter storage

sounds like rings stuck to me,,,i may be wrong but kerosene usually unsticks them but then again that and 2 stroke dont mix,,,i would google and see if maybe lucas oil or so has such a mechanic in a can solution to ur problem,,,,sorry for ur bad luck

1nebel0 · May 25, 2012

Re: 200 blackmax low compression after winter storage

Get some fogging oil and fog the hell out of each cylinder and turn over by hand...squirt some more in there and keep turning it over by hand...get it started and squirt Sea Foam into each carb to unstick rings and get rid of carbon. Then take a compression reading and let us know....

dwmmatt23 · May 26, 2012

Re: 200 blackmax low compression after winter storage

cool thats about what I was thinking

stephenpence · Jun 7, 2012

Re: 200 blackmax low compression after winter storage

any luck on this?? my compression is low across the board... i was wondering if the de-carb helped or if you had a bigger issue???

dwmmatt23 · Jun 20, 2012

Re: 200 blackmax low compression after winter storage

I left it a my buddys boat shop, he said he got some of the OMC ring free stuff in he was going to try on it to see if it will start at all, I should be hearing back from him this week when hes not to busy

dwmmatt23 · Aug 6, 2012

Re: 200 blackmax low compression after winter storage

So i started playing around with it today, it was really sluggish and turning over really slow, i hosed fogging oil in and spun by hand a few times. For a second turned over quickly and popped like it could start then it got really sluggish again. Hard starting killed the battery so fogged again and tried with both batteries and samething. Any ideas or thoughts?

dwmmatt23 · Aug 6, 2012

Re: 200 blackmax low compression after winter storage

I just charged both batteries and cranked it over and it started for a second with a really huge cloud of white smoke from prop (probably from all the fogging oil, smelled like it), shut it off hooked up muffs and tried to start, for @30seconds sounded good like it could have started then it coughed and went sluggish again then batteries died trying to turn over

Chris1956 · Aug 7, 2012

Re: 200 blackmax low compression after winter storage

Sounds like your battery cables are lousy, or dirty. Check insulation for bulges or thin spots. Those are caused by corrosion. Clean all terminals. That motor should spin for many minutes on a good battery. Maybe the starter is partially shorted?

dwmmatt23 · Aug 10, 2012

Re: 200 blackmax low compression after winter storage

Chris1956 said:
Sounds like your battery cables are lousy, or dirty. Check insulation for bulges or thin spots. Those are caused by corrosion. Clean all terminals. That motor should spin for many minutes on a good battery. Maybe the starter is partially shorted?

I did notice one of the main battery cables running up through the motor cover was worn like halfway through where it enters cover, could this cause low compression though? Also the starter is a newer used one I got from my mechanic friend, the old one really lagged bad and this one turns over well. I did pull the heads to inspect and cylinder walls and pistons looked really good, head gaskets were alil weak looking and for sure originals from 78. Two of the headbolts did however snap right off when removing, how can i get them out? They are going to be seized in there very tight. Would it harm it to try and start it up with all the other bolts torqued down but two missing?

Chris1956 · Aug 10, 2012

Re: 200 blackmax low compression after winter storage

You need to repair the two missing bolts. Heat them with a propane torch and then remove heat and spray with penetrating oil. Do this a few times and maybe you can turn them out with a vicegrip.

1nebel0 · Aug 11, 2012

Re: 200 blackmax low compression after winter storage

Chris is right on about batteries...I learned something as I have very good marine batteries and on my 90h.p it cranked very slowly so I took the starter apart, cleaned the armature and put it back together.. A little better but still slow cranking..This will effect the ignition system in outboards as they need a strong battery to produce good cranking speed... my friend gave me an Optima battery and all i can say is OMG..the 90 has never cranked faster or started easier...I will spend the $200 for all my boats instead of $75 for the reg ones that go dead in a year or two...The Optima is 5 years old and is still like new....Buy one and never go back to a wet cell battery....too bad you took the heads off because now you go another problem to deal with..good luck

dwmmatt23 · Aug 18, 2012

Re: 200 blackmax low compression after winter storage

Chris1956 said:
You need to repair the two missing bolts. Heat them with a propane torch and then remove heat and spray with penetrating oil. Do this a few times and maybe you can turn them out with a vicegrip.

These actually broke off below the head

Chris1956 · Aug 19, 2012

Re: 200 blackmax low compression after winter storage

well, that stinks. Well, either punch and drill them out or take it to a shop and have them do it. You want them to be drilled out fairly precisely.

dwmmatt23 · Aug 23, 2012

Re: 200 blackmax low compression after winter storage

tonight Im going to heat and spray with with penetrating lube and then drill and try a heavy duty extractor bit, then tomorrow ill bring my cables into work and make a new set. Hopefully Ill get her to fire

dwmmatt23 · Aug 23, 2012

Re: 200 blackmax low compression after winter storage

So if the motor wont spin over fast enough will that give a lower compression reading?

Dukedog · Aug 23, 2012

Re: 200 blackmax low compression after winter storage

You need to be really careful useing heat on that style (first genertion) block. Bolt bosse's are attached to tha sleeve. To much heat in tha wrong place can actually cause some problems with true "roundness" of tha hole and distortion of tha "flat" surface (where tha head gasket seals) which is very critical on tha style block. If there's anyway you can get it done without heat it would be a plus.............jmo

Needs ta turn 300+ ta get a good reading. So yeah, it needs ta be all good.

dwmmatt23 · Aug 23, 2012

Re: 200 blackmax low compression after winter storage

Dukedog said:
You need to be really careful useing heat on that style (first genertion) block. Bolt bosse's are attached to tha sleeve. To much heat in tha wrong place can actually cause some problems with true "roundness" of tha hole and distortion of tha "flat" surface (where tha head gasket seals) which is very critical on tha style block. If there's anyway you can get it done without heat it would be a plus.............jmo

Needs ta turn 300+ ta get a good reading. So yeah, it needs ta be all good.

Good to know, Ill try it first with no heat

Dave1027 · Aug 23, 2012

Re: 200 blackmax low compression after winter storage

dwmmatt23 said:
So if the motor wont spin over fast enough will that give a lower compression reading?

Yes. Also a low reading compression gauge.
Here's the thing. Suddenly all 6 cyls are low? All at once? What are the odds. What's the common element? I'd say it's the methodology not the motor.

PS: Make sure all the plugs are out. Squirt some 2 stroke oil into all the cyls, remove the lower unit and use a new battery.

samurai1988 · Jul 12, 2022

i have 2002 mercruser ..same basic steps on starting .
# 6 and # 4 were not sprayed and show 80 lbs and 100 lbs as others are 127 average . brand new starter and plugs and wires ..
almost seizing like action in efforts to start
wondering as proximity of 6 and 4 if i have cracked block after winter ?????

200 blackmax low compression after winter storage

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